Pulsatile perfusion: its effects on blood flow distribution in hypertrophied hearts

Pulsatile and nonpulsatile cardiopulmonary bypass: review of a counterproductive controversy

In the controversy over pulsatile and nonpulsatile perfusion, most authors have failed to recognize the fundamental physical differences between the two methods. Pulsatile perfusion is polymorphic and its form varies with both the pulsatile source and the vascular system being perfused; nonpulsatile perfusion is by definition unvarying and uniform. While many studies of hemodynamics, metabolism, organ function, microcirculation, and histology show benefits derived from pulsatile perfusion, others do not. The simplest explanation for these conflicts is that different investigators employ different forms of pulsatile perfusion, only some of which are effective. Failure to quantitate adequately the pulsatile components of flow in these studies prevents differentiation between effective and ineffective forms of pulsatile flow and makes comparison of studies difficult. Future research in this area should be directed toward definition of effective pulsatile perfusion by adequate measurement of the pulsatile components of perfusion.

Ventricular fibrillation induced prior to cardioplegic arrest in hypertrophied pig hearts

We hypothesized that by inducing ventricular fibrillation (VF) prior to cardioplegic arrest in nonvented hypertrophied hearts of pigs, the metabolic characteristics of the epicardial and endocardial regions would be compromised compared with animals in which cardioplegic solution was infused while the hearts were in normal sinus rhythm (NSR). These abnormalities would be reflected not only in greater deterioration of myocardial metabolism after reperfusion in the VF group, but they would also be more pronounced in the subendocardial layers of hypertrophied left ventricles. Results obtained in hypothermic hearts (28 degrees C) maintained at 8 degrees to 12 degrees C during cardioplegic arrest demonstrated no major consistent differences in the stores of glycogen, creatine phosphate, adenine nucleotides, and lactate in both groups of hearts, for either layer of the left ventricular myocardium. The only significant difference was slightly lower creatine kinase content in the VF hearts than in the NSR group. It is concluded that induction of VF in hypothermic (28 degrees C), nonvented, hypertrophied hearts prior to infusion of cardioplegic solution does not affect myocardial energy stores compared with hearts in NSR, provided that the period of VF prior to clamping is short (3 minutes) and that the myocardial temperature is lowered to 28 degrees C prior to VF and is maintained at 8 degrees to 12 degrees C during cardioplegic arrest.

Prevention and reperfusion injury following cardioplegic arrest by pulsatile flow

To assess the efficacy of pulsatile flow in minimizing reperfusion injury following cardioplegic arrest, 20 dogs supported by cardiopulmonary bypass underwent 60 minutes of hypothermic, hyperkalemic crystalloid cardioplegic arrest. The effects of pulsatile flow (Group 2), initiated during 30 minutes of reperfusion, on myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) stores, coronary blood flow, and myocardial water content were compared with the effects of linear flow reperfusion (Group 1). Myocardial ATP stores were maintained at preischemic levels by this mode of myocardial protection. However, pulsatile flow prevented the significant decline in ATP levels incurred during linear reperfusion. Creatine phosphate stores, although depleted during arrest, were restored equally, regardless of the mode of reperfusion. The decline in ATP stores was associated with no pathological increase in myocardial water content, but was associated with persistent reactive hyperemia. In contrast, after 30 minutes of pulsatile reperfusion, coronary blood flow was significantly decreased compared with preischemic flow. These data indicate that pulsatile reperfusion can prevent the unique decline in ATP levels associated with the restoration of coronary flow after cardioplegic arrest (reperfusion injury), and support its continuing evaluation as an adjunct to adequate intraoperative myocardial protection.