Paracorporeal Assistance System for Restoring Cardiac Activity

Two series of experiments were conducted to assess the potential of artificial ventricular bypass in restoring cardiac activity. One series evaluated use of a paracorporeal left ventricle in 17 calves; the other evaluated biventricular bypass in 11 calves. Module pumps with a seamless blood chamber of polyurethane were used. Pump function and system parameters were controlled by a Sinus VK-2 control system. Assisted perfusion began with the induction of ventricular fibrillation. The experiments showed that left ventricular bypass was an effective method for long-term maintenance of the hemodynamics during fibrillation, leading to certain biochemical corrections and restored electrical activity and myocardial contractile function. The hemodynamic state was maintained at a higher level with biventricular bypass and was accompanied by a greater percentage of restored myocardial function. Uneven restoration of contractile activity in the left and right ventricles points to the need for adequate support of both ventricles.     

Comparative Effects of Left Atrial or Left Ventricular Bypass on Coronary Sinus Flow and Oxygen Usage in Dogs

Comparative coronary sinus flow rates and oxygen AV difference were studied in dogs undergoing left heart bypass with left atrial or left ventricular drainage at similar maximum obtainable flow rates. Left atrial bypass decreased the coronary sinus flow rates and oxygen consumption when compared with control values. These values were further decreased when left ventricular bypass was used. The oxygen consumption data were highly significant and give further evidence of increased effectiveness of complete bypass of the left ventricle in myocardial support systems.     

Mechanical methods of treating refractory cardiac failure

Mechanical means tend to be used more frequently nowadays for the treatment of congestive heart failure which does not respond to more normal treatment. The indications and limits of such devices, as well as their cost, must be defined. The new problem created by these therapeutic tools is the evolution of the underlying cardiac disease: should it improve the patient will be weaned from the machine, whereas if it worsens heart transplantation would be the only answer. Three types of mechanical support are described. Balloon pumping, and especially intra-aortic balloon pumping, is the technique used most often. It has a true but limited efficacy. Its best indication is cardiogenic shock by left ventricular ischaemia with normal or slightly increased peripheral resistances. Intrapulmonary balloon pumping is occasionally used, but the system can only be set up surgically. Its best indication would seem to be right-sided heart failure by pulmonary hypertension. Circulatory assistance is the second type considered. All types of bypass pumps can be used. The output used is usually less than the patient's theoretical output, the aim being to allow the myocardium to recover. Vascular access for these pumps is either femoral or intrathoracic. An oxygenator may or may not be added to the bypass circuit, and support may be mono- or biventricular. Although the non pulsatile flow has not been shown to be detrimental, this has to be investigated further. The use of these devices is limited by their effects on blood coagulation and pulmonary function. The artificial heart or artificial ventricles are the last devices described.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surgical techniques for the implantation of heterotopic prosthetic ventricles

Mechanical support of the failing heart is becoming an increasingly useful tool for bridging to cardiac transplantation and for recovery of the natural heart. Several options exist for cannulation sites during the implantation of the heterotopic prosthetic ventricles. These options include the left atrial appendage, the left ventricular apex, the interatrial groove, and the left atrial roof. The indications, contraindications, advantages, disadvantages, and surgical technique for each option are described. Operation of the drive console and postoperative care are also discussed.     

Moyens mécaniques de traitement de l'insuffisance cardiaque réfractaire

Mechanical means tend to be used more frequently nowadays for the treatment of congestive heart failure which does not respond to more normal treatment. The indications and limits of such devices, as well as their cost, must be defined. The new problem created by these therapeutic tools is the evolution of the underlying cardiac disease : should it improve the patient will be weaned from the machine, whereas if it worsens heart transplantation would be the only answer. Three types of mechanical support are described. Balloon pumping, and especially intra-aortic balloon pumping, is the technique used most often. It has a true but limited efficacy. Its best indication is cardiogenic shock by left ventricular ischaemia with normal or slightly increased peripheral resistances. Intrapulmonary balloon pumping is occasionally used, but the system can only be set up surgically. Its best indication would seem to be right-sided heart failure by pulmonary hypertension. Circulatory assistance is the second type considered. All types of bypass pumps can be used. The output used is usually less than the patient's theoretical output, the aim being to allow the myocardium to recover. Vascular access for these pumps is either femoral or intrathoracic. An oxygenator may or may not be added to the bypass circuit, and support may be mono- or biventricular. Although the non pulsatile flow has not been shown to be detrimental, this has to be investigated further. The use of these devices is limited by their effects on blood coagulation and pulmonary function. The artificial heart or artificial ventricles are the last devices described. They are either orthotopic, such as the Jarvik type, or extracorporeal, such as the Pierce artificial ventricles. Their ability to support totally the circulation for weeks allows patients to recover somewhat from acute multiple organ failure, so that they can be transplanted in better conditions. The main difficulty in using such devices is patient selection, with the exclusion straight-off of those patients with chronic multiple organ failure who will in any case not be suitable for transplantation later on. Because there are numerous mechanical means now available for the treatment of congestive heart failure no longer responsive to drugs, the choice of device to be used depends on the ultimate goal aimed for, i.g. transplantation or not.     

