Atrioventricular Block Treatment & Management

Long-term medical therapy is not indicated in atrioventricular (AV) block. Permanent pacing is the therapy of choice in advanced AV block, and it does not require concomitant medical therapy. AV nodal blocking medications contributing to heart block should be discontinued if not necessary.

Pacemaker implantation is a routine surgical procedure, generally performed with conscious sedation and local anesthesia in the electrophysiology laboratory. The procedure usually requires an overnight observation period in the hospital.

Temporary transcutaneous or transvenous pacing is the treatment of choice for an emergency involving a slow heart rate (and for asystole) caused by AV blocks. Transfer to a specialized medical center may be advisable. Atropine administration (0.5-1.0 mg) may improve AV conduction in emergencies where bradycardia is caused by a proximal AV block (located in the atrioventricular node [AVN]) but may worsen conduction if the block is in the His-Purkinje system.

In general, the decision regarding implantation of a pacemaker must be considered with respect to whether or not AV block is permanent. Reversible causes of AV block, such as electrolyte abnormalities, if present, should be corrected first. Some diseases may follow a natural history to resolution (eg, Lyme disease), and some AV block can be expected to reverse (eg, hypervagotonia due to recognizable and avoidable physiologic factors, perioperative AV block due to hypothermia, or inflammation near the AV conduction system after surgery in this region).

Conversely, some conditions may warrant pacemaker implantation owing to the possibility of disease progression even if the AV block reverses transiently (eg, sarcoidosis, amyloidosis, neuromuscular diseases). Finally, permanent pacing for AV block after valve surgery follows a variable natural history, and, therefore the decision for permanent pacing is at the physician’s discretion.

Types of cardiac pacemakers implanted in patients with heart block may include ventricular (usually VVI) or dual chamber (usually DDD) modes of pacing. The cardiologist or electrophysiologist should make the decision regarding the optimal mode of pacing.

ACC/AHA/NASPE guidelines

The following recommendations are based on the 2008 guidelines for implantation of cardiac pacemakers and antiarrhythmia devices formulated by the American College of Cardiology (ACC), the American Heart Association (AHA), and the Heart Rhythm Society (HRS).^[4]

First-degree AV block and Mobitz I second-degree AV block do not generally require treatment unless they cause symptoms and are not due to a reversible cause. If a drug overdose is a possible cause, the drug must be withheld (and its future use or dosage subsequently should be decreased or reconsidered).

Small, uncontrolled trials have suggested that some symptomatic and functional improvement may be achieved in pacing patients with PR intervals longer than 300 msec by decreasing the time for AV conduction. This is rare. Although echocardiographic or invasive techniques may be used to assess hemodynamic improvement before permanent pacemaker implantation, such studies are not required for evaluation of symptoms due to first-degree and Mobitz I second-degree AV block.

Mobitz II second-degree AV block and third-degree AV block usually require temporary and/or permanent cardiac pacing. Mobitz II second-degree AV block and a wide QRS complex indicate diffuse conduction system disease and constitute an indication for pacing even in the absence of symptoms. Mobitz II with a wide QRS may degenerate into third-degree AV block, and this is another reason to consider permanent pacing. In the setting of acute anterior myocardial infarction, transcutaneous pacing initially and transvenous pacing subsequently are warranted.

With inferior myocardial infarction, the block usually resolves spontaneously within several days, and only a small percentage of patients require temporary or permanent pacing. Patients with persistent bundle branch block and transient third-degree AV block may benefit from permanent pacing therapy, especially after anterior myocardial infarction. Nonrandomized studies strongly suggest that permanent pacing does improve survival in patients with third-degree AV block, especially if syncope has occurred.

Indications/contraindications for treatment may be summarized according to the following ACC/AHA/HRS class I, II, and III recommendations:

• Class I - Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective
• Class IIa - Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment, but the weight of evidence/opinion is in favor of usefulness/efficacy
• Class IIb - Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment, but usefulness/efficacy is less well established by evidence/opinion
• Class III - Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/effective and in some cases may be harmful.

