Can hydralazine increase heart rate, specifically causing tachycardia?

Hydralazine Can Cause Reflex Tachycardia

Yes, hydralazine commonly causes an increase in heart rate (tachycardia) due to its mechanism of action as a direct vasodilator. 1, 2

Mechanism of Hydralazine-Induced Tachycardia

• Hydralazine lowers blood pressure through direct relaxation of vascular smooth muscle, causing peripheral vasodilation 1
• This vasodilation triggers a compensatory reflex increase in sympathetic tone, which leads to increased heart rate 2
• The preferential dilation of arterioles compared to veins promotes an increase in cardiac output, stroke volume, and heart rate 1
• The American Heart Association recognizes that hydralazine begins to decrease blood pressure within 10-30 minutes of administration, with effects lasting 2-4 hours 3

Clinical Implications

• When used for resistant hypertension, hydralazine is typically considered as a fifth-line agent after other medications have failed to achieve blood pressure control 3
• Due to its predictable effect of increasing heart rate, hydralazine is often administered with a beta-blocker to mitigate the reflex tachycardia 2
• The American College of Cardiology recommends using hydralazine with background diuretic and beta-blocker therapy due to its effect of increasing sympathetic tone and sodium retention 2
• In hypertensive emergencies, the unpredictability of response and prolonged duration of action make hydralazine less desirable as a first-line agent for acute treatment in most patients 3

Physiological Response

• Hydralazine increases renin activity in plasma, leading to production of angiotensin II, which stimulates aldosterone and causes sodium reabsorption 1
• This sodium retention, along with the reflex sympathetic discharge, contributes to the compensatory increase in heart rate 1
• Research has shown that hydralazine-induced tachycardia is not only reflexly induced but may also be mediated via direct excitation of the central nervous system 4

Special Considerations

• In rare cases, particularly when the arterial baroreflex is suppressed, hydralazine may paradoxically cause bradycardia through activation of a vagal cardiodepressant reflex 5
• Interestingly, hydralazine has been used therapeutically to increase heart rate in patients with symptomatic sinus bradycardia, with studies showing a 20% or greater increase in heart rate in approximately two-thirds of hypertensive patients 6
• When used with minoxidil for resistant hypertension, the reflexive increases in heart rate are so significant that concomitant use of a beta-blocker is generally necessary 3

Clinical Management

• To minimize reflex tachycardia, hydralazine should be administered with a beta-blocker 2
• Total daily doses of hydralazine should be kept below 150 mg to avoid drug-induced systemic lupus erythematosus 2
• In patients with heart failure, the reflex baroreceptor-mediated responses of tachycardia may be somewhat attenuated compared to hypertensive patients without heart failure 7

Understanding hydralazine's effect on heart rate is crucial for appropriate clinical use and management of potential side effects. The reflex tachycardia is a predictable physiological response that should be anticipated and managed appropriately.