Symptomatic Atrioventricular Block: When Pacing May Not Be the Solution!

It is well known that percutaneous coronary intervention is not required in most asymptomatic patients with nonproximal single vessel coronary disease despite the temptation on seeing the coronary blockage (“oculostenotic” reflex). Similarly, many asymptomatic patients having occurrences of first- and second-degree type 1 atrioventricular (AV) block especially during sleeping hours do not require pacing therapy. However, AV block of higher degree and/or associated with bradycardia symptoms warrants pacemaker implantation in general. Subramanian et al ¹ in this issue of the journal present a case report of a patient with symptoms suggestive of bradycardia who, despite having documented AV block, does not need pacing therapy.

The authors need to be congratulated for bringing out this commonly seen Holter test finding that often results in unnecessary pacemaker implantation and for enlightening the readers of a rare entity called vagally mediated AV block. Simultaneous occurrence of sinus slowing along with AV block of any degree and with absence of QRS prolongation or fascicular block suggests vagally mediated AV block. The AV block is considered to be functional and resides at the level of AV node. Rarity of this clinical entity and lack of necessary clinical studies have resulted in the absence of its mention in most guidelines on pacing therapy. In view of the benign nature of the disease and absence of any pathology in the AV conduction tissues, the consensus is that pacing is usually not required.

However, at the same time, it is imperative for the clinician to be absolutely certain of the presence of this entity as the cause and exclude all other pathological causes. The most important pathological entity that needs to be excluded is bradycardia-dependent AV block in which pacing therapy is essential. In bradycardia-dependent AV block, the block occurs on slowing of the sinus rate but presence of associated fascicular or bundle branch block, absence of PR prolongation, and initiation of block by premature ventricular or atrial complex usually clinches the diagnosis.

Another issue that is often puzzling is if a patient of vagally mediated AV block is symptomatic and has higher degrees of AV block what can be done for its treatment, if pacemaker is not required. Since the block is due to parasympathetic overactivity, radiofrequency catheter ablation of cardiac ganglionated plexi (cardioneuroablation) has been shown in few case reports and series to improve symptoms and eliminate AV block in this entity as also in neurocardiogenic syncope.^2–4 However, at the present time, the patient selection and steps of the technique of cardioneuroablation are not well defined and standardized for it to be applicable widely.