![]() Indications: diagnostic uncertainty in symptomatic patients.Suspected structural and/or infiltrative heart disease that cannot be confirmed with other diagnostic techniques: Consider advanced imaging.Concern for structural heart disease : transthoracic echocardiogram ( TTE).Sleep-related symptoms: Consider nocturnal polysomnography.Consider genetic testing (e.g., for SCN5A, HCN4 mutations) in consultation with a specialist.Seen in up to 50% of patients with SND Įvaluation for an underlying cause Laboratory studiesĮvaluate all patients for common reversible causes of SND as clinically indicated (i.e., based on history and physical examination).Heart rate does not increase sufficiently in response to increased activity or demand. ![]() Bradycardia alternating with intermittent atrial tachyarrhythmia.Isorhythmic dissociation: atria depolarization slower than ventricular depolarization.Sinoatrial exit block: impaired conduction between SA node and adjacent atrial tissue (e.g., intermittent dropped P wave).Inappropriate impulse transmission by the SA node transitional cells Sinus arrest or pause may be followed by an escape rhythm.Heart rate 3 seconds after the preceding atrial depolarization.Supportive findings: The presence of any of the following rhythm abnormalities of SND with accompanying symptoms of end-organ hypoperfusion is diagnostic of SND. ![]() External patch recorder or implantable loop recorder.Event monitor or mobile cardiovascular telemetry.Holter monitor or external patch recorder.Second line : ambulatory cardiac monitoring (typically in the following order).Preferred initial diagnostic study: 12-lead ECG.In hemodynamically unstable patients, start immediate treatment for unstable bradycardia without waiting for diagnostic confirmation. Refer for specialist evaluation for alternative diagnoses or advanced diagnostics if symptoms do not correlate with rhythm abnormalities.Obtain additional studies (e.g., nocturnal polysomnography, TTE) as needed.Evaluate all patients for reversible causes of SND: including medication review, BMP, HbA1c, thyroid function tests.Symptoms on exertion: Perform exercise stress test.Inconclusive ECG findings: Perform ambulatory cardiac monitoring.Correlate symptoms with rhythm abnormalities of SND.See also “ Management of bradycardia” for related information. Tachycardia-bradycardia syndrome is a subtype of SND that manifests as alternating episodes of tachycardia and bradycardia and is associated with increased risk of cardiovascular events and mortality. If reversible causes are not present, permanent pacemaker placement is preferred for long-term management of symptomatic patients. Reversible causes of SND should be identified and managed. Unstable bradycardia requires immediate implementation of advanced cardiac life support ( ACLS) measures. Establishing a temporal correlation between symptoms of bradycardia and rhythm abnormalities of SND (e.g., on ECG, stress testing, cardiac monitoring) confirms the diagnosis. Patients typically present with symptoms of end-organ hypoperfusion due to bradycardia (e.g., fatigue, presyncope, syncope, dyspnea on exertion). ![]() It can be caused by factors intrinsic to the SA node (e.g., fibrosis of the SA node, infiltrative diseases) or extrinsic factors (e.g., pharmacotherapy with negative chronotropes, hypothyroidism) and most commonly results in bradycardia. Sinus node dysfunction (SND), previously called sick sinus syndrome, is an abnormality in sinoatrial (SA) node action potential generation or conduction.
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