Modeling of asynchronous myocardial contraction by effective stroke volume analysis

Dynamic right and left ventricular interactions in the pig

NEW FINDINGS

What is the central question of this study? Are the mechanisms that cause ventricular interdependence different when due to primary right to left ventricular pressure loading? What is the main finding and its importance? An instantaneous selective increase in aortic pressure causes an immediate increase in right ventricular end-systolic pressure independent of the pericardium, whereas a selective increase in pulmonary artery pressure decreases left ventricular diastolic compliance owing to a subsequent increasing right ventricular end-diastolic volume as a function of an intact pericardium limiting biventricular volume. Changes in contraction synchrony of either ventricle do not appear to be causing these effects.

ABSTRACT

I characterized the dynamic factors determining ventricular interdependence with and without the pericardium. I measured right (RV) and left ventricular (LV) pressures and volumes simultaneously using conductance catheters in seven pentobarbitone-anaesthetized open-chested 5- to 7-week-old piglets. I studied these effects during apnoea, inferior vena caval occlusion and rapid partial aortic and pulmonary arterial occlusions. Conductance catheter-defined long-axis regional volumes were assessed to define regional contractile synchrony. Closed-pericardium measures were made from an initial (baseline) volume, then after two 20 ml kg^-1 fluid loads followed by an open-pericardium step. Baseline RV and LV volumes were similar. Aortic occlusion increased LV pressures and volumes and RV end-systolic pressure such that RV end-systolic elastance increased without changes in RV contraction synchrony, not affected by the pericardium. Pulmonary artery occlusion increased RV end-systolic pressure but not end-systolic volume. On the subsequent beat, RV end-diastolic pressure increased, whereas LV end-diastolic volume and diastolic compliance decreased. These effects were attenuated by opening the pericardium. Contraction synchrony across longitudinal segments was unaltered by either aortic or pulmonary artery occlusion. I conclude that the determinants of systolic and diastolic ventricular interdependence are different. Increasing RV pressures causes diastolic RV-to-LV interdependence, decreasing LV diastolic compliance and dependent on an intact pericardium. An increase in LV end-systolic pressure increases RV end-systolic elastance independent of the pericardium and has a minimal effect on RV diastolic function or contraction synchrony.

Interaction between left ventricular wall motion and intraventricular flow propagation in acute and chronic ischemia

Myocardial ischemia has been associated with left ventricular (LV) postsystolic shortening. The combination of tissue Doppler imaging and high frame-rate acquisition of two-dimensional color flow makes it possible to study the interaction between LV wall motion and intraventricular flow propagation. The aim of this study was to examine in a clinical model the impact that acute myocardial ischemia and prior myocardial infarct might have on LV flow patterns and to explain the underlying mechanisms from the tissue Doppler data. LV flow propagation and tissue velocities during early diastole were studied in 18 healthy individuals, 17 patients with prior anterior myocardial infarct, and 16 patients before and during percutaneous coronary intervention (PCI) of the left anterior descending artery. Normal individuals had intraventricular flow propagation toward the apex during isovolumic relaxation. During this early diastolic time phase, myocardial velocities measured at mid- and apical septal segment were directed away from the apex. Before PCI, patients without myocardial infarction had similar findings as in normal individuals. In contrast, each patient with either prior myocardial infarction or PCI-induced acute ischemia had flow propagation opposite to normal individuals, and tissue velocities reversed toward the apex during early diastole. Reversal of early diastolic LV flow propagation in acute and chronic anterior myocardial ischemia reflects postsystolic shortening in the dyskinetic apical and septal myocardial segments.