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

To determine the nature and time course of biventricular hypertrophy and co ncomitant electrical and mechanical changes after creation of complete atri oventricular block (CAVB), six adult dogs (22-30 kg) were subjected to seri al magnetic resonance imaging (MRI) and electrocardiography. After 6 days o f CAVB, left ventricular (LV) mass, ejection fraction (EF), and Q-T time at a paced rhythm of 60 beats/min were already significantly increased. Maxim al 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 +/- 3 5 ms, all P < 0.05. Cardiac output returned to baseline at day 14. End-dias tolic wall thickness increased only in the RV, in which angiotensin type 1 (AT(1)) receptor mRNA expression was significantly greater. The autopsy cor related well with the MRI results (r = 0.98, P <less than or equal to> 0.01 ). In conclusion, electrophysiological, mechanical, and structural adaptati on 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 AT(1) receptor mRNA.