A Modified Blood Cardioplegia Delivery System Designed to Provide Improved Right Heart Protection

_____________ _ Inadequate right heart protection during cardiac surgery with extracorporeal circulation is a complex problem. Rewarming of the right heart via collateral coronary blood flow, ambient room air, surgical lights and the proximity of the heart to other mediastinal structures, as well as inadequate initial cooling are some of the factors sited as causes of reduced myocardial protection. Recently there has been increased attention to the problem especially in the setting of adequate left heart protection. The goals of this paper are 1) To review and discuss the literature addressing right heart dysfunction and associated abnormalities of cardiac rhythm, 2) To explore the etiology of these complications and 3) To describe a newly designed system of right heart protection utilizing a modified blood cardioplegia delivery system which we feel will be helpful in reducing the incidence of these complications. Introduction ______________ _ Historically the focus of hypothermic cardioplegia for myocardial protection has been the preservation of left ventricular function. The importance of achieving this goal need not be emphasized to the surgeon or perfusionist confronted by a patient with compromised myocardial function. Considerable time and effort is usually required to wean him from cardiopulmonary bypass and a stormy post operative course often follows. During this period the assistance of the intra-aortic balloon pump or some other such aggressive invasive modality is often necessary. Even with the use of such heroic efforts too many of these patients die. Fortunately, the frequency of this event has been greatly reduced by the development and implementation of advances in surgical and perfusion theory and technique. With these advances now a part of our Direct communications to: Allen L. Evers, R.N., C.C.P., PSICOR, Inc., 810 East Grand River, Brighton, MI 48116 practice we can direct our focus to solving some of the more ellusive and less common problems and complications that are associated with cardiopulmonary bypass. Post-operative right ventricular dysfunction and peri-operative conduction disturbances are two such complications. Until recently it has been presumed that the right ventricle is less susceptible to peri-operative ischemic damage. Likewise, it was thought that such damage, when it occurred, could be well tolerated by volume loading the patient. However, recent studies indicate neither of these assumptions to be true. ••A·••• The frequency with which significant right heart dysfunction occurs, as measured by ejection fraction, has been reported at about 38 percent. 9 The incidence of peri-operative conduction disturbances, i.e., supraventricular tachyarrythmias, and varying degrees of atrio-ventricular block, has been reported to be as high as 40 percent. 10 The etiology of this complication has been attributed to the exquisite sensitivity to ischemia of the heart's conductive tissue relative to other myocardial tissues. 11 Since the sinus node, inter-atrial and internodal pathways and the atrio-ventricular node are located in the right atrium the argument has been proposed, when conduction abnormalities occur, that we have not provided adequate myocardial preservation for that region of the heart. It is the purpose of this paper to review and discuss recent medical literature that suggests we are not successfully protecting either right ventricular or right atrial function. We will also describe a modified blood cardioplegia delivery system designed to provide augmented right heart preservation. Literature Review In 1979 Rosenfeldt et al, 12 utilizing a porcine heart model, described the effects of various heat sources on myocardial rewarming during hypothermic cardioplegic arrest. The factors studied were 1) Pulmonary and systemic venous return and the effect of atrial cannulation technique, 2) Systemic body temperature