Metoprolol for tachycardia

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Metoprolol for Tachycardia: Efficacy and Applications

Introduction to Metoprolol and Tachycardia

Metoprolol, a beta-1 adrenergic blocker, is widely used in the management of various types of tachycardia, including ventricular tachyarrhythmias, multifocal atrial tachycardia, and inappropriate sinus tachycardia. This article synthesizes research findings on the efficacy and safety of metoprolol in treating these conditions.

Metoprolol in Ventricular Tachyarrhythmias

Acute Myocardial Infarction and Ventricular Fibrillation

In patients with acute myocardial infarction, metoprolol has shown a significant prophylactic effect against ventricular fibrillation. A double-blind trial revealed that metoprolol reduced the incidence of ventricular fibrillation compared to placebo (6 cases in the metoprolol group vs. 17 in the placebo group, P < 0.05). However, it did not significantly affect the occurrence of less severe ventricular tachyarrhythmias such as premature ventricular contractions or short bursts of ventricular tachycardia.

Post-ICD Implantation

In patients with implantable cardioverter defibrillators (ICDs), metoprolol significantly reduced the recurrence of ventricular tachycardia (VT) and ventricular fibrillation (VF). The actuarial rates for the absence of VT recurrence at 1 and 2 years were higher in the metoprolol group compared to the d,l-sotalol group (83% and 80% vs. 57% and 51%, respectively, P = 0.016).

Metoprolol in Multifocal Atrial Tachycardia

Efficacy in Conversion to Sinus Rhythm

Metoprolol has demonstrated efficacy in treating multifocal atrial tachycardia (MAT). In a study involving 25 patients, metoprolol significantly slowed the heart rate and converted 68% of patients to sinus rhythm without causing hemodynamic or respiratory deterioration. Another study confirmed these findings, showing that metoprolol restored sinus rhythm in all patients within 1 to 3 hours of administration.

Comparison with Verapamil

In a randomized, double-blind trial comparing metoprolol and verapamil, metoprolol was more effective in treating MAT. The response rates were 89% for metoprolol, 44% for verapamil, and 20% for placebo, with metoprolol significantly reducing the ventricular rate (P < 0.01).

Metoprolol in Inappropriate Sinus Tachycardia

Comparison with Ivabradine

For patients with inappropriate sinus tachycardia (IST) unresponsive to other treatments, metoprolol and ivabradine both significantly reduced resting heart rates. However, ivabradine was more effective in reducing heart rate during daily activities and was better tolerated, with fewer incidences of hypotension or bradycardia compared to metoprolol.

Metoprolol in Exercise-Induced Tachycardia

Duration of Effect

The duration of metoprolol's effect on exercise-induced tachycardia is influenced by its plasma elimination half-life. While metoprolol effectively reduced exercise tachycardia shortly after administration, its effect diminished after 24 hours, unlike atenolol and sotalol, which maintained their effects longer due to their longer half-lives.

Conclusion

Metoprolol is a versatile beta-blocker effective in managing various forms of tachycardia, including ventricular tachyarrhythmias, multifocal atrial tachycardia, and inappropriate sinus tachycardia. Its efficacy in reducing ventricular fibrillation in acute myocardial infarction and its superiority over verapamil in treating MAT highlight its clinical utility. However, its shorter duration of action compared to other beta-blockers and the potential for side effects such as hypotension and bradycardia necessitate careful patient selection and monitoring.