Cardiogenic shock (CGS) results in inadequate end organ perfusion and is associated with high mortality. For patients presenting with CGS following myocardial infarction (MI), reported rates of mortality range between 55% and 80% despite aggressive pharmacological therapy and use of the intra-aortic balloon pump (IABP). Patients with CGS due to ventricular septal defect (VSD) or ventricular rupture following MI have mortality rates approaching 100%. Accordingly, a minimally invasive therapeutic intervention beyond the capabilities of the IABP is needed to enhance cardiac output and organ perfusion for treating these patients as a bridge to recovery of function or to definitive therapy.
In addition, there is a great need for a device that can be used to support patients who are undergoing high risk procedures such as angioplasty or bypass surgery who may not tolerate cardiopulmonary bypass. Currently, many such patients are denied the procedure due to inordinate risk. Prior attempts to develop a minimally invasive system for this purpose have been fraught with difficulty in requiring general anesthesia and use of a full cardiopulmonary bypass pump team.
The Texas Heart Institute (THI) has used the TandemHeart™ percutaneous transseptal ventricular assistance (PTVA) with some success. It is a circulatory support system which may address these needs. The device is placed under fluoroscopic guidance in a cardiac catheterization laboratory and is designed to unload the left ventricle while providing adequate cardiac output and organ perfusion. It can be placed in a patient who is under conscious sedation and requires no incisions.This technology is a step up from IAPB support and can provide temporary circulatory support of 3-3.5L/min.
At the THI, patients were either weaned from TandemHeart support, transferred to another therapy (e.g. percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG)), or expired during support. Patients were weaned from the device when they remained clinically stable and able to maintain CI>2.2L/min/M2, MAP>70mmHg and PCWP<18mmHg without inotropic support during stepwise decreases of pump speed to a minimum of 0.5L/min for 1-2 hours. In this experience of 10 patients, there was only one device-related death, and the remaining patients were supported to PCI or CABG, or weaned.
Other US experience by Thiele et al., of 18 consecutive patients with post-MI cardiogenic shock had an overall 30-day mortality of 44% with a mean duration of cardiac support of 4±3 days. O'Neill et al. described the use of the system for a high-risk revascularization and mechanical rotational atherectomy. Moses et al. reported a case where the device was employed to reverse shock before a beating heart quintuple bypass procedure was performed.
Key hemodynamic parameters measured prior to, during, and after TandemHeart support from the THI experience are summarized in Figure 1.Average cardiac index increased to over 2.5L/Min/M2, mean arterial pressure (MAP) increased to greater than 80mmHg, and pulmonary capillary wedge pressure (PCWP) decreased markedly from more than 27mmHg to an average of less than 17mmHg. Central venous pressure trended lower, but was not significantly affected.
End Organ Perfusion
End organ perfusion in the THI experience was assessed by determining the serum levels of creatinine and total bilirubin. Baseline serum creatinine level averaged 1.6±0.8mg/dl prior to support (available from 10 subjects) and did not change significantly, averaging 1.3±0.4mg/dl during support (available from 10 subjects, p=0.14). There was no change in the total bilirubin values for these subjects, which averaged 1.0±0.8mg/dl at baseline (available from 11 subjects), and 1.2±1.2mg/dl during support (available from 12 subjects, p=0.5).
No Effect on Blood Elements
An assessment of hemolysis was made by measuring plasma-free hemoglobin prior to and during TandemHeart support. Baseline measurements were available from seven patients and there were 18 measurements made during support. These data show that there was no statistically significant difference in plasma-free hemoglobin during support, suggesting that there is no significant hemolysis. Similarly, there was no significant difference in platelet count before or during support. Baseline measurements were available from 10 subjects and there were 33 measurements made during support.
Device-related adverse events and their frequencies from the European experience have been recorded and it was found that the two most common events were distal leg ischemia and bleeding from the cannulation site. There was one patient with each of the following complications:
- limb amputation;
- arterio-venous fistula;
- limited femoral artery dissection;
- arterial cannula clot; and
- late cardiac tamponade.
Interestingly, residual atrial septal defects (ASDs) were evaluated by echocardiography after device removal and were found to be closed in most cases and not clinically significant.
The Present and the Future
Mechanical circulatory support (MCS) is a powerful technology that can reverse the physiologic consequences of heart failure. The indications for MCS currently are bridge to cardiac transplantation, bridge to recovery, or as permanent/destination therapy. With the advent of less invasive percutaneously inserted left ventricular assist devices (LVADs), the indications have expanded to short-term support during high-risk PTCA, post-infarct shock, post-cardiac surgery shock, acute myocarditis, and transplant rejection.
Two randomized trials are currently being conducted to judge the effectiveness of this new technology, and the data resulting from these trials may have a profound effect on the management of acute heart failure and coronary artery disease (CAD) in the future.
As the population ages and patients have more comorbidities, surgical coronary revascularization is becoming impossible in a growing number of patients. Thus, the future use of the device to support patients during high-risk coronary angioplasty is an exciting new potential realm. To date, six such cases have been performed at THI with good results. This strategy may allow revascularization options where none existed before.