Transvalvular left ventricular assistance in cardiogenic shock secondary to acute myocardial infarction. Evidence for recovery from near fatal myocardial stunning

Cardiogenic shock: therapy and prevention

Cardiogenic shock is defined as profound circulatory failure resulting in insufficient tissue perfusion to meet resting metabolic demands. It occurs in approximately 7.5% of patients with acute myocardial infarction. Treatment strategies include inotropic agents, use of intra-aortic balloon counterpulsation, and revascularization. Current evidence supports the use of primary angioplasty. Surgery should be considered in patients with triple-vessel disease. If early catheterization is not available, thrombolytic therapy should be given to eligible patients and transfer to an interventional facility should be considered. Effective therapy for shock must also include a prevention strategy. This requires identification of patients at high risk for shock development and selection of patients who are candidates for aggressive intervention.

Mechanical Circulatory Support for Cardiogenic Shock Complicating Acute Myocardial Infarction: An Experimental and Clinical Review

Cardiogenic shock (CS) occurs in 7% to 10% of cases after acute myocardial infarction and remains the most common cause of death in these patients. Despite aggressive treatment regimens such as fibrinolysis and percutaneous transluminal coronary angioplasty, mortality rates from CS remain extremely high. It has been shown that intra-aortic balloon pumping can result in initial hemodynamic stabilization. However, in the majority of studies, death was merely delayed. In recent years, efforts have been made to develop ventricular devices (LVAD) capable of providing complete short-term hemodynamic support. Seventeen major studies of LVAD support for CS complicating acute myocardial infarction are reported in the literature, with a mean weaning and survival rate of 58.5% and 40%, respectively. Patients considered in these studies are difficult to compare in terms of demographic and anatomic data, but taking these considerations into account, LVAD support seems to give no survival improvement in these patients compared with early reperfusion alone or associated with intra-aortic balloon pumping. Data emerging from experimental studies of acute myocardial infarction supported with LVAD are intriguing. In this review, we report the LVAD experience in the CS setting, starting from percutaneous extracorporeal support up to bridge therapy with implantable devices.

Mechanical left ventricular unloading prior to reperfusion reduces infarct size in a canine infarction model

We tested the hypothesis that unloading the left ventricle just prior to reperfusion provides infarct size reduction compared with left ventricular (LV) unloading postreperfusion and reperfusion alone. Twenty-four mongrel dogs were subjected to 2 hr of left anterior descending artery occlusion and 4 hr of reperfusion. A transvalvular (TV) left ventricular assist device (LVAD) was inserted just prior to reperfusion and maintained during the rest of the experiment (LV Assist Pre group). In the LV Assist Post group, the TV LVAD was inserted and activated just after reperfusion. A control group was subjected to reperfusion alone with a sham-TV LVAD. At baseline, the hemodynamic data were similar in the three groups. Myocardial infarct size expressed as percentage of area at risk was significantly reduced in the LV Assist Pre group compared to the control group (P = 0.011) and to the LV Assist Post group (P < 0.05). At 4 hr of reperfusion, transmural myocardial blood flow in the ischemic zone was slightly higher in the animals unloaded prior to reperfusion compared to controls and significantly higher than in the LV Assist Post group (P = 0.04). Postreperfusion end-diastolic wall thickness returned to baseline level in the TV LV Assist Pre group compared to both controls and TV LV Assist Post group. In these latter two groups, a significant increase in postreperfusion end-diastolic wall thickness and contraction band necrosis in the central ischemic zone correlated well with the degree of reperfusion injury. LV unloading prior to, but not after, reperfusion reduces the extent of myocardial necrosis in canine hearts subjected to 2 hr of left anterior descending artery occlusion and 4 hr of reperfusion compared to either reperfusion alone or LV unloading after reperfusion.

Management strategies for cardiogenic shock

PURPOSE OF REVIEW

Cardiogenic shock remains the most serious complication of acute MI, with an incidence of 6 to 8% and a 30-day mortality rate that remains close to 50%. While cardiogenic shock is due primarily to left ventricular failure, other causes such as acute mitral regurgitation and ventricular septal rupture must always be considered as emergency surgery may be life saving. The purpose of this review is to summarize recent advances in the care of these critically ill patients including the consideration of etiology and pathophysiology as well as the influence of age and adjunctive therapies.

