Hydralazine and Heart Rate Effects
No, hydralazine does not cause bradycardia—it causes reflex tachycardia as a common and well-documented adverse effect. 1, 2, 3
Mechanism of Tachycardia
Hydralazine is a direct arterial vasodilator that triggers compensatory cardiovascular responses:
- Reflex tachycardia occurs through baroreceptor-mediated mechanisms in response to the acute drop in blood pressure caused by arterial vasodilation 3, 4
- The American College of Cardiology/American Heart Association guidelines specifically identify hydralazine as being "associated with sodium and water retention and reflex tachycardia" 1, 3
- This tachycardia is a predictable pharmacologic consequence, not an idiosyncratic reaction 1, 2
Clinical Implications
The reflex tachycardia from hydralazine has important management considerations:
- Hydralazine should typically be combined with a beta-blocker and diuretic to counteract both the reflex tachycardia and sodium/water retention 3, 5
- The drug is no longer recommended as first-line therapy for acute hypertension due to its unpredictable blood pressure effects and adverse cardiovascular responses 2
- In heart failure patients, the reflex tachycardia response may be attenuated compared to hypertensive patients, though it still occurs 6
Paradoxical Use in Bradycardia
Interestingly, there is one older study that actually used hydralazine's tachycardic properties therapeutically:
- Hydralazine was successfully used to increase heart rate in patients with symptomatic sinus bradycardia, producing a 20% or greater increase in heart rate in approximately two-thirds of hypertensive patients and half of normotensive patients 7
- This demonstrates that hydralazine's cardiovascular effect is consistently in the direction of increasing, not decreasing, heart rate 7
Common Pitfalls
Do not confuse hydralazine's cardiovascular effects with other antihypertensive agents:
- Unlike beta-blockers or certain calcium channel blockers (diltiazem, verapamil), hydralazine does not have negative chronotropic effects 4
- The tachycardia can be problematic in patients with coronary artery disease, potentially provoking myocardial ischemia even without significant hypotension 8
- Modern antihypertensive agents (ACE inhibitors, ARBs, certain calcium channel blockers) typically do not cause reflex tachycardia and are preferred over hydralazine 4