Lingering misconceptions about type I second-degree atrioventricular block
Section snippets
Statements from the literature
“Type I block is AV nodal”14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 with no mention of QRS duration; type I block is “almost always in the AV node” without mention of QRS duration27, 28; type I block “is usually accompanied by a QRS of normal duration”29; “Type I block is localized in the AV node or the His bundle”30 without mention of QRS duration or bundle branches except that “type II block often occurs in the bundle branches”; “Type I block occurs in the AV junction”31 without
Statements from the literature
“Type I AV block with a wide QRS is infranodal in about 25% to 30% of cases”8, 9, 10, 11, 33, 34; “Type I block and bundle branch block (BBB) is more likely (or usually) to be within the AV node than the His-Purkinje system”11 or type I with BBB “is frequently at the AV node”; “a remote chance exists of Mobitz I block occurring in an infranodal structure,” if the QRS is wide.35
These statements probably stem from misinterpretation of data from the Puech group5, 6, 7 and that shown in Table 1,
Statement from the literature
“Wenckebach type of block in the His bundle is uncommon and may be seen in 9% of patients and may occur in the presence of a narrow or wide QRS complex.”42 This statement would be more precise by explaining that it refers to 9% (similar to the 8% in Table 1) of all patients (narrow and wide QRS complexes) with type I block and chronic conduction system disease. According to the data outlined in Table 2, 16% of narrow QRS type I blocks are intra-Hisian. This figure may be true for symptomatic
Relative frequency of type I and type II in the His-Purkinje system
In the His-Purkinje system, type II block is about twice as common as type I block (Table 1).
Incidence of narrow QRS type I block
“In patients with a narrow QRS, type I second-degree AV block is nodal in approximately 70% of cases.”10 Similarly, it has been stated (without mention of QRS duration) that “type I second-degree AV block is localized in the AV node in 75% of cases and in the His-Purkinje system in the remainder.”48 These general statements are misleading because they do not specifically refer to chronic conduction system disease. Considering all the causes of narrow QRS type I block, the vast majority of
Conclusion
Type I second-degree AV block should not be automatically labeled as AV nodal in the setting of chronic conduction system disease. Although uncommon, type I second-degree AV block with BBB as a manifestation of chronic conduction system disease requires special consideration because the second-degree AV block is in the His-Purkinje system in 60% to 70% of cases. A His bundle recording is required to determine the site of second-degree block.12 The prognosis of type I infranodal block is poor
References (50)
- et al.
Second-degree AV block. A reappraisal
Mayo Clin Proc
(2001) - et al.
Clinical electrophysiology of atrioventricular block
Cardiol Clin
(1983) - Barold SS, Barold HS. Pitfalls in the characterization of second-degree AV block. HeartWeb 2(6). April 1997. Available...
Atrioventricular block
Clinical concepts of spontaneous and induced atrioventricular block
- et al.
Corréllations entre E. C. G. de surface et topographie
- et al.
Incidence of different types of A-V block and their localization by His bundle recordings
Atrioventricular and intraventricular block
Circulation
(1987)- et al.
Pacing for acute and chronic atrioventricular conduction system disease
- et al.
Sinus node and AV node dysfunction and syncope
Bradycardias. Sinus nodal dysfunction and AV conduction disturbances
Indications for intracardiac electrophysiologic studies in patients with atrioventricular and intraventricular blocks not associated with acute myocardial infarction
Circulation
Cardiac pacing
N Engl J Med
Clinical electrophysiology
Arrhythmias
Arrhythmias
Atrioventricular block
The AV node
Glossary
Conduction blocks
Introducing the heart block rhythms
Cardiac arrhythmias
Nodal and infranodal atrioventricular block
Atrioventricular conduction disturbances
Diagnosis of cardiac rhythm
Cited by (16)
Classic and atypical Wenckebach periodicity in a late gestation fetus with maternal anti-Ro/SSA antibodies
2021, HeartRhythm Case ReportsCitation Excerpt :Type 1 second-degree AV block with a normal QRS complex typically occurs when inflammation and fibrosis are limited to the AV node. The finding of a wide QRS complex, however, is more consistent with infranodal disease.7,11 There is scant literature describing the incidence of infranodal anti-Ro/SSA antibody–mediated disease, but it has been described in both live-born and postmortem studies.12,13
2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society
2019, Journal of the American College of CardiologyAtrioventricular Block and Atrioventricular Dissociation
2004, Cardiac Electrophysiology: Fourth EditionAtrioventricular block and atrioventricular dissociation
2004, Cardiac Electrophysiology: From Cell to BedsideElectrocardiographic interpretation in athletes
2021, Minerva Cardiology and Angiology