A 60-year-old man with rheumatic mitral stenosis and atrial fibrillation is on therapy for a fast ventricular rate. While on treatment he develops a regular pulse of 64 beats/min. Which of the following is the probable drug that the patient is receiving?
**Core Concept**
The patient is experiencing a change in heart rhythm from atrial fibrillation (irregular) to a regular pulse, which suggests conversion to sinus rhythm. This is likely due to the effect of a medication that slows the conduction of electrical impulses in the heart, allowing the sinoatrial node to dominate the rhythm.
**Why the Correct Answer is Right**
The probable drug is likely a beta-blocker, which reduces the heart rate by decreasing sympathetic tone on the heart. Beta-blockers also decrease the contractility of the heart and reduce the heart rate response to stress. This allows the atrioventricular (AV) node to conduct impulses at a slower rate, potentially converting atrial fibrillation to sinus rhythm. The patient is also more likely to be on a beta-blocker due to his history of rheumatic mitral stenosis and atrial fibrillation.
**Why Each Wrong Option is Incorrect**
**Option A:** Digoxin is a cardiac glycoside used to slow the heart rate in atrial fibrillation but does not typically convert the rhythm to sinus. It is more commonly used to improve cardiac output in heart failure.
**Option B:** Calcium channel blockers, such as verapamil, can also slow the heart rate and are used in atrial fibrillation but are less likely to convert the rhythm to sinus.
**Option C:** Amiodarone is an anti-arrhythmic medication used for various types of arrhythmias but is not the most likely cause of conversion to sinus rhythm in this scenario.
**Option D:** Nitrates are primarily used for angina and do not have a significant effect on heart rhythm.
**Clinical Pearl / High-Yield Fact**
Beta-blockers are a mainstay in the management of atrial fibrillation with rapid ventricular response and are also used in patients with mitral stenosis to reduce symptoms and prevent complications. They should be used with caution in patients with heart failure or asthma.
**Correct Answer:** C. Amiodarone is an anti-arrhythmic medication used for various types of arrhythmias but is not the most likely cause of conversion to sinus rhythm in this scenario