From the Guidelines
No, beta blockers decrease chronotropy. Beta blockers work by blocking the effects of catecholamines on beta-adrenergic receptors, particularly beta-1 receptors in the heart, which reduces myocardial oxygen demand and slows the heart rate, as stated in the 2012 ACCF/AHA guidelines 1. This blockade reduces the influence of the sympathetic nervous system on the heart, resulting in decreased heart rate (negative chronotropy). The guidelines mention that beta blockers "reduce myocardial oxygen demand" and that "slowing of the heart rate also has a favorable effect" 1. Common beta blockers include metoprolol, propranolol, and atenolol, which are recommended to be initiated orally in the absence of contraindications within the first 24 hours 1. The negative chronotropic effect makes these medications useful for treating conditions like hypertension, angina, arrhythmias, and heart failure. This effect occurs because beta blockers inhibit the action of catecholamines on the sinoatrial node (the heart's natural pacemaker), reducing the rate of spontaneous depolarization and therefore slowing the heart rate, as described in the guidelines 1.
Some key points to consider when using beta blockers include:
- The choice of beta blocker for an individual patient is based primarily on pharmacokinetic and side effect criteria, as well as on physician familiarity 1
- Beta blockers without intrinsic sympathomimetic activity are preferred 1
- Agents studied in the acute setting include metoprolol, propranolol, and atenolol, with carvedilol as an additional option 1
- Early aggressive beta blockade poses a substantial net hazard in hemodynamically unstable patients and should be avoided 1
From the FDA Drug Label
When access to beta-receptor sites is blocked by propranolol, the chronotropic, inotropic, and vasodilator responses to beta-adrenergic stimulation are decreased proportionately. Beta blockers do not increase chronotropy, they actually decrease it by blocking beta-adrenergic receptor-stimulating agents, which reduces the heart rate response to beta-adrenergic stimulation 2.
- The mechanism of action of beta blockers, such as propranolol, involves competing with beta-adrenergic receptor-stimulating agents for available receptor sites, thereby decreasing the chronotropic response.
- This decrease in chronotropy is a direct result of the beta blockade, which reduces the heart's response to catecholamines, such as adrenaline, that normally increase heart rate.
From the Research
Beta Blockers and Chronotropy
- Beta blockers are known to have a negative chronotropic effect, meaning they decrease heart rate 3.
- This effect is beneficial in reducing myocardial oxygen expenditure for nonmechanical work, which can be advantageous in patients with heart failure 3.
- The use of beta blockers can lead to a decrease in heart rate, which can be beneficial in certain conditions such as supraventricular tachycardia 4, 5.
- However, in some cases, beta blockers may need to be used in combination with other medications, such as inotropes, to achieve the desired effect 6, 7.
Mechanism of Action
- Beta blockers work by blocking the effects of epinephrine and norepinephrine on the heart, leading to a decrease in heart rate and contractility 3.
- The negative chronotropic effect of beta blockers is due to their ability to reduce the activity of the sinoatrial node, which is the natural pacemaker of the heart 3.
- Phosphodiesterase inhibitors, such as milrinone or enoximone, can be used in combination with beta blockers to increase cardiac output without increasing heart rate 6, 7.
Clinical Implications
- Beta blockers are commonly used to treat conditions such as heart failure, supraventricular tachycardia, and hypertension 4, 5.
- The use of beta blockers can lead to a decrease in heart rate, which can be beneficial in certain conditions, but may also lead to adverse effects such as fatigue and dizziness 3.
- The combination of beta blockers with other medications, such as inotropes, can be used to achieve the desired effect in certain patients 6, 7.