What is the difference between multifocal atrial tachycardia (MAT) and atrioventricular (AV) re-entrant tachycardia with aberrant conduction in terms of management and treatment?

Distinguishing Multifocal Atrial Tachycardia from AV Re-entrant Tachycardia with Aberrant Conduction

These are fundamentally different arrhythmias with distinct mechanisms, ECG patterns, clinical contexts, and management strategies that should never be confused—MAT is an irregular rhythm from multiple atrial foci typically seen in critically ill patients with pulmonary disease requiring treatment of underlying conditions, while AVRT with aberrancy is a regular reentrant tachycardia with abrupt onset/termination that responds to AV nodal blockade and is definitively treated with catheter ablation. 1

Mechanism

MAT:

• Results from abnormal automaticity or triggered activity arising from multiple ectopic atrial foci 1
• Not a reentrant mechanism—does not involve a fixed circuit 1
• The mechanism is poorly understood but likely involves triggered activity from increased intracellular calcium stores, exacerbated by hypoxia, acidemia, hypokalemia, and increased catecholamines 2

AVRT with Aberrant Conduction:

• Classic reentrant tachycardia requiring a fixed circuit involving the AV node, ventricle, accessory pathway, and atrium 1
• Orthodromic AVRT uses anterograde conduction through the AV node and retrograde conduction over an accessory pathway 1
• Aberrant conduction occurs due to rate-related bundle branch block, pre-existing bundle branch block, or functional refractoriness 1

ECG Characteristics

MAT:

• Irregular rhythm with at least 3 distinct P-wave morphologies in the same lead 1
• Atrial rate >100 bpm with variable P-P, P-R, and R-R intervals 1
• Distinct isoelectric baseline between P waves (unlike atrial fibrillation) 1
• Narrow QRS complexes (unless pre-existing bundle branch block) 3

AVRT with Aberrant Conduction:

• Regular rhythm with 1:1 AV relationship 1
• Wide QRS complexes (>120 ms) due to aberrant conduction 1
• Retrograde P waves visible in early ST segment (short RP tachycardia) 1
• Abrupt onset and termination (paroxysmal) 1
• QRS morphology may be identical to sinus rhythm with pre-existing bundle branch block 1

Clinical Context

MAT:

• Predominantly elderly patients with severe cardiopulmonary disease 1
• Most commonly associated with COPD, pulmonary hypertension, coronary disease, valvular heart disease 1
• Also associated with hypomagnesemia and theophylline therapy 1
• Seen in critically ill patients with acute respiratory or cardiac decompensation 2
• Hospital incidence: 0.13% to 0.40% 2
• In children, may occur in healthy infants under 1 year or with mild cardiorespiratory disease 4

AVRT with Aberrant Conduction:

• Usually occurs in younger individuals without structural heart disease 1
• More than 60% occur in women 1
• Associated with Wolff-Parkinson-White syndrome (manifest or concealed accessory pathways) 1
• Symptoms include regular palpitations with sudden onset/termination 1
• Responds to vagal maneuvers 1

Acute Management

MAT:

• First-line: Treat underlying condition (hypoxia, heart failure, infection, theophylline toxicity) 1
• Intravenous magnesium (even with normal magnesium levels) 1
• Intravenous metoprolol or verapamil for rate control (Class IIa) 1
• Cardioversion is NOT useful 1
• Avoid digoxin—it is ineffective and potentially toxic 3, 2

AVRT with Aberrant Conduction:

• Vagal maneuvers (Class I) 1
• Adenosine 6-12 mg IV (Class I) 1
• Intravenous beta blockers, diltiazem, or verapamil (Class IIa) 1
• Synchronized cardioversion if hemodynamically unstable or pharmacologic therapy fails (Class I) 1

Ongoing Management

MAT:

• Continue treating underlying cardiopulmonary disease 1
• Oral verapamil or diltiazem for rate control (Class IIa) 1
• Beta blockers with caution if no respiratory decompensation, sinus node dysfunction, or AV block 1
• Antiarrhythmic medications generally NOT helpful for suppression 1
• AV junction modification with radiofrequency ablation for medically refractory cases (84% success rate, improves quality of life and left ventricular function) 5

AVRT with Aberrant Conduction:

• Catheter ablation is definitive therapy (Class I recommendation) 1
• Oral beta blockers, verapamil, or diltiazem if patient declines or is not a candidate for ablation (Class I) 1
• Flecainide or propafenone in patients without structural heart disease (Class IIa) 1

Critical Pitfalls

• Do not mistake MAT for atrial fibrillation—both are irregular, but MAT has distinct P waves with isoelectric baseline 1, 3, 2
• Do not treat MAT with digoxin—it is ineffective and increases toxicity risk in predisposed patients 3, 2
• Do not attempt cardioversion for MAT—it will not work 1
• Do not use beta blockers in MAT with severe bronchospasm or acute decompensated heart failure 1
• Do not misdiagnose AVRT with aberrancy as ventricular tachycardia—look for AV dissociation or fusion complexes to confirm VT 1

Prognosis

MAT:

• High mortality (38-62%) due to underlying disease, not the arrhythmia itself 2
• Need for mechanical ventilation indicates particularly poor prognosis 2
• In children, excellent long-term outcome if no underlying structural heart disease; median arrhythmia duration 4.9 months with spontaneous resolution 4

AVRT:

• Excellent prognosis with catheter ablation (safe and effective definitive therapy) 6
• May cause tachycardia-mediated cardiomyopathy if persistent 1