● 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.
● Coronary sinus and venous anatomy:
The anatomy of cardiac veins is depicted in 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).
● 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 (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).