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\begin{document}

\title{Contrast Removal from Coronary Sinus for Prevention of Contrast-Induced
Nephropathy, A Review}



\author[1]{Kyvan Irannejad }%
\author[1]{Mehrbod Vakhshoori }%
\author[1]{Rostam Khoubyari }%
\author[1]{Mohammad Reza Movahed}%
\affil[1]{Affiliation not available}%


\vspace{-1em}



  
  \date{June 14, 2024}


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\textbf{Introduction:}

\textbf{Epidemiology:}

Each year, there are millions of procedures done in the United States
that utilize iodinated contrast agents. The main risk of iodinated
contrast is kidney injury which could lead to morbidity and
mortality\textsuperscript{~(1--6)}. Contrast-induced nephropathy (CIN),
also known as contrast-induced acute kidney injury (CI-AKI), is one of
the most common causes of impairment of renal function in the United
States~(7--10)~and is the third common cause of hospital-acquired renal
insufficiency~(11). Different studies have used various definitions for
contrast-induced nephropathy including an increase in serum creatinine
[?]0.5 mg/dl or [?]25\% from baseline creatinine within 24 to~~72 hours
after contrast medium administration~(3,6,12--16). The mortality rate is
increased among patients who developed CIN during and after
hospitalization, especially among those who required dialysis~(6,17,18).
Therefore, any preventive measures that can reduce CIN risk can be
lifesaving with a reduction in mortality and morbidity in patients
undergoing iodinated contrast exposure.

\textbf{Brief Summary of CIN preventive measures:}

*~~~~~~\textbf{Hydration and fluid optimization}

Several methods have been proposed to prevent CIN in clinical settings.
However, none of them has been proved to be consistently effective
except for hydration and reduction in the amount of contrast exposure.
Hydration is the most common prophylactic technique to reduce CIN
occurrence in a way that all high-risk patients undergoing contrast
exposure should receive appropriate hydration if possible before the
procedure~in high-risk patients and after the procedure~in all patients
if feasible without contraindication to hydration~(14,19--23). It has
been shown that intravenous fluid administration with isotonic saline is
more effective compared to the half saline infusion~(14,22). However,
the optimal fluid volume and infusion rate is controversial. Current
guidelines recommend intravenous administration of 1-1.5 ml/kg/h of
normal saline six hours before and after contrast injection~(24). With
respect to proper fluid administration, left ventricular end-diastolic
pressure (LVEDP) can be assessed and adjusted accordingly. This theory
was assessed in the POSEIDON trial. Their findings suggested patients
who received adjusted fluid based on LVEDP had a significantly lower
risk of CIN after cardiac catheterization (relative risk: 0.41, 95\%
confidence interval (CI): 0.22 -- 0.79, P= 0.005). However, three cases
of shortness of breath, probably in the context of pulmonary edema, were
reported in both intervention and control groups~(25). Also, Maioliet et
al. used bioimpedance vector analysis (BIVA) for the assessment of body
fluid status. After randomization of low BIVA patients to normal or
double volume normal saline administration, they found no significant
difference in CIN occurrence defined by standard criteria (increase
serum creatinine by [?] 0.3 mg/dl within 48 hours) between those groups
(10.8\% vs. 4.7\%, P= 0.08, respectively)~(26).

*~~~~~~\textbf{Avoidance of nephrotoxic agents}

Another factor that can raise CIN risk might be related to nephrotoxic
drugs. Although there are not enough trials to strongly prove the
benefit of nephrotoxic drugs discontinuation before contrast exposure,
it is generally recommended to hold potentially nephrotoxic drugs
including nonsteroidal anti-inflammatory drugs, aminoglycosides,
vancomycin, sulfonamides, penicillins, amphotericin, loop diuretics, and
metformin in high-risk patients. The latter drug has been associated
with metabolic acidosis which might predispose kidneys to the
development of CIN but this concept has not been proven~(27,28).

*~~~~~~\textbf{N-Acetylcysteine administration}

N-Acetylcysteine (N-AC) was initially reported by Tepel et al. to be
protective against contrast-induced nephropathy in a small trial (29).
However, numerous trials and meta-analyses have completely failed to
show any benefit and therefore its use is not recommended~(29--31).

*~~~~~~\textbf{Type of contrast media}

Contrast media typed based on osmolality is thought to be important for
CIN pathogenesis and has been categorized into three different types
based on the osmolality (high osmolar, low osmolar, and
iso-osmolar)~(32). Initially, several studies have shown that
iso-osmolar contrast media have the lowest risk of CIN incidence in
comparison to low-osmolar contrast agents~(33--36), but numerous other
trials failed to show any significant differences in the occurrence of
contrast-induced nephropathy~(37--40).

*~~~~~~\textbf{Dialysis and hemofiltration}

In terms of dialysis and hemofiltration which directly removes the
contrast from the systemic circulation, there is no clinical evidence
suggesting prophylactic use of dialysis can prevent CIN~(41). No benefit
has been reported for post-procedural dialysis either~(42). Marenzi et
al. reported the use of hemofiltration might be beneficial in the
prevention of CIN~(43). However, it remains unclear whether it was
related to increased clearance through dialysis or due to alkalinizing
agents used during filtration.

*~~~~~~\textbf{Treatment of hypoperfusion}

Due to the negative effect of renal hypoperfusion, regardless of its
etiology, with contrast administration resulting in increased CIN risk,
utilization of short time assisted devices increasing cardiac output
might reduce this risk. Flaherty and colleagues performed a randomized
clinical trial and found usage of a Microaxial percutaneous assist
device (Impella) was associated with a lower likelihood of acute kidney
injury among high risk percutaneous coronary intervention (PCI) patients
with reduced left ventricular ejection fraction [?] 35\% (odds ratio (OR):
0.13, 95\% CI: 0.09 -- 0.31, P\textless{} 0.001)~(44). These findings
might be associated with resultant reduced CIN risk. However, larger
studies are warranted.

*~~~~~~\textbf{Balanced hydration system}

Another proposed mechanism in CIN prevention has been attributed to a
balanced hydration procedure. This process has been suggested based on
the theory that as urine output becomes higher, the contrast
concentration in kidneys would become lower ultimately resulting in
decreasing CIN risk. Briguori et al. implemented Renal Insufficiency
After Contrast Media Administration Trial II (REMEDIAL II) trial to
assess the feasibility of the RenalGuard system (PLC Medical Systems,
Inc, Franklin, MA) in the prevention of CIN. Briefly, the mentioned
system consists of closed-loop fluid management that consistently
monitors and evaluates hydration status and urine output. 294 candidates
for coronary or peripheral angiography/angioplasty with an estimated
glomerular filtration rate (eGFR) of [?] 30 ml/min/1.73
m\textsuperscript{2}~and/or risk score of at least 11 were selected and
randomly allocated to control (sodium bicarbonate and N-AC
administration) or RenalGuard (hydration with saline and N-AC under
RenalGuard system control with furosemide administration) group. The
intervention group received an initial bolus for 30 minutes and
furosemide (0.25 mg/kg) would be prescribed to increase urine output to
[?] 300 ml/h. They found CIN was significantly decreased in the RenalGuard
arm compared to controls (11\% (16 out of 146 subjects) vs. 20.5\% (30
out of 146 subjects), OR: 0.47, 95\% CI: 0.24 -- 0.92). Different
administration routes of N-AC (oral agent for controls and intravenous
route for intervention group) resulting in probable variable
bioavailability of the drug as well as their reported data applicable to
a subset of chronic kidney disease (CKD) patients might be considered
for extension of the outcomes~(45).

Likewise, the Induced Diuresis With Matched Hydration Compared to
Standard Hydration for Contrast-Induced Nephropathy Prevention (MYTHOS)
trial using the RenalGuard system was performed for CKD patients who
underwent coronary procedures. 170 subjects with eGFR\textless{} 60
ml/min/1.73 m\textsuperscript{2}~were randomly assigned to standard
intravenous saline hydration as a control group (n= 83) or furosemide
with matched hydration as an intervention group (n= 87). The
intervention arm received 250 ml of normal saline as well as 0.5 mg/kg
of furosemide to reach a urine output of more than 300 ml/h. Patients in
the intervention group experienced CIN less frequently rather than
controls (4.6\% vs. 18\%, P= 0.005). Single-center and not-blinded study
design, as well as pre-determined hydration protocol in the intervention
group, were some limitations related to the mentioned project~(46).

*~~~~~~\textbf{Renal cooling}

Also, a cooling renal method based on the theory of decreasing oxidative
injury in lower temperatures in the context of contrast injection has
been announced. However, it did not show any promising outcome in terms
of CIN prevention. For instance, Stone and colleagues performed a
randomized trial and allocated 128 cardiac catheterization candidates
with CKD (estimated creatinine clearance: 20-50 ml/min) to control (n=
70) and intervention (n= 58) groups. In addition to hydration, the
latter group underwent systemic hypothermia at 33-34 \selectlanguage{ngerman}°C starting before
contrast injection toward three hours post-procedure followed by
rewarming to 36 °C with a rate of 1 °C per hour afterward. CIN was
observed in 18.6\% and 22.4\% of normothermia and hypothermia groups,
respectively. However, there was no significant association neither in
unadjusted nor in adjusted models (OR: 1.27, 95\% CI: 0.53 -- 3.00, P=
0.59 and OR: 0.83, 95\% CI: 0.18 -- 3.78, P= 0.81, respectively)~(47).

\selectlanguage{english}*~~~~~~\textbf{Ischemic preconditioning}

The hypothesis of ischemic preconditioning, as multiple short cycles of
ischemia and reperfusion in one organ, could be effective on another
organ, on reduction of CIN has been tested in a randomized clinical
trial on 100 subjects which revealed four 5-minute inflation-deflation
cycles of blood pressure cuff to 50 mmHg above each patient systolic
blood pressure before coronary angiography (CA) had been associated with
a decreased likelihood of CIN compared to controls (OR: 0.21, 95\% CI:
0.07 -- 0.57, P= 0.002)~(48). Although this procedure can be applied in
all clinical settings, further studies with a larger sample size are
required.

\selectlanguage{english}*~~~~~~\textbf{~Other agents}

One small study showed infusion of sodium bicarbonate might be more
effective in the prevention of CIN rather than isotonic saline~(49).
However, subsequent larger trials failed to prove this
association~(25,26). Therefore, sodium bicarbonate is not recommended to
be used for this purpose by the Consensus Working Panel~(22).

Other pharmacologic agents include ascorbic acid, diuretics, mannitol,
calcium channel blockers, fenoldopam, dopamine, atrial natriuretic
peptide, L-arginine, theophylline, and statins have been reported in the
literature in terms of CIN prevention with controversial
results~(50--62).

\textbf{The role of contrast volume}

\selectlanguage{english}*~~~~~~\textbf{~Contrast volume as a risk for CIN}

Contrast volume has been shown to be an independent risk factor for
CIN~(63--65). It has been previously proved the amount of contrast
correlates with the incidence of CIN~(66). After a data analysis of
53780 vascular interventions, Lee et al. indicated CIN was correlated
with CKD stage in a way that the incidence of AKI in the context of
contrast administration raised with each CKD stage (CKD stage 1: 0.39\%,
CKD stage 2: 0.45\%, CKD stage 3: 1.5\%, CKD stage 4: 4.3\% and CKD
stage 5: 7.5\%). They suggested the risk of post-contrast AKI could be
reduced by using safe thresholds of contrast volume~(67).

Rihal et al.'s study reported the volume of contrast media administered
during the PCI was correlated with acute renal failure~(6). Kooiman and
colleagues analyzed data from 82,120 PCI procedures and found patients
who received high contrast, as defined by division of contrast volume
over calculated creatinine clearance resulting in more than 3, had
increased CIN odds in both univariate and multivariate regression models
(OR: 1.61, 95\% CI: 1.46 -- 1.79, P\textless{} 0.001 and OR: 1.77, 95\%
CI: 1.58 -- 1.98, P\textless{} 0.001, respectively)~(68). Likewise,
another observational study on 561 patients suffering from myocardial
infarction who underwent PCI revealed CIN was significantly higher among
those with a contrast ratio (measured by administered contrast volume
divided by calculated maximum contrast agent dose) of more than 1 in
comparison to the ratio of less than one (34.6\% vs. 3\%, P\textless{}
0.001)~(65).

~Kane et al. reported the rate of CIN in patients with CKD undergoing CA
could be reduced by ultra-low contrast volumes~(69). However, even small
amounts of contrast can deteriorate renal function, especially among
high-risk patients~(70). A small study on 30 patients with
eGFR\textless{} 45 ml/min/1.73m\textsuperscript{2}~underwent CA/PCI with
ultra-low volume contrast media showed utilization of this kind of agent
was safe with no reported increased serum creatinine 48 hours
post-procedure~(71). However, a single study design and small sample
size are potential limitations needed to be considered. 123 subjects
with at least stage 3 of CKD experienced CA/PCI was selected by Kelly
and colleagues. They used a novel ultra-low contrast delivery technique
with an automated contrast injector for their procedures and reported a
CIN rate of 3.3\%. Quite a small sample size, as well as retrospective
study design and performance in a single-center, should be considered
for the generalization of their findings~(72). Although the CIN rate was
lower among CKD patients who underwent PCI with ultra-low contrast (n=
8) compared with the conventional group (n= 103) in another
retrospective study, the difference was not statistically significant (0
vs. 15.5\%, P= 0.28). Asymmetric sample distribution between groups and
their small cohort size might limit their outcomes~(73).

Mariani et al. proposed the theory of zero contrast volume and performed
MOZART (Minimizing cOntrast utiliZation With IVUS Guidance in coRonary
angioplasTy) trial to assess whether intravascular ultrasound (IVUS)
could decrease contrast exposure compared to the routine method. 83 PCI
candidate patients were selected and randomly assigned to routine
angiography (n= 42) or IVUS method (n= 41) with matched clinical and
laboratory data. The median contrast volume was significantly lower in
IVUS rather than in the routine angiography group (20 ml, interquartile
range (IQR): 12.5 -- 30 ml vs. 64.5 ml, IQR: 42.8 -- 97 ml, P\textless{}
0.001). Also, the ratio of contrast volume to creatinine clearance was
remarkably lower in the IVUS group (0.4, IQR: 0.2 -- 0.6 vs. 1.0, IQR:
0.6 -- 1.9, P\textless{} 0.001)~(74). Although they found a promising
outcome, the higher cost of IVUS might be a limiting factor for usage in
clinical settings. On the other hand, it has been suggested that
contrast volume reduction before contrast exposure may lower the risk of
CIN~(75).

\selectlanguage{english}*~~~~~~\textbf{Methods for reducing contrast volume administration}

In terms of reducing contrast volume administration, few studies are
available. Mehran et al. performed a randomized clinical trial to assess
the efficiency of contrast reduction in patients with underlying renal
diseases who underwent CA. 578 patients in stage III (eGFR between 30
and 60 ml/min) and IV (eGFR between 20 and 30 ml/min) of CKD with at
least two further criteria of New York heart association (NYHA)
functional class of III or IV of heart failure, diabetes mellitus
(treated with either insulin or oral agents), anemia, hypertension,
albuminuria or age of at least 75 years were randomly assigned to
hydration (n= 286) or hydration plus AVERT system group (n= 292). The
latter system is a contrast modulation system designed to adjust the
pressure of contrast injection toward the patient. The relative
reduction in contrast volume was 15.5\% (hydration group: 101.3 +- 71.1
ml vs. hydration plus AVERT group: 85.6 +- 50.5 ml, P= 0.02). The
distribution of AKI induced by contrast did not differ significantly
(26.6\% vs. 27\%, P= 0.70, respectively)~(76). Likewise, Gurm and
colleagues performed an observational study on 114 patients with eGFR of
20 -- 60 ml/min/1.73m\textsuperscript{2}~to assess the feasibility of
contrast volume reduction during CA or PCI using
DyeVert\textsuperscript{TM}~Plus Contrast Reduction System (DyeVert Plus
System, Osprey Medical). Data analysis of 105 successfully recruited
patients revealed the contrast volume saving of 40.1 +- 8.8\% per each
performed procedure. AKI induced by contrast agent was observed in three
(2.6\%) of patients~(77). The small sample size and observational design
of the study should be considered for the generalization of reported
data.

\selectlanguage{english}*~~~~~~\textbf{Automated contrast injection devices}

Although data analysis of 60,884 candidates who underwent PCI revealed
contrast agent usage was lower in centers that used automated contrast
injectors compared to those centers not used this method (199 +- 84 ml
vs. 204 +- 82 ml, P\textless{} 0.0001), no difference had been found in
terms of CIN occurrence (3.11\% vs. 3.42\%, P= 0.15)~(78). On the other
hand, Minsinger and colleagues performed a meta-analysis and found
automated contrast injectors decreased contrast volume up to 45 ml per
subject (95\% CI: 0.78 -- 0.93, P\textless{} 0.001), and it was
associated with a 15\% reduction in CIN compared to manual injection
methods (OR: 0.85, 95\% CI: 0.78 -- 0.93, P\textless{} 0.001)~(79).

\selectlanguage{english}*~~~~~~\textbf{Direct contrast removal from general circulation}

Contrast removal during CA has been reported to be correlated with
decreased CIN occurrence.~This contrast removal can be done by direct
aspiration from general circulation through different methods including
hemodialysis or continuous veno-veno hemofiltration with conflicting
results~(80). Moreover, the contrast agent would be still in the
circulation and might damage the renal tissue.

A summary of potential methods to decrease CIN risk is shown
in~\textbf{Figure 1.}

\textbf{Review of contrast removal from coronary sinus:}

\selectlanguage{english}*~~~~~~~\textbf{Introduction:}

Any methods that can extract contrast from a coronary sinus (CS) prior
to reaching the general circulation may reduce CIN.~Anatomically, major
veins of the heart drain blood to the CS with minimal connection with
systemic veins through Thebesian veins. Thus, it might be theoretically
possible to be able to remove the injected contrast before it reaches
the systemic circulation and negatively affect the kidneys.

\selectlanguage{english}*~~~~~~~\textbf{Coronary sinus and venous anatomy:}

The anatomy of cardiac veins is depicted in~\textbf{Figure 2} . The
coronary venous system is anatomically divided into two groups, named
greater and lesser cardiac venous system. The former contains three
different groups including CS and tributary veins (CS, great and small
cardiac veins, anterior and posterior interventricular veins, left
marginal vein, left posterior vein, an oblique vein of Marshall,
ventricular septal veins), veins draining to the atria and veins
draining to the left ventricle (right marginal vein, anterior cardiac
veins, infundibular veins). The lesser cardiac venous system consists of
Thebesian veins including venous sinusoids and small vascular
channels~(81--84).

The CS is located in the inferior portion of the left atrioventricular
groove and drains to the posteromedial right atrium. CS is the largest
structure in the cardiac venous system with a normal diameter and length
of up to 12 mm and 30-63 mm, respectively. CS has two valves which
include the valve of Vieussens and the Thebesian valve. The former valve
is present at the junction between CS and the great cardiac vein. The
latter is found at the junction of the right atrium and SC~(81--83,85).

\selectlanguage{english}*~~~~~~\textbf{Animal studies regarding coronary sinus contrast removal}

Animal studies have shown the clinical utility of this procedure.
Movahed and colleagues performed first study of its kind and assessed
the safety and feasibility of contrast removal from CS in pigs for the
first time. They selected five swine.~~Through the left carotid artery
with an 8-F multipurpose catheter, the left main coronary artery was
accessed, and 5 ml of non-ionic iodinated contrast was injected.
Heartport catheter (Ethicon Inc., Cornelia, Georgia) was used for the
engagement of CS through the external jugular vein (\textbf{Figure 3} ).
For three times, each time for 10 seconds, the tip of the catheter was
inflated immediately after coronary injection and the CS blood was
collected. The Catharos SENTINEL system used for contrast capture
contains aspiration and 0.035 inches wire lumen as well as optical
fibers for contrast detection. The catheter would be connected to the
aspiration system and primed with normal saline. The catheter tip is
positioned in a desirable place in the CS and holding and slowly pulling
back the handle would result in deployment of the basket. They
quantified the contrast amount in aspirated blood with high-performance
liquid chromatography as well as a dual-energy technique. The latter
technique was used to assess iodine mass. Recovered iodine was
calculated from the collected iodine mass ratio which was assessed from
dual-energy logarithmic subtraction per injected iodine. The procedure
was tolerated well in all recruited samples. They finally reported that
50.6 +- 12\% of injected iodine contrast was successfully aspirated from
CS. It must be taken into account that although a pig's heart closely
resembles a human heart, a large left azygos vein drains into the CS and
this point might be a potential explanation for lower than expected
contrast removal~(86).

Michishita et al. selected eight swine and sedated them with ketamine
and xylazine with subsequent intubation using isoflurane. Five swine
were treated with an extracorporeal system with adsorbing columns and
three others were treated as controls. The right femoral vein was
accessed and an 8-F blood suction catheter with multiple holes at the
distal end was inserted into the CS. They also used a Fogarty catheter
on the ostium of CS through the left jugular vein to protect any blood
leakage from the CS to the right atrium. Due to the presence of the
azygos vein receiving blood from CS, another balloon was also utilized
to block this blood flow through the right jugular vein. The total
contrast volume was 155 +- 14 ml and the swine were treated for 90
minutes with an extracorporeal system. All subjects tolerated the
experiment with no adverse events. They found the mean contrast removal
rate was 49.4\% and iodine concentration was significantly lower
compared with controls (P= 0.0003)~(87).

Chang et al. introduced a novel method for contrast removal using a
reflectance typed optical sensor. Five canines were anesthetized, and an
8-Fr Judkins catheter was used to access the coronary artery. An
aspiration catheter with a fiberoptic sensor was inserted into the CS
(\textbf{Figure 4} ). They injected contrast to the coronary artery and
analyzed reflected signals with the fiber optic sensor in the CS. Also,
they assessed the contrast removal rate through a spectrophotometric
absorbance assay. The mean contrast removal rate was reported to be 59.3
+-11\% (range: 42-76\%)~(88).

Meyer and colleagues anesthetized two dogs and accessed CS from the
right jugular vein through a 6-F balloon-tipped catheter (Pressure
Products, Model BVCS 6180, San Pedro, CA). After contrast administration
to the left main coronary artery, the balloon was inflated and the
contrast agent was captured from CS (\textbf{Figure 5} ). The procedure
was performed two times for each recruited animal and the mean contrast
extraction was reported to be 70 +- 6\% (range: 60 -- 88\%)~(89).

\selectlanguage{english}*~~~~~~\textbf{Studies of coronary sinus contrast removal in human}

The effectiveness of contrast removal in the prevention of CI-AKI has
been shown in different human studies. Danenberg et al. recruited seven
male individuals (range of age: 56-83 years) who suffered from previous
renal failure with a mean serum creatinine of 262 +- 46 mg\% to assess
the safety and feasibility of contrast removal from CS during CA
procedure. They engaged CS in six patients through a femoral vein with
the usage of a 5-Fr Simmons II catheter (Cordis, Miami, FL) and via
jugular vein with the usage of a 6-Fr catheter (Cordis) in one patient.

A two-lumen balloon-tipped catheter equipped with multiple holes in its
distal end (Reverse Berman Angiography Catheter, 7 Fr, Arrow Int,
Reading, PA, USA) was exchanged over the wire in order to be positioned
in proximal CS. Although they could not deploy the catheter in four
patients, CS was successfully accessed in three subjects. The catheter
tip located at CS was inflated prior to each contrast injection.
Approximately 12-16 ml of blood was aspirated manually at 5-7 seconds
post-injection. The contrast removal rate was reported to be 44 +- 8\%.
None of the patients experienced creatinine rise and the procedure was
safely performed~(90)~(\textbf{Figure 6} ).

Likewise, in another study, a designed 11-F aspiration catheter (CINCOR
Contrast Removal System, Osprey Medical, St. Paul, Minnesota) was
inserted successfully in 31 out of 41 patients and the contrast
aspiration rate from the CS was 32 +- 3\% (range: 6-64\%) (\textbf{Figure
7} ). 26 of them had eGFR of less than 60 ml/min and were assessed for
further outcomes. No remarkable alteration in eGFR had been found from
the baseline to 72 hours after completion of the procedure (41.8 +- 2.2
ml/min to 41.1 +- 2.3 ml/min, P= 0.55). They also analyzed data with 148
matched comparators under standard care (no CS aspiration) with the
administration of the same contrast volume and figured out eGFR declined
significantly from 42.7 +- 0.8 ml/min to 40.1 +- 0.9 ml/min (P\textless{}
0.001) at 48-h post-procedure and the comparator group showed a greater
decrease in eGFR (-2.5 +- 0.5 ml/min vs. -0.7 +- 1.2 ml/min, P\textless{}
0.05). They also compared data of those with eGFR of less than 40 ml/min
(n=11) and the comparator group (n=56) and reported eGFR was not
significantly changed in the first group that underwent CS contrast
aspiration (from 30.7 +- 1.6 ml/min to 31.4 +- 1.8 ml/min, P= 0.42).
However, a significant decline was observed in the latter group that
underwent standard care (from 33.1 +- 0.7 ml/min to 31.7 +- 0.8 ml/min, P=
0.003). Between-group eGFR difference was also significant (+ 0.5 +- 0.7
ml/min vs. -1.5 +- 0.5 ml/min, P\textless{} 0.05)~(35,91,92)

Diab and colleagues recruited 43 CA candidates who suffered from
diabetes mellitus with a serum creatinine of 1.5 -- 3 mg/dl and divided
them into CS aspirate groups (n= 18) and controls (n= 25) with matched
laboratory and clinical parameters. A transseptal sheath (Mullins,
Medtronic, and St Jude Medical; 8 or 8.5 F) was used to access CS
through the left subclavian (n= 8) or right femoral vein (n= 10). The
contrast was aspirated directly through the sheath or a balloon-tipped
catheter (7 F, single lumen; Arrow Int, Reading, PA). The mean reported
contrast aspiration percentage was 39.35 +- 10.47\% (\textbf{Figures 8
and 9} ). All subjects in the CS group tolerated the experiment well.
Although one patient (5.55\%) in the CS arm experienced CI-AKI, this
percentage was higher among controls (n= 9 (36\%)) (P= 0.028)~(93).
Also, the contrast extraction rate was reported to be 27\% in a
60-year-old man who underwent CA using CINCOR contrast extraction
catheter from CS~(94)~(\textbf{Figure 10} ).

\selectlanguage{english}*~~~~~~\textbf{Devices and methods for coronary sinus contrast
extraction:}



\textbf{Heart Port Catheter:}

Different catheters have been used in animal and human studies to remove
contrast agents from CS. Movahed et al. used a Heartport catheter
(Ethicon Inc., Cornelia, Georgia) (\textbf{Figure 11} ) for engaging CS
through external jugular veins of pigs plus 11-Fr sheath. This catheter
has a balloon at its end and it was inflated after contrast injection to
collect blood from the CS. Fluoroscopy images were taken to confirm the
complete CS occlusion by injecting contrast to the distal of the
inflated balloon. Obstruction of CS by catheter tip did not show any
negative effects on CA findings and it was well tolerated in all five
recruited swine samples and no significant hemodynamic changes were
reported after blood extraction. They measured iodine concentration by
quantitative dual energy method~(86).

\textbf{Suction Catheter}

Michishita and colleagues used an 8-Fr suction catheter with distal
holes (\textbf{Figure 12} )~~and accessed CS with the usage of an inner
catheter as a guidewire control as well as for its stiffness. Another
balloon using Swan-Gantz catheter and a Fogarty catheter was implemented
to prevent blood leakage from CS to the right atrium and azygous vein,
respectively. They transferred the extracted blood to an absorbing
column with the usage of an extracorporeal system. Afterward, the blood
was returned back to the swine through the left femoral vein. The total
procedure time was 90 minutes and serial blood samples were taken at
different pre-and post-column time frames (0, 10, 20, 30, 40, 50, 60,
65, 75, and 90 minutes). Iodine contrast concentration was measured
through an inductively coupled plasma optical emission spectrophotometer
(CMC Development Department, Nihon Schering) with the use of ultraviolet
methods. None of the study samples experienced alterations in vital
signs including body temperature and blood pressure as well as an
electrocardiogram. They also suggested this system can be inserted
through femoral access into the CS by fluoroscopic guidance with no
usage of contrast administration. Also, the specific design of distal
holes on the catheter enables it to efficiently remove contrast from
left or right coronary arteries draining into or near the CS ostium.
They also claimed this system is quite time-saving because it does not
need any pre- or post-procedure interventions~(87).

\textbf{SENTINEL Catheter}

Another catheter was an optical catheter which was a Sentinel catheter
(SENTINEL Catheter, Catharos Medical Systems, Campbell, California) with
a fiber-optic probe. This designed catheter contains aspiration lumen
and basket tip as well as fiber optic sensors. This Catharos Sentinel
system detected signal changes upon contrast injection to the CS. The
mechanism was associated with signal variation in a way that after CS
administration of the contrast agent, the alteration in hematocrit (Hct)
was detected by fiber optic sensors located in the catheter tip. A
guidewire (Terumo Corp., Japan) was used for engaging CS and the
Sentinel catheter was introduced to the CS through GlideWire.
Fluoroscopic images were used to confirm the proper location of the
expanded basket in CS (\textbf{Figure 13} ). The contrast removal rate
was calculated using a spectrophotometric assay. In order to assess the
safety of this method, the hearts of two canines were fixed with
formaldehyde. The gross pathology report on CS integrity and other major
branches including great and middle cardiac veins as well as anterior
interventricular vein revealed all lumens were patent and no evidence of
hemorrhage or thrombosis had been observed. Although some places of
superficial endothelial cell disruption were found on histological view,
the underlying stroma was normal. Additionally, they found insignificant
mural inflammation in their samples. Their study was the first in the
literature to evaluate the usage of endovascular detection methods for
contrast removal. By defining signal to noise ratio as s trigger point,
they also indicated this system is an active method for contrast removal
and no interventionist's attention is required during the procedure.
However, some points should be considered. Despite the reflectance
signal for contrast aspiration being somewhat noisy, signal detection
could be differentiated from baseline signals. The aspiration threshold
was set to sown-crossing four volts in their study, but it was possible
that some portion of the contrast agent escaped from the collection
before crossing this threshold. Therefore, the implementation of exact
algorithms to detect this falling edge in an automatic manner rather
than by noise seems pivotal~(88).

\textbf{Balloon Tip Catheters}

In another study, an 80-cm balloon-tipped 6-Fr catheter (Pressure
Products, Model BVCS 6180, San Pedro, CA) (\textbf{Figure 14} ) was
inserted into the right jugular veins of two dogs and advanced to CS.
Their left main coronary arteries were also engaged through a 5-Fr AL2
catheter. A small amount of contrast was injected to confirm the CS
occlusion after inflation of the balloon followed by its deflation to
clear the contrast agent from the CS. Concurrently with contrast
injection, the balloon located in CS was inflated and manual blood
suction into a heparinized syringe was performed for 30 seconds.
Captured contrast was calculated according to grayscale analysis using a
polynomial regression curve. Meyer and colleagues suggested due to the
presence of small lumen in currently available CS balloon catheters, the
flow rate is low leading to enhanced withdrawal times. Thus, increasing
the flow capacity of available catheters might be associated with
heightened contrast removal efficiency. They also claimed this technique
can be applied in any circumstances when a noxious agent should be
administered in a selected organ if the draining venous system can be
accessed~(89).

On the other hand, different catheters are used in humans. Danenberg et
al. used a~balloon-tipped catheter with two lumens and multiple distal
holes (Reverse Berman Angiography Catheter, 7 Fr, Arrow Int, Reading,
PA, USA) (\textbf{Figure 15} ) for accessing the CS. They occluded CS
before contrast injection and blood was manually extracted 5-7 seconds
post coronary contrast administration and the balloon was deflated for
20-30 seconds after contrast disappearance shown by fluoroscopic images.
Extracted contrast concentration was measured by assessing reduction in
Hct levels in collected samples compared with simultaneous Hct levels
from aorta using the following formula: (1 -- Hct in CS extracted blood
/ Hct in the aorta) * collected blood volume. Although CS was
successfully accessed in all seven enrolled patients, the catheter
slipped out of the CS led to procedure failure in four participants.
However, the entire process was one without difficulties in the
remaining three subjects. Another issue was related to fluoroscopy time.
The extra time needed for CS cannulation increased the mean fluoroscopy
tome in comparison to routine interventions. However, they reported this
method can be done in most catheter laboratories with no special
equipment. The additional benefit was associated with intermittent CS
obstruction. It has been reported that periodic occlusion of CS
decreases coronary artery blood flow regardless of the aortic pressure
or CS obstruction~(95,96)~. This reduced flow could be used to decrease
contrast volume per injection. Therefore, a reduced amount of used
contrast agent and significant contrast extraction can additively
decrease CIN risk. They also suggested using superior vena cava to enter
the right atrium for CS cannulation as a common technique. However,
using femoral access might be quite difficult with standard catheters
and they used Simmons II catheter for CS engagement~(90).

