Biomedical subjects
Publications and source records attributed to W E Pae.
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This controlled study was undertaken to quantitate the effect of R-wave synchronization (counterpulsation) on myocardial oxygen consumption (MVO2) as reflected by the tension time index (TTI) during pulsatile left atrial to aortic bypass. Pulsatile ventricular assist devices were implanted in eight anesthetized, fully hemodynamically instrumented animals. After baseline measurement of TTI, heart rate, cardiac output, mean aortic and left atrial pressures, pulsatile left atrial to aortic bypass was instituted. Measurements were then continuously recorded during both left atrial pulsatile synchronous (LAPS) and asynchronous (LAPAS) bypass periods of pumping. Heart rate and mean aortic pressure were controlled throughout the experiment. TTI = 1819 +/- 95 mmHg-sec (control); 987 +/- 127 mmHg-sec (LAPAS); and 763 +/- 89 mmHg-sec (LAPS). The results indicate TTI, and therefore MVO2, is reduced significantly from control levels by either LAPS or LAPAS bypass. However, R-wave synchronization (counterpulsation) offers no further benefit in reducing TTI over the less complex LAPAS or full-to-empty mode pumping.
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Between February 1984 and December 1987, 63 patients were accepted as candidates for heart transplantation. Eighteen patients (29%) required some form of mechanical circulatory support before transplantation; eight patients received an intraaortic balloon pump, five patients had left ventricular assist devices, two patients received biventricular assist devices, and in three patients the total artificial heart was implanted. Fourteen of the 18 patients underwent transplantation with seven longterm survivors.
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Mechanical ventricular assist devices (VADs) have led to survival in patients who develop postcardiotomy cardiogenic shock (PCCS) refractory to conventional therapies. To elicit determinants of survival, the authors reviewed records of 26 patients at our institution who required Pierce-Donachy VADs for PCCS. Thirteen patients were weaned from ventricular assistance (50%), nine (34.6%) achieved long-term survival, and 17 died. Survivors and those that died were equivalent in terms of age, sex, NYHA class, type of operation, and preoperative hemodynamics. Ventricular assist pumping was established earlier in survivors (P = 0.006) although aortic cross-clamp and total cardiopulmonary bypass times were equivalent between the groups. The development of biventricular failure was significantly associated with the inability to wean from mechanical circulatory assistance. Despite an equal incidence of biventricular failure, survivors had milder forms of this entity and all patients with severe biventricular failure requiring a biventricular assist device failed to wean and ultimately died (N = 5). Of all complications, inadequate cardiac output was a significant determinant of weaning. Perioperative myocardial infarction and renal failure were found to be univariate determinants of survival. Inadequate cardiac output and biventricular failure preclude weaning from mechanical circulatory assistance. Survival is associated with the expeditious establishment of assist pumping, and with the avoidance of irreversible perioperative myocardial injury and renal failure.
Now that long-term survival can be achieved in animals with mechanical circulatory devices, reliable permanent arterial access for physiologic and pharmacologic studies has become important. A novel approach has been developed eliminating the need for repeated arterial cannulation. The arterial access system (AAS) consists of a 7 Fr Silastic catheter, which is threaded into the internal mammary artery, and an attached access well, which is placed in the subcutaneous tissue over the sixth rib. The AAS is implanted during the initial operation. The access well is punctured percutaneously with a 23 gauge needle to obtain arterial blood or to measure arterial pressure, and patency is maintained by flushing the access well with 2,000 U of heparin each week. The AAS was implanted in six calves (three with a total artificial heart, three with a ventricular assist device) for a mean duration of 124 days (range, 20-323 days). There were no infections related to the AAS, and none of them thrombosed. All of the AAS had excellent arterial wave forms when punctured. The AAS is simple to implant, provides reliable long-term arterial access, and does not appear to increase the risk of infection.
A 26-year-old man with end-stage idiopathic cardiomyopathy was supported with a Pierce-Donachy left ventricular assist device for 31 days before orthotopic heart transplantation. Fungal endocarditis was discovered at the time of recipient cardiectomy, and antifungal therapy was begun. Fungal mediastinitis developed 4 days after transplantation and was treated with mediastinal irrigation. Massive mediastinal hemorrhage caused by fungal aortitis occurred on two occasions and was successfully treated with a bovine pericardial patch. The patient is well 9 months after transplantation.
At The Pennsylvania State University, we have performed four bridge-to-heart transplantation procedures in the past year. Two patients were supported with an LVAD, and two patients were supported with a TAH. One patient had a successful transplantation and remains well 10 months after operation; two patients died of sepsis after transplantation. A fourth patient has had a TAH in place for greater than 110 days and is currently awaiting transplantation. The problems that remain to be solved are developing strategies to minimize the risk of infection, defining the indications for use of an LVAD vs a BVAD vs a TAH, developing an effective regimen to prevent thromboembolism, and determining the proper interval for transplantation after the insertion of a mechanical pump as a bridge.
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Our experience with six patients has demonstrated that the Pierce-Donachy VAD is capable of providing adequate circulatory support with acceptable morbidity and mortality in patients awaiting cardiac transplantation. Four of the six patients received cardiac allografts and three patients have been discharged.
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Current data indicate that temporary ventricular support in patients who cannot be weaned from cardiopulmonary bypass is a reasonable and therapeutic treatment to extend life. Ventricular recovery and quality of life are satisfactory in long-term hospital survivors, and noncardiac disability is rare. Although the role of temporary ventricular support for acute myocardial infarction and cardiogenic shock is undefined, the expansion of indications to include these patients is reasonable and future clinical trials are warranted. Additionally, there is sufficient evidence to indicate that temporary mechanical support is useful as a bridge to heart transplantation. The superiority of one support system over another in any given clinical instance can only be settled after the results of continued and carefully controlled clinical experiences have been reported.
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