Septal perfusion defects in LBBB (left bundle branch block)

Septal perfusion defects in LBBB (left bundle branch block)

Isolated reversible perfusion defects can occur in the interventricular septum with nuclear cardiology imaging in left bundle branch block (LBBB). It is partly due to the heterogeneity in blood flow between left anterior descending and left circumflex coronary arteries due to the delayed septal relaxation. It may be noted that myocardial blood flow is better in diastole when the myocardium relaxes as the systolic contraction reduces blood flow in systole into the intramyocardial vessels. There may be a reduced oxygen demand due to the late septal contraction which occurs when the wall stress is less.

LBBB often causes septal perfusion defects in radionuclide myocardial perfusion imaging during exercise test. But this is rare with vasodilator stress. A study comparing 10 patients with LBBB, 10 age matched controls and 10 pacemaker patients with right ventricular pacing off and on has been reported. They concluded that the apparent septal perfusion defect in LBBB is mainly due relative lateral hypoperfusion rather than an absolute decrease in septal flow. Switching pacemaker on during exercise decreased the ratio of septal/lateral myocardial blood flow by 17% [1].

Reference

  1. Koepfli P, Wyss CA, Gaemperli O, Siegrist PT, Klainguti M, Schepis T, Namdar M, Bechir M, Hoefflinghaus T, Duru F, Kaufmann PA. Left bundle branch block causes relative but not absolute septal underperfusion during exercise. Eur Heart J. 2009 Dec;30(24):2993-9.