What is the diagnostic workup for Permanent Junctional Reentrant Tachycardia (PJRT)?

Diagnostic Workup for Permanent Junctional Reentrant Tachycardia (PJRT)

The diagnosis of PJRT is established through 12-lead ECG during tachycardia showing a narrow QRS complex with a characteristic long RP interval (RP > PR) and inverted P waves in the inferior leads, followed by electrophysiologic study to confirm the presence of a slowly conducting, decremental accessory pathway. 1

ECG Characteristics During Tachycardia

The surface ECG provides the critical diagnostic clues for PJRT:

• Long RP interval: The RP interval exceeds the PR interval (RP > PR), distinguishing PJRT from typical AVNRT and orthodromic AVRT which have short RP intervals 1
• Narrow QRS complex: QRS duration <120 ms unless pre-existing bundle branch block or aberrant conduction is present 1
• Inverted P waves: Deeply inverted retrograde P waves appear in leads II, III, and aVF due to the posteroseptal location of the accessory pathway in most cases 2, 3
• P wave location: The P wave is visible near the end of or shortly after the T wave, closer to the subsequent QRS complex than the prior one 1
• Regular rhythm: The tachycardia maintains a regular ventricular rate with 1:1 AV relationship 1

Clinical Presentation Features

Key clinical features that should raise suspicion for PJRT:

• Incessant or nearly incessant tachycardia: Present >50% of the time on 24-hour Holter monitoring in approximately 69% of cases, though paroxysmal forms occur in 53% of adults 4, 5
• Tachycardia rate: Typically ranges from 100-250 beats/min, with slower rates (146±30 bpm in adults) compared to other SVTs 4, 5
• Tachycardia-induced cardiomyopathy: Develops in 16-28% of patients due to the persistent nature of the arrhythmia 4, 5, 3
• Age of presentation: Can present from fetal life through adulthood, with mean age of 43±16 years in adult series 5

Differential Diagnosis Algorithm

When evaluating a narrow QRS tachycardia with long RP interval, systematically exclude:

• Atrial tachycardia: P wave morphology differs from sinus and shows abnormal atrial activation sequence; atrial rate may exceed ventricular rate 1
• Atypical (fast-slow) AVNRT: P wave closer to subsequent QRS but typically has different P wave morphology and location compared to PJRT 1, 2
• Sinus tachycardia: P wave morphology identical to sinus rhythm with normal PR interval 1

Electrophysiologic Study Confirmation

Definitive diagnosis requires electrophysiologic study demonstrating:

• Decremental retrograde conduction: The accessory pathway exhibits slow, decremental conduction properties in the retrograde direction (ventricle to atrium) 1, 5
• Accessory pathway location: Most commonly right posteroseptal (59-76% of cases), but can be in atypical locations including left posterior, left lateral, or within the coronary venous system 6, 5, 7
• Inducibility: Tachycardia inducible with both atrial and ventricular programmed stimulation 6, 4
• Ventricular entrainment: A premature ventricular depolarization delivered when the His bundle is refractory can advance the next atrial electrogram, confirming accessory pathway participation 6

Ambulatory Monitoring

Extended ECG monitoring is essential for diagnosis:

• 24-hour Holter monitoring: Documents the incessant or nearly incessant nature of the tachycardia and quantifies the burden (>50% of recording time suggests PJRT) 4
• Event monitors: Useful for capturing paroxysmal episodes in the 53% of adult patients with non-permanent forms 5

Echocardiographic Assessment

Echocardiography must be performed to:

• Assess left ventricular function: Screen for tachycardia-induced cardiomyopathy, which occurs in 16-28% of patients and is reversible after successful ablation 4, 5, 3
• Evaluate for structural heart disease: Exclude other causes of cardiomyopathy 5

Common Diagnostic Pitfalls

• Misdiagnosis as atrial tachycardia: The long RP interval mimics AT, but the inverted P waves in inferior leads and decremental retrograde conduction distinguish PJRT 1
• Confusion with junctional rhythm: True junctional rhythms show AV dissociation and marked irregularity, unlike the regular 1:1 relationship in PJRT 8
• Missing paroxysmal forms: In adults, 53% have paroxysmal rather than incessant tachycardia, requiring extended monitoring for diagnosis 5
• Overlooking atypical pathway locations: While 59-76% are right posteroseptal, 24-40% occur in atypical locations requiring careful mapping 5, 7