ANTEGRADE AND RETROGRADE CONTINUOUS WARM BLOOD CARDIOPLEGIA - A P-31 MAGNETIC-RESONANCE STUDY

Background. Retrograde normothermic blood cardioplegia has been shown to provide myocardial protection during certain bypass procedures. How ever, a number of animal studies have shown less than optimal myocardi al protection with this technique. Methods. Isolated, beating porcine hearts were perfused antegradely (aortic root pressure = 75 to 95 mm H g) for 30 minutes. Arrest was induced and maintained for 60 minutes wi th high K+ blood cardioplegia delivered either antegradely (n = 8) or retrogradely (n = 8) (coronary sinus pressure = 35 to 55 mm Hg). Perfu sate was switched to normokalemic blood for recovery of sinus rhythm ( 30 minutes). Intracellular pH, creatine phosphate, inorganic phosphate , and adenosine triphosphate were monitored continuously and noninvasi vely with phosphorus 31 magnetic resonance spectroscopy throughout the experiment, and functional variables (rate-pressure product and the p ositive and negative first derivatives of left ventricular pressure) w ere assessed concurrently. Results. Antegrade cardioplegia maintained high-energy metabolites, intracellular pH, and myocardial function. Re trograde normothermic blood cardioplegia resulted in an increase in in organic phosphate (197% +/- 15% of control) and a decrease in creatine phosphate (51% +/- 6% of control). There was no significant differenc e in myocardial function between the two groups (p > 0.05). The magnet ic resonance spectroscopy data indicate ischemia occurred within 2 min utes of the initiation of retrograde perfusion. Conclusions. This stud y suggests that retrograde normothermic blood cardioplegia causes a tr ansition of the myocardium to ischemic metabolism in the normal porcin e heart.