d,l-sotalol enhances baroreflex sensitivity in conscious rats surviving acute myocardial infarction

Influence of D,L-sotalol on baroreflex sensitivity response to posture following coronary artery bypass graft surgery in men and women

Low baroreflex sensitivity (BRS) following coronary artery bypass graft (CABG) surgery increases the risk of sympathetically mediated cardiac arrhythmias. To reduce this risk, D,L-sotalol, a nonselective β-adrenergic receptor antagonist (Class II) and an antiarrhythmic (Class III), is prescribed postoperatively. However, its effect on BRS has not been reported. The purpose of this study was to characterize the influence of D,L-sotalol on BRS measures in supine and standing postures 4 days following CABG surgery. BRS was measured in 27 men and 10 women receiving D,L-sotalol and compared with archival data for 21 men and 10 women obtained prior to the routine administration of D,L-sotalol. In the latter (control) group, 61% had BRS of less than 3 ms/mmHg in the supine posture and 74% in the standing posture compared to 42% with less than 3 ms/mmHg in the supine posture and 65% in the standing posture in the D,L-sotalol group. Men in the D,L-sotalol group showed higher R-R interval and BRS in both supine and standing postures compared with controls. Women in the D,L-sotalol group had higher R-R interval in the supine posture. The higher BRS in men not only reduces the risk of arrhythmias after CABG surgery but may also allow a more rapid circulatory response to the standing posture, thereby decreasing the risk of syncope.

Preservation of the baroreceptor heart rate reflex by chemical sympathectomy in experimental heart failure

BACKGROUND

The mechanisms underlying impaired baroreflex sensitivity in congestive heart failure (CHF) are incompletely understood. The purpose of the present study was to test the hypothesis that this alteration depends on the marked degree of sympathetic overactivity known to characterize the CHF syndrome.

METHODS AND RESULTS

Eight-week-old rats were subjected to induction of postmyocardial infarction CHF obtained by coronary ligation (Lig), chronic chemical sympathectomy by 6-hydroxydopamine (Sx), both interventions (Sx-Lig), or neither intervention (Veh-Sham, sham surgery, and vehicle administration). Four weeks after infarction, in conscious state, baroreflex sensitivity was assessed from the bradycardic responses to graded phenylephrine-induced elevations in blood pressure (BP). Left ventricular (LV) diameter was assessed by echocardiography, and plasma catecholamines were assayed to estimate sympathetic activity. Lungs were eventually excised and weighed (LW). CHF was associated with the following: (1) no changes in BP and heart rate; (2) sympathetic overactivity (norepinephrine, 320.2+/-53.8 pg/mL for Veh-Lig versus 173.4+/-20.5 pg/mL for Veh-Sham, P<0.01), prevented by Sx (181.2+/-35.5 pg/mL for Sx-Lig versus 159.8+/-33.1 pg/mL for Sx-Sham, P=NS); (3) LV enlargement (10.3+/-0.7 mm for Veh-Lig versus 6.8+/-0.6 mm for Veh-Sham, P<0.01), irrespective of Sx (9.7+/-0.7 mm for Sx-Lig versus 6.6+/-0.5 mm for Sx-Sham, P<0.01); (4) pulmonary congestion (LW, 7.55+/-0.40 mg per gram of body weight for Veh-Lig versus 5.21+/-0.44 mg per gram of body weight for Veh-Sham, P<0.01), marginally attenuated by Sx (6.54+/-0.28 mg per gram of body weight for Sx-Lig versus 4.98+/-0.22 mg per gram of body weight for Sx-Sham, P<0.05); (5) reduction in baroreflex sensitivity (0.443+/-0.032 ms/mm Hg for Veh-Lig versus 0.860+/-0.420 ms/mm Hg for Veh-Sham, P<0.01), entirely prevented by Sx (1.217+/-0.058 ms/mm Hg for Sx-Lig versus 1.345+/-0.093 ms/mm Hg for Sx-Sham, P=NS).

CONCLUSIONS

In early post-MI CHF, sympathectomy only partially attenuated LV dysfunction and entirely prevented baroreflex sensitivity impairment that arises from enhanced sympathetic activity.