Altered cardiac histology following apical right ventricular pacing in patients with congenital atrioventricular block

Previous studies have demonstrated that right ventricular apical pacing inh erently alters ventricular contraction, regional blood flow, wall stress, a nd predisposes to diminished function. However, histological consequences o f chronic apical pacing potentially contributing to the observed ventricula r dysfunction remain conjectural. Previous canine studies have demonstrated histopathological cellular abnormalities with apically initiated ventricul ar pacing that map result in the observed diminished ventricular function. To determine if comparable adverse changes also occur in the clinical setti ng, 16 endomyocardial biopsies were obtained from 14 age-matched patients w ith congenital complete atrioventricular block (CCAVB) and otherwise normal anatomy, divided into two groups: eight biopsies (median patient age 15.5 years) from patients prior to pacemaker implant and another eight biopsies (median patient age 16 years) from patients following 3-12 pears (median 5. 5) of chronic ventricular pacing. In one patient, biopsy samples were obtai ned before and after pacing. Results demonstrated a significant (P < 0.05) increase in histopathological alterations among the patient biopsy samples following pacing, consisting of myofiber size variation, fibrosis, fat depo sition, sclerosis, and mitochondrial morphological changes. These findings indicate that chronic apical right heart ventricular pacing may adversely a lter myocellular growth, epecially among the young, on the cellular and sub cellular level, potentially contributing to the diminished function observe d clincially.