From the Guidelines
Complete heart block is a serious cardiac conduction disorder that requires immediate placement of a permanent pacemaker, as recommended by the most recent guidelines 1.
Definition and Diagnosis
Complete heart block, also known as third-degree atrioventricular (AV) block, is defined as the absence of all atrioventricular conduction, resulting in the atria and ventricles beating independently of each other 1. This condition can be diagnosed through ECG, which shows independent atrial and ventricular rhythms with no relationship between P waves and QRS complexes.
Treatment and Management
The decision to implant a pacemaker in a patient with abnormal AV conduction depends on the presence of symptoms related to bradycardia or ventricular arrhythmias and their prognostic implications 1. Symptomatic third-degree AV block is a class I indication for permanent pacing, whereas asymptomatic third-degree AV block is a class IIa indication 1. While waiting for definitive treatment, temporary pacing may be necessary, especially in symptomatic patients. Atropine (0.5-1mg IV) can be administered for temporary rate increase in bradycardic patients, and if unsuccessful, dopamine (2-10 mcg/kg/min) or epinephrine (2-10 mcg/min) infusions may be used.
Recent Guidelines and Recommendations
The most recent guidelines recommend resynchronization pacing in patients with reduced ejection fraction 1. The patient underwent resynchronization pacemaker implantation for complete heart block and mildly reduced LV systolic function, and experienced improvement in symptoms soon after the procedure 1. The guidelines also recommend the implementation of medical therapy, including diuretics, SGLT-2 inhibitors, ARNI, ACE-I, ARB, and MRA.
Key Points
- Complete heart block requires immediate placement of a permanent pacemaker
- Symptomatic third-degree AV block is a class I indication for permanent pacing
- Asymptomatic third-degree AV block is a class IIa indication for permanent pacing
- Resynchronization pacing is recommended in patients with reduced ejection fraction
- Medical therapy, including diuretics, SGLT-2 inhibitors, ARNI, ACE-I, ARB, and MRA, should be implemented as per guidelines.
From the FDA Drug Label
Atropine also may lessen the degree of partial heart block when vagal activity is an etiologic factor In some patients with complete heart block, the idioventricular rate may be accelerated by atropine; in others, the rate is stabilized.
Atropine may have an effect on complete heart block by accelerating the idioventricular rate in some patients or stabilizing the rate in others. However, the effect of atropine on complete heart block is not uniform and may vary from patient to patient 2.
- Key points:
- Atropine may accelerate the idioventricular rate in some patients with complete heart block
- Atropine may stabilize the rate in other patients with complete heart block
- The effect of atropine on complete heart block is not uniform and may vary from patient to patient
From the Research
Definition and Causes of Complete Heart Block
- Complete heart block, also known as third-degree atrioventricular (AV) block, is a cardiovascular emergency that requires prompt recognition 3.
- It occurs when no atrial impulses reach the ventricular conduction system, and the most common etiology is ischemic heart disease, with up to 1 in 5 patients developing some type of conduction disturbance after a myocardial infarction (MI) 3.
- Other causes include myocarditis, infectious endocarditis, infiltrative cardiac disease, congenital AV blocks, non-ischemic cardiomyopathy, electrolyte disturbances, and drug side effects 3.
Clinical Presentation and Diagnosis
- Patients with complete heart block can present with hypotension, syncope, and bradycardia, and the diagnosis is typically made using a 12-lead EKG 3.
- The EKG will show a lack of association between the P waves and QRS complexes, and the ventricular rate will depend on the location of the block and the presence of a functioning secondary pacemaker 3.
- Analysis of the EKG will determine the location of the escape rhythm, and patients with ventricular escape rhythms can destabilize and develop asystole and cardiac arrest if no escape rhythm generates 3.
Management and Treatment
- Effective management of complete heart block includes accurate interpretation of a 12-lead EKG, assessment of hemodynamic stability and systemic perfusion, and time-sensitive pharmacologic or procedural intervention 3.
- Treatment options include administering IV atropine, attempting transcutaneous pacing, placing a transvenous pacemaker, and consulting with interventional cardiology 3.
- Permanent pacemaker implantation is the standard of care in patients with complete heart block and second-degree type II AV block, regardless of symptoms, when the conduction abnormality is irreversible 4.
Prognosis and Outcomes
- Complete heart block is associated with a high mortality rate, particularly in the early post-traumatic period, and recurrent or permanent complete heart block requiring pacemaker implantation occurs in approximately 50% of survivors 5.
- The temporal course of complete heart block after blunt cardiac injury is poorly understood, but clinical manifestation typically occurs within 72 hours of injury, and 1:1 AV conduction is restored within 7-10 days in about half of early survivors 5.