Ventricular Assist Device Support

Abstract

We describe herein the cases of 2 patients who had ventricular arrhythmias. In one, a short-term biventricular assist device, the ABIOMED BVS 5000, was placed because the patient had sustained ventricular tachycardia and could not be weaned from cardiopulmonary bypass. Excellent hemodynamic support was maintained for several days while the antiarrhythmic therapy was maximized. Sinus rhythm was restored, and the patient was successfully weaned from the ventricular assist device. However, the substrate for the arrhythmia persisted, and a recurrence, 1 week later, resulted in the patient's death.

In the 2nd patient, the use of an implantable left ventricular assist device was successful in temporarily alleviating the ventricular tachycardia associated with ischemic cardiomyopathy. However, after 2 days of device assistance, the patient experienced a recurrence of the tachycardia, which degenerated into ventricular fibrillation with a marked deterioration in the patient's hemodynamics. The arrhythmia persisted despite multiple attempts at external cardioversion, and internal cardioversion and placement of an automatic implantable cardioverter-defibrillator were necessary. This treatment, along with repeated boluses of amiodarone, led to successful suppression of the arrhythmias, and the patient eventually underwent transplantation.

The mechanical hemodynamic support of the circulation by ventricular assist devices was effective in supporting these 2 patients who had sustained ventricular arrhythmias. (Tex Heart Inst J 2002;29:33–6)

The treatment of ventricular tachycardia and ventricular fibrillation (VT/ VF) is typically managed by pharmacologic or electrical intervention or both; however, the condition is sometimes refractory to these methods. In such cases, patients with incessant VT/VF generally die of this disorder. One alternative treatment for VT/VF consists of mechanical control of the circulation with artificial pumps, which provides hemodynamic stability during the arrhythmia. In recent years, the use of ventricular assist devices (VADs) for treating acute cardiogenic shock has been shown to be efficacious in restoring circulatory stability. The most common application of VADs has been in cases of postcardiotomy shock. More recently, the usefulness of VADs for the management of refractory ventricular arrhythmia in patients undergoing medical rather than surgical treatment has been recognized. We describe the cases of 2 patients who had ventricular arrhythmia, each treated with a different type of VAD.

Case Reports

Patient 1

In February 1999, a 59-year-old woman with chest pain was admitted to a local hospital. Cardiac evaluation revealed an acute anterior-wall myocardial infarction. She was treated medically with intravenous heparin and nitroglycerin. Her condition deteriorated with the development of VT and hypotension. She became short of breath, which necessitated endotracheal intubation. At cardiac catheterization, she was found to have severe triple-vessel coronary artery disease, along with high pulmonary artery and pulmonary capillary wedge pressures. An intra-aortic balloon pump (IABP) was placed, and the patient was returned to the coronary care unit; she was not considered a candidate for percutaneous transluminal coronary angioplasty. Her condition did not improve, and she was transferred to our institution for further treatment.

The patient was immediately taken to the operating room for emergency coronary artery bypass grafting. Cardiopulmonary bypass was established, and the patient underwent a triple bypass. Despite the use of inotropic agents and the IABP, the patient could not be weaned from cardiopulmonary bypass because of biventricular cardiac failure and an associated ventricular arrhythmia. A biventricular support system (BVS® 5000; ABIOMED, Inc.; Danvers, Mass) was implanted on the left and right sides (LVAD and RVAD, respectively). The mechanical support allowed smooth weaning of the patient from cardiopulmonary bypass with minimal need for inotropic agents. The BVS flow rates were between 5.0 and 5.5 L/min bilaterally. The patient was transferred to the cardiothoracic intensive care unit with stable hemodynamics despite the persistent VT that was refractory both to intraoperative cardioversion and to intravenous amiodarone administration (Fig. 1).

Fig. 1 Circulatory support with the ABIOMED BVS® 5000 biventricular assist device in the setting of sustained ventricular tachycardia.

During the postoperative period, the patient's electrolyte levels (such as potassium and magnesium) were corrected, and she was treated for acidosis. She was given another bolus dose of intravenous amiodarone (150 mg), and a continuous infusion (1 mg/min) was resumed. The patient remained hemodynamically stable with VT for 2 days. On the 3rd postoperative day, the use of external cardioversion was successful in restoring sinus rhythm. The patient was subsequently extubated and was able to sit up in bed. She was weaned from the ABIOMED BVS on the 7th day. One week later, however, she experienced another episode of sustained rapid VT and died.