\textbf{CINCOR Contrast Removal System}

Another catheter is a 11-Fr aspiration catheter (CINCOR Contrast Removal
System, Osprey Medical, St. Paul, Minnesota) (\textbf{Figure 7A).~}
~Duffy and colleagues were able to successfully cannulate the CS with an
aspiration catheter using a 14-Fr right internal jugular vein sheath in
31 out of 41 recruited patients. Contrast aspiration was done by pushing
the foot pedal in this contrast removal system after coronary contrast
injection. Using inductively coupled plasma optical emission
spectroscopy, the amount of contrast extraction was measured. Those who
underwent CS aspiration, they did not observe any serious adverse events
associated with the device~(91).

This system was also successfully placed in CS ostium through a 12-Fr
femoral venous sheath in one case. After four seconds of delay post each
cine angiography acquisition, contrast extraction was done using the
11-Fr CINCOR system for 10 seconds (\textbf{Figure 10A} ). The procedure
was performed uneventfully and the patient did not experience an
apparent hemoglobin drop~(91,94).



\textbf{Arrow Int PA Catheter}

Another device was a 7-Fr balloon-tipped catheter (7 F, single lumen;
Arrow Int, Reading, PA)~~used by Diab et al (\textbf{Figure 16} ). After
accessing the CS through either right femoral or left subclavian veins
and before contrast injection, the balloon was inflated by air to
obstruct the CS and contrast aspiration was performed using a syringe.
In order to determine the volume of extracted contrast, reduction of
patients' blood Hct from Hct levels in CS blood was calculated and the
result was divided by the patients' Hct. Finally, the result of this
equation was multiplied by the volume of aspirated blood from the CS.
All the procedures are done without any failures. However, direct CS
cannulation was just performed successfully in six patients and CS
quadripolar or decapolar catheters were used to help cannulation in the
remaining 12 individuals. Contrast aspiration was performed through a
balloon-tipped catheter in 10 patients or direct extraction from the
sheath in the other eight participants. Although patients who underwent
CS contrast removal through the balloon catheter had remarkably higher
time to clearance of the contrast compared to the direct aspiration
group, the fraction of extracted contrast was not significantly
different between groups. The possible mechanisms for shorter contrast
clearance time in those undergoing CS contrast extraction via the sheath
might be associated with the faster rate of aspiration and wider sheath
caliber. Also, the sheath tip has a lower probability of collapsing or
facing the vessel wall during the procedure and it also creates a more
negative suction pressure. They suggested the possible safety of CS
cannulation using trans-septal sheath due to its favorable curves and
proper manipulation and rotation with or even without dilator support.
They also claimed the simplicity of this method as well as its
cost-effectiveness without the requirement of advanced technologies.
Despite their suggestion for optimal choice between balloon catheter or
direct sheath is defined by CS caliber in relation to the sheath,
complementary studies are required. Their potential concern on CS
obstruction on limitation of coronary arterial blood flow might be
explained by reactive hyperemia leading to increased microcirculation
after balloon deflation. Additionally, this enhanced coronary transit
time in the context of CS occlusion might be associated with decreased
necessary contrast volume~(93).

\selectlanguage{english}*~~~~~~\textbf{Expected challenges in CS engagement for contrast
removal:}

Although the safety and feasibility of CS contrast removal have been
indicated in several animal and human studies and this procedure is
quite accessible in most clinical settings, there are still some
possible challenges that should be considered. Despite its rareness, CS
anatomical abnormalities are one of the culprits in this regard. CS
length of less than 20 mm is considered to be short CS and might be
associated with difficult CS cannulation~(97--99). Also, the CS can be
varied from enlarged to hypoplastic or even absent in a few individuals.
CS enlargement could be either primary or secondary to other pathologies
including unroofed CS, interrupted inferior vena cava, coronary artery
fistula, and total or partial anomalous pulmonary venous return. The
former abnormality is a unidirectional left to right or a bidirectional
shunt between the left atrium and superior segment of CS~(99,100). Also,
CS manipulation during catheterization or contrast aspiration might be
associated with CS trauma or thrombosis, or ectopia of atria or
ventricles~(90). It seems CS morphology and proper catheter placement
might play pivotal roles in successful cannulation and should be
individually assessed. Moreover, blood loss per coronary injection might
be considerable. Danenberg et al. reported aspiration of 12-16 ml of
blood per injection~(90). This was 16.6 +- 3.23 ml per injection in Diab
et al.'s study. Also, post-procedural hemoglobin was slightly lower in
the CS group in the aforementioned study, but it was statistically
insignificant (10.85 +- 1.3 g\% vs. 11.62 +- 1.3 g\%, P= 0.06)~(93).

Patient discomfort, unstable sheath position, and difficulty in
advancing the sheath to the CS ostium have been reported to be some
difficulties during CS cannulation~(100). Another study reported an
approximate 10\% of minor myocardial damage during CS catheter
placement, but all complications were not clinically evident~(97).
Another considerable factor might be attributed to CS cannulation time
which has been reported in different ranges. The time was 19.27 +- 3.54
minutes in one study compared to 11.1 +- 9.3 minutes in another
one~(80,93). The equipment, the procedure (angiography versus
intervention) as well as skillfulness of the interventionist might be
some possible explanations for these reported differences.

\selectlanguage{english}*~~~~~~\textbf{Future directions:}

Contrast extraction from CS seems to be a novel method ultimately
leading to a decrease in CIN incidence among CA/PCI patients. However,
some questions are currently needed to be investigated by further
comprehensive studies. For instance, despite PCI or CA being common in
origin, the required time for completion of each method is quite
different. Acceptable catheter sheath size should also be more
investigated. Appropriate training for proper CS manipulation should
also be considered. The blood loss amount is another potential concern
that needs to be evaluated and probably corrected by returning the
aspirated blood without contrast media to the patient. Normal blood loss
during conventional CA should be less than 300 cc~~(86). Moreover,
studies are probably necessary to define the exact CS contrast
aspiration time to prevent CIN.

