Snapshot A 22-year-old man presents to his primary care physician for an annual examination. He currently has no acute complaints but is worried he has "heart disease" since his father died from a "heart attack." He denies any episodes of lightheadedness or syncopal episodes. He exercises regularly as he is part of his university's basketball team. An electrocardiogram demonstrates sinus rhythm with a PR interval of 250 ms. He is provided reassurance that nothing needs to be done. (First-degree atrioventricular block) Introduction Overview electrical activation of the heart usually is initiated by the sinatrial (SA) node bradycardia results from impaired impulse initiation from the SA node or impaired impulse conduction from the SA node to the atria or ventricles leads to a pulse < 60/min common causes of bradycardia include SA node dysfunction atrioventricular (AV) node conduction block Etiology SA and AV node dysfunction sick sinus syndrome (seen in SA node dysfunction) carotid sinus hypersensitivity inferior wall myocardial infarction (seen in SA node dysfunction and sometimes AV node dysfunction) electrocardiogram demonstrate ST-segment elevation in II, III, and aVF senile amyloidosis medications (e.g., beta-blockers) increased intracranial pressure malignancy radiation infectious Presentation Symptoms lightheadedness fatigue generalized weakness presyncope or syncope angina Physical exam hypotension bradycardia Studies Electrocardiogram diagnostic study of choice sinus bradycardia login to view 1 more bullet first-degree AV block login to view 1 more bullet second-degree AV block login to view 4 more bullets third-degree AV block (complete heart block) login to view 2 more bullets Treatment Overview management of bradycardia depends on the patient's hemodynamic stability and type of bradycardia hemodynamically unstable patients are managed with login to view 4 more bullets management of bradycardia depends on the underlying cause e.g., bradycardia secondary to hypothyroidism is managed by treating the hypothyroidism Conservative observation indication login to view 2 more bullets Medical atropine indication login to view 1 more bullet comments login to view 2 more bullets Procedural tranvenous pacing indication login to view 1 more bullet permanent pacemaker indication login to view 1 more bullet Complications Syncope Cardiac death