What is the best initial treatment for a patient with palpitations, nonproductive cough, malaise, and a regular tachycardia?

Adenosine is the Best Initial Treatment for This Patient

For a hemodynamically stable patient presenting with regular tachycardia at 150-170 bpm, adenosine is the drug of choice for initial treatment. 1, 2

Clinical Assessment and Rationale

This patient is hemodynamically stable based on the clinical presentation:

• Blood pressure 118/70 mm Hg (adequate perfusion) 2
• No signs of shock, acute altered mental status, or ischemic chest pain 2
• Heart rate 150-170 bpm with regular rhythm suggests supraventricular tachycardia (SVT) 1

The regular rhythm at this rate strongly indicates AV nodal re-entrant tachycardia or another form of SVT, making adenosine the optimal first-line agent. 1, 2

Why Adenosine is Superior

Adenosine is the drug of choice for terminating AV nodal re-entrant tachyarrhythmias because it:

• Selectively blocks AV nodal conduction with a success rate of approximately 93% for SVT 1, 3
• Has an extremely short half-life (less than 10 seconds), making adverse effects transient 1, 3
• Does not cause depression of myocardial contractility, unlike calcium channel blockers 1
• Can be safely combined with beta-blockers if needed 1
• Provides both therapeutic and diagnostic value by slowing the rhythm to identify the underlying mechanism 1, 2

Dosing Protocol

Initial dose: 6 mg rapid IV push followed immediately by saline flush 1, 2

• If no effect after 1-2 minutes: 12 mg rapid IV push 1, 2
• If still no response: Final dose of 12 mg (maximum total) 1

Recent evidence suggests that starting with 12 mg may be more effective, with 65% increased odds of conversion and less need for re-dosing, though the standard 6 mg initial dose remains guideline-recommended. 4

Why Other Options Are Inferior

Beta-blockers and Calcium Channel Blockers

• Reserved for second-line therapy if adenosine fails or for rate control in atrial fibrillation 1, 2
• Calcium channel blockers (verapamil) are negatively inotropic and contraindicated if beta-blockers have already been given due to risk of profound bradycardia and hypotension 1
• Both have longer half-lives and greater potential for sustained adverse effects compared to adenosine 3

Normal Saline

• Has no role in treating the arrhythmia itself 1
• Only indicated if hypovolemia is contributing to compensatory tachycardia, which is not suggested by this patient's stable blood pressure 2

Critical Safety Considerations

Adenosine must be administered in a monitored environment (emergency department or critical care unit) because:

• It can cause transient complete heart block 1
• Bronchospasm can occur, particularly in asthmatic patients (contraindication) 1, 5
• Common transient side effects include flushing, chest pain, and dyspnea lasting less than 60 seconds 1, 3

Important Pitfalls to Avoid

• Do not delay treatment to obtain a 12-lead ECG if the patient is stable and the rhythm is clearly regular narrow-complex tachycardia 2
• Avoid adenosine if the rhythm is irregular or if pre-excitation (Wolff-Parkinson-White) is suspected, as it may precipitate ventricular tachycardia/fibrillation 1, 2
• Do not use if the patient has known severe asthma or COPD due to bronchospasm risk 1, 5
• Ensure rapid IV push followed immediately by saline flush, as the drug's short half-life requires it to reach the heart quickly 1, 6

The nonproductive cough mentioned in this case is a minor consideration but does not contraindicate adenosine unless there is underlying severe reactive airway disease. 1, 5