Atrial septal defects (ASDs) and ventricular septal defects (VSDs) account for the majority of congenital heart disease and may remain clinically relevant from infancy into adulthood. Echocardiography is the gold standard for diagnosis and detailed anatomical assessment of these defects; however, the electrocardiogram (ECG) may provide additional pathophysiological and prognostic insights. This review summarizes ECG findings in ASD and VSD before and after repair, with respect to the effects of defect type, timing of intervention, and postoperative evolution of electrical disturbances. A structured literature search was conducted to identify studies reporting ECG or rhythm abnormalities before and after repair. In hemodynamically significant ASD, ECG changes before repair generally correlate with chronic right-sided chamber volume overload. Secundum defects present with right-axis deviation and incomplete right bundle branch block. Primum defects are mainly associated with left-axis deviation and atrioventricular conduction delay, whereas sinus venosus defects may present with sinus node dysfunction. After closure, right-sided overload markers may return to normal; however, persistent atrial arrhythmias and conduction-system lesions frequently occur. In VSD, preoperative findings may include a normal ECG in small restrictive defects, to left, right, or combined ventricular overload patterns when associated with elevated left ventricle preload or right ventricle afterload. After surgery, the ECG tends to reflect evolving conduction-system injury and late rhythm-related vulnerability, such as right bundle branch block, atrioventricular block, QTc prolongation, progressive PR/QRS widening, and late complete atrioventricular block. Future studies with standardized timing and outcome-related follow-up are warranted to solidify the clinical relevance of specific ECG findings.

The case was a 15-year-old male with a history of paroxysmal supraventricular tachycardia refractory to medical therapy and prior catheter. A repeat electrophysiology study and catheter ablation were applied. Baseline AH and HV intervals were 100 and 55 ms during normal sinus rhythm (NSR), respectively. Programmed atrial stimulation induced a short RP narrow complex tachycardia (HV interval 22 ms) with an incomplete right bundle branch block configuration and right axis deviation. Tachycardia was terminated with ATP 5 mg injection. An atrial premature beat within the His refractory period advanced and reset tachycardia. Entrainment performed from the coronary sinus and left ventricle both showed a post-pacing interval minus tachycardia cycle length (TCL) of 90 ms. After confirming the diagnosis, left atrial mapping along mitral annulus was performed using trans-septal access and accessory pathway potentials were recorded during NSR and tachycardia at the superior mitral annulus. An irrigated ablation catheter guided by 3-D mapping was used to perform ablation during tachycardia. Tachycardia terminated immediately during the first RF application with ensuing automaticity exhibiting a warm-up during radiofrequency delivery and a cooling down upon the suspension of ablation. Therefore, all phenomena of Mahaim-fiber associated tachycardia were observed. In this case, we describe an antidromic atrio-ventricular reentry tachycardia using a left atrio-fascicular fiber inserting into the proximal left anterior fascicle.