A direct comparison of right and left ventricular performance in the isolated neonatal pig heart

A comparison is presented between the performance of the right ventricle (RV) and the left ventricle (LV) in neonatal hearts studied under conditions of volume loading and tachycardia. Isolated, atrially paced (150 or 300 bpm), isovolumically beating pig hearts (1-3 days of age) underwent retrograde aortic perfusion with a nonrecirculating, crystalloid solution. Ventricular pressure was assessed with saline-filled balloon catheters, which allowed separate loading of the RV or LV. Both ventricles showed an initial increase followed by a leveling off, but no decline, in peak systolic pressure (PSP) and +dP/dt(max) with volume loading up to an end-diastolic pressure (EDP) of 18 mmHg. The LV generated a higher PSP and +dP/dt(max) compared to the RV at equivalent pressure or volume preloads. However, the maximal systolic elastance (E(max)) was comparable for both ventricles. Although the RV demonstrated a greater compliance than the LV, the myocardial relaxation time constant (tau) was similar for both chambers at equivalent volume preloads (sarcomere stretch). Positive dP/dt(max) correlated closely and in the same linear fashion with -dP/dt(max) for both ventricles, indicating that the RV and LV exhibited similar contraction-relaxation coupling. Increasing the heart rate to 300 bpm decreased PSP, +dP/dt(max), and -dP/dt(max) and increased EDP for both ventricles, whereas E(max) and tau were not significantly altered. Thus, although there are differences between the functional properties of the neonatal RV and LV, there are also important similarities, especially with regard to myocardial relaxation.