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.