Differences in the recovery of right and left ventricular function after ischaemic arrest and cardioplegia.

Differential susceptibility of right (RV) and left (LV) ventricles to plain ischaemia and the contribution of cardioplegia in reducing the ischaemic damage was evaluated in a sheep model of cardiopulmonary bypass. Sheep (n = 16) were equally divided for the two protocols of the study. Each sheep served as its own control. RV and LV functions were studied and compared by plotting ventricular function curves (Starling and Sarnoff). The mathematical centre of mass (COM) for each curve was computed by a polynomial regression program. The COM values of the contractility indices [stroke volume (SV), stroke work (SW)] represented ventricular heterometric reserve. RV and LV heterometric reserve was significantly (P less than 0.01) reduced after 1 h plain ischaemia, and quantitatively this change was more for RV than for LV (P less than 0.05). As compared to LV, a significantly greater reduction in RVSW was brought about by a significantly (P less than 0.01) greater reduction in RVSV, because there were no significant differences between the post-ischaemic recovery in the RV and LV afterloads. Cardioplegic protection nearly normalized filling pressure and contractility (SV, SW) of both ventricles, but major differences were observed in the recovery of compliance. Recovery in the RV compliance exceeded the control values, and quantitatively the recovery in RVSW was slightly more than in LVSW. The results of this study indicate that the RV suffers more damage from plain ischaemic arrest and hence benefits more from the cardioplegic protection.

Recovery of the conduction system from ischemic arrest and cardioplegia in perfused rat heart.

Normothermic ischemic arrest of the perfused rat heart for 1 h was followed by severe reperfusion arrhythmias, depressed excitability, atrioventricular (AV) node and sinoatrial (SA) node conduction blocks and by marked impairment of contractility. Excitability and conduction recovered within 10 to 15 mins whereas contractility remained greatly depressed. This finding is in agreement with a theoretically based assumption of lesser sensitivity of conduction system to ischemia compared to the working myocardium. When the hearts were exposed to ischemia at 20 degrees C, the sinus rhythm recovered instantaneously upon reperfusion; excitability and SA node conduction times were not significantly different from control; and contractility was much less depressed than after 34 degrees C ischemia. However, AV node conduction times did not normalize even after 15 mins of reperfusion. Potassium cardioplegia (34 degrees C) did not prevent post ischemic arrhythmias but evidently protected both SA node and AV node conduction. Optimum recovery of the conduction system and contractility was achieved by hypothermic (20 degrees C) potassium cardioplegia. Other cardioplegic additives did not further improve the hypothermic potassium protection of the conduction system.

Influence of temperature and rate on the effectiveness of nifedipine in isolated rat heart preparations.

The negative inotropic effect of nifedipine (0.1-2.5 mg/l) was studied on isolated atria at different temperatures (36 degrees, 29 degrees, 22 degrees C) and frequencies of stimulation (20, 60, 180/min). The effect on peak force and dF/dt increased with dose, frequency and cooling from 36 degrees to 29 degrees. Rate of contraction was affected slightly more than rate of relaxation. The effect on time to peak was small, dose and frequency independent but potentiated by lowering the temperature. An analysis of mechanical transients showed that at 22 degrees C and 180/min stimulation the effect of nifedipine gradually diminished and only slowly reappeared upon transition to 20/min stimulation. In spontaneously beating perfused hearts the effects of nifedipine (0.5 mg/l) in general did not differ significantly at 36 degrees and 23 degrees C. The heart rate was reduced and atrioventricular conduction prolonged. At constant heart rate, nifedipine considerably depressed contractions, shortened the action potential duration and reduced the height of plateau. These effects of nifedipine are similar to those of verapamil in other animal species and the results support the idea that calcium antagonists might have secondary intracellular effects apart from direct consequences of slow current inhibition.

Inotropic effects of ionic and nonionic contrast materials in isolated heart preparations.

The inotropic effects of ionic (amidotriazoate) and nonionic (iohexol) contrast material were compared in isolated rat heart preparations. Left atria exposed to amidotriazoate for 10 mins exhibited a dose dependent depression of contractile force approximately twice as large as that brought about by equiosmolar sucrose. When the driving rate was reduced from 60 to 20 beats/min, this specific effect was abolished. The spontaneously beating hearts perfused with amidotriazoate-containing medium had increased resting tension and depressed force of contractions. These effects tended to spontaneously normalize. Upon bolus administration of amidotriazoate the contractile force of perfused hearts was briefly depressed and heart rate, action potential duration and time to peak force decreased. Iohexol did not produce any significant changes in the contractile force. The experiments illustrated direct action of ionic contrast dye on cardiac inotropy probably resulting from an immediate, slowly compensated ionic imbalance, and demonstrated a definite superiority of the nonionic contrast material.

Preservation of left ventricular function during coronary artery bypass graft surgery.

Effects of hypothermic potassium cardioplegia on left ventricular performance and myocardial damage were assessed in 35 patients undergoing coronary artery bypass surgery. Hemodynamic data and enzymatic evidence of left ventricular ischemic damage were examined and compared in the immediate postoperative period. Left ventricular stroke work index showed a significant depression during the first hour with gradual recovery and a significant increase after 24 h. Myocardial specific isoenzyme creatine kinase (CK-MB) showed a very good nonlinear relationship with stroke work index within the whole range, whereas lactate dehydrogenase isoenzyme (LDH-I) had no relationship with the stroke work index. There was a high incidence of transient postoperative arrhythmias and electrical activity took a long time to stabilize. Left ventricular ultrastructure was generally well preserved. The results of this study demonstrate adequate structural and functional preservation of left ventricle by hypothermic potassium cardioplegia.