Emergent Care / Stabilization:
If hemodynamically unstable, the patient should be treated with intravenous (IV) atropine 0.5-1 mg push every 3-5 minutes, for a total 3 mg dose. Patients who have undergone cardiac transplantation are unlikely to respond given that the vagal innervation of the heart no longer exists. Other etiologies, including second-degree type II atrioventricular (AV) blocks or third-degree blocks, may not respond to atropine. Consider other beta-adrenergic agonists (eg, epinephrine, isoproterenol) in patients who have failed to improve with atropine while other measures are taken.

If the patient remains hemodynamically unstable, either dopamine or epinephrine should be considered:

• Dopamine: 5-20 μg/kg per minute IV (titrate to patient response; taper slowly)
• Epinephrine: 2-10 μg per minute IV (titrate to patient response)

If symptoms do not improve, a temporary pacemaker should be placed. The first step in a hemodynamically unstable patient is transcutaneous pacing, which is a temporary and potentially painful intervention that should be considered with adjuncts such as analgesics and/or anxiolytic medications. Placement of a temporary transvenous pacemaker should be performed afterward to ensure more stable and reliable pacing until definitive management can be achieved.

See also flowchart (Adult Bradycardia) in image stack.

Diagnosis Overview:
Sinus bradycardia is a heart rhythm originating in the sinoatrial (SA) node with a slow heart rate, usually classified as a heart rate less than about 50 beats per minute. Although generally benign, patients may report transient dizziness, lightheadedness, near syncope, or syncope in some cases. Severe symptoms such as heart failure or confusion may be present in extreme cases due to poor perfusion.

The SA node is the main pacemaker of the heart's conduction system. The vagus and sympathetic nerves innervate it. The SA nodal artery, which supplies the SA node, originates from the right coronary artery or the left circumflex artery.

Potential causes of sinus bradycardia include but are not limited to athletic conditioning, sick sinus syndrome, rate-lowering medications (eg, beta blockers, nondihydropyridine calcium channel blockers, ivabradine, amiodarone, digoxin, lithium), other medications (eg, narcotics, cannabinoids, remdesivir), obstructive sleep apnea, enhanced vasovagal activity, hypothyroidism, electrolyte derangements (eg, hypokalemia), acute myocardial infarction and other acute / chronic coronary spectrum disease, elevated intracranial pressure, familial ion channelopathies, certain infectious causes (eg, COVID-19, Lyme disease, babesiosis, Chagas disease), infiltrative diseases, and collagen vascular diseases.