With respect to pacemaker implantation in the setting of AV block, class I is defined as third-degree and advanced second-degree AV block at any anatomic level, associated with any 1 of the following conditions:

• Bradycardia with symptoms (including heart failure) presumed to be due to AV block (level of evidence: C)
• Arrhythmias and other medical conditions that require drugs that result in symptomatic bradycardia (level of evidence: C)
• Documented periods of asystole greater than or equal to 3.0 sec or any escape rate less than 40 beats/min in awake, symptom-free patients, or with an escape rhythm that is below the level of the AV node (level of evidence: C)
• Third-degree or second-degree AV block at any anatomic level in atrial fibrillation and bradycardia with 1 or more asymptomatic pauses greater than 5 seconds (level of evidence: C).
• After catheter ablation of the AV junction - No trials have assessed outcomes without pacing after AV node ablation, and pacing is virtually always planned in this situation unless the operative procedure is AV junction modification (level of evidence: C)
• Postoperative AV block that is not expected to resolve after cardiac surgery (level of evidence: C)
• Postoperative AV block in third-degree or second-degree heart block at any anatomical level in post surgical patients not expected to resolve (level of evidence: C)
• Neuromuscular diseases with AV block, such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy (limb-girdle), and peroneal muscular atrophy, with or without symptoms, because unpredictable progression of AV conduction disease may occur (level of evidence: B)
• Asymptomatic third-degree heart block with heart rates greater than 40 beats/min and with associated cardiomegaly or left ventricular dysfunction or if the level of block is below the AV node (level of evidence: B)
• Exercise-associated second- or third-degree heart block in the absence of myocardial ischemia (level of evidence: C)

Class IIa is defined as follows:

• Asymptomatic third-degree AV block at any anatomic site with average awake ventricular rates of 40 beats/min or faster, especially if cardiomegaly or left ventricular (LV) dysfunction is present (level of evidence: C)
• Asymptomatic type II second-degree AV block with a narrow QRS - When Mobitz II second-degree AV block occurs with a wide QRS, pacing becomes a class I recommendation(level of evidence: B)
• Asymptomatic Mobitz I second-degree AV block at intra-His or infra-His levels found on electrophysiologic study performed for other indications (level of evidence: B)
• First- or second-degree AV block with symptoms similar to those of pacemaker syndrome (level of evidence: B)

Class IIb is defined as follows:

• AV block in the setting of drug use or drug toxicity when the block is expected to recur even when the offending agent is withdrawn (level of evidence: C)
• Neuromuscular diseases such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy (limb-girdle), and peroneal muscular atrophy with any degree of AV block (including first-degree AV block), with or without symptoms, because unpredictable progression of AV conduction disease may occur (level of evidence: B)

Class III is defined as follows:

• First-degree AV block without symptoms (level of evidence: B)
• Asymptomatic type I second-degree AV block at the level of the AV node (level of evidence: C)
• AV block that is expected to resolve and unlikely to recur (level of evidence: B)

Complications of pacing

Pacing therapy (temporary or permanent) may be complicated acutely by tamponade, hemothorax, or pneumothorax. Dysfunction of the pacemaker, lead fracture, and malfunction (eg, inappropriate capture or sensing) are infrequent complications of pacing therapy. Infection of the pacemaker or lead wires is a rare, but important, short-term and long-term complication of pacemaker implantation.

Restrictions after permanent pacemaker implantation include restricted weight lifting with the ipsilateral hand/arm to the pacemaker until healing occurs (approximately 4-6 wk). Contact sports are restricted unless a protective shield is worn over the implanted pacemaker. Electromagnetic interference—from power lines and arc welding, for example—may cause inhibition of pacing. This is problematic for patients who are pacemaker dependent.

Consultation with a cardiologist or cardiac electrophysiologist is indicated in the case of advanced heart block or unexplained syncope. An electrophysiologist must be consulted when invasive electrophysiology testing is needed to determine the level and/or magnitude of conduction disturbance.

Patients with first-degree and benign Mobitz I second-degree AV block do not require hospitalization. Patients with symptomatic second- or third-degree AV block require hospitalization with telemetry monitoring. Transcutaneous or transvenous pacing should be utilized, and indications for permanent pacing need to be determined.

Patients with first- and second-degree Mobitz I AV block may require follow-up ECG or Holter monitoring to determine the likelihood and rate of progression of the AV conduction disorder. Patients with implanted pacemakers require routine follow-up to monitor pacemaker function.