T-vector and T-loop morphology analysis of ventricular repolarization in ischemic heart disease

Background: Sudden cardiac death (SCD) is responsible for about half of all cardiovascular deaths in the western world. Heterogeneous ventricular repolarization (VR) is a common denominator in the genesis of malignant ventricular arrhythmias responsible for SCD and the presence of coronary artery disease (CAD) is an aggravating factor. A non-invasive method reliably reflecting VR heterogeneity could therefore play a significant role in the preventive strategy against SCD. This thesis focuses on VR in CAD and acute ischemia. Aims: To study VR abnormalities in patients with CAD using 3-dimensional (3-D) vectorcardiography (VCG). To assess VR at rest and during acute ischemia in patients with/without major co-morbidities, including hypertension and left ventricular hypertrophy (LVH), applying recently developed VCG parameters. To assess VR alterations in relation to the amount of the ischemic myocardium. To explore the prognostic value of these parameters in terms of cardiovascular (CV) mortality and morbidity during long-term follow-up. Studies I-II: As a first step, VR measures at rest and during acute ischemia were analyzed in a subgroup of 56 CAD patients selected to create a relatively homogeneous group without obvious confounders affecting the VR response, e.g. previous myocardial infarction (MI) or LVH. They were identified from a cohort of 187 patients planned for an elective single-vessel percutaneous coronary intervention (PCI). In the next step, the electrophysiological consequences of myocardial hypertrophy were assessed in all 187 CAD patients, including 33 with LVH and 54 with a history of hypertension. VR was examined in terms of the maximum T-vector orientation in space by azimuth and elevation and the angular relationship with the main depolarization vector, the QRS-T angle. The planarity of the T loop (Tavplan), its shape and roundness (Teigenv) and the area under the 3-D T-wave (Tarea) were analyzed as well. At rest, the Tarea and Teigenv differed si