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 P wave is upright in leads I, II, and aVL, and a negative P wave in lead aVR first-degree AV block PR interval is > 200 ms second-degree AV block Mobitz type I progressive PR interval lengthening with a subsequent "dropped" QRS complex Mobitz type II fixed prolonged PR interval (> 200 ms) with a "dropped" QRS complex third-degree AV block (complete heart block) no supraventricular pulses are conducted to the ventricles due to an absence of AV node condution the atria and the ventricles independently contract Treatment Overview management of bradycardia depends on the patient's hemodynamic stability and type of bradycardia hemodynamically unstable patients are managed with intravenous atropine temporary transvenous pacing once hemodynamic stability is achieved, patients are monitored with transcutaneous pacing pads patients are also evaluated for underlying and reversible causes of their bradycardia management of bradycardia depends on the underlying cause e.g., bradycardia secondary to hypothyroidism is managed by treating the hypothyroidism Conservative observation indication asymptomatic first degree AV block asymptomatic Mobitz type I Medical atropine indication hemodynamically unstable bradycardia comments 0.5 mg is given every 3-5 minutes if needed maximum dose is 3 mg Procedural tranvenous pacing indication hemodynamically unstably bradycardia in patients unresponsive to intravenous atropine permanent pacemaker indication hemodynamically stable patients with Mobitz type II and third degree AV heart block with no identifiable reversible cause Complications Syncope Cardiac death