From the Guidelines
Mobitz type 2 heart block in the bundle of His is a serious cardiac conduction abnormality that typically requires permanent pacemaker implantation, as recommended by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. This condition occurs when electrical impulses are intermittently blocked within the bundle of His, resulting in dropped heartbeats without the progressive PR interval prolongation seen in Mobitz type 1.
Key Considerations
- Patients should be hospitalized for continuous cardiac monitoring while awaiting pacemaker placement, as this condition can progress to complete heart block and cause syncope, hemodynamic instability, or sudden cardiac death.
- Temporary pacing may be needed if the patient is symptomatic with bradycardia, hypotension, or altered mental status.
- Unlike Mobitz type 1 (Wenckebach), which often occurs at the AV node and may be benign, Mobitz type 2 typically indicates structural heart disease affecting the His-Purkinje system and has a poorer prognosis without intervention.
Management
- Medications that slow AV conduction (beta-blockers, calcium channel blockers, digoxin) should be avoided as they may worsen the conduction block.
- Atropine may be used temporarily for symptomatic bradycardia while preparing for pacemaker implantation, but it is not a definitive treatment for this condition.
- The guideline recommends permanent pacing in patients with acquired second-degree Mobitz type II atrioventricular block, high-grade atrioventricular block, or third-degree atrioventricular block not caused by reversible or physiologic causes, regardless of symptoms 1.
Additional Recommendations
- In patients with a left ventricular ejection fraction between 36% to 50% and atrioventricular block, who have an indication for permanent pacing and are expected to require ventricular pacing >40% of the time, techniques that provide more physiologic ventricular activation (e.g., cardiac resynchronization therapy, His bundle pacing) are preferred to right ventricular pacing to prevent heart failure 1.
- Shared decision-making and patient-centered care are endorsed and emphasized in the guideline, and treatment decisions should be based on the best available evidence and on the patient’s goals of care and preferences 1.
From the Research
Diagnosis of Bundle of His Block with Mobitz Type 2
The diagnosis of a patient with a Bundle of His (atrioventricular bundle) block with Mobitz type 2 (second-degree atrioventricular block) can be made using standard ECG and long-term ECG monitoring 2. The following key points are relevant to the diagnosis:
- Bradyarrhythmias, including atrioventricular (AV) block, can be subclassified clinically and diagnosed using ECG 2
- Second-degree AV block Mobitz Type II is a specific type of AV block that can be diagnosed using ECG and may require additional testing for diagnosis 2, 3
- Patients with second-degree AV block Mobitz Type II may present with symptoms such as dizziness, shortness of breath, and exercise intolerance 3
Diagnostic Criteria
The diagnostic criteria for second-degree AV block Mobitz Type II include:
- ECG evidence of second-degree AV block with a narrow QRS complex 4
- Presence of Mobitz Type II AV block on ECG, characterized by intermittent blocking of P waves without preceding PR prolongation 2, 3
- Symptoms such as syncope, presyncope, or palpitations may be present 3, 4
Additional Testing
Additional testing, such as electrophysiology studies, may be necessary to confirm the diagnosis and determine the location of the block within the conduction system 4. The following tests may be used: