ABSTRACT
BACKGROUND: Right bundle branch block (RBBB) evident in the precordial ECG leads may be associated with evidence of left bundle branch involvement in the limb leads. Any of the components of the left bundle can be involved, and this complex interventricular conduction abnormality has previously been described in patients with underlying heart disease. OBJECTIVES: To analyze the electro-vectorcardiographic manifestations of RBBB with left middle septal fiber block (LMSFB), with or without left anterior fascicular block (LAFB) in premature atrial beats of patients without apparent structural heart disease. METHODS: Twelve patients (8 men/4 women; mean age: 32±8years) with premature atrial contractions with this conduction abnormality were included. Surface 12 simultaneous lead ECG recordings and the corresponding vectorcardiographic loops were analyzed. RESULTS: The QRS complexes with RBBB and also LMSFB persisted for between 150 and 190ms. There were no q waves in lead I. The maximum spatial vector (72-86ms) was directed posteriorly, superiorly, and leftward, and the terminal forces were oriented anteriorly, inferiorly and rightward. In 10 patients, small q waves were apparent in leads V1-V2 and the frontal QRS axis was -60° and -70°, with the 46ms vector located at -50°±5. All of these patients most probably had LAFB in addition to LMSFB. In two patients, the initial electrical forces were directed anteriorly, inferiorly, and leftward, and the 46ms vector axis in the frontal plane was 6° and 11°, respectively, indicating absence of LAFB. CONCLUSIONS: The combination of RBBB and LMSFB occurring in patients without apparent structural heart disease may be related to the simultaneous occurrence of block of conduction through these components of the Purkinje network. The anterior fascicle of the left bundle may also be involved.
