Q. Rate Related Bundle Branch Block?
The term has often implied the absence of significant coronary or myocardial pathology. It cannot be judged without taking the total clinical picture into consideration. It was believed that in older subjects with LAD, the block would occur at slower heart rates. Wayne and colleagues however, found that 14 to 16 patients with rate related bundle branch blocks had evidence strongly suggestive of CAD. Whenever a block pattern spontaneously occurs during exercise or with hyperventilation, one should consider the possibility of Wolff-Parkinson-White (WPW) syndrome. It is very important to recognize WPW syndrome because the ST-segment depression in this condition does not mean ischaemic heart disease and the short PQ wave and delta wave are easy to overlook. In patients with right bundle branch block, ST depression in leads V2 and V3 is not ischaemia whereas that in V5 and V6 is suggestive of ischaemia. There is a consensus as stated in ACC/AHA guidelines that one cannot diagnose exercise induced ischaemia in patients with left bundle branch block from the ECG. The concept that patients who convert to LBBB at low heart rates are more likely to have CAD than those who convert at high heart rates has not been confirmed.