Class IV Antiarrhythmic Drugs

Introduction

Class IV antiarrhythmic drugs are medications that primarily affect the calcium channels in the heart. They are used to treat certain arrhythmias by slowing down the conduction of electrical signals through the atrioventricular (AV) node.

Mechanism of Action

These drugs primarily inhibit L-type calcium channels, which are responsible for calcium influx into cardiac cells. By blocking these channels, Class IV drugs: - Reduce the heart rate (negative chronotropic effect) - Decrease the conduction velocity through the AV node (negative dromotropic effect) - Reduce myocardial contractility (negative inotropic effect)

Main Drugs

The two primary drugs in this class are: 1. Verapamil – More selective for the myocardium, used especially in supraventricular tachycardias (SVT). 2. Diltiazem – Has both cardiac and vascular effects, commonly used for rate control in atrial fibrillation.

Indications

Class IV antiarrhythmics are mainly used for: - Supraventricular tachycardias (SVT) - Atrial fibrillation and atrial flutter (for rate control) - Hypertension and angina (due to their effect on blood vessels)

Side Effects and Contraindications

Side Effects:

• Hypotension
• Bradycardia
• Constipation (especially with verapamil)

• Peripheral edema

  Contraindications:

• Severe heart failure (due to negative inotropic effects)

• Second- or third-degree AV block
• Severe hypotension

Important Considerations

• Should not be used in combination with beta-blockers due to the risk of excessive bradycardia.
• Should be used cautiously in patients with reduced ejection fraction.
• Verapamil can increase digoxin levels, requiring careful monitoring.

Conclusion

Class IV antiarrhythmics play a crucial role in the management of arrhythmias, especially supraventricular tachycardias and atrial fibrillation. Understanding their benefits, limitations, and contraindications helps optimize patient safety and efficacy in treatment.

Source recommendations

1. European Society of Cardiology Guidelines on the Management of Supraventricular Tachycardia

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
2. https://academic.oup.com/eurheartj/article/41/5/655/5556821
3. https://pubmed.ncbi.nlm.nih.gov/31504425/
4. https://www.acc.org/Latest-in-Cardiology/ten-points-to-remember/2019/09/10/12/36/2019-ESC-Guidelines-for-Supraventricular-Tachycardia
5. https://www.ahajournals.org/doi/10.1161/cir.0000000000000311

2. American Heart Association Guidelines for the Management of Atrial Fibrillation

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193
2. https://professional.heart.org/en/science-news/2023-acc-aha-accp-hrs-guideline-for-the-diagnosis-and-management-of-atrial-fibrillation
3. https://www.heart.org/en/health-topics/atrial-fibrillation
4. https://pubmed.ncbi.nlm.nih.gov/38033089/
5. https://www.heart.org/en/health-topics/atrial-fibrillation/treatment-and-prevention-of-atrial-fibrillation/treatment-options-of-atrial-fibrillation-afib-or-af