Initial Treatment for Supraventricular Tachycardia (SVT)
Begin with vagal maneuvers immediately as first-line treatment, followed by intravenous adenosine if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients or when pharmacological therapy is ineffective. 1, 2
Immediate First-Line Intervention: Vagal Maneuvers
Perform vagal maneuvers with the patient in the supine position as the initial intervention 1, 2
Modified Valsalva maneuver is the most effective vagal technique, achieving significantly higher conversion rates than standard carotid sinus massage 3
For the Valsalva maneuver, have the patient bear down against a closed glottis for 10-30 seconds, generating at least 30-40 mm Hg of intrathoracic pressure 1
For carotid sinus massage, first confirm absence of carotid bruits by auscultation, then apply steady pressure over the right or left carotid sinus for 5-10 seconds 1
The diving reflex technique (applying an ice-cold wet towel to the face) is an alternative vagal maneuver 1
Never apply pressure to the eyeball—this practice is dangerous and has been abandoned 1, 2
Switching between different vagal maneuver techniques achieves an overall success rate of approximately 27.7% 1
Second-Line Treatment: Adenosine
Administer intravenous adenosine if vagal maneuvers fail, as it terminates SVT in 90-95% of patients 1, 2
Recent evidence suggests that an initial dose of 12 mg adenosine is more effective than 6 mg (54.2% vs 40.6% conversion rate, p=0.03), though this contradicts traditional stepwise dosing 4
Have electrical cardioversion equipment immediately available when administering adenosine, as it may precipitate atrial fibrillation that could conduct rapidly to the ventricles and potentially cause ventricular fibrillation 1
Minor side effects occur in approximately 30% of patients but are brief (lasting <1 minute) 1
Third-Line Pharmacological Options (Hemodynamically Stable Patients)
Intravenous diltiazem or verapamil (calcium channel blockers) are highly effective alternatives with a Class IIa recommendation for converting AVNRT to sinus rhythm 1, 2
Intravenous beta-blockers have a Class IIa recommendation but are less effective than calcium channel blockers 1, 2
Intravenous amiodarone carries a Class IIb recommendation if other agents are ineffective or not feasible 1
Immediate Cardioversion (Hemodynamically Unstable Patients)
Perform synchronized cardioversion immediately for hemodynamically unstable patients when adenosine and vagal maneuvers fail or are not feasible 1, 2
Synchronized cardioversion is also indicated for hemodynamically stable patients when pharmacological therapy is ineffective or contraindicated 1
Critical Pitfalls to Avoid
Never use AV nodal blocking agents (verapamil, diltiazem, beta-blockers) in patients with suspected pre-excitation (Wolff-Parkinson-White syndrome), as they may accelerate ventricular rate during atrial fibrillation and precipitate ventricular fibrillation 1, 2
For patients with pre-excited atrial fibrillation who are hemodynamically stable, use ibutilide or intravenous procainamide instead 1, 2
For hemodynamically unstable patients with pre-excited atrial fibrillation, proceed directly to synchronized cardioversion 1, 2
Obtain proper ECG diagnosis before treatment to distinguish SVT from ventricular tachycardia 2
Avoid calcium channel blockers and beta-blockers in patients with systolic heart failure 2