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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 e400 CLINICAL STATEMENTS AND GUIDELINES Although no prospective studies have defined the outcome of echocardiography-guided management in asymptomatic LBBB, the presence of LBBB in patients referred for echocardiography in evaluation of suspected congestive heart failure confers nearly a 4-fold increased likelihood of left ventricular systolic dysfunction.S4.2.4-3 2. Transthoracic echocardiography can identify various structural cardiac abnormalities underlying bradycardia or conduction disturbance, including cardiomyopathy, valvular heart disease, congenital anomalies, tumors, infections, infiltrative processes, immunologically mediated conditions, and diseases of the great vessels and pericardium.S4.2.4-12 However, the yield is higher when there are clinical indications of structural disease, including in patients with syncope who manifest signs or symptoms of cardiac disease (eg, bradycardia or conduction disorders).S4.2.4-11,S4.2.4-22,S4.2.4-24 Transthoracic echocardiography can be prognostic, as well, both in those presenting with syncopeS4.2.4-39 and in those who are less profoundly symptomatic. A prospective study of 35 untreated patients age >45 years with symptomatic SND suggested that echocardiographic parameters like left ventricular enddiastolic diameter and ejection fraction predict adverse cardiac events such as syncope, heart failure, and atrial tachyarrhythmias, when followed for up to 4 years.S4.2.4-13 3. Cardiac MRI and computed tomography can be helpful in carefully selected patients to identify conditions known to contribute to conduction disturbance or SND. Specifically, MRI can be helpful in diagnosing infiltrative processes, including sarcoidosis, hemochromatosis, and amyloidosis.S4.2.4-16–S4.2.4-19,S4.2.4-40–S4.2.4-56 Cardiac computed tomography can be similarly helpful, particularly when MRI is contraindicated or unavailable. It offers superior information regarding calcification of cardiac structures and has some advantages in evaluating coronary artery anatomy when epicardial coronary atherosclerotic disease is suspected.S4.2.4-14,S4.2.4-57 Both computed tomography and MRI offer high-quality information regarding cardiovascular structure in the setting of congenital heart disease.S4.2.4-21,S4.2.4-57 Cardiac nuclear imaging techniques can be useful to detect and/or discriminate amongst infiltrative cardiomyopathies, most notably in distinguishing between wild-type transthyretin and light chain cardiac amyloidosis and diagnosing cardiac sarcoidosis using fluorodeoxyglucose positron emission tomographic imaging.S4.2.4-15,S4.2.4-20 Transesophageal echocardiography can be a useful adjunct for endocar- ditis with or without perivalvular complications, aortic dissection, or unruptured sinus of Valsalva aneurysm which have all been occasionally associated with bradycardia or conduction block.S4.2.4-58–S4.2.4-64 When bradycardia or conduction disorders are accompanied by clinical suspicion of structural heart disease undiagnosed by echocardiography, ≥1 of these advanced imaging tests is usually helpful. 4. The diagnostic yield of transthoracic echocardiography in patients without clinical evidence (eg, history, physical examination, ECG) of heart disease is low and echocardiography is not recommended in such patients.S4.2.4-12 In some clinical circumstances, patients may manifest symptoms that might indicate cardiac disease, including symptoms potentially related to bradycardia or conduction disorders, such as syncope and presyncope. Individuals presenting with such symptoms but without other clinical evidence of structural heart disease are unlikely to benefit from routine imaging, as recently reviewed in the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope.S4.2.4-65 4.2.5. Laboratory Testing in Patients With Documented or Suspected Bradycardia or Conduction Disorders Recommendation for Laboratory Testing in Patients With Documented or Suspected Bradycardia or Conduction Disorders COR LOE Recommendation IIa C-LD 1. In patients with bradycardia, laboratory tests (eg, thyroid function tests, Lyme titer, potassium, pH) based on clinical suspicion for a potential underlying cause are reasonable.S4.2.5-1–S4.2.5-4 Synopsis Bradycardia attributable to SND or atrioventricular block may be secondary conditions such as hypothyroidism, rheumatologic disorders, and infectious disorders. Although there are many case reports of specific diseases associated with bradycardia where the diagnosis was aided by laboratory testing, there has been no study evaluating the diagnostic yield and benefits of routine comprehensive laboratory testing in patients presenting with bradycardia or conduction tissue abnormalities. Potential causes for bradycardia and conduction abnormalities are provided in Tables 3 and 4. Recommendation-Specific Supportive Text 1. Isolated case reports have identified medical conditions that can be associated with bradycardia in which laboratory testing directed toward a specific Downloaded from http://ahajournals.org by on October 7, 2026