\textbf{Summary:}

CIN in the context of CA and PCI is a major concern. Despite several
proposed methods to prevent CIN, CIN occurs in high rates with high
morbidity and mortality. New means that can reduce CIN is desirable.
Contrast removal from CS has been shown to be such a mean with future
potential in order to decrease CIN risk during coronary procedures with
a great safety profile. Large randomized trials are required to assess
the efficacy and safety of this approach.

\textbf{Competing interests} : Mohammad Reza Movahed has the Patent
holder for the contrast removal device.

\textbf{Abbreviations:}

-~~~~~~~BIVA: Bioimpedance Vector Analysis -~~~~~~~CA: Coronary
Angiography -~~~~~~~CI: Confidence Interval -~~~~~~~CI-AKI:
Contrast-Induced Acute Kidney Injury -~~~~~~~CIN: Contrast-Induced
Nephropathy -~~~~~~~CKD: Chronic Kidney Disease -~~~~~~~eGFR: estimated
Glomerular Filtration Rate -~~~~~~~Hct: hematocrit -~~~~~~~IQR:
Interquartile Range -~~~~~~~IVUS: Intravascular Ultrasound
-~~~~~~~LVEDP: Left Ventricular End-Diastolic Pressure -~~~~~~~MOZART:
Minimizing Contrast UtiliZation With IVUS Guidance in Coronary
AngioplasTy -~~~~~~~MYTHOS: Induced Diuresis With Matched Hydration
Compared to Standard Hydration for Contrast-Induced Nephropathy
Prevention -~~~~~~~N-AC: N-Acetyl Cysteine -~~~~~~~NYHA: New York Heart
Association -~~~~~~~OR: Odds Ratio -~~~~~~~PCI: Percutaneous Coronary
Intervention -~~~~~~~REMEDIAL II: Renal Insufficiency After Contrast
Media Administration Trial II\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1. Potential methods to decrease the risk of
contrast-induced nephropathy}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2. Anatomy of cardiac veins}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3. Contrast agent presented in coronary sinus after
simultaneous contrast injection in the left main coronary artery and
coronary sinus obstruction, reported by Movahed et al. (86). (with
permission from the journal of the American college of cardiology)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4. Fluoroscopic image of successful deployed Sentinel
catheter in canine coronary sinus, reported by Chang et al. (88) (with
permission from journal of invasive cardiology). 1: centering basket, 2:
aspiration catheter, 3: guidewire, 4: great cardiac vein, 5: right
atrium, 6: arterial catheter}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 5. Fluoroscopic image of contrast filling the dog
coronary sinus and occluded coronary sinus by the balloon, reported by
Meyer et al. (with permission from journal of interventional
cardiology)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 6. Coronary angiography images during left coronary
contrast injection (A) and contrast collection from CS (B), reported by
Danenberg et al. (90). (with permission from the journal of
cardiovascular revascularization medicine)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 7. Contrast removal system used for contrast removal in
the schematic (A) and fluoroscopic (B) images, reported by Duffy et al.
(91).}

\textbf{(with permission from the journal of the American college of
cardiology)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\textbf{Figure 8. Serial fluoroscopic images of contrast injection
(subclavian approach: A, femoral approach: D), contrast retention
(subclavian approach: B, femoral approach: E), and contrast aspiration
(subclavian approach: C, femoral approach: F) from coronary sinus with a
balloon-tipped catheter, reported by Diab et al. (93).(with permission
from the journal of circulation: cardiovascular intervention)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

\textbf{Figure 9. Serial fluoroscopic images of coronary contrast
injection (A), contrast emergence in the coronary sinus (B), and
contrast clearance (C) from coronary sinus with direct sheath aspiration
through the subclavian approach, reported by Diab et al. (93).(with
permission from the journal of circulation: cardiovascular
intervention)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image10/image10}

\end{center}
\end{figure}

\textbf{Figure 10. Schematic CINCOR contrast removal system (A) and the
CINCOR catheter in the coronary sinus (B), reported by Watson et al.
(94).}

\textbf{(with permission from the international journal of cardiology)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image11/image11}

\end{center}
\end{figure}

\textbf{Figure 11. Catharose image (A) and schematic illustration of
contrast capture from a coronary sinus (B). MCV: middle cardiac vein}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image12/image12}

\end{center}
\end{figure}

\textbf{Figure 12. 8-Fr suction catheter with distal holes, reported by
Michishita et al. (87). (with permission from the journal of the
American college of cardiology)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image13/image13}

\end{center}
\end{figure}

\textbf{Figure 13. Schematic view of ideal basket position, reported by
Chang et al. (88) (with permission from journal of invasive cardiology).
1: great cardiac vein, 2: middle cardiac vein, 3: marker band for middle
cardiac vein, 4: line of three marker band, 5: right atrium}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image14/image14}

\end{center}
\end{figure}

\textbf{Figure 14. Balloon-tipped 6-Fr catheter (Pressure Products,
Model BVCS 6180, San Pedro, CA), reported by Meyer et al. (89). (with
permission from}

\emph{www.pressure-products.com}\textbf{)}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image15/image15}

\end{center}
\end{figure}

\textbf{Figure 15. Balloon-tipped catheter with two lumens and multiple
distal holes (Reverse Berman Angiography Catheter, 7 Fr, Arrow Int,
Reading, PA, USA), reported by Danenberg et al. (90). (with permission
from\emph{www.teleflex.com})}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image16/image16}

\end{center}
\end{figure}

\textbf{Figure 16. 7-Fr balloon-tipped catheter (7 F, single lumen;
Arrow Int, Reading, PA), reported by Diab et al. (93). (with permission
from\emph{www.teleflex.com})}

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