Is nitroglycerin effective for slowing the heart rate in patients with tachycardia?

Nitroglycerin Does Not Slow Heart Rate—It Typically Increases It

Nitroglycerin causes reflex tachycardia, not bradycardia, and should never be used with the intention of slowing heart rate in tachycardic patients. 1, 2

Mechanism of Heart Rate Effects

Nitroglycerin's primary action is venous and arterial vasodilation, which decreases preload and afterload, leading to reduced blood pressure. 1, 2 This drop in blood pressure triggers a compensatory reflex increase in heart rate and contractility—the opposite of slowing the heart. 1, 3

• The FDA drug label explicitly states that "heart rate is usually slightly increased, presumably due to a compensatory response to the fall in blood pressure." 2
• Research in conscious dogs demonstrated that intravenous nitroglycerin caused substantial increases in heart rate (up to 100 beats/min increase), with secondary peaks in contractility occurring after blood pressure dropped. 3
• This reflex tachycardia can actually worsen myocardial ischemia by increasing myocardial oxygen demand, particularly problematic in acute coronary syndromes. 1, 4

Clinical Guidelines on Heart Rate Management

The American College of Cardiology guidelines specifically recommend concurrent beta-blocker administration with nitroglycerin to prevent the undesired reflex tachycardia. 1 This recommendation exists precisely because nitroglycerin alone increases heart rate.

• When titrating intravenous nitroglycerin, an increase in heart rate >10 beats/min (but not usually >110 beats/min) is an expected titration endpoint, not a contraindication. 1
• The European Society of Cardiology position document lists "reflex tachycardia" as a known adverse effect of nitroglycerin in multiple clinical contexts. 1, 4
• Beta-blockade prevents the reflex increases in contractility and most of the reflex tachycardia caused by nitroglycerin. 3

When Bradycardia Occurs (Rare Exception)

In rare circumstances, nitroglycerin can cause bradycardia through a completely different mechanism—the Bezold-Jarisch reflex—but this is paradoxical and typically occurs only with intracisternal (brainstem) administration or in specific pathological states. 5

• The FDA warns that "hypotension associated with inappropriate bradycardia has been reported to occur rarely" with nitroglycerin. 1, 2
• Research shows that intracisternal injection of nitroglycerin induced hypotension and bradycardia (medulla-mediated), while intravenous and intraventricular routes caused the typical hypotension with tachycardia. 5
• This bradycardic response is not therapeutically useful and represents a dangerous adverse effect requiring atropine administration. 6, 4

Appropriate Agents for Heart Rate Control

If the clinical goal is to slow heart rate in tachycardic patients, the European Society of Cardiology recommends beta-blockers (esmolol, metoprolol, labetalol) as first-line agents. 1

• Esmolol has onset of action in 1-2 minutes with duration of 10-30 minutes, making it ideal for acute rate control. 1
• Labetalol combines alpha and beta blockade, providing both rate control and afterload reduction without the reflex tachycardia seen with pure vasodilators. 1
• Nitroglycerin should be reserved for its intended indications: reducing preload in heart failure, relieving anginal pain through coronary vasodilation, and managing hypertensive emergencies—not for rate control. 1