Discussion
The development of postcardiotomy cardiogenic shock is a feared
complication following cardiac surgery. Though risk factors for this
condition are not well described, many cases are often attributed to
poor preoperative cardiac function, prolonged cardiopulmonary bypass and
cross-clamp times, poor myocardial protection, and or ongoing ischemia.
Once believed to be a mortal complication, early mortality following
these cases have been high, ranging from 40% to
90%,11,12 with rates highest following coronary
bypass grafting or combined bypass grafting and valvular
operations.13 Due to this low rate of survival, the
discussion regarding the practicality of postoperative transition to
MCS, especially higher-level forms such as ECMO, remains ongoing in
efforts to mitigate futile and costly practices.
The interpretation of the results from our series can be viewed from
different perspectives. The fact that 56% survived to 1-year suggests
that postcardiotomy MCS in general is not a futile practice, and that
patients can survive not only the early postoperative period but
longitudinally for several years as well. Even in those requiring ECMO
support, over one third of these patients survived to one year, with a
quarter reaching five-year survival. These outcomes are comparable to
those reported by Biancari and colleagues,14 who
reported a five-year survival of 27.7% in a series of 665 patients
bridged with veno-arterial ECMO following development of postcardiotomy
shock. In their series, increased age was the greatest pre-ECMO
predictor of mortality for these patients, with a five-year survival of
13.0% in those 80 years or older. In our analysis, we observed a 4%
increase in hazards for mortality per year of age (HR 1.04, 95% CI 1.01
to 1.07, P=0.01), once again drawing attention to this pre-MCS risk
factor. Thus age and overall life expectancy should be considered prior
to initiation of MCS for this advanced age subset.
Another interpretation of our data is that nearly half of patients die
within 1-year of postcardiotomy MCS support. Although not all of these
patients likely succumb to advanced heart failure, close follow-up of
this patient cohort appears to be prudent. Other measures and
interventions such as continued rehabilitation, prevention of infection,
nutritional optimization, and early referral to advanced heart failure
providers may all be important in improving survival and quality of life
in this challenging cohort.
The choice of MCS for the patient in postcardiotomy shock is nuanced,
and decisions are often tailored to the specific needs of the patient.
For the patient with depressed left ventricular function and/or high
inotropic requirement in order to separate from cardiopulmonary bypass,
an IABP is often inserted as a first measure to support hemodynamic
performance and/or coronary perfusion. Should these measures be
insufficient, or the patient develops overwhelming right ventricular
dysfunction/failure and/or pulmonary insufficiency, consideration for
ECMO cannulation is entertained.
Insertion of a durable left ventricular assist device or a temporary
device such as the Impella is not routinely considered at the time of
index operation. In these patients, the more typical course is the
presence of preexisting ventricular dysfunction that fails to improve
after surgical intervention and/or revascularization, or more rarely,
left ventricular dysfunction that develops as a consequence of the
operation without recovery. For these patients, they may be initially
stabilized with another form of MCS, and once left ventricular recovery
is deemed improbable, these devices are considered. Depending on
baseline characteristics at this time, durable ventricular assist
therapy may be chosen, or an Impella may be inserted with the goal of
transplantation. The benefits of durable or temporary ventricular assist
devices is their ability to unload the left ventricle, reduce
ventricular distension, and thereby improve myocardial recovery. Several
types of MCS devices may also be used in combination to achieve the
goals of left ventricular unloading, oxygenation, and improved
perfusion.
One of the most important tenets of MCS is early initiation. This
concept was solidified in our analysis where postoperative placement of
ECMO had a greater impact on mortality risk than intraoperative
placement. Patients who are weaned from cardiopulmonary bypass on very
high levels of inotropic support and with marginal hemodynamics
typically will deteriorate over the ensuing minutes or hours. Poor
perfusion and associated acidosis can lead to lethal arrhythmias or end
organ failure in a short period of time and dramatically increase
mortality risk in these patients. As has been shown in the cardiogenic
shock literature, early MCS including in the postcardiotomy setting
should be employed to help offload demands of the myocardium and to
improve perfusion and limit acid-base disturbances.