Recent advances in cardiopulmonary bypass and the clinical application of myocardial protection

Coronary Artery Bypass Surgery in Peritoneal Dialysis Patients

Over the last two years, in the Toronto Western Hospital, five chronic renal failure patients suffering from severe symptomatic ischemic heart disease, who had been maintained on peritoneal dialysis underwent coronary artery bypass surgery. One of the five had simultaneous mitral valve replacement. Of the five, four survived with substantial improvement in symptoms, the fifth died soon after the operation. This paper describes the management of these patients and the dialysis technique used in the preand postoperative periods.

Coronary artery bypass surgery (CABG) is effective in the treatment of symptoms of ischemic heart disease and under some circumstances it seems to improve life expectancy (1–4). Cardiovascular disease, which frequently is associated with chronic renal failure (CRF) remains the most common cause of death in dialysis patients (5, 6). Several workers have reported successful cardiac surgery in hemodialysis patients (7–10); however, we know of no relevant literature on similar operations in those maintained on peritoneal dialysis. During the last 5 years there has been a considerable increase in the number of CRF patients receiving peritoneal dialysis (11), and this paper describes five of our patients who underwent bypass operations while maintained on this fonn of therapy.

Controlled cross circulation in dogs: effects on donor hemodynamics

Controlled cross circulation (CCC) was performed in six pairs of dogs for 45 minutes with aortic cross clamping and cardioplegia. Data were collected in donor dogs at 10 minute intervals three times before, three times during, and three times after CCC and included arterial blood pressure, pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), cardiac index (CI), heart rate (HR), blood gas analysis, temperature, maximum rate of rise of left ventricular pressure dP/dt max/End diastolic volume (EDV), blood volume (BV), complete blood count (CBC) and activated clotting times (ACT). Pulse pressure (PP), systemic vascular resistance (SVR), oxygen delivery (DO2), and left ventricular cardiac work (LVCW) were calculated. Arterial blood pressure, CVP, blood gas analysis, temperature, BV, CBC, and ACT were measured in recipient dogs. During CCC, donor hemodynamic changes resembled those observed in models of acute onset arteriovenous fistulas. Insidious BV shifts can occur despite the use of occlusive roller pumps. After CCC, donor hemodynamics resembled acute blood loss, characterized by decreases in mean arterial pressure (MAP), CVP, PCWP, and CI, and increases in SVR and dP/dt max/EDV. These changes were probably caused by pump imbalance and BV shift to the recipient dog.

Crystalloid cardioplegia and hypothermia do not impair endothelium-dependent relaxation or damage vascular smooth muscle of epicardial coronary arteries

Canine hearts were arrested with crystalloid cardioplegic solution (45 minutes at 7 degrees C) to determine whether either cardioplegia or hypothermia impairs the production of endothelium-derived relaxing factor or damages the vascular smooth muscle of epicardial coronary arteries. In addition, isolated coronary artery segments were exposed to either cold (7 degrees C) or warm (37 degrees C) crystalloid cardioplegic solution and physiologic salt solution in vitro for 45 minutes. After cardiac arrest or incubation with the solutions, segments of epicardial coronary artery were prepared and studied in organ chambers. Cardioplegic arrest of the heart or exposure to cardioplegic solution in vitro (7 degrees or 37 degrees C) did not alter endothelium-dependent relaxation of epicardial coronary artery segments in response to adenosine diphosphate or acetylcholine (10(-9) to 10(-4) mol/L). Cardioplegic arrest did not alter G protein-mediated, endothelium-dependent relaxation in response to sodium fluoride. In addition, smooth muscle contraction in response to potassium ions (voltage-dependent) or prostaglandin F2 alpha (receptor-dependent) and relaxation in response to isoproterenol (cyclic adenosine monophosphate-mediated) or sodium nitroprusside (cyclic guanosine monophosphate-mediated) was unaltered after exposure to cardioplegic solution or hypothermia. These experiments demonstrate that hyperkalemic crystalloid cardioplegia does not irreversibly alter function of epicardial coronary arteries. We hypothesize that coronary artery endothelial cell dysfunction identified in previous studies of cardioplegia may have been due to the effects of barotrauma or shear stress on the vasculature and not the effect of cardioplegia per se.

