Changes in ventricular repolarization during percutaneous transluminal coronary angioplasty in humans assessed by QT interval, QT dispersion and T vector loop morphology

Objectives. Based on clinical, epidemiological. and experimental data, tran sient cardiac ischaemia is one of the major triggering factors of malignant ventricular arrhythmia. According to animal studies. Increased dispersion of repolarization is of pathophysiological relevance in this context. There fore we explored the impact of myocardial ischaemia during single vessel co ronary angioplasty on the change in ventricular repolarization, measured by QT and JT intervals and their dispersion in the 12-lead electrocardiogram. We also assessed a novel method, the 3-dimensional T vector loop. to find out whether it was sensitive to changes in ventricular repolarization durin g ischaemia, and whether there was any correlation with changes in the disp ersion of the QT and/or JT intervals. Design. This study was prospective with consecutive patients, Only patients in sinus rhythm and without bundle branch block were included. Setting. All coronary angioplasties were performed at Norrlands University Hospital, Umea. The analysis of the material was performed at the Karolinsk a Hospital, Stockholm. Subjects. Twenty-nine consecutive patients went through 30 elective one-ves sel percutaneous transluminal coronary angioplasty (PTCA) procedures. PTCA was performed in 10 stenoses of the left anterior descending, 10 of the lef t circumflex, and 10 of the right coronary artery. Interventions. A 12-lead electrocardiogram was recorded continuously as par t of routine monitoring of the patient during PTCA and the T vector loop wa s calculated from the simultaneously recorded. X, Y, Z leads. Main outcome measures. Repolarization was assessed by the QRS, QT and JT in tervals as 12 ell as by the T vector loop parameters (Tarea, Tavplan, and T eigenv) before and at the end of the first occlusion during PTCA. Results. PTCA. with an average occlusion time of 171 +/- 60 s (mean -C SD), induced ischaemia on the 12-lead electrocardiogram in 73% of cases. The ov erall response for the 30 procedures was a significantly increased dispersi on of ventricular repolarization, both corrected and uncorrected for heart rate. QT dispersion increased by, on average, 19% from 74 +/- 35 to 88 +/- 36 ms, QT(c) dispersion by 27% from 71 +/- 33 to 90 +/- 12 ms, and JTc disp ersion by 19% from 78 +/- 32 to 94 +/- 43 ms (P < 0.05). The T Vector loop became more circular and bulgy during occlusion tall three parameters chang ed by between 33% and 59%). There was a significant correlation between cha nges in one of the T vector loop parameters (Teigenv), and changes in JT an d QT dispersion in the left anterior descending group. Conclusions. Transient ischaemia during PTCA induced significant changes in ventricular repolarization, especially during occlusion of the left anteri or descending artery and resulted in a significant increase in both QT and QT(c) dispersion. The degree of QT dispersion was such that several patient s were at risk of ventricular arrhythmia, if a proper triggering extrasysto le had occurred. In addition, and as an original observation, the 3-dimensi onal T vector loop morphology seemed even more sensitive to coronary occlus ion than QT dispersion.