This case report is kindly provided by Michael Rosengarten from McGill and is part of the McGill Cases. These cases come from the McGill EKG World Encyclopedia.
These are two interesting strips that show a rate dependent bundle branch block that is probably a left bundle branch morphology. In the first recording a PVC (labeled V) creates a long RR interval and then allows the left bundle to recover and hence the narrow QRS complex. The lower strip shows the opposite where a PVC couplet shortens the RR interval and induces the left bundle branch again.