RECENT FINDINGS

Early revascularization is now an American College of Cardiology/American Heart Association guideline class 1 indication for percutaneous coronary intervention (PCI) particularly for younger patients in cardiogenic shock. Recent studies suggest there may also be a benefit in elderly patients with cardiogenic shock.

SUMMARY

Prompt triage of all patients in cardiogenic shock for early angiography, intra-aortic balloon pump counterpulsation, and early revascularization with PCI or bypass surgery is now the preferred management strategy.

Cardiogenic Shock

In the setting of acute myocardial infarction, the timely recognition and treatment of cardiogenic shock are essential in reducing the incidence of death. Patients with cardiogenic shock should be treated aggressively with a combination of pharmacologic agents and mechanical support devices to achieve stabilization. Once stabilization has been achieved, the ultimate goal should be the restoration of flow in the infarct-related artery. This is best achieved with angioplasty or bypass surgery. In those centers not equipped for these procedures, thrombolysis should be performed, and the patient should then be transferred to a higher-level facility.

[Reperfusion therapy and mechanical circulatory support in patients in cardiogenic shock]

Cardiogenic shock is a state of inadequate tissue perfusion due to cardiac dysfunction, which is most commonly caused by acute myocardial infarction. The pathophysiology of cardiogenic shock is characterized by a downward spiral: ischemia causes myocardial dysfunction, which, in turn, augments the ischemic damage and the energetical imbalance. With conservative therapy, mortality rates for patients with cardiogenic shock are frustratingly high reaching more than 80%. Additional thrombolytic therapy has not been shown to significantly improve survival in such patients. Emergency cardiac catheterization and coronary angioplasty, however, seem to improve the outcome in shock-patients, which most probably is due to rapid and complete revascularization generally reached by angioplasty. In addition to interventional therapy with rapid coronary revascularization, the use of mechanical circulatory support may interrupt the vicious cycle in cardiogenic shock by stabilizing hemodynamics and the metabolic situation. Different cardiac assist devices are available for cardiologists and cardiac surgeons: 1. intraaortic balloon counterpulsation (IABP), 2. implantable turbine-pump (Hemopump), 3. percutaneous cardiopulmonary bypass support (CPS), 4. right heart, left heart, or biventricular assist devices placed by thoracotomy, and 5. intra- and extrathoracic total artificial hearts. Since percutaneous application is possible with IABP, Hemopump and CPS, these devices are currently used in interventional cardiology. The basic goals of the less invasive intraaortic balloon counterpulsation (IABP; Figure 1) are to stabilize circulatory collapse, to increase coronary perfusion and myocardial oxygen supply, and to decrease left ventricular workload and myocardial oxygen demand (Figure 2). Since the advent of percutaneous placement, IABP has been used by an increasing number of institutions (Figure 3). In addition to cardiogenic shock, the system may be of use in a variety of other indications in the catheterization laboratory and intensive care unit, including weaning from percutaneous cardiopulmonary bypass, in ischaemic left ventricular failure, in unstable angina, in high risk PTCA, and in prophylactic support in patients with myocardial infarction and successful revascularization. Animal experimental data showed that IABP may improve success of thrombolysis and recent clinical data suggest that survival is enhanced and transfer for revascularization is facilitated when patients with myocardial infarction and cardiogenic shock undergo thrombolysis and IABP rather than thrombolysis alone. A lot of studies had demonstrated before, that combined use of counterpulsation and revascularization therapy (i.e. coronary bypass surgery or angioplasty) may improve prognosis in patients with myocardial infarction complicated by cardiogenic shock (Table 1). In such patients, early treatment with IABP is most important: Multivariate analysis identified early IABP-support with a duration of shock to IABP-treatment of > or = 4 hours as an independent predictor of a positive short-term outcome. In shock-patients with postinfarction ventricular septal defect, IABP provides a marked hemodynamic improvement, and a significant decrease in shunt-flow (Figure 5). However, despite initial stabilization with IABP, such patients need immediate surgical repair of the septal defect to avoid hemodynamic deterioration. The rate of complications related to percutaneous IABP was significantly attenuated by employing catheters of reduced size. Using 9.5-F catheters, a long duration of counterpulsation emerged as the most significant factor associated with complications. In our hospital, those patients with 9.5-F catheters in whom counterpulsation did not exceed 48 hours had a low complication rate of 3.9%. The Hemopump is a catheter-mounted transvalvular left ventricular assist device intended for surgical placement via the femoral artery (Figures 6 and 7). (ABSTRACT TRUNCATED)

