Interventricular septal wall motion abnormality in left bundle branch block

: An experimental study was performed to clarify the mechanism of perfusion defects in the interventricular septum on T1-201 scintigraphy, as seen in patients with left bundle branch block (LBBB) having normal coronary arteries. In anesthetized open-chest dogs, the following parameters were assessed during right atrial pacing as a control, left ventricular pacing to produce right bundle branch block (RBBB), and right ventricular pacing for LBBB; 1. intramuscular pressure in the interventricular septum, 2. blood flow of the left anterior descending coronary artery (LAD) measured by an electromagnetic flowmeter; 3. regional myocardial blood flow (MBF) determined at three sites, including the interventricular septum, LAD area, and left circumflex coronary artery (LCx) area using the H2-washout method. Aortic pressure, left ventricular pressure, and M-mode echocardiograms were recorded during the procedures. During right ventricular pacing, LAD flow remained unchanged; whereas MBF at the interventricular septum decreased from 99.6 +/- 23.4 to 79.2 +/- 17.6 ml/min/100 g, but MBF at the LCx area increased from 103.2 +/- 19.8 to 122 +/- 18.4 ml/min/100 g. In contrast, there were no significant changes in regional flow in any sites during left ventricular pacing. During right ventricular pacing, an early systolic dip was observed in the septal wall concomitantly with the onset of rise in intramuscular pressure in the interventricular septum. However, the beginning of the rise in left ventricular pressure was delayed 33 +/- 4 msec after that of the septal intramuscular pressure.(ABSTRACT TRUNCATED AT 250 WORDS)