II. Interference with local myocardial cooling by heat gain during aortic cross-clamping.

We have used a physical model of the thermal conditions of open-heart surgery to study sources of heat input to the heart during local cardiac cooling. Pulmonary and systemic venous return entering the cardiac chambers were the most important sources of heat to the hypothermic heart. In 5 excised hearts, venous return of 100 ml per minute or more entering the left atrium and left ventricle increased mean septal temperature significantly from 8 +/- 1 degrees C to 16 +/- 1 degree C (p less than 0.01). When venous return passed through the right side of the heart and then the left side, it increased mean septal temperature significantly from 7 +/- 0.5 degrees C to 23 +/- 1 degree C (p less than 0.001). Conduction of heat through the pericardium, heat radiation from standard operating room lights, and heat uptake from room air had relatively minor effect and produced no significant increase in myocardial temperature provided all surfaces of the ventricles were irrigated with cold saline. The hypothermic heart can be isolated from heat input by individual caval cannulation, low bypass perfusion rate, systemic cooling to 30 degrees C, and irrigating all surfaces of the ventricles with cold saline.     

Intercontinental LVAS patient transport

Mechanical circulatory support is currently indicated for patients with cardiac insufficiency as a bridge to transplantation or as a bridge to recovery. These systems continue to evolve and improve, and many patients (after they are stabilized) are now able to be discharged from the hospital. This article reports our experience with the intercontinental transportation of a patient while being supported with a Novacor left ventricular assist system (WorldHeart Corp, Ottawa, Canada). While in Japan, the Canadian patient suffered a myocardial infarction and despite coronary artery bypass grafting, the patient remained in a low cardiac output state. After implantation of the left ventricular assist system in Japan, the patient was stabilized and transported by a commercial airline to Canada where he underwent successful heart transplantation.     

Bridge-to-recovery from acute myocarditis in a 12-year-old child

Fulminant myocarditis causes substantial morbidity and mortality, especially in children and young adults. Mechanical circulatory support has become the standard therapy to bridge patients with intractable heart failure to either transplantation or myocardial recovery. Yet, successful weaning from biventricular support with full recovery is extremely rare in the pediatric population. This report describes the successful use of the MEDOS HIA ventricular assist device to bridge a 12-year-old girl to myocardial recovery in a biventricular bypass configuration. The left and right ventricle were completely off-loaded by the pumps and the device provided sufficient cardiac output to normalize end-organ function. Anticoagulation was maintained with i.v. heparin infusion. No neurological complications were detectable and the pump system was free of any macroscopic thrombi. After 19 days of support, cardiac function had recovered and the patient was successfully weaned from the device. Following physical rehabilitation, the patient was discharged home.     

Myocardial protection by retrograde cardioplegic perfusion through the right atrium

Three types of cardioplegic delivery with ink into the isolated canine hearts were compared: (1) antegrade aortic root perfusion (AARP), (2) retrograde coronary sinus perfusion (RCSP) and (3) retrograde right atrium perfusion (RRAP). Ink was not distributed in the area distal to the coronary occlusion by AARP but well distribution in the same area by RCSP or RRAP. The right ventricular wall and ventricular septum were poorly perfused by RCSP but well perfused by RRAP. During cardiopulmonary bypass, RRAP created a fairly rapid cardiac arrest and satisfactory myocardial cooling. During Perfusion, the right heart was somewhat dilated but all the 10 canine hearts rebeat well. The left and right ventricular ejection fraction showed no significant change after bypass. No marked myocardial ultrastructural injury was found in left and right ventricles at the end of 90 minutes' ischemia. 4 patient, 1 of whom had 162 minutes' aortic cross-clamping received RRAP in operations on ascending aorta or coronary arteries and the myocardial protect ion was satisfactory. No complication was found pertaining to RRAP.     

Effects of left heart bypass on cardiac performance following myocardial ischemia.

