Hydralazine and Reflex Tachycardia
Yes, hydralazine does cause reflex tachycardia as a common side effect due to its vasodilatory mechanism of action. 1
Mechanism of Tachycardia with Hydralazine
- Hydralazine is a direct arterial vasodilator that exerts its antihypertensive effect through direct relaxation of vascular smooth muscle 2
- This peripheral vasodilating effect results in decreased arterial blood pressure (affecting diastolic more than systolic pressure) and decreased peripheral vascular resistance 2
- The vasodilation triggers baroreceptor-mediated compensatory mechanisms, leading to:
- Hydralazine usually increases plasma renin activity, presumably due to increased renin secretion by renal juxtaglomerular cells in response to reflex sympathetic discharge 2
Clinical Implications
- Hydralazine is classified as a "direct vasodilator" in hypertension guidelines and is specifically noted to cause sodium and water retention and reflex tachycardia 1
- Due to these effects, hydralazine is typically recommended to be used with a diuretic and beta-blocker to counteract these compensatory mechanisms 1
- The American College of Cardiology/American Heart Association guidelines specifically note that hydralazine is "associated with sodium and water retention and reflex tachycardia" 1
Management Considerations
- When using hydralazine for hypertension, it is typically administered 2-3 times daily (100-200 mg/day total) 1
- The reflex tachycardia can be effectively managed by combining hydralazine with beta-blockers 4
- In a comparative study, patients taking hydralazine alone had a mean increase in heart rate of 12.4 beats/min, while those taking a propranolol-hydralazine combination had only a 1.8 beats/min increase 4
- The preferential dilation of arterioles compared to veins by hydralazine minimizes postural hypotension while promoting the increase in cardiac output 2
Special Considerations
- In patients with heart failure, the reflex baroreceptor-mediated responses of tachycardia may be attenuated compared to hypertensive patients without heart failure 5
- In some experimental conditions, particularly when baroreflexes are impaired, hydralazine can paradoxically cause bradycardia rather than tachycardia 6
- In patients with ischemic cardiomyopathy, hydralazine-induced tachycardia may potentially provoke myocardial ischemic events 7
Conclusion
Hydralazine reliably causes reflex tachycardia through its vasodilatory mechanism, which is why guidelines consistently recommend combining it with beta-blockers when used for hypertension management 1, 4.