Differential Diagnosis and Management of Irregular Supraventricular Tachycardia

Key Diagnostic Considerations

The American College of Cardiology suggests that irregular palpitations specifically suggest premature depolarizations, atrial fibrillation (AF), or multifocal atrial tachycardia (MAT), rather than the regular, paroxysmal rhythms seen in AVNRT or AVRT 1
Multifocal atrial tachycardia is most commonly encountered in patients with underlying pulmonary disease, according to the American College of Cardiology 1
Regular, paroxysmal palpitations with sudden onset and termination that respond to vagal maneuvers indicate AVNRT or AVRT, as stated by the American College of Cardiology 1

Synchronized cardioversion is mandatory for hemodynamically unstable patients with pre-excited AF, as recommended by the American Heart Association 2
For hemodynamically stable patients with pre-excited AF, the American Heart Association suggests using ibutilide or IV procainamide 2
The American Heart Association advises against using AV nodal blocking agents (adenosine, diltiazem, verapamil, beta-blockers) in pre-excited AF, as these may accelerate ventricular rate and precipitate ventricular fibrillation 2, 3
The initial approach to irregular SVT of unknown mechanism involves attempting vagal maneuvers, which have an approximately 27.7% overall success rate, according to the American Heart Association 4, 5
If vagal maneuvers fail and the patient is hemodynamically stable, adenosine 6-12 mg IV is the next step, with a 90-95% success rate for AVNRT/AVRT, but may precipitate AF, as noted by the American Heart Association 2, 4, 5
Alternative pharmacologic agents if adenosine fails include IV diltiazem or verapamil (64-98% success rate) for hemodynamically stable patients, as recommended by the American Heart Association 3, 5
Immediate synchronized cardioversion is highly effective and should be performed promptly when patients show hypotension, altered mental status, signs of shock, chest pain, or acute heart failure, according to the American Heart Association 3, 5

The American College of Cardiology warns against assuming all SVTs are regular, as irregular rhythm changes your differential and management approach 1
The American Heart Association advises against giving verapamil or diltiazem if you cannot definitively exclude VT or pre-excited AF, as this may cause hemodynamic collapse or ventricular fibrillation 3, 4
Recording a 12-lead ECG during tachycardia is essential to differentiate mechanisms, particularly to identify QRS duration >120 ms which requires distinguishing VT from SVT with aberrancy, as recommended by the American Heart Association 4

The American Heart Association recommends determining hemodynamic stability immediately, looking for signs of shock, chest pain, or acute heart failure symptoms, as these mandate immediate synchronized cardioversion in patients with SVT 6, 7

The American College of Cardiology recommends administering adenosine 6 mg as a rapid IV bolus through a proximal/large vein, followed immediately by a saline flush, with a success rate of 78-96% for AVNRT and AVRT 6, 7
Adenosine achieves 90-95% effectiveness in orthodromic AVRT and AVNRT specifically, with expected side effects including chest discomfort, shortness of breath, and flushing, and has diagnostic utility in unmasking atrial flutter or atrial tachycardia 6, 7

The American Heart Association recommends proceeding immediately to synchronized cardioversion when vagal maneuvers or adenosine are ineffective or not feasible in hemodynamically unstable patients with SVT 6, 7
Synchronized cardioversion successfully restores sinus rhythm in essentially all hemodynamically unstable patients, with an initial energy of 50-100J recommended for SVT 6, 7