Immediate Synchronized Cardioversion for Hemodynamically Unstable Tachycardia

Indications and Recommendations

The American Heart Association recommends immediate cardioversion (Class I, Level B) for tachycardic patients who are unstable with severe signs and symptoms related to a suspected arrhythmia, including hypotension or other signs of shock, as seen in patients with systolic blood pressure of 72 mmHg and heart rate of 165 bpm 1, 2.
The European Society of Cardiology guidelines state that patients presenting with sustained ventricular tachycardia and hemodynamic instability should undergo direct cardioversion, regardless of the rhythm etiology 3.
Immediate cardioversion is indicated for hemodynamically unstable patients with tachycardia, regardless of whether the rhythm is ventricular tachycardia or supraventricular tachycardia with aberrancy, due to the high risk of degeneration to ventricular fibrillation 4, 5.

Adenosine is not recommended for patients with hypotension (systolic BP of 72 mmHg) due to the risk of worsening hypotension and the need for immediate rhythm conversion 1, 2, 4, 5.
Amiodarone's antiarrhythmic effect may take up to 30 minutes to manifest, making it unsuitable as first-line therapy for hemodynamically unstable patients who require immediate rhythm conversion 7, 8.
Beta-blockers are contraindicated in hemodynamically unstable tachycardia due to their negative inotropic effects, which can further compromise cardiac output in an already hypotensive patient 9.

Sedate the patient immediately if conscious, but do not delay cardioversion if the patient is extremely unstable, and use synchronized cardioversion to avoid shock delivery during the relative refractory period 10, 4.
Do not delay cardioversion to obtain a 12-lead ECG in unstable patients, as this can delay necessary treatment 4, 11.
For wide-complex tachycardia in an unstable patient, presume ventricular tachycardia and cardiovert immediately 12.
After successful cardioversion, establish IV access, obtain a 12-lead ECG, and consider antiarrhythmic prophylaxis with amiodarone to prevent recurrence, and consult cardiology urgently even if the arrhythmia self-terminates 3, 11, 12.