Methods for analysis of heart function

Sammanfattning: There is a continuous demand for improvements in methods foranalysis of heart function. This thesis investigates both themeasurement of left ventricular (LV) volume for evaluating theheart function and the exercise electrocardiographic (ECG) testfor diagnosis of coronary artery disease (CAD).Measurements of LV volume curve are important for theassessment of cardiac function. Echocardiography is anon-invasive method that today can provide area and volumecurves. However, it is easier to obtain reliable measurementsof cross-sectional area curves than measurement of the volumecurve. It is hence of interest to show how well the area curvecan predict the volume curve. In a study volume changes wererecorded in six pigs in five intraventricular segments using aconductance catheter. The instantaneous absolute differencebetween the curve shape of global and normalised segmentalvolume was calculated as a percentage of global stroke volume.The mean difference over a cardiac cycle was 4% (range 1-8) atbaseline. The volume curve from a segment at mid-ventricularlevel seems to be a good estimator of the global volume curve.This result also suggests that the conductance catheter mightbe simplified to one segment of measurement.The diagnostic performance in conventional analysis of theexercise ECG test for the detection of CAD is limited to70-75%. The exercise ECG test is the most widely usednoninvasive method for assessing CAD and even a smallimprovement in the diagnostic performance is important. In astudy, aimed at finding the time for the optimal diagnosticinformation during the exercise and recovery phase, 1877electrocardiograms selected from 8322 consecutive patientsundergoing routine exercise test on bicycle ergometer wereevaluated. ST segment amplitude and the difference betweenheart rate matched recovery and exercise ST segment amplitudes(ST/HR difference) were measured. CAD was verifiedangiographically in 669 patients and excluded in 1208 patients,by angiography (119 patients), by myocardial scintigraphy (250patients), or on clinical grounds (839 patients).The diagnostic performance of the two ECG methods employedwas assessed by constructing receiver operating characteristic(ROC) curves for each sample point every 12th second during 10minutes of recovery as well as the last 4 minutes of exercisefor the ST segment amplitude. ST segment amplitude performedbetter after exercise than during exercise and best within thefirst 2 minutes of recovery. Its diagnostic ability did notdiffer from the ST amplitude hysteresis assessed by ST/HRdifference. Both methods performed better in men than in womenand the diagnostic information appeared mainly in leads I,-aVR, II, V4, V5 and V6. The best discrimination of CAD isprovided by analysis of ST segment amplitude changes in 6specific leads early during the recovery phase. Thisinformation should be targeted by exercise ECG diagnosticmethods.Keywords:left ventricular volume, exercise ECG test,coronary artery disease