Esmolol and percutaneous cardiopulmonary bypass enhance myocardial salvage during ischemia in a dog model.

Despite recent advances in techniques of reperfusion for acute myocardial ischemia, myocardial salvage remains suboptimal. Beta-blockers have been shown to limit infarct size during acute ischemia, but their negative inotropic properties have limited their use. Cardiopulmonary bypass is an attractive technique for cardiac resuscitation because it can stabilize a hemodynamically compromised patient and potentially reduce myocardial oxygen consumption. In an attempt to maximize myocardial salvage in the setting of acute ischemia, the combination of esmolol, an ultrashort-acting beta-blocker, with percutaneous cardiopulmonary bypass was evaluated. Four groups of instrumented dogs underwent 2 hours of myocardial ischemia induced by occlusion of the proximal left anterior descending coronary artery, followed by 1 hour of reperfusion. Throughout the period of ischemia and reperfusion, esmolol plus percutaneous cardiopulmonary bypass was compared with esmolol alone, percutaneous cardiopulmonary bypass alone, and control conditions. After the reperfusion period, the extent of infarction of the left ventricle at risk was determined. Four animals had intractable arrhythmias: one in the esmolol plus bypass group, one in the esmolol group, and two in the control group. The extent of infarction of the left ventricle at risk was significantly reduced in the esmolol plus bypass group (30%) compared with bypass alone (52%), with esmolol alone (54%), and with the control groups (59%; p < 0.05). We conclude that in this experimental model the combination of esmolol with bypass improves myocardial salvage after ischemia and reperfusion.

Efficacy of autologous peritoneum as a biological membrane in cardiac surgery.

The risks for reoperative cardiac surgery are related to the presence of intrapericardial adhesions and the possibility of catastrophic injury at repeat sternotomy. In an attempt to develop an improved pericardial substitute and vascular patch, the feasibility of using autologous peritoneum was evaluated. Twelve mongrel dogs were studied. A peritoneal-rectus fascia patch, including the overlying posterior rectus sheath was harvested, via a lateral abdominal incision, and stored in normal saline. In the first group of six animals, a pulmonary artery (PA) window was created and then closed with the peritoneal-rectus fascia patch. In the second group a secundum atrial septal defect was created and then closed with the peritoneal patch on cardiopulmonary bypass (CPB). In each animal, the peritoneal-rectus fascia patch was used to permit pericardial closure. Autopsies performed at 90 days postoperatively revealed only slight intrapericardial adhesion formation and a mild epicardial reaction. Histological examination of the peritoneal-rectus fascia patches revealed intact morphology with active fibroblasts and smooth muscle cells. Proline 14C absorption and autoradiography detected viable cells in the implanted patches. These findings suggest that a peritoneal-rectus fascia allograft could be useful as a biological membrane, and as a satisfactory pericardial substitute in the development of strategies to reduce the risk for reoperative cardiac surgery.

Physical manipulation of subcutaneously implanted cardiac muscle in rat increased plasma atrial natriuretic peptide concentration.

UNLABELLED: To examine the effects of physical stretch on cardiac muscle endocrine activity, the authors transplanted whole neonatal hearts subcutaneously into the back and the ears of the correspondent mother (n = 9). Seven days later, physical manipulation was applied on the implanted heart by stretching the skin and the subcutaneous tissue encasing the implanted cardiac muscle, for a period of five to ten minutes. Such manipulation was repeated approximately every seven days postoperatively for a total of two to four times for each rat. The plasma atrial natriuretic peptide (ANP) levels were measured by radioimmunoassay prior to and immediately following manipulation. Postmanipulation plasma ANP levels were found to increase from the premanipulation levels. At two weeks postimplant, the average increase was 290% with the highest single-specimen increase being nearly twelvefold. The increases observed at two and three weeks following implantation had Signed Rank Test p values of 0.015 and 0.042 respectively. The viability of the implanted hearts was confirmed by cell culture. Light microscopic immunocytochemistry detected ANP immunoreactivity in the implanted cardiocytes. The elevated plasma ANP concentration induced by the manipulation appeared to be correlated with the functional status of the implanted cardiocytes. IN CONCLUSION: (1) Subcutaneously transplanted neonatal myocardiocytes survived for at least three to four weeks while retaining the ability to produce ANP. (2) Physical manipulation of implanted heart induced ANP release. Therefore, cardiac ANP production and release is indeed stimulated by physical stretching.

The cryopreserved stented pulmonary homograft valve in the tricuspid position.

This study was designed to evaluate the early phase events occurring in a stented pulmonary homograft valve implanted in the tricuspid position. A human pulmonary homograft was sterilized in antibiotic solution for 48 hours and cryopreserved in liquid nitrogen (-176 degrees C). Following thawing and trimming, the pulmonary valve was mounted on a Dacron cloth-covered Delrin stent and implanted into the tricuspid position in 3-month-old sheep, for a mean of 95 +/- 5 days. Seven animals were studied. Morphological assessment indicated good structural tissue preservation despite a decrease in viable fibroblasts noted in the distal part of the leaflets. The collagen fibers remained unchanged, and no tissue calcification was found. Viability of the mounted homograft was evaluated using an in vitro tissue culture method, and the viable cells underwent chromosomal analysis to identify whether they originated from the donor or host. Cells with 56 chromosomes, a number intrinsic to sheep cells, were cultured from the donor recipient junctional area. Hemodynamic and angiographic data, which were collected at the time of both implantation and explantation, revealed no functional deterioration of the implanted valve over 3 months. At the time of explantation, six of the seven valves were competent and no cusp retraction or thickening was noted. The seventh valve had deteriorated due to endocarditis. We conclude that stented cryopreserved pulmonary homografts may be useful as bioprostheses in the tricuspid position.

