Application of dipole analysis for the diagnosis of myocardial infarction in the presence of left bundle branch block.

The residue value on dipole analysis (the ratio of non-dipolar component to the measured body surface potentials) was estimated mathematically in 16 patients with left bundle branch block. Patients were classified into those with (group A, nine patients) and those without (group B, seven patients) a perfusion defect on thallium-201 myocardial scintigraphy. For the entire QRS complex the residue of group B was smaller than that of normal subjects (20.0 +/- 4.1% versus 24.6 +/- 3.5%, p less than 0.05). Group A showed a greater mean residue value than group B (27.4 +/- 4.4% versus 20.3 +/- 2.4%, p less than 0.01) only during the initial one-third of the QRS complex. All but one patient of group A and only one patient in group B showed a high peak on the residue curve during the initial stage of the QRS complex. The maximal residue value of group A during the initial QRS complex was significantly greater than that of group B (40.9 +/- 10.9% versus 23.4 +/- 5.4%, p less than 0.01). An arbitrarily selected criterion of the maximal residue value greater than or equal to 30% during the initial QRS complex showed a sensitivity of 89% with a specificity of 86% for the diagnosis of myocardial infarction in the presence of left bundle branch block. These results might be related to the complex ventricular activation around the infarcted area even in the presence of left bundle branch block in which intramyocardial conduction with a simple activation front predominates. Dipole analysis appeared to be a valuable method of diagnosing myocardial infarction in the presence of left bundle branch block.