Admittance-based pressure-volume loop measurements in a porcine model of chronic myocardial infarction

The aim of this study was to validate admittance-based pressure-volume (PV) loop measurements for the assessment of cardiac function in a porcine model of chronic myocardial infarction. The traditional PV loop measurement technique requires hypertonic saline injections for parallel conductance correction prior to signal conversion into volume. Furthermore, it assumes a linear relationship between conductance and volume. More recently, an admittance-based technique has been developed, which continuously measures parallel conductance and uses a non-linear equation for volume calculation. This technique has not yet been evaluated in a large-animal model of myocardial ischaemia. Eleven pigs underwent invasive PV measurements with the admittance system (AS) and the traditional conductance system followed by three-dimensional echocardiography (3DE). After baseline measurements, pigs were subjected to 90 min left anterior descending coronary artery occlusion, followed by the same measurements at 8 weeks follow-up. In the healthy heart, the AS showed good agreement with 3DE for left ventricular volumes and a reasonable correlation for ejection fraction (r = 0.756, P = 0.007). At follow-up, an increase in end-systolic volume was observed with 3DE (+15.4 ± 14.4 ml, P = 0.005) and the AS (+34.6 ± 36.1 ml, P = 0.010). The ejection fraction measured with 3DE (-13.2 ± 5.2%, P < 0.001) and the AS (-20.3 ± 11.2%, P < 0.001) significantly decreased. We conclude that the AS can be used for quantitative monitoring of changes in cardiac function induced by myocardial infarction and provides comparable results to 3DE, rendering it a useful tool for functional testing in large-animal cardiac models.