How does verapamil work (its mechanism of action)?
Verapamil is a calcium-channel blocker. It mainly blocks L-type voltage-gated calcium channels in the heart and blood vessels, which reduces calcium entry into cells. With less intracellular calcium, it slows electrical conduction through the AV node and reduces cardiac contractility. It also relaxes vascular smooth muscle, lowering peripheral resistance and blood pressure.
What does that mean for heart rate and AV-node conduction?
Because verapamil suppresses calcium influx in cardiac tissue, it slows AV-node conduction. This can reduce heart rate and is why verapamil is used for certain supraventricular rhythm problems where slowing AV nodal conduction is helpful.
How does verapamil affect blood pressure?
By relaxing vascular smooth muscle (through reduced L-type calcium-dependent contraction), verapamil decreases systemic vascular resistance, which lowers blood pressure.
What conditions is verapamil commonly used for because of this mechanism?
The same actions—slower AV-node conduction and reduced calcium-dependent cardiac contraction plus vasodilation—are what make it useful in:
- Some supraventricular tachyarrhythmias (when AV nodal slowing is desired)
- Hypertension and certain forms of angina (via decreased vascular resistance and cardiac workload)
What are the main risks tied to its mechanism (and why)?
Since verapamil reduces AV-node conduction and cardiac contractility by limiting calcium entry, it can cause or worsen:
- Bradycardia (slow heart rate) and heart block (over-slowing conduction)
- Worsening heart failure in patients with reduced pumping function, because it can reduce contractility
- Hypotension from vasodilation (lower blood pressure)
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