Management of Unstable Supraventricular Tachycardia

Defining Hemodynamic Instability

The American Heart Association recommends that hemodynamic instability in SVT includes any of the following: hypotension (systolic BP typically <90 mmHg), syncope or altered consciousness, signs of myocardial ischemia (chest pain with ST-segment changes), or severe heart failure (acute pulmonary edema) 1
The American College of Cardiology suggests that syncope or altered consciousness is a sign of hemodynamic instability in SVT 2
The American Heart Association states that signs of myocardial ischemia, such as chest pain with ST-segment changes, indicate hemodynamic instability in SVT 1
Severe heart failure, such as acute pulmonary edema, is a sign of hemodynamic instability in SVT, according to the American College of Cardiology 1

The American Heart Association recommends that if the patient has a regular narrow-complex tachycardia and is not in shock, one dose of adenosine 6 mg rapid IV push through a proximal line with saline flush may be attempted, even in unstable patients, with a success rate of 90-95% for AVNRT and orthodromic AVRT 2
The American College of Cardiology advises having cardioversion equipment immediately available because adenosine may precipitate atrial fibrillation that conducts rapidly, potentially causing ventricular fibrillation 3, 1

The American Heart Association states that calcium channel blockers, such as diltiazem and verapamil, are contraindicated in unstable patients as they can precipitate cardiovascular collapse 2

The American College of Cardiology recommends immediately proceeding to synchronized cardioversion without attempting adenosine in cases of pre-excited atrial fibrillation (Wolff-Parkinson-White with AF) 3, 1
The American Heart Association advises against using AV nodal blocking agents, such as adenosine, calcium channel blockers, beta blockers, or digoxin, as they may enhance accessory pathway conduction and precipitate ventricular fibrillation in pre-excited atrial fibrillation 3, 1
The American College of Cardiology suggests anticipating premature atrial or ventricular complexes immediately after cardioversion that may reinitiate tachycardia, and having antiarrhythmic drugs ready to prevent acute reinitiation if this occurs 3, 1

The American College of Cardiology, American Heart Association, and Heart Rhythm Society recommend synchronized cardioversion for hemodynamically unstable patients with SVT when vagal maneuvers or adenosine are ineffective or not feasible 4, 5
The American College of Cardiology, American Heart Association, and Heart Rhythm Society suggest that adenosine may be considered first if the tachycardia is regular and has a narrow QRS complex, even in unstable patients 6
Adenosine 6 mg rapid IV push through proximal IV line followed by saline flush is recommended, with a success rate of 90-95% for orthodromic AVRT and AVNRT 4, 5, 7
If adenosine is unsuccessful after 1-2 minutes, a 12 mg rapid IV push may be given 4

Synchronized cardioversion is the Class I, Level B-NR recommendation for hemodynamically unstable SVT, with an initial energy level of 50-100 J 4, 5, 6
Procedural sedation should be provided before cardioversion if the patient is conscious 4
Cardioversion has a success rate of 100% in restoring sinus rhythm in hemodynamically unstable SVT patients in prehospital studies 4, 6

Beta blockers are contraindicated in hemodynamically unstable patients due to the risk of worsening hypotension 8, 6
IV metoprolol is not recommended for severely hypotensive patients, as it can worsen hypotension 8
Procainamide is indicated for pre-excited atrial fibrillation, not regular narrow-complex SVT, and would be too slow-acting for a patient in shock 7

A narrow QRS complex confirms that the tachycardia is supraventricular in origin, likely AVNRT or orthodromic AVRT 4, 5
An alcohol trigger suggests possible accessory pathway involvement 7

Calcium channel blockers and beta blockers should not be used in hemodynamically unstable patients, as they can precipitate cardiovascular collapse 8, 6