A series of nine dogs underwent 20 minutes of myocardial ischemia by cross clamping the aorta while total cardiopulmonary bypass. The four dogs that did not have subsequent left bypass all showed a deterioration of ventricular function curve 30 minutes after restarting the heart beat when compared to their own preischemic values. The five animals which were supported for 30 minutes in left heart after bypass all showed essentially unchanged cardiac function after bypass. This study suggests that an improvement of myocardial performance after ischemic damage can be achieved with left heart bypass.     

Myocardial metabolism during fixed-rate pulsatile left ventricular bypass

Fixed-rate pulsatile cardiopulmonary bypass may improve subendocardial perfusion during ventricular fibrillation and has been employed during intermittent aortic cross-clamping. Variable-rate pulsatile left heart bypass that is governed by venous inflow and is asynchronous to the electrical activity of the heart is currently used in clinical practice. To study the effect of fixed-rate pulsation on myocardial metabolism during left heart bypass, six adult pigs underwent alternating periods of pulsatile (PLS) and nonpulsatile (NPLS) centrifugal pump left atrial-to-aortic bypass in randomized block design. Coronary sinus, aortic, and bypass circuit flows were recorded. Oxygen content and lactate concentration of coronary sinus and aortic blood were measured. Pulsatility index and pulse power index during pulsatile bypass were 4.4 and 4.7 (cycles/s)2, respectively. Percent bypass was maximal at a mean pulsation rate of 41.3 and averaged 92.2 and 91.3 for PLS and NPLS, respectively. Myocardial oxygen consumption per minute was reduced 14.3% during NPLS but was unchanged during PLS compared to control (CTRL). Percent lactate extraction was significantly lower than CTRL during NPLS only. Competition for inflow with the ejecting heart appeared to limit circuit pulsation rate and pulse power index. Fixed-rate pulsation is ineffective in reducing myocardial metabolism and should be avoided in left heart bypass.     

Myocardial Metabolism during Fixed-Rate Pulsatile Left Ventricular Bypass

Fixed-rate pulsatile cardiopulmonary bypass may improve subendocardial perfusion during ventricular fibrillation and has been employed during intermittent aortic cross-clamping. Variable-rate pulsatile left heart bypass that is governed by venous inflow and is asynchronous to the electrical activity of the heart is currently used in clinical practice. To study the effect of fixed-rate pulsation on myocardial metabolism during left heart bypass, six adult pigs underwent alternating periods of pulsatile (PLS) and nonpulsatile (NPLS) centrifugal pump left atrial-to-aortic bypass in randomized block design. Coronary sinus, aortic, and bypass circuit flows were recorded. Oxygen content and lactate concentration of coronary sinus and aortic blood were measured. Pulsatility index and pulse power index during pulsatile bypass were 4.4 and 4.7 (cycles/s)², respectively. Percent bypass was maximal at a mean pulsation rate of 41.3 and averaged 92.2 and 91.3 for PLS and NPLS, respectively. Myocardial oxygen consumption per minute was reduced 14.3% during NPLS but was unchanged during PLS compared to control (CTRL). Percent lactate extraction was significantly lower than CTRL during NPLS only. Competition for inflow with the ejecting heart appeared to limit circuit pulsation rate and pulse power index. Fixed-rate pulsation is ineffective in reducing myocardial metabolism and should be avoided in left heart bypass.     

Inotropic stimulation and oxygen consumption in a canine model of dilated cardiomyopathy

Inotropic support for the dilated, failing ventricle results in complex hemodynamic changes affecting preload, afterload, contractility, and heart rate, each of which affects myocardial oxygen consumption. Appreciation of a hierarchy of hemodynamic determinants of myocardial oxygen consumption may be helpful to the clinician trying to balance oxygen demands and hemodynamic performance. We tested the hypothesis that epinephrine alters the hierarchy of hemodynamic determinants of myocardial oxygen consumption in a canine model of dilated cardiomyopathy created by rapid ventricular pacing. Dogs (n = 10) were instrumented to record left ventricular pressure and dimension, and a modified right heart bypass preparation was used to control left ventricular workload. Coronary sinus effluent was quantitatively collected and analyzed for oxygen content and used to calculate myocardial oxygen consumption. Epinephrine administration significantly increased myocardial oxygen consumption in the empty, beating heart; however, when the relationships of multiple determinants of left ventricular work and load were compared before and after epinephrine administration, no oxygen wasting effect was observed. Using multivariate linear regression analysis, a hierarchy of hemodynamic determinants of myocardial oxygen consumption was created. In the untreated heart, stroke work and cardiac output were the primary hemodynamic determinants of oxygen consumption; epinephrine significantly altered the determinants such that wall stress became the dominant hemodynamic determinant of myocardial oxygen consumption. Focused manipulation of wall stress in the treated, failing heart may limit the potentially deleterious effects of inotropic stimulation in this setting.     

