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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 e426 CLINICAL STATEMENTS AND GUIDELINES 6.4.3. Additional Testing for Chronic Therapy/ Management of Bradycardia Attributable to Atrioventricular Block Recommendations for Additional Testing for Chronic Therapy/ Management of Bradycardia Attributable to Atrioventricular Block Referenced studies that support recommendations are summarized in Online Data Supplements 37 and 38. COR LOE Recommendations IIa B-R 1. In patients with symptoms (eg, lightheadedness, dizziness) of unclear etiology who have first-degree atrioventricular block or second-degree Mobitz type I atrioventricular block on ECG, ambulatory electrocardiographic monitoring is reasonable to establish correlation between symptoms and rhythm abnormalities.S6.4.3-1–S6.4.3-4 IIa C-LD 2. In patients with exertional symptoms (eg, chest pain, shortness of breath) who have first-degree or second-degree Mobitz type I atrioventricular block at rest, an exercise treadmill test is reasonable to determine whether they may benefit from permanent pacing.S6.4.3-5,S6.4.3-6 IIb B-NR 3. In selected patients with second-degree atrioventricular block, an EPS may be considered to determine the level of the block and to determine whether they may benefit from permanent pacing.S6.4.3-7–S6.4.3-9 IIb C-LD 4. In selected patients with second-degree atrioventricular block, carotid sinus massage and/or pharmacological challenge with atropine, isoproterenol, or procainamide may be considered to determine the level of the block and to determine whether they may benefit from permanent pacing.S6.4.3-10–S6.4.3-12 Synopsis In patients with second-degree atrioventricular block, differentiation between Mobitz type I and Mobitz type II is important because they have different prognostic implications. Similarly, the presence of severe first-degree atrioventricular block (PR >0.30 s) and a narrow QRS usually indicates atrioventricular node delay. In both cases, symptom correlation with rhythm changes observed on ECG is important to determine whether permanent pacing will be beneficial. Testing options are shown in Table S2 in the Web Supplement. Recommendation-Specific Supportive Text 1. In patients with first-degree atrioventricular block or second-degree Mobitz type I atrioventricular block, the need for pacemaker implantation is symptom driven. It may be challenging to attribute symptoms to atrioventricular block if they occur intermittently. Event monitors, worn for 30 to 90 days, and ICDs, which can be left in place for >2 years, tend to have greater diagnostic yield than 24- to 48-hour ambulatory electrocardiographic monitoring.S6.4.3-1–S6.4.3-4 In 1 study, atrioventricular block was more commonly identified as a cause for syncope in those patients with structural heart disease compared with patients without structural heart disease (34% versus 13%).S6.4.3-13 In addition, monitors can be used to look for changes in QRS morphology such as alternating bundle branch block. Although Mobitz type I atrioventricular block is usually associated with a narrow QRS and Mobitz type II atrioventricular block most often has a wide QRS, in some cases Mobitz type I atrioventricular block and an associated narrow QRS can be attributable to infranodal block.S6.4.3-14 The type of monitor chosen will depend on the frequency of symptoms. 2. Treadmill exercise stress testing can be diagnostic in the setting of exertional symptoms. The development of atrioventricular block or sudden change in atrioventricular conduction on a treadmill may provide diagnostic clues for exertional symptoms.S6.4.3-15 Ischemia as a cause of the symptoms and bradycardia during treadmill testing can be assessed. An exercise treadmill stress test may help differentiate whether 2:1 atrioventricular block is Mobitz type I or II or identify the presence of infranodal disease. Exercise causes vagal withdrawal and increased sympathetic tone leading to improved atrioventricular nodal conduction. If the baseline atrioventricular block is infranodal, the atrioventricular block will not resolve and will likely worsen as the sinus rate increases.S6.4.3-5,S6.4.3-16 The resting ECG may be helpful if it shows a bundle branch block or hemiblock that may raise suspicion for episodic high-grade or complete atrioventricular block.S6.4.3-6,S6.4.3-16 Exercise may also be useful in patients with profound first-degree atrioventricular block and exertional symptoms to help determine if nonphysiologic timing of atrial and ventricular contraction (pseudopacemaker syndrome) is contributing to symptoms. 3. If the type of second-degree atrioventricular block cannot be determined from electrocardiographic and telemetry recordings, the EPS can be informative to determine the anatomic site of atrioventricular block: atrioventricular node, intra-His, or infra-His.S6.4.3-9 In second-degree atrioventricular block with concomitant bundle branch block, the block is likely but not necessarily (70% likelihood).S6.4.3-8 Similarly, 2:1 atrioventricular block with bundle branch block is frequently assumed to be indicative of infranodal block; however, 15% to 20% of these patients can have block in the atrioventricular node.S6.4.3-8 EPS may Downloaded from http://ahajournals.org by on October 7, 2026