From the Guidelines
Mobitz type I heart block, also known as Wenckebach phenomenon, typically requires immediate medical attention when accompanied by certain red flag symptoms, including syncope, pre-syncope, chest pain, shortness of breath, severe dizziness, confusion, and exercise intolerance, as indicated by the 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Red Flag Symptoms
These warning signs are particularly concerning because they suggest hemodynamic compromise or progression to more severe forms of heart block. Other concerning symptoms include:
- Heart failure signs such as peripheral edema, fatigue, and decreased exercise capacity
- Palpitations or irregular heartbeats
Clinical Significance
Mobitz type I block involves progressive prolongation of the PR interval until a beat is dropped, and while it's often benign and can occur in healthy individuals (especially athletes with high vagal tone), the presence of these red flag symptoms indicates potential myocardial ischemia, medication toxicity, or underlying structural heart disease. Immediate evaluation is necessary as these patients may require temporary or permanent pacemaker placement, especially if the block is occurring below the AV node or if symptoms are severe.
Treatment Approach
Treatment depends on the underlying cause but may include atropine for acute symptomatic bradycardia, discontinuation of offending medications like beta-blockers or calcium channel blockers, and correction of electrolyte abnormalities, as suggested by the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.
Key Considerations
It is essential to identify signs and symptoms of poor perfusion and determine if those signs are likely to be caused by the bradycardia, and to evaluate the patient’s clinical status and identify potentially reversible causes, as recommended by the 2010 American Heart Association guidelines 1.
From the Research
Red Flag Symptoms of Mobitz Type 1 (Wenckebach) Block
The following are potential red flag symptoms associated with Mobitz type 1 (Wenckebach) block:
- Chest pain 2, 3
- Shortness of breath 4, 5
- Palpitations 4, 5
- Dizziness 4
- Presyncope or syncope 6, 5
- Difficulty breathing 4
Associated Conditions
Mobitz type 1 (Wenckebach) block may be associated with various conditions, including:
- Myocardial bridge of coronary artery 2
- Acute myocardial infarction 3
- Severe three-vessel coronary artery disease 3
- Inappropriate sinus tachycardia (IST) 4
- Lithium cardiotoxicity 6
- Excessive respiratory sinus arrhythmia 5
Diagnostic Considerations
When evaluating a patient with Mobitz type 1 (Wenckebach) block, it is essential to consider the following:
- Electrocardiogram (ECG) findings, including the presence of Wenckebach phenomenon 2, 3, 4, 6
- Echocardiogram results to exclude valvular abnormality and systolic/diastolic dysfunction 2, 4
- Coronary angiography to confirm the diagnosis of coronary artery disease 2, 3
- Serum lithium concentration to rule out lithium cardiotoxicity 6