[Narrow complex tachycardia in patients with congenital heart defects and following cardiac surgery : How can the ECG help?]

With the growing number of adults with congenital heart disease (ACHD), the incidence of arrhythmias as a late complication is also increasing. Narrow QRS tachycardias are the most common form of supraventricular arrhythmias in this population, typically arising from postoperative scarring, anatomical reconstruction, and altered conduction pathways. The 12-lead surface ECG remains a key tool for mechanism diagnosis, distinguishing between typical and atypical atrial flutter circuits, focal atrial tachycardias, and atrioventricular (AV) reentrant tachycardias, as well as for guiding interventional therapy planning. Following complex atrial surgeries such as Mustard, Senning, Fontan procedures, or biatrial heart transplantation, conventional ECG interpretation reaches its limits: atypical electrical activation, an abnormal heart axis, multiple reentry substrates, and altered P‑wave morphologies complicate classification. In such cases, the combination of ECG findings, detailed knowledge of the individual postoperative anatomy, three-dimensional electroanatomical mapping, and complementary imaging is essential. Catheter ablation in this patient group achieves high acute success rates with acceptable safety, yet remains prone to recurrences. Structured ECG analysis, modern imaging, and treatment in specialized centers are key to improving long-term outcomes and prognosis.