Aberrant Ventricular Conduction: Revisiting an Old Concept.

The well-defined concept of aberrant ventricular conduction was introduced over 100 years ago and, despite advances in cardiac physiology and electrophysiologic testing, it is still widely misunderstood. Aberrant ventricular conduction is due to physiologic refractoriness of the His-Purkinje system and in most cases does not reflect underlying conduction system disease. Electrophysiologically, aberrant ventricular conduction can manifest with premature atrial ectopics, the Ashman phenomenon with atrial tachyarrhythmias, concealed conduction, echo beats and with the sinus mechanism including rate dependent bundle branch block, bradycardia dependent bundle branch block and early sinus beats. It is important to recognise aberrant ventricular conduction in the context of a broad complex tachycardia, as the differentiation between supraventricular tachyarrhythmias with aberrant ventricular conduction and ventricular tachyarrhythmias carry different therapeutic and prognostic implications. This review will define the ECG footprints of aberrant ventricular conduction to allow accurate ECG interpretation.

Wide complex tachycardia in a patient with non-ischemic cardiomyopathy: What is the diagnosis?

A 55-year-old male presented with acute heart failure and incessant wide complex tachycardia resembling an outflow tract ventricular tachycardia. Meticulous analysis of the electrocardiograms established the diagnosis of pre-excitation with prolonged atrio-ventricular (A-V) conduction over a decrementally conducting accessory A-V pathway. "Linking" between the accessory A-V pathway and normal A-V conduction system resulted in sustained maximal pre-excitation as well as periodic transition to normal A-V conduction without appreciable change in heart rate. Successful radiofrequency ablation of this unusual accessory A-V pathway was performed at the aortic-mitral junction. This ameliorated the mechanical dysynchrony, allowed discontinuation of hemodynamic/inotropic support, and resulted in sustained symptomatic improvement.

Atrial activation sequence changes during ventricular overdrive pacing: What is the mechanism?

We describe atrial activation sequence changes during ventricular overdrive pacing in a patient with a concealed left-sided accessory pathway and discuss its potential mechanism.

Role of concealed conduction and allied phenomena in the genesis, maintenance, and termination of cardiac arrhythmias.

Concealed conduction is a common electrocardiographic phenomenon whereby a series of events may occur as a result of incomplete propagation of an impulse. The occurrence, maintenance, and resolution (termination) of several events such as functional block and cardiac arrhythmias are linked to concealed conduction. This phenomenon should be suspected on the surface electrocardiogram whenever an arrhythmic event occurs unexpectedly. Several electrophysiological concepts such as transseptal conduction and linking phenomenon are close allies of concealed conduction. His-bundle electrocardiography and comprehensive electrophysiology may be needed to verify this phenomenon.

Sinus tachycardia presenting as a wide and narrow complex tachyarrhythmia: What is the 'link'?

We describe a neonate that developed alternating wide and narrow complex tachycardias following heart surgery for congenital heart defect. Although the etiology was sinus tachycardia, a premature atrial complex initiated aberrancy due to phase 3 block that was perpetuated due to 'linking' at similar or even slower heart rates. Similarly, there was abrupt transition from wide to narrow complex tachycardia following a premature ventricular complex without a change in subsequent heart rate. This was explained by interruption of linking phenomenon by premature ventricular activation. While the above mechanisms are described in the setting of a supraventricular tachyarrhythmia, this has not been reported during sinus tachycardia.

Is It Complete Left Bundle Branch Block? Just Ablate the Right Bundle.

Complete left bundle branch block (LBBB) is established according to standard electrocardiographic criteria. However, functional LBBB may be rate-dependent or can perpetuate during tachycardia due to repetitive concealed retrograde penetration of impulses through the contralateral bundle "linking phenomenon." In this brief article, we present two patients with basal complete LBBB in whom ablating the right bundle unmasked the actual antegrade conduction capabilities of the left bundle. These cases highlight intriguing overlap between electrophysiological concepts of complete block, linking, extremely slow, and concealed conduction.

Mobitz type II second-degree atrioventricular block with narrow QRS and junctional extrasystoles: what is the mechanism?

A 74-year-old man underwent an electrophysiological study because of Mobitz type II second-degree atrioventricular (AV) block with narrow QRS and frequent junctional extrasystoles. During the study, there were very frequent single His bundle depolarizations with multiple coupling intervals that reproduce the ECG findings. In this case, some His bundle extrasystoles result in retrograde concealed conduction and prolonged local refractoriness in the AV node that manifest as block of the next atrial impulse.

Direct recording of concealed ventricular extrasystoles producing pacer inhibition.

We report a case of concealed extrasystoles recorded from a pacing lead. The concealed extrasystoles were observed with right ventricular pacing, biventricular unipolar, and biventricular bipolar pacing. The simultaneous surface EKG did not show manifest ventricular extrasystoles with the concealed intracardiac potentials. This case highlights a cause of oversensing that has been theoretically reported in the literature but never directly observed.

Double, double...What's the trouble?

Parasystole can be subtle, making the diagnosis difficult to recognize.

Syncope in the setting of trifascicular block and retrograde concealed conduction: A case report.

In clinical practice, the accurate diagnosis of the causes of syncope is often challenging and demanding. Moreover, certain rare electrocardiographic phenomena may complicate the diagnostic workup, leading to imprecise diagnoses. The present study briefly describes the case of an 82-year-old male patient with ischemic cardiomyopathy who suffered syncopal episodes in the setting of trifascicular block. The 12-lead electrocardiogram revealed premature ventricular contractions and non-conducted P waves due to the phenomenon of retrograde concealed conduction. Following the exclusion of myocardial ischemia, an electrophysiological study yielded abnormal results and a biventricular pacemaker was implanted. Although retrograde concealed conduction is considered a benign phenomenon caused by the transient modification of antegrade atrioventricular conduction characteristics, further meticulous investigation is required in patients with concomitant baseline conduction abnormalities and/or structural heart disease.

Transient narrowing of a wide QRS tachycardia. What is the mechanism?

Electrocardiogram showing a regular wide QRS tachycardia with left branch block (LBBB) like in morphology at 200 beats per minute (bpm). During electrophysiology study, it suddenly gets narrow and faster. What is the mechanism of the switch from a broad complex to a narrow complex tachycardia?