Acute effects of pulmonary artery banding in sheep on right ventricle pressure–volume relations: relevance to the arterial switch operation
The first stage of the two-stage arterial switch operation (ASO) for transposition of the great arteries (TGA) is associated with depressed ventricular function and an unstable immediate post-operative course. It is unclear if this is because of the acute increase in afterload of the thin-walled, low-pressure ventricle by pulmonary artery banding (PAB). To determine the acute effects of afterload increase on the contractile function of thin-walled ventricles, we studied the right ventricular pressure–volume relations of seven sheep before and 30 min after PAB using combined pressure–conductance catheters during inflow reduction. Load independent indices of systolic and diastolic performance were derived from these relations. Pulmonary artery banding increased the mean ratio between right and left ventricular systolic pressure from 0.34 ± 0.05 to 0.64 ± 0.10, P < 0.05 (mean ± SD). There were no significant changes in heart rate and end-systolic volume after banding although there was an incremental trend in the end-diastolic volume and stroke volume. Right ventricular output (530 ± 163–713 ± 295 mL min–1, P < 0.05), slope of the end-systolic pressure–volume relation (ESPVR) (3.7 ± 2.8–10.0 ± 4.8 mmHg mL–1, P < 0.05) and slope of the pre-load recruitable stroke work (PRSW) relation (9.6 ± 1.8–15.0 ± 3.1 mmHg, P < 0.05) were significantly increased indicating improved contractile state after banding. The diastolic function curve was unchanged after banding although the right ventricle (RV) was operating at a larger end-diastolic volume. Hence, the RV of sheep responded to acute pressure overload by demonstrating enhanced contractility and evidence of the Frank–Starling mechanism without associated change in right ventricular diastolic performance.