Type I Wenckebach second-degree AV block: A matter of definition

Variability of the PR intervals in Wenckebach atrioventricular block

The duration of the PR intervals in atypical Wenckebach atrioventricular block before and after a non-conducted P wave can exhibit a wide range of values and patterns. Understanding the different or at times puzzling manifestations of Wenckebach atrioventricular block in terms of its PR intervals can avoid diagnostic errors, especially the erroneous more serious diagnosis of Mobitz type II atrioventricular block.

Definitions and Pitfalls in the Diagnosis of Atrioventricular Block

The widespread use of disparate definitions of atrioventricular block has created important diagnostic problems. Adherence to the correct definitions provides a logical and simple framework for clinical evaluation. This review focuses on the clinical importance of the definitions in the diagnosis of the various types of atrioventricular (AV) block and the associated diagnostic pitfalls.

Unusual manifestation of atypical type I second degree atrioventricular block

A 25 year-old woman exhibited atypical type I second degree atrioventricular block characterized by constant PR intervals except the PR interval of the beat after the block. This was attributed to vagally induced AV block with failure of the vagal effect to depress the sinus node.

Problematic definitions of Mobitz type II second degree AV block: Historical aspects

Problems with the definition of type II second degree AV block are best understood by reviewing the historical aspects that include Mobitz's original description, the contributions of the Chicago Arrhythmia School and the growing importance of excluding slowing of the sinus rhythm.

The Wenckebach Phenomenon

Medicine has many great pioneers, and in 1899, one such pioneer - Karel Frederik Wenckebach made a discovery which, even to this day, remains one of the fundamental concepts within electrophysiology.

Since the Wenckebach Phenomenon was first described, the field of electrophysiology has developed at a rapid pace, allowing us to observe this behaviour, and its complexities, in many new ways. In a similar way, this chapter will illustrate Wenckebach behaviour across a spectrum of modalities from the 12 lead ECG, through to the intra-cardiac recordings from both electrophysiological studies and implantable cardiac devices. In doing so, we continue to shed light on the phe-nomenon first identified through Wenckebach’s meticulous attention to detail some 120 years ago.

Conduction Disorders: The Value of Surface ECG

PURPOSE OF REVIEW

The purpose of the current mini-review is to describe the importance of surface ECG for the diagnosis of conduction disorder.

METHODS

The MEDLINE/PubMed database was used, with the keywords "ECG" and "conduction disorders"; over the past 10 years. Other documents were included because of their relevance.

MAIN FINDINGS

Data on the anatomy and function of the cardiac electrical system have been described. Conduction disorders including sinus node dysfunction, atrioventricular blocks, intraventricular conduction disorders are exposed as to their epidemiology, etiology, presentation, anatomical site of impaired conduction of the electrical stimulus. The importance of ECG in patients with a cardiac implantable electronic device was also discussed, in addition to future perspectives.

CONCLUSION

Surface ECG allows the diagnosis of atrioventricular and intraventricular conduction disorder and its anatomical block site most of the time, without the need for invasive tests such as electrophysiological study. Dysfunctions of cardiac implantable electronic devices can be diagnosed by ECG, as well as the prediction of response to cardiac resynchronization therapy.

Regular ventricular rate and "reverse bigeminy" in 3:2 Wenckebach periodicity

One of the more common causes of bigeminy at the ventricular level is type 1 second-degree atrioventricular (AV) block with 3:2 conduction ratio. In 3:2 Wenckebach, the shorter cycles reflect the consecutively conducted impulses and the longer cycles coincide with the blocked P waves. Theoretically, however, depending on the degree of conduction delay between the first and second transmitted impulses, other types of spacing of the QRS complexes may become possible. In this retrospective study of 180 patients who underwent electrophysiologic studies for symptomatic arrhythmias, atrial pacing-induced 3:2 Wenckebach periodicity resulted in a regular ventricular rate and/or in "reverse bigeminy" in 16 cases (8.9%). Reverse bigeminy was characterized by the shorter R-R intervals including both the blocked P waves and the first conducted beats of the subsequent cycles, and the longer R-R intervals coinciding with the second conducted beats during 3:2 Wenckebach. In 14 cases, regular ventricular rate and reverse bigeminy was triggered by marked conduction delay in the AV node and in 2 cases, the conduction delay was in the His-Purkinje system. Reverse bigeminy appeared to be related to dual AV nodal physiology in 8 patients. In 2 cases, sophisticated maneuvers such as termination of atrial pacing at critical intervals during the AV Wenckebach were required to expose the true conduction pattern. This study demonstrates that during rapid atrial rhythms, one cannot always be sure which P wave is responsible for which QRS complex. Rarely, extreme conduction delays can result in P waves conducting across the subsequent ventricular beats and be responsible not for the first, but for the following QRS complexes.

Assessing Dynamic Atrioventricular Conduction Time to RR-interval Coupling in Athletes and Sedentary Subjects

Background Atrioventricular conduction time ( AVCT ) is influenced by autonomic input and subject to physiological remodeling. Objective To evaluate beat-by-beat AVCT and RR-interval variability in athletes and healthy sedentary subjects. Methods Twenty adults, including 10 healthy sedentary (Controls) and 10 elite long-distance runners (Athletes), age, weight and height-adjusted, underwent maximal metabolic equivalent (MET) assessment, and 15-min supine resting ECG recording seven days later. The interval between P-wave and R-wave peaks defined the AVCT . Mean (M) and standard deviation (SD) of consecutive RR-intervals (RR) and coupled AVCT were calculated, as well as regression lines of RR vs. AVCT (RR-AVCT) . Concordant AV conduction was defined as positive RR-AVCT slope and discordant otherwise. A multivariate linear regression model was developed to explain MET based on AVCT and RR-interval variability parameters. Significance-level: 5 %. Results In Athletes, M-RR and SD-RR values were higher than in Controls, whereas M-AVCT and SD-AVCT were not. RR-AVCT slopes were, respectively, 0.038 ± 0.022 and 0.0034 ± 0.017 (p < 0.05). Using a cut-off value of 0.0044 (AUC 0.92 ± 0.07; p < 0.001), RR-AVCT slope showed 100% specificity and 80% sensitivity. In a multivariate model, SD-RR and RR-AVCT slope were independent explanatory variables of MET (F-ratio: 17.2; p < 0.001), showing 100% specificity and 90% sensitivity (AUC 0.99 ± 0.02; p < 0.001). Conclusion In elite runners, AVCT to RR -interval dynamic coupling shows spontaneous discordant AV conduction, characterized by negative AVCT vs. RR -interval regression line slope. RR -intervals standard deviation and AVCT vs. RR -interval regression line slope are independent explanatory variables of MET (Arq Bras Cardiol. 2020; [online].ahead print, PP.0-0).