Noninvasive electrocardiographic parameters to assess interventricular dyssynchrony in dogs with bundle branch blocks

To define electrocardiographic features of complete left bundle branch block (LBBB) and right bundle branch block (RBBB), and the use of R-peak time (RPT) to identify interventricular dyssynchrony in dogs with BBB.

Twelve-lead ECG tracings of 20 dogs with RBBB, 20 with LBBB, and 60 healthy dogs were retrospectively analyzed and RPT was measured in precordial leads. Interventricular dyssynchrony index (IDI) was than calculated.

In RBBB, mean electrical axis (MEA) was -111° [-120/-100°], V₁RPT was significantly longer (61 ms [55-72 ms]) than left precordial leads RPT (V₂:25 ms [22-30 ms]; V₃:25 ms [22-29 ms]; V₄:24 ms [21-29 ms]; V₅:25 ms [22-29 ms]; V₆:25 ms [22-29 ms]) and when compared to normal dogs (P < 0.001). In LBBB, MEA was 76° [70/81°], RPT in left precordial leads was significantly longer (V₂:49 ms [34-58 ms]; V₃:49 ms [43-57 ms]; V₄:52 ms [45-62 ms]; V₅:53 ms [45-63 ms]; V₆:55 ms [45-63 ms]) than V₁RPT (17 ms [15-20 ms]) and when compared to normal dogs (P < 0.001). V₁RPT > 28 ms and V₅RPT > 36 ms were found to predict the presence of RBBB and LBBB with a sensitivity of 100% and 96.7%, and a specificity of 96.7% and 99.5%, respectively. The IDI was 23% [16-29%] in normal dogs and significantly greater in dogs with RBBB (33% [30-38%]; P < 0.001) and LBBB (32% [23-41%]; P = 0.006).

This study defines ECG features and RPT in dogs with BBB. Electrical interventricular dyssynchrony can be defined using IDI in dogs with BBB.