Does retrograde warm blood cardioplegia provide equal protection to both ventricles? A magnetic resonance spectroscopy study in pigs.

BACKGROUND: The degree of protection provided to the right ventricle during retrograde continuous normothermic blood cardioplegia (RCNBC) remains controversial. The purpose of this study was to determine whether RCNBC is able to provide "adequate" nutritive flow to both ventricles to prevent ischemic metabolism in normal swine hearts. Localized 31P magnetic resonance spectroscopy (MRS) was used to monitor the changes in energy metabolism and intracellular pH (pHi) in each ventricle separately. METHODS AND RESULTS: Isolated normal swine hearts received 20 minutes of antegrade continuous normothermic blood cardioplegia (ACNBC) for collection of control (baseline) data, followed by 20 minutes of RCNBC. This protocol was repeated four times in five hearts and twice in two hearts. Perfusion pressure was maintained between 70 to 85 and 38 to 43 mm Hg during ACNBC and RCNBC, respectively. pHi, creatine phosphate (PCr), inorganic phosphate (Pi), and ATP were measured continuously in each ventricle during ACNBC and RCNBC, using localized 31P MRS with two surface coils. RCNBC resulted in a significant increase in Pi (LV 222% and RV 244% of the baseline levels, respectively) and a decrease in PCr (left ventricle [LV] to 68% and right ventricle [RV] to 31% of the baseline levels, respectively) in both ventricles relative to ACNBC. The PCr level was significantly lower in the RV than in the LV (31% versus 68%, P<.001) during RCNBC. In one series of experiments (n=5) where ACNBC and RCNBC were alternated every 20 minutes (ACNBC, RCNBC, ACNBC, RCNBC, ACNBC) for a total of 100 minutes, Pi and PCr recovered completely. A continuous and significant decrease in ATP was observed in the RV, and no recovery of ATP was found when switching from RCNBC to ACNBC. No significant decrease in ATP was observed in the LV. pHi remained unchanged in both ventricles during alternate ACNBC and RCNBC. CONCLUSIONS: Energy metabolism in the RV is less well preserved than in the LV during RCNBC. A combination of ACNBC and RCNBC seems to provide good cardiac protection as measured by the recovery of cardiac energetics and pHi.

Beyond hyperkalemia: beta-blocker-induced cardiac arrest for normothermic cardiac operations.

BACKGROUND: Four experimental protocols were carried out to assess the ability of esmolol to induce and maintain reversible cardiac arrest under continuous normothermic (37 degrees C) perfusion. METHODS AND RESULTS: In the first protocol, 8 perfused rat hearts were subjected to 20, 60, 90, and 120 minutes of esmolol arrest, after which positive and negative first derivative of pressure, heart rate, left ventricular developed pressure, and left ventricular end-diastolic pressure were evaluated. Arrest was achieved 45 to 60 seconds after beginning the infusion of esmolol. Mechanical arrest was achieved before electrical arrest. In the second protocol, dose-response curves were obtained using isolated (Langendorff) rat and rabbit (n = 6) hearts. The concentrations of esmolol varied from 0.084 to 6.7 mmol/L and from 0.12 to 1.45 mmol/L in the rat and rabbit heart experiments, respectively. In the third protocol, the effects of 20 minutes of normothermic (37 degrees C) ischemia on the function of isolated rat hearts perfused with esmolol-containing Krebs solution were compared with those using high-potassium (25 mmol/L) Krebs solution. Group A subjects (n = 9) received the ischemic injury after being perfused (and arrested) for 20 minutes with either esmolol or potassium (KCl, 25 mmol/L). Group B subjects (n = 10) received the same ischemic insult before being perfused with either esmolol or potassium. Esmolol-treated hearts showed better recovery than those receiving potassium, in terms of +/- dP/dt (p < 0.01), left ventricular systolic pressure (p < 0.01), and left ventricular developed pressure (p < 0.009). Finally, the fourth protocol was done to evaluate the effects of esmolol in a clinically relevant experimental model. Pigs were divided into esmolol (n = 6) and potassium (n = 5) groups and subjected to normothermic cardiopulmonary bypass and a 1-hour period of cardiac arrest. Twenty minutes after stopping infusion of the cardioplegic agents, all animals were weaned off bypass. There were no statistically significant differences between the groups. CONCLUSIONS: Esmolol hydrochloride can be used as effectively as potassium for inducing and maintaining predictable and reversible cardiac arrest during normothermic cardiac operations.