Makindo Medical Notes

Related Subjects: | Wolff-Parkinson White Syndrome (WPW) AVRT | Lown-Ganong-Levine Syndrome AVRT | Supraventricular Tachycardia (SVT) | Atrioventricular Nodal Reentrant Tachycardia (AVNRT) | Atrial Flutter | Atrial Fibrillation | Sinus Tachycardia | Sinus Arrhythmia | Multifocal Atrial Tachycardia | Resuscitation – Adult Tachycardia Algorithm

⚠️ Do NOT give Verapamil in wide-complex tachycardia where ventricular tachycardia cannot be excluded. It is a potent negative inotrope and chronotrope and can cause cardiovascular collapse in VT, WPW with AF, or if combined with beta-blockers.

📘 About: Always check the BNF link here

• Non-dihydropyridine calcium channel blocker (unlike amlodipine or nifedipine).
• Inhibits slow inward L-type calcium current in cardiac myocytes and nodal tissue.
• Used mainly for SVT termination, rate control in AF/flutter, and angina.

⚙️ Mechanism of Action

• Blocks L-type calcium channels → reduces calcium influx into cardiac and vascular smooth muscle.
• Slows conduction through the AV node and prolongs its refractory period → effective in AVNRT and re-entrant SVT.
• Decreases myocardial contractility (negative inotrope) and heart rate (negative chronotrope).
• Reduces systemic vascular resistance → lowers blood pressure.

🎯 Indications / Clinical Uses

• SVT (narrow complex): Adenosine remains first-line, but Verapamil is an effective alternative if adenosine fails or is contraindicated.
• Rate control in AF / Atrial flutter: Especially in those intolerant to beta-blockers.
• Angina: Both stable and variant (Prinzmetal’s) angina — due to coronary vasodilatation and afterload reduction.
• Hypertension and off-label use in cluster headache prophylaxis.

💊 Dosing (Always check BNF / Datasheet)

• Always give IV Verapamil slowly while monitoring ECG and blood pressure.
• Avoid concurrent IV beta-blocker within 24 h.

⚠️ Contraindications

• Suspected or known Ventricular Tachycardia (may precipitate cardiac arrest).
• 2nd / 3rd degree AV block or sick sinus syndrome (unless paced).
• Heart failure with reduced ejection fraction — worsens contractility.
• WPW with AF or Atrial flutter — may accelerate conduction down the accessory pathway.
• Severe hypotension or acute porphyria.

⚡ Interactions

• IV beta-blockers: Dangerous bradycardia, AV block, or asystole — avoid combination.
• Amiodarone: Increased risk of AV block and hypotension.
• Digoxin: Verapamil increases serum digoxin concentration via P-glycoprotein inhibition — monitor closely.
• CYP3A4 inhibitors (e.g. erythromycin, clarithromycin, grapefruit juice) increase verapamil levels.

💥 Side Effects

• Cardiovascular: Bradycardia, hypotension, AV block, worsening of heart failure.
• GI: Constipation (very common), nausea.
• Other: Headache, dizziness, ankle oedema, gingival hyperplasia.

🧠 Teaching Point

Verapamil’s ability to slow AV nodal conduction makes it life-saving in SVT but dangerous in pre-excited AF — where blocking the AV node shifts conduction to the accessory pathway, producing VF. Always interpret the ECG carefully before giving IV Verapamil. Its dual role as antianginal and antiarrhythmic highlights how one drug’s benefit in one system can become catastrophic in another if used without full context.

📚 References

• BNF: Verapamil
• NICE CKS: Atrial Fibrillation
• Resuscitation Council UK: Tachycardia Algorithm