George L. Anstadt

Direct mechanical ventricular actuation: A review

Direct mechanical ventricular actuation (DMVA) is a non-blood contacting method of circulatory support that can be rapidly instituted for resuscitation. DMVA is superior to conventional methods (open and closed-chest cardiac massage) in providing reliable cardiovascular stabilization for resuscitation following cardiac arrest. Furthermore, DMVA has important advantages including rapid application, technical simplicity, and avoidance of blood contact compared to other resuscitation devices (cardiopulmonary bypass and blood pumps). This review summarizes laboratory and clinical applications of DMVA.

First successful bridge to cardiac transplantation using direct mechanical ventricular actuation.

Currently available ventricular assist devices are technically difficult to implant, require continuous anticoagulation, and are associated with hemorrhagic and thromboembolic complications. Direct mechanical ventricular actuation is a biventricular assist device that can be applied in 3 to 5 minutes through a left anterior thoracotomy and has no direct blood contact or need for anticoagulation. The present study was designed to determine the effects of direct mechanical ventricular actuation in total biventricular circulatory support. Cardiogenic shock refractory to standard therapy developed in 2 patients awaiting cardiac transplantation. Direct mechanical ventricular actuation was applied and provided immediate hemodynamic stabilization in both. All inotropic agents and intraaortic balloon support were then discontinued. Fifty-six hours of circulatory support bridged the first patient to successful cardiac transplantation without complication. The patient is alive and well more than 1 year later without incident of infection or rejection. The second patient suffered cardiac arrest and required closed chest cardiopulmonary resuscitation before device application. After 45 hours of support, it was determined that irreversible neurologic injury had occurred and direct mechanical ventricular actuation was discontinued. Neither patients native heart exhibited any histologic evidence of device-related trauma. Direct mechanical ventricular actuation has undergone limited clinical investigation since its original description 25 years ago, but in these initial trials, the device has proved effective. The concept of mechanically actuating the ventricles appears to be a valuable, yet under-utilized method of total circulatory support.

Effect of direct mechanical ventricular assistance on myocardial hemodynamics during ventricular fibrillation

Direct mechanical ventricular assistance (DMVA) is a method of biventricular circulatory support that employs a pneumatic device to apply both systolic and diastolic forces directly to the ventricular myocardium. This study investigated the effects of DMVA on myocardial hemodynamics when applied after a prolonged cardiopulmonary arrest. Seven swine weighting 28.3 +/- 2.5 kg were instrumented for regional myocardial blood flow (MBF) measurements using tracer microspheres. Ventricular fibrillation was then induced. After 10 min of ventricular fibrillation, CPR was initiated for 3 min. DMVA was then applied through median sternotomy. Defibrillation was attempted after 3.5 min of DMVA. If unsuccessful, DMVA was instituted for another 17.5 min and a subsequent defibrillation attempt was made. Arterial oxygen content (CaO2), coronary sinus oxygen content (CcSO2), myocardial oxygen delivery/consumption (mDO2/mVO2), extraction ratio (ER), and endocardial/epicardial blood flow ratio (EN/EP) were determined during CPR, during the initial application of DMVA (DMVA1), and after the subsequent 17.5 min of DMVA in those animals not initially defibrillated (DMVA2). Three of the seven animals were successfully defibrillated during DMVA1. After the additional 17.5 min of DMVA, only one other animal was defibrillated. There was a significant improvement in CaO2, CcSO2, MBF, mDO2, mVO2, ER, and EN/EP after DMVA1 compared to CPR. Only mVO2 and ER improved significantly after DMVA2. These findings support the concept that physical diastolic augmentation may improve myocardial hemodynamics when DMVA is applied during cardiac arrest.

Myocardial tolerance to mechanical actuation is affected by biomaterial characteristics

Direct mechanical ventricular actuation (DMVA) uses a pressure regulated heart cup, fabricated from silicone rubber (SR) for mechanical massage of the heart. Because DMVA has demonstrated potential for long-term circulatory support, investigations are currently exploring the use of more durable materials for fabricating DMVA heart cups. This study assessed the acute effects of heart cups fabricated from SR versus polyurethane (PU) on the myocardium. Dogs (n - 18) received DMVA for 4 hr of ventricular fibrillation (VF) using either SR (n = 10) or PU (n = 8) cups. Microspheres were used to determine perfusion during sinus rhythm (control) and at 2 and 4 hr of support. After support, myocardial biopsies were assayed for high energy phosphate content. Results demonstrated that PU cups required relatively frequent adjustments in drive line parameters that were likely due to material softening during PU cup support. Both PU and SR cups achieved similar hemodynamics during 4 hr of support. Myocardial perfusion, however, demonstrated a marked hyperemia at 4 hr of PU versus SR cup support. Regional high energy phosphate content was significantly decreased in hearts supported by PU versus SR cups. These results suggest that the relatively compliant characteristics of SR materials are important for achieving effective DMVA support without injuring the myocardium.

Mechanical Ventricular Assistance in Human Beings

which Di is rect mechanical ventricular assistance using the system described by Anstadt, Schiff, and Baue [l] can provide total temporary circulatory support. Assistance is given by a cup lined with an inner diaphragm and is held on the cardiac ventricles by suction. Alternating positive and negative pressures delivered through a side arm into the space between the cup and diaphragm effect systole and diastole. Animal experiments reported previously demonstrated the physiological effects and potential uses of ventricular assistance [4-61. For initial human trials, the selection of patients was limited to those who would surely die from their disease if not assisted. The choice was further restricted to those in whom studies could be made to assess the effectiveness of the method. Patients dying from myocardial infarction in spite of vigorous medical treatment and patients whose hearts could not maintain adequate circulation following open-heart surgery met these criteria. Further animal experiments were performed to evaluate the safety of the method in such cases.t

Experimental aortocoronary saphenous vein graft function after mechanical cardiac massage with the Anstadt Cup

Direct mechanical ventricular actuation (DMVA) using the Anstadt Cup can achieve total circulatory support by massaging the fibrillating, asystolic, or failing heart. The device does not contact the blood or cause significant myocardial trauma. The purpose of this study was to assess the functional integrity of saphenous vein grafts (SVGs) subjected to DMVA vs cardiopulmonary bypass (CPB). Human SVGs were used to bypass the ligated left anterior descending coronary artery in 11 dogs. Animals then received 2 hrs of either DMVA (n=5) or CPB (n=6) during sustained ventricular fibrillation. Grafted and non grafted (control) SVG segments were then studied in vitro. SVG patency was confirmed by radiolabeled microspheres and pathologic evaluation. Matched SVG specimens (control) were not exposed to circulatory support. All SVGs were subjected to isometric tension studies. SVG contractile responses to norepinephrine, bradykinin, serotonin, and histamine were assessed. Maximal response to all agonists were similar between control SVG segments compared to either CPB or DMVA support (p=NS, ANOVA). All cumulative dose response curves were similar after DMVA vs CPB support. In conclusion, the smooth muscle function of SVGs in this study was not significantly altered by DMVA support. Therefore, short-term DMVA support does not impair patency or adversely effect the functional integrity of smooth muscle within SVGs.