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Functional significance of chronotropic response during chronic amiodarone therapy
Insights
Chronic amiodarone therapy significantly lowers resting and exercise heart rates in patients with ventricular arrhythmias. This potent antiarrhythmic agent does not affect blood pressure or functional capacity during graded exercise testing.
Area of Science:
- Cardiology
- Pharmacology
- Exercise Physiology
Background:
- Amiodarone is a widely used antiarrhythmic medication.
- It is known to potentially affect sinus node function.
- The impact of chronic amiodarone on heart rate during exercise requires further investigation.
Purpose of the Study:
- To evaluate the effect of chronic amiodarone therapy on heart rate.
- To assess changes during graded exercise testing in patients with ventricular arrhythmias.
- To determine if amiodarone alters heart rate reserve, blood pressure, or functional capacity.
Main Methods:
- 13 patients with ventricular arrhythmias receiving amiodarone underwent symptom-limited graded exercise testing.
- Testing was performed before and after 12 weeks of amiodarone therapy.
- Measurements included resting heart rate, maximal heart rate, heart rate at comparable exercise levels, systolic blood pressure, and functional capacity (METs).
Main Results:
- A significant decrease in mean resting heart rate (75 to 60 bpm) and maximal heart rate (135 to 109 bpm) was observed after amiodarone therapy (p < 0.005).
- Heart rate at comparable exercise levels was also significantly reduced (124 to 104 bpm; p < 0.025).
- No significant changes were found in heart rate reserve, systolic blood pressure, or estimated maximal functional capacity (METs).
Conclusions:
- Chronic amiodarone therapy significantly reduces heart rate at rest and during exercise.
- The drug does not appear to alter systolic blood pressure or functional capacity during exercise.
- These findings highlight the chronotropic effects of amiodarone during physical exertion.
Abstract:
Amiodarone, a potent antiarrhythmic agent, has been shown to depress sinus node function. Therefore, this study was undertaken to assess the effect of chronic amiodarone therapy on heart rate during graded exercise testing. 13 patients treated with amiodarone for ventricular arrhythmias were administered symptom-limited graded exercise testing before and 12 weeks after drug therapy. None of the patients had prior evidence of sinus node dysfunction. The mean resting heart rate (beats per minute; bpm) before and after amiodarone therapy was 75 +/- (SD) 13 versus 60 +/- 7 bpm, respectively (p less than 0.005), and the maximal heart rate was 135 +/- 30 versus 109 +/- 24 bpm (p less than 0.005). However, the change in heart rate from rest to maximum exercise (heart rate reserve) was not affected by the drug. Heart rate measured at comparable exercise levels before and during amiodarone therapy was 124 +/- 25 versus 104 +/- 31 (p less than 0.025). There was no change in the systolic blood pressure readings at these respective measured heart rates. Estimated maximal functional capacity before and after drug therapy was 4.9 +/- 1.8 versus 4.7 +/- 2.2 METs (p = NS). In conclusion, chronic amiodarone therapy significantly decreases heart rate at rest and during exercise without altering systolic blood pressure and functional capacity.