Background: L-type dihydropyridine calcium channel blockers (CCBs) have been implicated in increased cardiovascular events in patients with hypertension, perhaps due to adverse effects on autonomic nervous system (ANS) function. Blockade of T-type calcium channels may limit ANS dysfunction by inhibition of T channel-mediated neuroendocrine effects.
Objective and design: This double-blind, parallel group study compared the effect of nifedipine gastrointestinal transport system (GITS) (L-type CCB) versus mibefradil (T-type CCB) on ANS function in patients with mild-moderate essential hypertension.
Methods: Sixteen patients (10 male, 6 female; age 57.2 +/- 2.3 years), diastolic blood pressure (DBP) < 95 mmHg were randomized to nifedipine 30 mg daily or mibefradil 50 mg daily (2 weeks), then nifedipine 60 mg daily or mibefradil 100 mg daily (4 weeks). Sympathetic nervous system activity (SNSA) was assessed using norepinephrine kinetics. Parasympathetic nervous system activity (PSNA) was assessed from 24 h Holter recordings of heart rate variability (HRV). Non-invasive baroreflex sensitivity (BRS) provided integrated assessment of ANS.
Results: Patient groups were well matched at baseline. Achieved DBP was lower in patients treated with mibefradil compared with nifedipine, (83.4 +/- 1.7 versus 95.25 +/- 3.3 mmHg). There were no significant differences in SNSA and BRS between groups, however the root mean square of successive differences and high frequency power (HFP) were increased in mibefradil compared with nifedipine-treated patients [(+ 1.07 +/- 1.6 versus -3.36 +/- 1.2 ms, P < 0.05) and (+ 0.28 +/- 0.1 versus -0.23 +/- 0.1 ms2, P < 0.01), respectively]. Furthermore, Ln HFP/Ln total power was increased from week 0 to week 6 in the mibefradil-treated group, (0.71 +/- 0.02 versus 0.74 +/- 0.03, P = 0.046).
Conclusion: No differences existed between effect of L- and T-type CCBs on SNSA and BRS. However, T-type CCBs increased PSNA, independent of achieved changes in heart rate.