Reconsideration of heart rate-cardiac output relationships and resting cardiac function in patients with brady-arrhythmias.

Abstract

Different types of heart rate (HR)-cardiac output (COP) relationships were compared with their clinical features and hemodynamic findings in 56 patients with brady-arrhythmias (BA). HR was raised by increments of 10 beats per minute (bpm) at 3 min intervals, from spontaneous rates to 100 or 110 bpm by right ventricular pacing. Cardiac and left ventricular (LV) functions at BA were evaluated by intra-cardiac pressures, COP measured by the thermo-dilution method and echocardiographic data. HR-COP relationships were divided into the following 3 types: 24 patients of flat (F), 18 of peaked (P) and 14 of increased (I) type. There were more patients with complete atrio-ventricular block, particularly His-ventricular block, and cardiomyopathic patients with the "P" type than with the other types. Cardiac index, stroke index, stroke work index and systemic vascular resistance were greater in "I", but these differences were not significant. LV peak systolic pressure (LVSP) and end-diastolic pressure (EDP) in "I" increased more than in "F". EDP, LV end-diastolic and end-systolic dimension (ESD) in "P" increased more than in "F". Systolic excursion and LVSP/ESD ratio in "I" increased more than in the other types. Heart failure prior to implantation of pacemaker (PM) and post-PM occurred more frequently in "P". "F" and "I" patients showed comparatively good clinical courses after PM. Thus, cardiac and LV function during BA are maintained in "F" and are impaired in "P", as reported previously. On the other hand, cardiac functions are maintained in "I" as they are in "F", mainly due to contributions of the Frank-Starling mechanism and partly due to maintenance or slight augmentation of contractility.