Device-supported myocardial revascularization: safe help for sick hearts.

Although advances in both the technology of artificial oxygenation and our understanding of myocardial preservation have made aortocoronary bypass operations safer, clinical settings remain where even these improvements have limited efficacy. We have recently treated 43 severely ill patients with aortocoronary bypass, using a ventricular assist device for intraoperative hemodynamic support and ventricular decompression. For 34 of the patients, preoperative ejection fractions (multigated acquisition) ranged from 0.12 to 0.28 (average, 0.22); 6 patients manifested cardiogenic shock preoperatively, and emergency operations precluded multigated acquisition studies. Twenty-nine patients had preoperative evidence of congestive heart failure, 10 had a prior bypass operation, 9 had major chronic obstructive pulmonary disease, and 2 were Jehovah's Witnesses. The operative technique involved minimal doses of heparin (1 to 1.5 mg/kg), no cardioplegia, and no cardiopulmonary bypass. Revascularization was accomplished on beating, nonworking hearts, with right (40 of 43) and left (43 of 43) ventricles supported by Nimbus Hemopumps (4 of 43) or Bio-Medicus centrifugal ventricular assist devices for an average of 112 minutes. In each case, the patient's lungs were used as the oxygenator. An average of 3.7 bypass grafts per patient were constructed. The left internal mammary artery was used in 41 patients, whereas at least one coronary endarterectomy was required in 20. Six patients had concomitant placement of an automatic implantable cardioverter defibrillator. Two patients (4.6%) died: 1 (with preoperative cardiogenic shock) of low cardiac output on postoperative day 1, and 1 of a severe neurologic deficit on day 8. Follow-up ranged from 2 to 18 months (average, 8.9 months), with all survivors demonstrating improvement in cardiac function in both the early and late postoperative periods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-Term Circulatory and Respiratory Support Using Two Artificial Ventricles and a Fluorocarbon Oxygenator

Using a new heart-lung machine developed at our Institute, experiments were conducted on dogs, donkeys, and monkeys, providing complete and assisted artificial circulation, assisted oxygenation, and perfusion preservation of the heart. The new apparatus consists of two sequentially mounted artificial ventricles working in an antiphase mode; blood oxygenation is accomplished by a reusable oxygenator with a fluorocarbon preoxygenator. Experimental results indicate that clinical use of the apparatus is promising and deserves consideration. The conditions of perfusion were close to physiological conditions and provided long-term survival of the animals. Performance in left ventricular bypass was optimized by monitoring myocardial PO2 and the state of the quick-connect/cut-off assemblies.     

Skeletal Muscle Ventricles: Frontiers in 1995

Abstract: Skeletal muscle ventricles (SMVs) constructed from electrically conditioned latissimus dorsi muscle (LDM) may become an alternative for assisting the failing heart. Left and right heart circulatory assist using SMVs has been performed successfully in both acute and chronic animal models. The configurations used to connect SMVs to the circulation have included a left atrium to aorta bypass, a left ventricle apex to aorta bypass, aortic counterpulsators, a cavopulmonary bypass, and a right ventricle to pulmonary artery bypass. One SMV used as an aortic counterpulsator functioned effectively in the circulation for more than 27 months. Recent application of the pericardium to the SMV as an inner layer and design changes in the connection of the SMV to the circulation have reduced the risk of thrombus formation and SMV rupture. Although several problems have yet to be solved, the goal of the SMV as a permanent circulatory assist device without the limitation of an external power source seems within reach.     

The enabler right ventricular circulatory support system for beating heart coronary artery bypass graft surgery.

BACKGROUND: Beating heart coronary artery bypass graft surgery of the left anterior descending, diagonal, and right coronary artery can be performed safely with the Octopus Stabilization System. However, tilting of the heart, which is necessary to reach the obtuse marginal and distal right coronary arteries, causes hemodynamic instability. This study was performed to investigate the possible role of the Enabler right ventricular circulatory support system in counteracting this instability. METHODS: In 8 sheep, the Enabler cannula was introduced via the jugular vein and positioned with the inlet valve in the right atrium and outlet valve in the pulmonary artery. The Octopus was used to expose the inferior wall and the posterior wall of the left ventricle. The hemodynamic effects of this tilting with and without Enabler right ventricular support were recorded, including Pressure Volume (PV) loops measured by conductance catheters in both ventricles. RESULTS: Tilting caused a reduction in stroke volume (inferior 31%, posterior 17%) and Enabler activation increased stroke volume (inferior 13%, posterior 31%). CONCLUSIONS: Tilting the heart has severe hemodynamic consequences that can be partially counteracted by the use of the Enabler for right ventricle support.     

