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Kusumoto et al 2018 Bradycardia Clinical Practice Guidelines Circulation. 2019;140:e382–e482. DOI: 10.1161/CIR.0000000000000628 August 20, 2019 e413 CLINICAL STATEMENTS AND GUIDELINES 5.4.2. Transient/Reversible Causes (Including Medications) of Bradycardia Attributable to SND Recommendation for Transient/Reversible Causes of Sinus Bradycardia COR LOE Recommendation I C-EO 1. Patients presenting with symptomatic SND secondary to a reversible cause should first be managed by directing the therapy at eliminating or mitigating the offending condition. Synopsis Patients may present with symptomatic sinus bradycardia attributable to reversible causes (Table 7).S5.4.2-1 Medications are frequent culprits. Negative chronotropic drugs such as beta blockers, calcium channel blockers, and digoxin are frequently prescribed drugs that can decrease the sinus rate. Sodium-channel and potassium-channel blocking antiarrhythmic drugs can also exacerbate bradycardia in patients with preexisting SND. Hypothyroidism can cause clinically significant bradycardia.S5.4.2-2–S5.4.2-5 Such cardiovascular abnormalities respond well to replacement therapy with thyroxine (T4).S5.4.2-6 Metabolic abnormalities such as severe systemic acidosis or hypokalemia can uncommonly cause sinus bradycardia in acute settings. Reversible physiological disturbances should be considered and treated first. Recommendation-Specific Supportive Text 1. When sinus bradycardia is the consequence of nonessential medications, permanent cardiac pacing should not be considered a first-line treatment. In such cases, withdrawal of offending drug or dosage reduction can improve the heart rate and symptoms. For example, a beta-blocking drug that is used solely to control hypertension but is causing significant bradycardia could be switched to a diuretic, angiotensin converting enzyme inhibitor, or an angiotensin receptor blocking drug that are devoid of negative chronotropic effect. If the offending drug cannot be discontinued completely, a simple dosage reduction may increase the heart rate and therefore improve symptoms. Other treatable conditions predisposing to sinus bradycardia include elevated intracranial pressure, acute MI, severe hypothermia, and obstructive sleep apnea. 5.4.3 Additional Testing of Bradycardia Attributable to SND Recommendations for Additional Testing of Bradycardia Attributable to SND COR LOE Recommendations IIb C-EO 1. In patients with symptoms suggestive of bradycardia (eg, syncope, lightheadedness) who are also undergoing an EPS for another indication, evaluation of sinus node function as part of the EPS may be considered. IIb C-EO 2. In symptomatic patients with suspected SND, EPS for the assessment of sinus node function may be considered when the diagnosis remains uncertain after initial noninvasive evaluations.S5.4.3-1–S5.4.3-5 III: No Benefit C-LD 3. In patients with asymptomatic sinus bradycardia, an EPS should not be performed unless other indications for electrophysiological testing exist.S5.4.3-6,S5.4.3-7 Synopsis SND is a clinical diagnosis based on the combination of history and rhythm documentation. However, in very rare circumstances, when the diagnosis remains elusive, the clinician may elect to perform an invasive EPS to ascertain the diagnosis. Broadly speaking, there are 2 established electrophysiology measures of sinus node function: 1) sinus node recovery time (SNRT)S5.4.3-4 and 2) SACT.S5.4.3-3,S5.4.3-5 These values can contribute to the assessment of sinus node function. Pharmacologic blockade of the autonomic nervous system using intravenous propranolol (0.1 mg/kg) and atropine (0.02 mg/kg) can be performed before assessment of sinus node function. The measured intrinsic heart rate can then be compared with the calculated intrinsic heart rate (intrinsic heart rate: 118.1–(0.57 x age)) for assessment of SND.S5.4.3- 1,S5.4.3-2 Both SNRT and SACT are limited by variable and modest specificity and sensitivity. EPS for the assessment of sinus node function is currently not widely used in clinical practice and its precise role in the overall diagnostic strategy of SND is not well defined, and there are no data to suggest that an abnormal SNRT or SACT in isolation should be used to justify PPM implantation. Recommendation-Specific Supportive Text 1. It would be rare that EPS would be performed for the sole purpose of evaluating sinus node function. Most patients undergo diagnostic EPS for Downloaded from http://ahajournals.org by on October 7, 2026