Repeatability of haemodynamic responses to cardiac stimulations by ambulatory monitoring of left ventricular function.

Ambulatory monitoring (VEST) of left ventricular (LV) function has been shown to be accurate and repeatable. The aim of this study was to assess VEST repeatability in the evaluation of haemodynamic responses to different cardiac stimulations. Twelve patients (all men, mean age 59 +/- 8 years) underwent two separate VEST studies 5-day apart. In both studies, LV function was continuously monitored at rest and during different cardiac stimulations: 1) changing position from supine to upright (tilt); 2) sustained isometric exercise (handgrip); and 3) sublingual administration of 5 mg of nitroglycerin (NTG). Changes from baseline to peak response (delta) in the heart rate, ejection fraction, end-diastolic volume, end-systolic volume, stroke volume and cardiac output were evaluated. Reproducibility was assessed by computing, the coefficient of repeatability. In addition, the differences between the delta values obtained with the two VEST studies were plotted against their mean. This plot allowed us to detect whether there was any relationship between the error in the measurements and the best estimate of the "true value". No statistically significant differences between the two VEST studies were found in the haemodynamic changes in heart rate, ejection fraction, end-diastolic volume, end-systolic volume, stroke volume and cardiac output induced by handgrip, tilt and NTG. For each parameter the mean difference was not significantly different from zero and no significant relationship between the error and the "true value" was observed. Our results demonstrate that VEST has a good repeatability in measuring cardiac haemodynamic responses to different types of stimulations.