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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Wide QRS tachycardia (left bundle branch block and superior-axis morphology)

  • Diagnosis confirmed at electrophysiologic study

  • Progressive decrease in atrioventricular (AV) conduction through the pathway (anterograde decremental conduction)

  • Coexistence with AV nodal reentrant tachycardia and other accessory pathways

GENERAL CONSIDERATIONS

  • These pathways do not conduct retrogradely

  • Antidromic tachycardia is the most common clinical tachycardia

  • Minimal preexcitation during sinus rhythm

  • More preexcitation during right atrial than lateral coronary sinus pacing (differential pacing)

  • Earliest ventricular activation during tachycardia occurs at the right ventricular apex

  • Atriofascicular pathways course along the right atrial free wall at the level of the tricuspid annulus and insert distally into right bundle branch

  • Fasciculoventricular pathways give rise to fixed preexcitation and serve as bystanders during reentrant tachycardia

  • Retrograde right bundle branch block prolongs the tachycardia cycle length

  • Intermittent retrograde right bundle branch block causes long, short fluctuating cycle length of the tachycardia

  • Mahaim pathway potentials and mechanical compression with the ablation catheter leading to loss of conduction are successful sites for ablation

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Palpitations

  • Presyncope

  • Syncope

PHYSICAL EXAM FINDINGS

  • When associated with congenital heart disease (Ebstein’s anomaly), features of tricuspid regurgitation may be present

DIFFERENTIAL DIAGNOSIS

  • Ventricular tachycardia

  • Supraventricular tachycardia with aberrancy

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • CBC, basic metabolic panel

ELECTROCARDIOGRAPHY

  • During sinus rhythm, ECG may appear normal because of negligible preexcitation

  • During tachycardia, ECG may resemble ventricular tachycardia

    • – If the patient has structurally normal heart, Mahaim tachycardia should be in the differential diagnosis

  • Holter monitoring to document rhythm disturbances

IMAGING STUDIES

  • Echocardiogram if there is an associated murmur to identify Ebstein’s anomaly

DIAGNOSTIC PROCEDURES

  • Electrophysiologic study to confirm mechanism of tachyarrhythmias and establish diagnosis

TREATMENT

CARDIOLOGY REFERRAL

  • All patients with an episode of symptomatic supraventricular tachycardia should be referred to a cardiologist

HOSPITALIZATION CRITERIA

  • Symptomatic tachycardia, particularly syncope

  • When ventricular tachycardia cannot be excluded

THERAPEUTIC PROCEDURES

  • Radiofrequency (RF) ablation of the pathway

SURGERY

  • Rarely required

MONITORING

  • ECG monitoring in the hospital

DIET AND ACTIVITY

  • No specific restrictions

  • General healthy lifestyle

ONGOING MANAGEMENT

HOSPITAL DISCHARGE CRITERIA

  • Twenty-four hours after RF ablation

FOLLOW-UP

  • Four weeks after initial ablation

  • Long-term follow-up with primary care physician

COMPLICATIONS
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