Warm blood cardioplegia as an adjunct to myocardial preservation during coronary artery bypass grafting

A review of the first 52 consecutive coronary artery bypass surgery patients to receive oxygenated blood cardioplegia, with warm reperfusion cardioplegia ('hot shot'), was undertaken to evaluate its effectiveness in myocardial protection. The chosen parameters of ischaemia were: (i) the occurrence of ventricular fibrillation (VF) on release of the aortic cross-clamp (ACC); (ii) the occurrence of bradycardia due to cardiac conduction defects; (iii) the use of inotropes with or without the use of the intra-aortic balloon pump (IABP); (iv) evidence of myocardial infarction (MI) on the postoperative electrocardiograph (ECG); and (v) peri-operative cardiogenic mortality. Warm induction cardioplegia was cooled after cardiac standstill. Repeat cold cardioplegia was given as required at intervals and warm reperfusion cardioplegia was given prior to release of the ACC. Of the 52 patients studied none developed VF after release of the ACC; one patient with pre-operative complete heart block required temporary cardiac pacing; no patient required inotropes or IABP and there was no postoperative MI or mortality. The warm blood cardioplegia technique has not resulted in any detectable evidence of inadequate myocardial protection. A beneficial effect has been demonstrated by the absence of VF, cardiac conduction defects, myocardial failure, MI and mortality.

Guidelines for transfusion support in patients undergoing coronary artery bypass grafting. Transfusion Practices Committee of the American Association of Blood Banks

We have reviewed the impact of evolving issues in coronary artery bypass grafting (CABG) on transfusion support for these patients. Issues include increased awareness of transfusion risks, reappraisal of traditional indicators triggering transfusion, and evolving alternatives to homologous blood transfusion such as autologous blood and pharmacologic therapy. These issues have been prompted by programs, such as the National Institutes of Health Consensus Conferences, to provide physicians with guidelines for appropriate use of blood components. However, evidence suggests that transfusion practice in coronary artery bypass grafting procedures remains variable and does not take into account the results of recently published clinical studies. We have therefore developed guidelines and recommendations for transfusion support in patients undergoing coronary artery bypass grafting. In summary, they are the following. 1. Institutions with coronary artery bypass grafting programs should establish a multidisciplinary approach to use a combination of interventions designed to minimize homologous blood exposure. 2. Prophylactic transfusion of plasma and platelets are of no benefit and therefore carry an unnecessary risk to the patient. 3. Special request products such as designated blood donation from first-degree relatives should not be used because of the risk of transfusion-associated graft versus host disease. 4. For support of intravascular volume, crystalloids or colloids should be used because they do not have the potential to transmit infection.

Colloid versus crystalloid cardioplegia. A prospective, randomized clinical study

The effects of adding colloid (dextran 40, Rheomacrodex) to cardioplegic solution were studied in 55 men undergoing bypass grafting for uncomplicated coronary artery disease. The patients were randomly allocated to group I (n = 27), in which 35 g dextran 40 was added to the St Thomas II cardioplegic solution, or group II (n = 28), which received a standard crystalloid cardioplegic solution. The groups were comparable in regard to preoperative and intraoperative data. In group I the pulmonary vascular resistance index was transiently elevated after extracorporeal circulation and both oxygen consumption and arteriovenous oxygen content difference 2 hours postoperatively were greater than in group II, suggesting better microcirculation. Postoperative normalization of the chest X-rays was more rapid in group I. The clinical course was similar in the two groups.

Preservation of myocardial high energy phosphates during cardioplegic arrest with nifedipine

Nifedipine used both as an additive to cardioplegia solution (CPS) and as pretreatment prior to arrest was studied in a rat model to determine its effect upon ischemic ventricular electromechanical work during arrest and upon high energy phosphate levels. Fifty-one normothermic rats were studied in vivo with infusion of hypothermic (4 degrees C) CPS into the cross-clamped aortic root according to one of the following eight protocols: Group 1, baseline beating hearts; Group 2, CPS containing 15 mEq potassium chloride/liter (KCl/liter); Group 3, CPS containing 30 mEq KCl/liter; Group 4, CPS containing 15 mEq KCl/liter combined with stimulation of the vagus nerve; Groups 5 and 6, CPS with 15 mEq KCl/liter and containing 250 or 500 micrograms of nifedipine per liter; Groups 7 and 8, pretreatment with 100 or 200 micrograms nifedipine/kg given as an intravenous bolus 15 min prior to infusion of CPS with 15 mEq KCl/liter. Time to arrest, number of ischemic ventricular contractions after aortic cross clamping, and ATP and creatine phosphate (CP) levels were recorded. All nifedipine groups arrested more quickly and with fewer ventricular contractions and had ATP and CP levels higher than those of Group 2 (P less than 0.05). There were no differences between the nifedipine groups and Group 3 except that Group 8 (200 micrograms/kg pretreatment) resulted in higher levels of CP than Groups 3, 5, and 6 (P less than 0.05 for all groups). When all groups were combined, time to arrest correlated negatively with ATP (r = -0.863, P less than 0.01) and CP (r = -0.824, P less than 0.01) levels.(ABSTRACT TRUNCATED AT 250 WORDS)