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Kusumoto et al 2018 Bradycardia Clinical Practice Guidelines

August 20, 2019 Circulation. 2019;140:e382–e482. DOI: 10.1161/CIR.0000000000000628 e418

CLINICAL STATEMENTS AND GUIDELINES associated with slower progression, a faster and more reliable atrioventricular junctional escape mechanism, and greater responsiveness to autonomic manipulation such as atropine, isoproterenol, and epinephrine administration. In contrast, atrioventricular block within or below the His bundle may progress rapidly and unexpectedly, is associated with a slower and more unpredictable ventricular escape mechanism, will not respond to atropine but will sometimes improve with catecholamines.

First-degree atrioventricular block is a misnomer; true block is not present, as each P wave is conducted, but with a prolonged PR interval >200 ms. Although for historical reasons, management of first-degree atrioventricular block is considered in the discussion of atrioventricular block, it is more accurately referred to as first-degree atrioventricular delay. Second-degree atrioventricular block is sub-classified into Mobitz I (Wenckebach conduction) and Mobitz II. Mobitz I block occurs after gradual PR prolongation and Mobitz II does not. The ECG will show group beating as a result of “dropped” QRS complexes. Atrioventricular block where only 2:1 block is present cannot be classified as Mobitz I or II, so it is important to elucidate the level of block. High-grade, high-degree, or advanced atrioventricular block refers to situations where ≥2 consecutive P waves at a normal rate are not conducted without complete loss of atrioventricular conduction. High-degree atrioventricular block is generally considered to be intra- or infra-Hisian and treated with pacing. In unusual circumstances (at night, with accompanying sinus slowing) a vagal etiology may be considered especially when the QRS in narrow. Third-degree or complete atrioventricular block implies no conduction at all from atria to ventricles and may be paroxysmal or persistent and is usually associated with either a junctional or ventricular escape mechanism. Complete atrioventricular block may be imputed in the setting of AF when the ventricular response is slow (<50 bpm) and regular, although junctional rhythm in the setting of atrioventricular conduction abnormalities may be associated with this electrocardiographic finding. Careful evaluation of the ECG is required for the diagnosis of atrioventricular block. A 1:1 relationship between P waves and QRS complexes may not be present if the atrial rate and ventricular rates are similar (isorhythmic dissociation) or if the atrial rate is slower than the ventricular rate (sinus bradycardia coupled with an accelerated junctional rhythm without consistent retrograde ventriculoatrial conduction). In atrial bigeminy, a repetitive premature atrial contraction could be associated with normal conduction, atrioventricular delay, or blocked conduction; any of these scenarios could lead to an erroneous diagnosis of atrioventricular block.

Table 9.  Etiology of Atrioventricular Block

Congenital/genetic Congenital AV block (associated with maternal systemic lupus

erythematosus) Congenital heart defects (eg, L-TGA) Genetic (eg, SCN5A mutations) Infectious Lyme carditis Bacterial endocarditis with perivalvar abscess Acute rheumatic fever Chagas disease Toxoplasmosis Inflammatory/infiltrative Myocarditis Amyloidosis Cardiac sarcoidosis Rheumatologic disease: Systemic sclerosis, SLE, RA, reactive arthritis

(Reiter’s syndrome) Other cardiomyopathy—idiopathic, valvular Ischemic Acute MI Coronary ischemia without infarction—unstable angina, variant angina Chronic ischemic cardiomyopathy Degenerative Lev’s and Lenegre’s diseases Vagotonic-associated with increased vagal tone Sleep, obstructive sleep apnea High-level athletic conditioning Neurocardiogenic Metabolic/endocrine Acid-base disorders Poisoning/overdose (eg, mercury, cyanide, carbon monoxide, mad

honey) Thyroid disease (both hypothyroidism and hyperthyroidism) Adrenal disease (eg, pheochromocytoma, hypoaldosteronism) Other diseases Neuromuscular diseases (eg, myotonic dystrophy, Kearns-Sayre

syndrome, Erb’s dystrophy) Lymphoma Iatrogenic Medication related Beta blockers, verapamil, diltiazem, digoxin Antiarrhythmic drugs Neutraceuticals Catheter ablation Cardiac surgery, especially valve surgery TAVR, alcohol septal ablation RA indicates rheumatoid arthritis; MI, myocardial infarction; SLE, systemic lupus erythematosus; and TAVR, transcatheter aortic valve replacement.

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