A new biological membrane for pericardial closure.

In an attempt to develop a new and better biological membrane for the pericardium, we evaluated the use of glutaraldehyde treated human amniotic membrane (AM) and compared it to polytetraflouroethylene (PTFE) membrane as a pericardial substitute. Four dogs underwent a right thoracotomy. Two 4 x 3-cm portions of pericardium, 3-4 cm apart, were excised in each animal and both sites replaced with a similar sized patch of 0.8% glutaraldehyde-treated AM and 0.2-mm PTFE membrane respectively. The AM was sutured to the pericardial defect with its smooth surface facing the epicardium. After 18 weeks, the materials were evaluated. The AM patches revealed minimal extrapericardial and no epicardial adhesion. The PTFE patches had moderate to severe epicardial adhesions and severe extrapericardial adhesions. Histopathological examination of AM patches revealed that the integrity of the AM was preserved, however, neovascularization and slight lymphocytic infiltration were observed. In the PTFE patches, there were severe inflammatory infiltration and fibroblast proliferation into both surfaces. AM patches by virtue of their low immunogenicity evoke very minimal host to graft reaction. These AM grafts, however, tear easily unless carefully sutured. Improved methods of treatment may improve suturing strength. We conclude that AM performs satisfactorily and is superior to PTFE as a pericardial substitute.

Novel system for percutaneous cardiopulmonary bypass.

Percutaneous cardiopulmonary bypass (PCPB) has recently come to the forefront of medicine as a technique for resuscitating and supporting patients in various clinical situations. Current systems utilize small-diameter cannulas to aspirate blood under high suction into the cardiopulmonary bypass circuit. Aspiration-based systems have several disadvantages including risk of air embolism, blood hemolysis, and cavitation. Additionally, they are suboptimal for use during open-heart surgical procedures. A system with a venous cannula that employs gravity drainage has been evaluated. Once advanced into position over a guide-wire, the stylet is removed, causing the basket near the end of the cannula to expand. Blood flows into the cannula from side holes and the basket region, which prevents the vessel wall or atrium from collapsing around the catheter and impeding venous drainage. Hemodynamic, hematologic, and histologic examinations were performed on eight anesthetized mongrel dogs during 2 h of PCPB. All animals exhibited adequate tissue perfusion and right and left heart decompression. All animals were successfully weaned from PCPB and after 30 min exhibited normal myocardial function. No ischemic changes were observed in the heart, lung, kidney, or liver by light and electron microscopy. We conclude that full PCPB can be satisfactorily achieved by using a novel percutaneous venous cannula and gravity drainage.

Pulmonary artery balloon counterpulsation for right ventricular failure after right ventriculotomy in the swine.

To assess the efficacy of intrapulmonary balloon counterpulsation in the management of right ventricular failure after right ventriculotomy, we undertook an experimental study in a swine model. To mimic the clinical settings more closely, (1) we left the automatic control of the heart intact (2) did not use cardiopulmonary bypass to support the left side of the heart, and (3) induced right ventricular failure by means of a generous surgical incision (50% to 70% of the anterior wall) of the right ventricle. The criteria set for right ventricular failure were (1) 50% increase in right ventricular end-diastolic pressure, (2) 30% decrease in mean arterial pressure, and (3) 30% decrease in cardiac output. Right ventricular failure was attained in all animals studied: A 230% increase in right ventricular end-diastolic pressure, a 43% decrease in cardiac output, and a 34% decrease in mean arterial pressure were evident after the right ventriculotomy. A specially designed intrapulmonary balloon catheter (Datascope Corp., Oakland, N.J.) was placed into the left pulmonary artery through the right ventricular outflow tract. A Datascope console was used for counterpulsation. Effects of counterpulsation for 40 minutes in a 1:1 mode were assessed after surgical induction of right ventricular failure in 14 swine. Each animal served as its own control. The mean hemodynamic changes are outlined: Right ventricular end-diastolic pressure decreased by 48.9% (p = 0.01). Mean arterial pressure increased by 68.8% (p = 0.01) and cardiac output by 44.2% (p = 0.01). Histologic studies disclosed no morphologic damage to the pulmonary artery or valve in the specimens analyzed. In addition, these results were compared with those in a second group of seven swine in which right ventricular failure was induced by right ventriculotomy and a balloon was placed into the left pulmonary artery but not activated. These results of short-term counterpulsation should be evaluated in a longer term model so as to mimic more closely the clinical setting. If the hemodynamic benefits are duplicated, intrapulmonary balloon counterpulsation should be considered as a simple, effective device when right ventricular failure develops after right ventriculotomy. It effectively improves right ventricular function without damaging the pulmonary artery or valve.