How does Hydralazine (Hydralazine) affect heart rate (HR)?

From the Guidelines

Hydralazine can affect heart rate by causing reflex tachycardia, which is a compensatory response to the decrease in blood pressure caused by the medication's vasodilatory effects. When hydralazine dilates blood vessels, it lowers blood pressure, which triggers an increase in heart rate as the body attempts to maintain adequate blood flow. This reflex tachycardia typically manifests as an increase in heart rate by 10-20 beats per minute, though individual responses vary 1. The mechanism involves activation of the sympathetic nervous system and baroreceptor reflex in response to decreased peripheral vascular resistance. This side effect is more pronounced with higher doses and rapid administration. To manage this effect, hydralazine is often prescribed alongside beta-blockers or other medications that can counteract the tachycardia. Patients with pre-existing cardiac conditions should be monitored closely when starting hydralazine therapy, as the increased heart rate could potentially exacerbate certain cardiac conditions. The tachycardia effect typically diminishes with continued use as the body adapts to the medication.

Some key points to consider when using hydralazine include:

• The initial dose of hydralazine is typically 10 mg via slow IV infusion, with a maximum initial dose of 20 mg, and can be repeated every 4-6 hours as needed 1.
• Hydralazine is associated with sodium and water retention and reflex tachycardia, and can also cause drug-induced lupus-like syndrome at higher doses 1.
• The combination of hydralazine and nitrates is recommended to improve outcomes for patients with moderate-severe symptoms on optimal therapy with ACE inhibitors, beta blockers, and diuretics 1.
• Hydralazine can be added to the treatment regimen of patients with resistant hypertension, with a starting dose of 25 mg three times daily and titrated upward to a maximum dose 1.

Overall, hydralazine's effect on heart rate is an important consideration in its use, and patients should be closely monitored for signs of reflex tachycardia and other cardiac effects.

From the FDA Drug Label

Although the precise mechanism of action of hydrALAZINE is not fully understood, the major effects are on the cardiovascular system. HydrALAZINE apparently lowers blood pressure by exerting a peripheral vasodilating effect through a direct relaxation of vascular smooth muscle HydrALAZINE, by altering cellular calcium metabolism, interferes with the calcium movements within the vascular smooth muscle that are responsible for initiating or maintaining the contractile state The peripheral vasodilating effect of hydrALAZINE results in decreased arterial blood pressure (diastolic more than systolic); decreased peripheral vascular resistance; and an increased heart rate, stroke volume, and cardiac output.

• Hydralazine affects heart rate (hr) by increasing it, as a result of the peripheral vasodilating effect and the subsequent reflex sympathetic discharge 2.
• The increase in heart rate is accompanied by an increase in stroke volume and cardiac output.

From the Research

Effects of Hydralazine on Heart Rate

• Hydralazine has been shown to increase heart rate in various studies 3, 4.
• The increase in heart rate is mainly observed in the standing position 3.
• The magnitude of the cardiac response to hydralazine correlates with heart rate responses to standing and to the Valsalva maneuver 3.
• Hydralazine-induced tachycardia is thought to be reflexly induced and depends on individual baroreceptor sensitivity 3.

Comparison with Other Antihypertensive Agents

• Hydralazine has been compared with nifedipine in several studies, with nifedipine being more effective in lowering systolic blood pressure 4, 5.
• Neither hydralazine nor nifedipine significantly altered heart rate in one study 5.
• Hydralazine improved left ventricular diastolic function, whereas nifedipine increased the rate of ejection 4.

Clinical Implications

• Hydralazine can be used in combination with beta-blockers and diuretics to control blood pressure in hypertensive patients 6, 7.
• Patients who are slow acetylators may have better blood pressure control and more side effects when taking hydralazine 7.
• Prior institution of beta-adrenergic blocking drugs is desirable to minimize the frequency of hydralazine-related side effects 7.