Levosimendan in cardiac surgery: current best available evidence

Recent upsurge in referral of patients with high perioperative risk or compromised left ventricular function for cardiac surgery has lead to an increasing use of pharmacologic support in the form of vasodilator and inotropic therapy to achieve improvement of tissue perfusion in the perioperative period or to support weaning from cardiopulmonary bypass. Traditionally, perioperatively used inotropic agents, epinephrine, dobutamine, and milrinone, are limited by significant increases in myocardial oxygen consumption, proarrhythmia, or neurohormonal activation. Levosimendan, a new inodilator for the treatment of decompensated heart failure, has also shown promise in elective therapy of cardiac surgical patients with high perioperative risk or compromised left ventricular function, as well as in rescue therapy of patients with difficult weaning from cardiopulmonary bypass. This review article briefly discusses the pharmacology of levosimendan and evaluates current best available evidence to assess the safety and efficacy of levosimendan usage in cardiac surgery.     

Myocardial protection with intermittent cold blood during aortic valve operation: antegrade versus retrograde delivery

BACKGROUND: Intermittent antegrade cold blood cardioplegia is superior to warm blood cardioplegia in patients who have aortic valve operation. This study compared the cardioprotective efficacy of intermittent antegrade and retrograde cold blood cardioplegia with emphasis on metabolic stress in the left and right ventricles. METHODS: Thirty-nine patients who had elective aortic valve replacement were prospectively randomly selected to receive intermittent antegrade or retrograde cold blood cardioplegia. Left and right ventricular biopsies were collected 5 minutes after institution of cardiopulmonary bypass and 20 minutes after cross-clamp removal and were used to determine metabolic changes. Metabolites (adenine nucleotides, amino acids, and lactate) were measured using high-powered liquid chromatography and enzymatic techniques. Serial measurement of troponin I release was also used as a marker of myocardial injury. RESULTS: Preoperative characteristics were similar between groups. There was no in-hospital mortality, and no differences were observed in postoperative complications. Preischemic concentration of taurine was significantly higher in left ventricular biopsies, whereas adenosine triphosphate tended to be lower in the left ventricle. At reperfusion adenosine triphosphate levels were significantly lower than preischemic levels in right but not left ventricles irrespective of the route of delivery. The alanine-glutamate ratio was significantly elevated in both ventricles. Myocardial injury as assessed by troponin I release was also significantly increased in both groups. CONCLUSIONS: Retrograde and antegrade intermittent cold blood cardioplegic techniques are associated with suboptimal myocardial protection. Metabolic stress was more pronounced in the right than the left ventricle irrespective of the cardioplegic route of delivery used.     

Coronary malperfusion due to acute type A aortic dissection; surgical strategy and results

Coronary malperfusion due to acute type A aortic dissection (DAA) is a lethal complication. It is especially difficult to rescue the patients with left coronary malperfusion because of acute global myocardial infarction (AMI), even with successful surgical treatments, including the replacement of the ascending aorta and coronary artery bypass grafting (CABG). We review our experience and illustrate our approach to these critically ill patients. In addition, we classify the mechanism of malperfusion into 4 types based upon perioperative findings and discuss surgical management indivisually. From January 1990 to April 2005, a total of 260 patients were operated for DAA in our institution. Twenty (7.7%) patients, 11 men and 9 women were suffering from coronary malperfusion due to DAA. The mean age was 55 (range 28-72) years. The right coronary artery was involved in 9 patients, and the left in 11. All procedures such as graft replacement and CABG were done on an emergent or urgent basis. Hospital mortality rate of right coronary malperfusion was 22% (2/9 patients), and that related to left coronary malperfusion was 5/11 (45%). Assisting device was required in 9 cases, veno-arterial bypass (VAB) in 6 cases, left ventricular assist system (LVAS) in 1, left heart bypass (LHB) in 1, LHB+right heart bypass (RHB) in 1. We lost all patients using VAB. Only 3 patients supported with strong assist device survived. Aggressive myocardial resuscitation and early operation are the key factors in the management of these critically ill patients. But once severe myocardial infarction occurs, V-A bypass (percutaneous cardiopulmonary support) is useless in treating patients with DAA who develop severe heart failure. We recommend to implant stronger assist device including LVAS immediately before exacerbation of multiple organ failure. In conclusion, surgical management is not easy for emergency patients with DAA in association with myocardial ischemia. However, reasonable surgical results can be obtained with supplemental CABG and strong mechanical support of the left ventricle.