Introduction:In coronary bifurcation lesions, clinical events mainly occur due to main branch occlusion even in big side branch bifurcations. However, its mechanism has not been fully evaluated. QT prolongation and QT time variability have been suggested as markers for electrical instability and sudden cardiac death. This study was performed to evaluate the different arrhythmogenic potential of main and side branches using QT segment changes during transient coronary flow occlusion.
Methods: Patients with true bifurcation lesions of left anterior descending coronary artery (LAD) and diagonal branch (Dg) were enrolled. A 12-lead ECG was obtained at rest and after 1-minute balloon occlusion of LAD and Dg. QT/QTc dispersion (QTD/QTcD) was defined as the difference between the maximal and minimal QT/QTc intervals.
Results: 62 patients with high quality ECG were included in this analysis. Mean baseline QT, QTc and QTD was 376.9짹35.1, 400.1짹33.3 and 81.9짹28.9 msec, respectively. ST segment elevation during 1-minute balloon occlusion was more frequent in LAD than in Dg (92% vs. 35%, p<0.001). There was no hemodynamically significant arrhythmic event during 1-minute of balloon occlusion. Mean QTc was prolonged significantly in LAD, but not in Dg (412.7짹33.8 msec in LAD and 406.0짹30.3 msec in Dg, p=0.05). Mean QTD after 1-minute occlusion was 100.0짹35.2 msec in LAD and 83.7짹27.2 msec in Dg (p=0.001). The change of QTcD from baseline was also higher in LAD occlusion than in Dg occlusion (20.4짹46.6 vs. 2.4짹32.5 msec, p<0.001). There was no difference in QTc and QTcD between patients with and without ST segment elevation during Dg occlusion.
Conclusion: The increase in QTc and QTcD after LAD occlusion was greater than those of Dg occlusion and suggests that total occlusion of main vessel can cause more electrical instability and arrhythmogenic potential. These differences may explain more favorable outcome of side branch stenosis than main branch stenosis in coronary bifurcation lesions.