Patient 2

In December 2000, a 49-year-old man presented at our institution with progressive shortness of breath. He was found to be in congestive heart failure. An echocardiogram showed severe biventricular dysfunction and mitral regurgitation. Cardiac catheterization revealed triple-vessel coronary artery disease that was not amenable to angioplasty or surgical revascularization. In addition, right-heart catheterization showed severe pulmonary hypertension and elevated right-atrial pressures. Ventricular tachycardia with hemodynamic compromise necessitated electrical cardioversion and intravenous amiodarone administration. An IABP was inserted and the patient was transferred to the coronary care unit.

Members of the heart failure service were consulted, and the patient's name was placed on the cardiac transplantation waiting list. His condition deteriorated, with further episodes of sustained VT requiring multiple cardioversions and repeated bolus doses of amiodarone. We decided to place a VE (vented electric) Heartmate® implantable LVAD (Thermocardio-Systems, Inc. [now part of Thoratec Corporation]; Woburn, Mass).

The patient was brought to the operating room, placed on cardiopulmonary bypass, and prepared for insertion of the LVAD. Intraoperative findings included a minimally contractile, markedly distended heart. There was severe pulmonary hypertension as well as low cardiac output. The patient went into VT several times and required cardioversion. The LVAD was placed in the standard fashion, with inflow established from the left ventricular apex and outflow to the ascending aorta. The patient was weaned from cardiopulmonary bypass. The LVAD flow rates were between 5.0 and 6.0 L/min. The patient was transferred to the cardiothoracic intensive care unit and given moderate-dose inotropic agents.

The immediate postoperative course was smooth; the levels of inotropic agents were lowered, and the LVAD flow rates were excellent (6.0–7.0 L/min). The patient was extubated, and he was hemodynamically stable. On the 2nd postoperative day, several episodes of VT occurred. Although the patient's hemodynamics remained stable, the LVAD flows decreased to 4.0 L/min. Occasional electrical cardioversion was required when the LVAD flows dropped below 4.0 L/min. Another bolus of amiodarone was given. Despite amiodarone and lidocaine administration, the patient continued to have episodes of sustained VT, which degenerated into VF. External defibrillation was unsuccessful. We decided to take the patient to the operating room for internal defibrillation, placement of an automatic implantable cardioverter-defibrillator (AICD), and possible placement of an RVAD. In the operating room, internal cardioversion was successful and sinus rhythm was restored. The LVAD flows improved enough that RVAD implantation was unnecessary. An AICD/pacemaker was inserted in the left subclavian position. Atrioventricular pacemaking was begun at a rate of 120 beats/min.

The remainder of the patient's recovery was uneventful. No further episodes of VT occurred. Intravenous amiodarone administration was changed to an oral form. On the 28th postoperative day, a donor heart became available. The patient underwent successful transplantation and was subsequently discharged from the hospital.

Discussion

Ventricular tachycardia can be a life-threatening disorder, particularly when it results in hemodynamic compromise. The standard management is antiarrhythmic drug therapy and electrical cardioversion. The variety of antiarrhythmic agents for this disorder has grown to include drugs with powerful combinations of membrane stabilization and receptor blocking properties. Amiodarone, for example, is labeled as a class III antiarrhythmic agent. Pharmacologically, however, amiodarone demonstrates the actions of all 4 antiarrhythmic classes. Failure of medical therapy with use of such an agent requires the prompt initiation of electrical therapy with direct-current cardioversion-defibrillation. If sinus rhythm is not restored, other available resources are limited. One method to control incessant VT is mechanical circulatory assistance. Ventricular assist devices (VADs) are becoming a standard treatment for refractory VT, because of beneficial results that have been achieved recently in patients with this arrhythmia. ¹

Mechanical circulatory support for intractable ventricular arrhythmia can be provided by various devices. Fotopoulos and co-authors ² stabilized medically refractory ventricular arrhythmia by use of intra-aortic balloon counterpulsation (IABCP). In their retrospective study, 21 patients underwent IABCP for control of either monomorphic VT (10 patients); or paroxysmal VT, VF, or both (11 patients). Intra-aortic balloon counterpulsation suppressed the ventricular arrhythmia in 18 patients, 13 of whom were weaned from the IABP. In the other 5 patients, the IABCP was continued until cardiac transplantation. Overall, 19 patients were discharged from the hospital.

