A diagnostic challenge of dual atrioventricular nodal nonreentrant tachycardia revealed by ambulatory electrocardiographic monitoring: a case report

Background: Dual atrioventricular nodal nonreentrant tachycardia (DAVNNT) is an uncommon arrhythmia caused by simultaneous antegrade conduction of a single atrial impulse through fast and slow atrioventricular nodal pathways, resulting in double ventricular activation without a reentrant circuit. Because its electrocardiographic manifestations are variable and may mimic other supraventricular arrhythmias, DAVNNT is frequently overlooked. Case summary: A 57-year-old woman was admitted with cough and chest tightness lasting for more than 1 month. During hospitalization, she developed paroxysmal palpitations and exertional chest tightness. Coronary computed tomography angiography showed no obvious stenosis, and cardiac biomarkers were unremarkable. Initial electrocardiograms suggested sinus rhythm with junctional or atrial ectopic activity. However, 24-hour Holter monitoring demonstrated the absence of a strict 1:1 relationship between P waves and QRS complexes, recurrent short and long PR intervals, fast- and slow-pathway Wenckebach conduction, and 1:2 atrioventricular conduction. These findings were highly suggestive of DAVNNT. The patient was referred for further electrophysiological evaluation. Conclusion: This case highlights the diagnostic value of careful surface ECG and Holter analysis in recognizing DAVNNT before invasive electrophysiological confirmation becomes available. A diagnosis highly suggestive of DAVNNT should be considered when organized atrial activity is associated with more ventricular activations than atrial depolarizations and when fixed short and long PR intervals recur during ambulatory monitoring.