THE CONTEXT
Management of atrioventricular (AV) block depends on symptoms, the type of block and the clinical setting. Block accompanying inferior myocardial infarction (MI) differs from block accompanying acute anterior MI.
AV block in inferior MI
•
Inferior MI can cause transient AV block because the right coronary artery supplies the AV node.
•
A reliable escape rhythm is usually present. No treatment is required if the patient remains well.
•
Symptomatic second-degree or third-degree AV block may respond to intravenous atropine, 0.6 mg repeated as necessary. A temporary pacemaker may be required if atropine fails.
•
In most cases, the AV block resolves within 7–10 days.
AV block in acute anterior MI
•
Second-degree or third-degree AV block complicating acute anterior MI indicates extensive ventricular damage involving both bundle branches and carries a poor prognosis.
•
For a patient presenting with asystole, intravenous atropine, 3 mg, or intravenous isoprenaline may help maintain the circulation until a temporary pacing electrode is inserted.
•
The stated isoprenaline regimen is 2 mg in 500 mL of 5% dextrose, infused at 10–60 mL/hour.
•
Temporary pacing can provide effective rhythm support in the short term.
Permanent pacing and observation
•
Patients with symptomatic bradyarrhythmias associated with AV block should receive a permanent pacemaker.
•
Asymptomatic first-degree AV block and Mobitz type I second-degree AV block do not require treatment, although they may indicate underlying heart disease.
•
A permanent pacemaker is usually indicated even in asymptomatic Mobitz type II second-degree AV block or third-degree AV block because of the risk of asystole and sudden death.
•
Pacing improves prognosis.
Bundle branch block: associated conditions
•
Right bundle branch block may be a normal variant or accompany right ventricular hypertrophy or strain, including pulmonary embolism.
•
Other listed causes of right bundle branch block include congenital heart disease, such as an atrial septal defect, and coronary artery disease.
•
Listed causes of left bundle branch block are coronary artery disease, hypertension, aortic valve disease and cardiomyopathy.
Right bundle branch block: ECG appearance
•
The illustrated right bundle branch block has wide QRS complexes with an M-shaped configuration in leads V1 and V2 and a wide S wave in lead I.