Time course of structural adaptations in chronic AV block dogs: evidence for differential ventricular remodeling

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Abstract
To determine the nature and time course of biventricular hypertrophy and concomitant electrical and mechanical changes after creation of complete atrioventricular block (CAVB), six adult dogs (22–30 kg) were subjected to serial magnetic resonance imaging (MRI) and electrocardiography. After 6 days of CAVB, left ventricular (LV) mass, ejection fraction (EF), and Q-T time at a paced rhythm of 60 beats/min were already significantly increased. Maximal values were reached within 14–21 days of CAVB: LV mass, from 116 ± 11 to 143 ± 12 g; right ventricular (RV) mass, from 40 ± 3 to 55 ± 6 g; EF, from 68 ± 6% to 86 ± 5%; and Q-T time, from 285 ± 25 to 330 ± 35 ms, allP < 0.05. Cardiac output returned to baseline atday 14. End-diastolic wall thickness increased only in the RV, in which angiotensin type 1 (AT1) receptor mRNA expression was significantly greater. The autopsy correlated well with the MRI results (r = 0.98, P≤ 0.01). In conclusion, electrophysiological, mechanical, and structural adaptation processes after bradycardia-induced volume overload develop rapidly and are completed within 3 wk. The degree of hypertrophy was greater in the RV, which was associated with an increase in AT1 receptor mRNA.