| Snapshot |
| A 20-year-old man presents to his primary care physician for an annual exam. He is currently feeling well. Medical history is unremarkable and he takes a daily multivitamin. He denies any alcohol or smoking history. He is a college student and part of the school’s track team, which he continued since he was a student in high school. He is concerned because a classmate of his passed out during practice and ended up dying due to sudden cardiac death. He is requesting an electrocardiogram (ECG) to ensure his heart is healthy. An ECG demonstrates a PR interval of 0.25 sec and is otherwise unremarkable. (First-degree heart block) |
| Introduction |
| Clinical definitionan impairment of the electrical transmission from the atria to the ventriclesEtiologyidiopathic (most common) e.g., fibrosis and sclerosis of the conduction systemischemic heart disease (2nd most common)↑ vagal tonefamilial causesiatrogenicmedicationse.g., β-blockers, calcium channel blockers, adenosine, digoxin, and amiodaronecardiac procedurese.g., cardiac surgery and transcatheter aortic valve implantation |
Atrioventricular (AV) Block
| Types | Electrocardiogram Findings | Treatment | Comments |
| First degree AV block | ↑ PR interval (> 0.2 secs) | No treatment is required | Typically seen in young patients with a ↑ vagal toneWell-trained athletes |
| Second degree AV block (Mobitz type I) | Progressive ↑ PR interval until a P wave is not followed by a QRS complex (Wenckebach phenomenon) the sequence then repeatsQRS complex is narrow | Treatment is unnecessary unless the patient is symptomaticuse atropine or a temporary pacemaker in symptomatic cases | Patients are typically asymptomaticCan be seen in patients withdrug intoxication (e.g., β-blockers and digitalis) ↑ vagal tone |
| Second degree AV block (Mobitz type II) | Fixed PR intervals with occasional dropped QRS complexes QRS complex is typically wide | Permanent pacemaker | May progress to a third-degree heart block |
| Third degree (complete) AV block | Atria and ventricles depolarize independently P waves and QRS complexes are not rhythmically synchronized | Permanent pacemaker unless the cause is reversible | Can be a complication of Lyme disease |