Reperfusion therapy in cardiogenic shock complicating acute myocardial infarction

The most frequent cause of cardiogenic shock complicating acute myocardial infarction is extensive myocardial damage involving a relevant amount of myocardium. Treatment is aimed at support for the circulation with the use of drugs and mechanical devices and at restoration of perfusion to the ischemic myocardium as soon as possible. Therefore, emergency coronary angiography is indicated in all patients. Coronary angioplasty is the first option in patients with suitable anatomy because it is the fastest available technique able to recanalize the infarct-related vessel. Stenting of the infarct artery must be considered because stent implantation has been shown to improve results in comparison with the balloon alone. Complete revascularization is likely to offer a better outcome in patients with multivessel disease. Coronary surgery is indicated as first-line intervention in patients who have a coronary anatomy not suitable for angioplasty; it may also serve to complete revascularization in patients with multivessel disease initially treated with emergency coronary angioplasty. In a hospital without facilities for emergency coronary interventions, mechanical circulatory support with an intra-aortic balloon pump should be instituted and thrombolysis started; then patients should be transferred immediately to a tertiary center to undergo coronary angiography and revascularization procedures, if needed. In patients not benefiting from this aggressive revascularization strategy who develop irreversible extensive myocardial damage, heart transplantation must be considered.

Effects of postischemic left ventricular pressure-volume unloading on contractile recovery and myocardial blood flow in the regionally stunned canine heart

OBJECTIVE

Myocardial stunning remains a clinical problem without definitive therapy. This study tested the hypothesis that mechanical therapy with a ventricular assist device would accelerate recovery of contractility in stunned myocardium by increasing the postischemic myocardial blood flow.

METHODS

Regional stunning was induced in dogs (25 kg) by 15 minutes of coronary occlusion and 180 minutes of reperfusion. One group (ventricular assist device; n = 10) was reperfused in conjunction with left ventricular unloading with a centrifugal-pump ventricular assist device. A second group (control; n = 8) underwent unmodified reperfusion. Hemodynamic and regional function data were acquired in all dogs with the heart in the working state before and during ischemia and after 180 minutes of reperfusion. Regional myocardial blood flow was measured at these same intervals and after 30 minutes of reperfusion, at which time the left ventricle was mechanically unloaded in animals with a ventricular assist device.

RESULTS

Regional stunning was observed in all animals, but cardiogenic shock developed in none of them. After 180 minutes of reperfusion, animals with a ventricular assist device had greater systolic shortening in the risk segment than did control animals (11.5% +/- 2.8% vs 1.1% +/- 1.3%; P <.05) and had no differences in either the slope or x-axis intercept of regional preload recruitable stroke work relations compared with preischemic values. Differences in contractile recovery did not correlate, however, with postischemic myocardial blood flow. Hyperperfusion mediated by the ventricular assist device was not observed in either stunned or remote segments.

CONCLUSIONS

Mechanical left ventricular unloading attenuates regional myocardial stunning within 3 hours in normotensive dogs, independent of effects on myocardial blood flow. The mechanism underlying this effect remains undefined, but these data support expanded use of mechanical therapy for stunned myocardium in clinical settings.

Ventricular assistance for recovery of cardiac failure

Mechanical assist devices have been used increasingly to support patients who await heart transplantation. The initial goal was to provide sufficient circulatory function to keep these patients alive and to allow them to recover from secondary organ dysfunction. A recent observation showed an improvement in native heart performance in some transplant candidates who receive support with mechanical assist devices. Under these conditions, myocardial recovery has been mostly restricted to patients with primary dilated cardiomyopathy and with extended periods of ventricular support. Also, the exact mechanisms that lead to substantial myocardial recovery remain unknown. Several investigations have demonstrated improved myocyte performance, reduced fibrosis, reduced cytokine levels, and reduced autoantibodies during long-term mechanical support; therefore, the observation of cardiac recovery during mechanical support is in accordance with currently discussed models of end-stage heart failure.