An intermediate-term (weeks to months) VAD—the Thoratec left ventricular device—has been placed for treatment of refractory ventricular arrhythmia by several groups. ^1,3 Swartz and colleagues ¹ described 2 middle-aged men who had ischemic cardiomyopathy and a history of refractory VT despite the use of amiodarone, an AICD, a pacemaker, and ectopic ablation. Thoratec LVADs were placed for incessant VT, resulting in temporary relief of the arrhythmia. Although VT recurred many times during their postoperative courses, the patients' hemodynamics remained stable. Both patients underwent cardiac transplantation. A similar case was described by Holman's group, ³ in which a 45-year-old man had an acute myocardial infarction with accompanying refractory VT. A Tho-ratec LVAD was placed and amiodarone infusion was initiated. On the 2nd postoperative day, episodes of sustained VT occurred with a mild decrease in the LVAD flows (from 4.6 L/min to 3.8 L/min). The systemic blood pressure ranged from 80 to 90 mmHg and the right atrial pressure ranged from 16 to 18 mmHg. The arrhythmia continued for 12 days until it was controlled with amiodarone and metoprolol. The patient underwent transplantation on the 60th day of circulatory support. Both groups using the intermediate-term VAD ^1,3 reported that univentricular support was successful in maintaining hemodynamic stability during VT.

Farrar and colleagues ⁴ performed a study that showed successful results with biventricular support. Twenty-seven cardiac transplant candidates were given Thoratec VADs as a bridge to transplantation (21 biventricular; 6 LVADs). Six of the patients who received biventricular VADs experienced successful support of the systemic and pulmonary circulations. It should be noted, however, that this subgroup of 6 patients had VF, not incessant VT. In theory, patients with sustained VF would not benefit from univentricular support because of the ineffective blood flow across the right heart associated with this dysrhythmia. In patients with refractory VT, particularly VT with a rate of less than 150 beats/min, univentricular mechanical support should be capable of sustaining adequate hemodynamics, because the right heart contributes some forward flow. Two of the most important factors affecting the physiologic flow across the pulmonary vascular bed are the status of the right ventricle and the pulmonary vascular resistance (PVR). If the PVR is elevated, whether because of VT or VF, the flow across the pulmonary vascular bed will be compromised, resulting in diminished LVAD flow. Conversely, if the PVR is low or normal, the LVAD should provide satisfactory flow. Therefore, selective agents to reduce the workload of the right ventricle and decrease the PVR, such as nitric oxide, could be useful in this setting.

The long-term use of VADs (months to years) has been shown to be effective in the treatment of refractory ventricular arrhythmia. In a report by Oz and associates, ⁵ the implantable Heartmate Left Ventricular Assist System (LVAS) (Thoratec), designed as a bridge to transplantation, was successful in supporting 9 patients who continued to experience malignant ventricular arrhythmia during device support. The arrhythmias occurred from zero to 186 days after device implantation and lasted from 10 minutes to 12 days. The patients reported weakness, but none reported syncope. At the onset of the arrhythmia, there was a mean 1.4 ± 0.6 L/min decrease in device flow. No thromboembolic event occurred. The authors concluded that malignant arrhythmias are well tolerated in LVAD recipients. ⁵ Nonetheless, early electrical cardioversion should be administered to avoid the formation of thrombus in the native heart and to prevent damage of the right ventricle by prolonged fibrillation. ⁶

In our 2 patients, the use of antiarrhythmic therapy and the mechanical unloading of the ventricle with short-term VADs proved to be a powerful combination in the management and control of VT/VF. Amiodarone provided excellent pharmacologic activity in suppressing ventricular irritability. However, other more-rapidly acting agents, such as lidocaine, and short-acting β-blockers (for example, esmolol) should be used in situations requiring immediate activity.

In conclusion, refractory ventricular arrhythmia can be successfully managed with a variety of VADs. Previous reports have described the use of intermediate- and long-term VADs. Our report adds the use of a short-term biventricular VAD for the support of a patient with malignant ventricular arrhythmia and the successful use of an implantable LVAD for temporary relief of refractory VT in another patient. On the basis of our experience and that of others, we advise aggressive amiodarone therapy in conjunction with the use of ventricular assist devices in patients with refractory ventricular arrhythmias. In addition, transplantation should be strongly considered in such patients.