Can a Mobitz II (second-degree atrioventricular block) heart block be caused by an infection?

Mobitz Type II Heart Block Can Be Caused by Infection

Yes, Mobitz type II second-degree atrioventricular block can be caused by infection, particularly myocarditis resulting from viral or other infectious agents. According to guidelines, infection-induced myocarditis is a recognized cause of Mobitz II heart block, which can lead to significant morbidity and mortality if not properly diagnosed and managed 1.

Infectious Causes of Mobitz II AV Block

Myocarditis

• Viral myocarditis is the most common infectious cause of Mobitz II AV block
• The inflammation of the cardiac conduction system can directly affect the His-Purkinje system, leading to infra-Hisian block characteristic of Mobitz II 1
• Endomyocardial biopsy (EMB) is recommended in patients with unexplained heart failure associated with new ventricular arrhythmias, Mobitz type II second-degree or third-degree AV heart block 1

Specific Infectious Agents

• Dengue virus has been documented to cause transient variable AV conduction block, including Mobitz type II, particularly during the recovery phase 2
• Other viral agents implicated in myocarditis that can lead to conduction disorders include:
  • Coxsackievirus
  • Adenovirus
  • Parvovirus B19
  • Herpes viruses
  • HIV (which can cause cardiomyopathy with associated conduction abnormalities) 1

Clinical Significance and Prognosis

Mobitz II AV block differs significantly from Mobitz I (Wenckebach) in terms of prognosis and management:

• Mobitz II block typically results from disease in the distal His-Purkinje system, making it more concerning than Mobitz I block 1
• It has a higher risk of progressing to complete heart block with unreliable escape rhythms 3
• When associated with infection/myocarditis, it may indicate more extensive myocardial inflammation 1

Diagnostic Approach for Suspected Infectious Cause

1. Cardiac biomarkers: Obtain cardiac troponin levels to assess for myocardial injury 1
2. 12-lead ECG: Essential for confirming Mobitz II block (characterized by constant PR intervals with occasional non-conducted P waves) 1
3. Echocardiogram: To evaluate for structural abnormalities and ventricular function 1
4. Consider endomyocardial biopsy: Particularly indicated in patients with:
   • Unexplained heart failure with Mobitz II block
   • Failure to respond to usual care within 1-2 weeks
   • Need for inotropic support or mechanical circulatory support 1

Management Considerations

Acute Management

• Temporary pacing is indicated in cases of failure to respond to positive chronotropic medication 1
• Urgent angiography with revascularization is indicated if the patient has not received previous reperfusion therapy (in cases of ischemic etiology) 1
• For infection-related Mobitz II block:
  • Treat the underlying infection
  • Provide supportive care
  • Monitor closely for progression to complete heart block 1

Long-term Management

• Permanent pacemaker implantation is often necessary for persistent Mobitz II block
• If myocarditis is the underlying cause, immunosuppressive therapy may be considered, especially in cases of giant cell myocarditis or cardiac sarcoidosis 1
• Avoid medications that slow AV conduction (beta-blockers, calcium channel blockers, digitalis, amiodarone) 1

Important Caveats

• Mobitz II block due to infection may be transient and resolve with treatment of the underlying infection 2
• Other non-infectious causes of Mobitz II block should be considered, including:
  • Ischemic heart disease (particularly anterior MI)
  • Medication effects (e.g., lithium toxicity) 4
  • Immunotherapy complications (e.g., pembrolizumab-induced cardiotoxicity) 5
  • Sclerodegenerative conduction system disease 3

Remember that Mobitz II block is considered more dangerous than Mobitz I block because it typically occurs below the AV node in the His-Purkinje system, making progression to complete heart block more likely and escape rhythms less reliable. This is why aggressive monitoring and management are essential, particularly when infection is the suspected cause.