Do alpha blockers affect heart rate?

From the Guidelines

Alpha blockers do not directly change heart rate as their primary effect, but may cause a reflex tachycardia in some patients due to their blood pressure-lowering effect. Alpha blockers work by blocking alpha-adrenergic receptors, primarily causing blood vessel relaxation and lowering blood pressure. Unlike beta blockers, which directly slow heart rate, alpha blockers like doxazosin, prazosin, and terazosin have minimal direct effect on heart rate. The recent 2024 ESC guidelines for the management of atrial fibrillation 1 recommend beta-blockers, diltiazem, verapamil, or digoxin as first-choice drugs to control heart rate and reduce symptoms, but do not mention alpha blockers as a primary treatment for heart rate control. Some patients may experience a reflex tachycardia when starting alpha blockers, especially with the first dose, due to the sudden drop in blood pressure triggering the body's compensatory mechanisms to maintain blood pressure by increasing heart rate. This reflex tachycardia is typically temporary and diminishes as the body adjusts to the medication. Key points to consider when prescribing alpha blockers include:

• Starting with a low dose that gradually increases to minimize the risk of reflex tachycardia
• Recommending the first dose be taken at bedtime to reduce the risk of orthostatic hypotension
• Monitoring patients with heart conditions when starting alpha blockers, as they may be more susceptible to the effects of blood pressure changes on heart rate.

From the FDA Drug Label

The antihypertensive effect of doxazosin results from a decrease in systemic vascular resistance... Maximum reductions in blood pressure usually occur 2 to 6 hours after dosing and are associated with a small increase in standing heart rate.

Syncopal episodes occurred in 3 of the 14 subjects given terazosin at doses of 2.5 and 7. 5 mg, which are higher than the recommended initial dose; in addition, severe orthostatic hypotension (blood pressure falling to 50/0 mmHg) was seen in two others and dizziness, tachycardia, and lightheadedness occurred in most subjects.

Less frequent adverse reactions which are reported to occur in 1% to 4% of patients are: ... Cardiovascular: edema, orthostatic hypotension, dyspnea, syncope, ... tachycardia

In post-marketing experience, the following adverse events have been reported: ... Heart Rate/Rhythm: bradycardia.

Alpha blockers can change heart rate. They can cause a small increase in standing heart rate due to the decrease in systemic vascular resistance and blood pressure. Additionally, tachycardia and bradycardia have been reported as adverse reactions in some patients taking alpha blockers 2, 3, 4.

From the Research

Alpha Blockers and Heart Rate

• Alpha blockers are a class of drugs that lower blood pressure by reducing peripheral arterial resistance 5, 6, 7, 8.
• Unlike non-selective alpha blockers or direct vasodilators, selective alpha-1 blockers such as prazosin cause less reflex tachycardia, which means they do not significantly increase heart rate 5, 7.
• In fact, alpha blockers tend to increase exercise stroke volume and cardiac output during chronic treatment, without causing reflex tachycardia 6.
• The mechanism behind this effect is thought to be due to the blockade of central alpha 1-adrenoceptors, which blunts the reflex tachycardia via the baroreceptor mechanism 7.
• Additionally, alpha blockers such as doxazosin have been shown to lower elevated blood pressure without increasing heart rate or reducing cardiac output 8.

Comparison with Other Antihypertensive Drugs

• Beta blockers, on the other hand, reduce heart rate and cardiac output immediately, but may cause a reflex increase in total peripheral resistance index, which can lead to unchanged or only slightly reduced blood pressure 6.
• In contrast, alpha blockers reduce blood pressure through a reduction in total peripheral resistance index, without causing reflex tachycardia 6, 7, 8.
• The combination of beta and alpha blockers, or the use of hybrid drugs such as labetalol, can induce marked reductions in blood pressure at rest and during exercise, mainly through a reduction in total peripheral resistance index 6, 7.

Clinical Implications

• The lack of reflex tachycardia associated with alpha blockers makes them a useful treatment option for patients with hypertension, particularly those who may be at risk for cardiovascular complications 9, 8.
• Alpha blockers have also been shown to have additional beneficial effects, such as reducing left ventricular hypertrophy, improving lipid profiles, and reducing the risk of thrombotic complications 8.