Background: Atrioventricular (AV) node normally has decremental conduction property and a longer refractory period than His-Purkinje system (HPS). This results in AV conduction delay or block at the level of AV node in response to short-coupled atrial premature beats. Prolonged refractoriness in HPS can produce unusual physiological patterns of AV conduction such as conduction delay or infra-nodal block in the distal elements of HPS.Case presentation: We present a case in which atrial premature stimulation produces infra-nodal Wenckebach conduction block which initiates long-short cycle sequence within the bundle branches resulted in alternating bundle branch block and atypical pattern of Ashman phenomenon. Conclusions This case highlights the importance of recognizing the unusual physiological AV conduction patterns of HPS. The long-short cycle sequence in the bundle branches of distal HPS and linking phenomenon can result in alternating bundle branch block without the presence of HPS disease.

Background: Ablation of idiopathic ventricular arrhythmias (VAs) in the cardiac crux region is one of the challenging procedures due to the complex anatomical structure where the four chambers of the heart are offset. Although this region is complex, the contiguous cardiac structures allow for the ablation of arrhythmias from adjacent sites.Case presentation: We present different anatomical approaches in radiofrequency ablation and the ECG character‑ istics from a case series of VAs originated from the basal inferior ventricular septum, the corresponding endocardial aspect of the basal cardiac crux region. Conclusions Ablation of VAs originated from the basal cardiac crux region requires detailed mapping in the proxi‑ mal coronary venous system and the adjacent structures including the RV, RA, and LV. In addition to the characteristic ECG of basal crux VAs, our three cases present an abrupt precordial transition in V2 with R wave amplitude greater than in V1 and V3.

Background: Atrioventricular (AV) node normally has decremental conduction property and a longer refractory period than His-Purkinje system (HPS). This results in AV conduction delay or block at the level of AV node in response to short-coupled atrial premature beats. Prolonged refractoriness in HPS can produce unusual physiological patterns of AV conduction such as conduction delay or infra-nodal block in the distal elements of HPS.Case presentation: We present a case in which atrial premature stimulation produces infra-nodal Wenckebach conduction block which initiates long-short cycle sequence within the bundle branches resulted in alternating bundle branch block and atypical pattern of Ashman phenomenon. Conclusions This case highlights the importance of recognizing the unusual physiological AV conduction patterns of HPS. The long-short cycle sequence in the bundle branches of distal HPS and linking phenomenon can result in alternating bundle branch block without the presence of HPS disease.

Background: Ablation of idiopathic ventricular arrhythmias (VAs) in the cardiac crux region is one of the challenging procedures due to the complex anatomical structure where the four chambers of the heart are offset. Although this region is complex, the contiguous cardiac structures allow for the ablation of arrhythmias from adjacent sites.Case presentation: We present different anatomical approaches in radiofrequency ablation and the ECG character‑ istics from a case series of VAs originated from the basal inferior ventricular septum, the corresponding endocardial aspect of the basal cardiac crux region. Conclusions Ablation of VAs originated from the basal cardiac crux region requires detailed mapping in the proxi‑ mal coronary venous system and the adjacent structures including the RV, RA, and LV. In addition to the characteristic ECG of basal crux VAs, our three cases present an abrupt precordial transition in V2 with R wave amplitude greater than in V1 and V3.