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[Treatment of heart arrhythmias with calcium antagonists]
Abstract:
The depressing effect of calcium antagonists on sinus node and AV node function is well documented in the experimental animal and in man. Other cardiac fibers may be depolarized to a level at which the slow inward current determines the rise of the action potential and may become sensitive to calcium antagonists, thus abolishing extrasystoles or tachycardias. However, effects of the drugs on heart rate, coronary perfusion, and pre- and afterload of the left ventricle must be taken into account, which may affect the electrophysiologic basis for the dysrhythmia. The conversion rate of atrial fibrillation to sinus rhythm (n = 200) amounted to 77% when quinidine was combined with verapamil. Monotherapy of these drugs or combination of quinidine with diltiazem or pindolol did not elevate the atrial fibrillation threshold compared to quinidine/verapamil. Reduced ventricular fibrillation thresholds in the experimental animal after coronary occlusion increased significantly during the early reperfusion period after verapamil and nifedipine by cardioprotection. Due to a reduced renal clearance the bio-availability of digoxin increased with a concomitant medication of quinidine and verapamil.
Insights
Calcium antagonists, like verapamil, effectively convert atrial fibrillation to sinus rhythm when combined with quinidine. This combination also shows cardioprotective effects and influences digoxin bioavailability.
Area of Science:
- Cardiology
- Pharmacology
Context:
- Calcium antagonists depress sinus and AV node function.
- Cardiac fibers can become sensitive to calcium antagonists, potentially abolishing arrhythmias.
Purpose:
- To evaluate the efficacy of calcium antagonists in treating cardiac arrhythmias.
- To assess the impact of drug combinations on atrial fibrillation conversion and ventricular fibrillation thresholds.
Summary:
- Combining quinidine with verapamil achieved a 77% conversion rate of atrial fibrillation to sinus rhythm in 200 patients.
- This combination was more effective than monotherapy or other combinations (quinidine/diltiazem, quinidine/pindolol).
- Verapamil and nifedipine demonstrated cardioprotection by increasing ventricular fibrillation thresholds post-coronary occlusion.
- Concomitant use of quinidine and verapamil increased digoxin bioavailability due to reduced renal clearance.
Impact:
- Highlights the synergistic effect of quinidine and verapamil in managing atrial fibrillation.
- Suggests potential cardioprotective roles for verapamil and nifedipine during myocardial reperfusion.
- Indicates a need to adjust digoxin dosage when co-administered with quinidine and verapamil.