Clinical experience with the percutaneous hemopump during high-risk coronary angioplasty

The percutaneous Hemopump showed beneficial effects during coronary angioplasty in 32 high-risk patients with unloading of the left ventricle during ischemia and maintaining cardiac output with mean aortic pressures of 50 mm Hg in case of cardiac arrest (3 patients). High procedure-related morbidity (occlusion of femoral artery in 2 patients; bleeding with need of transfusion in 4 patients) and mortality (4 of 32 patients) rates demonstrate the need for a very careful selection of patients.

The use of an implantable left ventricular assist device in a patient with cardiogenic shock following acute myocardial infarction

We report the successful long-term use of an implantable left ventricular assist device in a 42-year old patient who suffered cardiogenic shock after an acute anterior myocardial infarction unresponsive to recanalisation of the infarct-related artery and intra-aortic balloon counterpulsation. Attempts to wean our patient from the assist device were not successful and the patient underwent cardiac transplantation after 35 weeks on device assistance. The intermediate and long-term use of an implantable left ventricular assist device may be lifesaving in post-myocardial infarction cardiogenic shock and may allow sufficient time for any stunned myocardium to recover. Should there be no recovery, the device acts as a bridge to cardiac transplantation.

Noncardiac surgery in long-term implantable left ventricular assist-device recipients

OBJECTIVE

The authors describe their experience with left ventricular assist-device (LVAD) recipients undergoing noncardiac surgery and delineate surgical, anesthetic, and logistic factors important in the successful intraoperative management of these patients.

SUMMARY BACKGROUND DATA

Left ventricular assist-devices have become part of the armamentarium in the treatment of end-stage heart failure. As the numbers of patients chronically supported with long-term implantable devices grows, general surgical problems that are commonly seen in other hospitalized patients are becoming manifest. Of particular interest is the intraoperative management of patients undergoing elective noncardiac surgical procedures.

METHODS

The anesthesia records and clinical charts were reviewed for eight ventricular assist-device recipients undergoing general surgical procedures between August 1, 1990 and August 31, 1994.

RESULTS

A total of 12 procedures were performed in 6 men and 2 women averaging 52.7 years of age. Mean time elapsed from device implantation to operation was 68 +/- 35 days. Conventional inhalational and intravenous anesthetic techniques were well tolerated in these patients undergoing diverse surgical procedures. No perioperative mortality was observed. Five of eight patients went on to successful cardiac transplantation.

CONCLUSIONS

Hemodynamic recovery after LVAD insertion has defined a new group of patients who develop noncardiac surgical problems often seen in other critically ill patients. Recognition of the unique potential problems that the LVAD recipient may encounter in the perioperative period--in particular patient positioning, device limitations, and fluid and inotropic management--will ensure an optimal surgical outcome for LVAD recipients undergoing noncardiac surgery.

Transvalvular left ventricular assistance in acute myocardial infarction with cardiogenic shock and high risk angioplasty: experimental and clinical results with the Hemopump

The Hemopump has been shown to be an effective left ventricular assist device. It is capable of supporting the circulation in patients with profound left ventricular dysfunction in the setting of cardiogenic shock. In experimental animals it seems possible that supporting the circulation immediately prior to reperfusion will produce a significant decrease in infarct size, which has important clinical ramifications, particularly in the setting of patients with large anterior myocardial infarction. The mechanism for this infarct salvage is unclear at the present time and requires further investigation, at a more basic level. The current tools available to the cardiologist include the intraaortic balloon pump and the cardiopulmonary support system (CPS), (PCs, BARD, Inc.). The Hemopump is available in Europe, but not in the United States at the present time. Clearly, the CPS system is the most powerful of the devices available, producing up to 61/m of flow. Unfortunately, there are a number of drawbacks with the CPS system, including its need for an oxygenator, which limits its useful period of support to approximately 8 hours. Additionally, support with the PCS system may be associated with adverse physiological events. The intraaortic balloon pump requires synchronization with the cardiac cycle, and hence, is not suitable for patients with significant tachyarrhythmias. Patients with overt cardiac arrest, similarly, cannot be supported with the intraaortic balloon pump. Nonetheless, the balloon pump has been associated with improved infarct salvage in an experimental animal model. On the other hand, the Hemopump, in its first version, required a surgical incision and placement of a graft onto the femoral artery.(ABSTRACT TRUNCATED AT 250 WORDS)