Second-Degree Atrioventricular Block Treatment & Management

Second-degree atrioventricular (AV) block in the asymptomatic patient does not require any specific therapy in the prehospital setting. If the patient is symptomatic, standard advanced cardiac life support (ACLS) guidelines for bradycardia, including the use of atropine and transcutaneous pacing, are indicated.^{[6, 26]}

No specific therapy is required in the emergency department (ED) for Mobitz I (Wenckebach) second-degree AV block, unless the patient is symptomatic. Patients with suspected myocardial ischemia should be treated with an appropriate anti-ischemic regimen. Second-degree block at the level of the atrioventriocular node (AVN) may be due to digoxin, beta-blockers, or calcium channel blockers. Decreasing the dose and/or discontinuing these medications may restore normal AV conduction.

Mobitz II block is more likely to progress to complete heart block and thus requires a different approach. As with Mobitz I block, AV nodal agents should be avoided, and an anti-ischemic regimen should be instituted if ischemia is suspected.

Permanent pacing is considered in accordance with the relevant guidelines (see Pacemaker Implantation). Except for the use of atropine in selected cases of transient AV block, permanent cardiac pacing has replaced medical interventions in the treatment of patients with symptomatic, otherwise untreatable, AV block.

Mobitz I block

Admit patients who have symptoms or who have concomitant acute myocardial ischemia or myocardial infarction (MI). Admission should be to a unit with telemetry monitoring, which has transcutaneous pacing capabilities.

Symptomatic patients should be treated with atropine and transcutaneous pacing. However, atropine should be administered with caution in patients with suspected myocardial ischemia, as ventricular dysrhythmias can occur in this situation.

The goal of atropine administration is to improve conduction through the AVN by reducing vagal tone via atropine-induced receptor blockade. However, this goal will only be effective if the level of the blockade is at the site of the AVN. Patients with infranodal second-degree AV block are unlikely to benefit from atropine. In addition, in patients who have denervated hearts (eg, patients who have undergone a cardiac transplant), atropine is also not likely to be effective.

Mobitz II block

Admit all patients to a unit with monitored beds, where transcutaneous and transvenous pacing capabilities are available. The admitting cardiologist should determine whether permanent pacemaker implantation is indicated.

Transcutaneous pacing pads should be applied to all patients with Mobitz II second-degree AV block, including those who are asymptomatic patients, because such patients have a propensity to progress to complete heart block. The transcutaneous pacemaker should be tested to ensure capture. If capture is not able to be achieved, then insertion of a transvenous pacemaker is indicated, even in asymptomatic patients.

Urgent cardiology consult is indicated for patients who have symptomatic type II block and for those asymptomatic patients who are unable to achieve capture with transcutaneous pacing.

Some institutions recommend insertion of a transvenous pacemaker for all new Mobitz type II blocks, although this practice varies greatly from institution to institution.

Patients who are hemodynamically unstable for whom an emergency cardiology consult is not available should undergo placement of a temporary transvenous pacing wire in the ED. A chest radiograph is required to confirm position of the wire and to exclude complications, including hemothorax or pneumothorax.

2:1 block

In cases where there is a 2:1 block and one is unable to determine if there is a Mobitz I block or Mobitz II block, the patient should be admitted and cardiology consultation should be obtained. In such cases, it is safest to assume that a Mobitz II second-degree AV block exists.

Indications for permanent pacing in second-degree AV block are explained in detail in the guidelines published by the American College of Cardiology (ACC), the American Heart Association (AHA), and the North American Society for Pacing and Electrophysiology (NASPE) in 2002^[27] and by the ACC, the AHA, and the Heart Rhythm Society (HRS) in 2008.^[28] A summary of indications is as follows.

• Second-degree AV block associated with signs such as bradycardia, heart failure, and asystole greater than or equal to 3 seconds
• Second-degree AV block with neuromuscular diseases, such as myotonic muscular dystrophy, Erb dystrophy, and peroneal muscular atrophy, even in asymptomatic patients (progression of the block is unpredictable in these patients); in some of these patients, an implantable cardioverter defibrillator (ICD) may be appropriate
• Mobitz II second-degree AV block with wide QRS complexes
• Asymptomatic Mobitz I second-degree AV block with the block at intra- or infra-His level found on electrophysiologic testing (level II recommendation)

Second-degree AV block may occur after MI, and it may be transient or asymptomatic. In this case, pacemaker placement may not be needed. However, persistent and symptomatic second-degree AV block after MI, especially if it is associated with bundle-branch block, warrants permanent pacemaker placement. High-grade AV block after anterior MI, even if transient, may warrant permanent pacing.

Second-degree AV block after cardiac surgery may be persistent and necessitate pacemaker placement.

Second-degree AV block in patients with drug toxicity, Lyme disease, or hypoxia in sleep apnea is expected to resolve. In any situation where second-degree AV is expected to resolve as a result of correction of the underlying pathology, permanent pacemaker placement is not indicated.

For symptomatic patients with Mobitz I AV block, a cardiology consultation is indicated. Asymptomatic patients with a Mobitz I block can be referred to a cardiologist on an outpatient basis.

For any patient with a new Mobitz II AV block, cardiology consultation is indicated, regardless of symptoms.

Patients who are discharged from the ED with a Mobitz II AV block should have prompt follow-up arranged with a cardiologist.

If high-grade AV block and, possibly, symptoms due to AV block are present, consider monitoring the patient and then performing Holter monitoring or treadmill testing in the future. If the AV block occurs at night, consider sleep apnea as the cause.