Blockages in any of the three intraventricular conduction pathways (the right bundle branch, and anterior superior radiations and posterior inferior radiations of the left bundle branch) have specific effects on the QRS pattern as seen on the standard electrocardiogram. The presence of block in two of the three pathways (manifested by right bundle branch block and left axis deviation, right bundle branch block and right axis deviation, alternating complete right and left bundle branch block, or to a lesser extent left bundle branch block) has been found in many patients with documented intermittent heart block or in patients who subsequently develop permanent complete heart block. The presence of this QRS pattern in patients with histories of syncope or dizziness suggests that their symptoms may be due to intermittent heart block. Such patients should be monitored to document heart block, or should have permanent demand pacemakers implanted, or both.
Haft JI, Lasser RP. ECG Patterns Useful in the Diagnosis of Intermittent Heart Block. JAMA. 1972;222(2):184-188. doi:10.1001/jama.1972.03210020034008