ECG left anterior fascicular block reveals diverse patterns on scintigraphic phase analysis

Abstract

Left anterior fascicular block (LAFB) remains an uncertain diagnosis by scalar ECG, particularly with coexisting inferlor infarction. To assess the use of phase analysis in LAFB, left ventricular phase and amplitude maps were evaluated in the 70-degree left anterior oblique projection in eight control patients and 13 patients with LAFB who met the ECG criteria of Warner et al. The left ventricular region was divided into anterior (A) and inferior (I) segments. Contraction patterns were assessed by examination of the sequence of phase angies (φ), relative contraction time of the anterior versus inferior segments was assessed from the difference between segment mean phase angles, Δ φ A−1, determined from the phase histogram, and duration of contraction was assessed by histogram width. Relative stroke volume was assessed on the amplitude image. Eight control subjects had normal amplitude, contraction of the anterior before inferior segment, narrow histrogram width, and a normal ECG. Among the 13 patients with ECG LAFB, seven were concordant, with phase analysis demonstrating anterior contraction delay. Two of seven patients had narrow histograms and normal amplitude, which were compatible with isolated anterior conduction delay, and five of seven patients had broad histograms and reduced anterior amplitude, compatible with anterior infarction. Phase analysis was discordant with ECG LAFB diagnosis in six patients. All showed contraction of anterior segments before inferior segments as in normal subjects. Four had broad histograms and reduced inferior amplitude, compatibie with prior inferior infarction without LAFB, and two had normal phase and amplitude maps. Phase patterns appear characteristic of LAFB with or without associated infarction. Phase and amplitude analysis may ciarify the ECG diagnosis of LAFB and provide etiologic insight.