Background: Discrepancy exists between anatomical and functional severity and clinical outcomes in bifurcation lesions. However, its mechanism has not been fully evaluated. We performed this multicenter, prospective study to compare the physiologic, electrocardiographic and clinical differences between main and side branches in bifurcation lesions.
Methods: Patients with de novo proximal or mid LAD true bifurcation lesions with a planned diagonal (Dg) branch intervention were prospectively enrolled. A total of 73 pateints were enrolled to detect >25% difference in the rate of ST segment elevation during 1-min balloon occlusion between LAD and Dg. To be included, Dg branch needs to be >2.25mm in diameter. Fractional flow reserve (FFR) was measured before intervention and coronary wedge pressure (Pw) was measured during 1-minute balloon occlusion in both LAD and Dg branch using a pressure wire. Severity of chest pain and 12-lead ECG changes were assessed during 1-minute balloon occlusion in each branch. To estimate the myocardial mass supplied by a Dg branch, new scoring system (SNUK score) was developed (Table).
Results: Mean FFR of LAD and Dg branch before intervention were 0.67짹0.10 and 0.71짹0.11, respectively (p=0.02). Presence of ST-segment elevation during 1-minute balloon occlusion was more frequent in LAD than in Dg branch (92% vs 35%, p<0.001) and pain score was higher in LAD than in Dg branch (4.1짹3.5 vs 2.3짹2.7, p<0.001). The mean corrected QT interval during balloon occlusion was longer in LAD than in Dg branches (412짹34 vs 406짹30 msec, p<0.001). Coronary wedge pressure(Pw) and Pw/Pa were significantly higher in Dg branches than in LAD (Pw:26.7짹9.4 vs 21.0짹6.5, p<0.001; Pw/Pa: 0.27짹0.08 vs 0.22짹0.07, p=0.001). There was no diffirence in vessel size, lesion length and % diameter stenosis between Dg branches with and without ST-segment elevation during balloon occlusion. However, SNUK score was higher in Dg branches with ST-segment elevation (3.4짹0.9 vs 2.3 짹1.4, p<0.001). Among lesions with SNUK score<3, 92% (24/26) of lesions did not show ST-segment elevation during 1-minute balloon occlusion.
Conclusion: There were differences in electrocardiographic, physiologic and clinical relevance between LAD and Dg branch in true bifurcation lesions. These differences seem to be the mechanism of the discrepancy between anatomical and functional severity and clinical outcomes in coronary bifurcation lesions.