Pump Physiology in the Remodeled Heart

Abstract: This thesis aimed to increase the understanding of pump physiology in the remodeled heart compared to normal pump physiology.Study I was a cross-sectional observatory study investigating the regional contributions to stroke volume in patients with heart failure prior to cardiac resynchronization therapy (CRT) and tested the hypothesis that this characterization of pumping could predict CRT response. 70 patients underwent cardiac MRI (CMR) at baseline and echocardiography at 6-month follow-up. 20 healthy controls were included for comparison. Patients prior to CRT had impaired longitudinal and septal contribution to stroke volume, and increased lateral contribution compared to controls. However, regional contributions to stroke volume did not predict CRT outcome.Study II was a cross-sectional observatory study investigating the feasibility of measuring pressure-volume loops during exercise with CMR and comparing the hemodynamic response during exercise in endurance-trained subjects and sedentary controls. 13 endurance-trained subjects and 10 sedentary controls underwent CMR at rest and during moderate cycling exercise with non-invasive blood pressure measurements in conjunction. Contractility and ventricular efficiency increased, and ventricular-arterial coupling decreased from rest to exercise in both groups. The findings on the hemodynamic response during exercise are in line with known physiology, demonstrating feasibility of the method.Study III was a cross-sectional observatory study investigating the cardiac four-chambered volume response during exercise in endurance-trained athletes and sedentary controls. 20 athletes and 13 controls underwent CMR at rest and during moderate and vigorous exercise. Left and right ventricular and atrial volumes were measured. Athletes decreased right ventricular volumes during exercise, while controls had unchanged right ventricular volumes. Athletes had higher cardiac output than controls for any given exercise intensity.Study IV was a retrospective observatory study investigating the association between ventricular and atrial longitudinal function in patients with different degrees of left ventricular (LV) dysfunction, athletes, and healthy controls. 382 study participants who underwent CMR were included in the analysis. Left atrial (LA) function was to about 50% determined by LV function in the whole cohort.This thesis concludes that the cardiac pump physiology in the remodeled heart differs from the normal heart. In patients with LV dysfunction, LV and LA longitudinal function are impaired compared to the normal heart, andregional contributions to SV are altered in the specific subgroup of patients eligible for CRT. LA function is to a higher degree determined by LV longitudinal function in patients with LV dysfunction and in athletes than in healthy controls, indicating greater dependence on atrioventricular coupling in the remodeled heart compared to the normal heart. The decreased RV and RA volumes from rest to vigorous exercise in athletes, but absent in controls, suggest that the RV undergoes adaptations from regular exercise that may increase pumping capacity.