From the Guidelines
Second-degree heart block type 2 (Mobitz type 2) is a serious cardiac conduction abnormality that requires prompt medical attention and typically necessitates permanent pacemaker implantation as the definitive treatment, regardless of symptoms, as recommended by the 2018 ACC/AHA/HRS guideline 1.
Diagnosis and Treatment
The diagnosis of second-degree heart block type 2 is based on the presence of dropped heartbeats without progressive PR interval prolongation on electrocardiogram. This condition often indicates disease in the His-Purkinje system and can progress to complete heart block, making it a more serious disruption of the heart's electrical system compared to Mobitz type I. The underlying pathology is usually fibrosis of the conduction system, often due to coronary artery disease, cardiomyopathy, or degenerative changes.
Key Considerations
- Permanent pacing is recommended for 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.
- Temporary transcutaneous or transvenous pacing may be necessary for unstable patients while awaiting definitive treatment.
- Atropine (0.5-1mg IV) can be used as a temporary measure for symptomatic bradycardia, though its effectiveness in Mobitz type II is limited.
- Techniques that provide more physiologic ventricular activation, such as cardiac resynchronization therapy or His bundle pacing, are preferred to right ventricular pacing in patients with a left ventricular ejection fraction between 36% to 50% and atrioventricular block who are expected to require ventricular pacing >40% of the time 1.
Patient-Centered Care
- Treatment decisions should be based on the best available evidence and the patient's goals of care and preferences, emphasizing shared decision-making and patient-centered care 1.
- Patients with decision-making capacity or their legally defined surrogate have the right to refuse or request withdrawal of pacemaker therapy, even if the patient is pacemaker dependent, which should be considered palliative, end-of-life care, and not physician-assisted suicide 1.
From the FDA Drug Label
Atropine also may lessen the degree of partial heart block when vagal activity is an etiologic factor The diagnosis of second-degree heart block type 2 (Mobitz type 2) is not directly addressed in the provided drug label. However, treatment with atropine may be considered if vagal activity is an etiologic factor, as it may lessen the degree of partial heart block. Key points to consider:
- Vagal activity: Atropine may be effective if vagal activity is contributing to the heart block.
- Partial heart block: Atropine may lessen the degree of partial heart block. 2
From the Research
Diagnosis of Second-Degree Heart Block Type 2 (Mobitz Type 2)
- Second-degree heart block type 2, also known as Mobitz type 2, is a form of "incomplete" heart block, in which some, but not all, atrial beats are blocked before reaching the ventricles 3.
- The diagnosis of Mobitz type 2 second-degree block is characterized by periodic atrioventricular block with constant PR intervals in the conducted beats 3.
- The site of the block in Mobitz type 2 is almost always below the AV node, which is usually infranodal 3.
Treatment of Second-Degree Heart Block Type 2 (Mobitz Type 2)
- Permanent pacemaker (PPM) implantation is the standard of care in patients with second-degree type II atrioventricular (AV) block, irrespective of patient symptoms, when the conduction abnormality is irreversible 4.
- The treatment of Mobitz type 2 second-degree block is crucial, as it is more likely to progress to complete heart block and Stokes-Adams arrest 3.
- In some cases, patients with Mobitz type 2 second-degree block may refuse pacemaker implantation, but they should be closely monitored for symptoms related to the AV block, as the condition can worsen over time 5.
- Electrophysiological studies can be performed to determine the mechanism of the block and to guide treatment decisions 6.
Prognosis and Complications
- Second-degree heart block type 2 is considered to be at high risk for progression to complete heart block (CHB) 4.
- The prognosis of patients with Mobitz type 2 second-degree block depends on the underlying cause of the block and the presence of symptoms 3.
- Patients with Mobitz type 2 second-degree block are at risk of developing symptomatic high-degree AV block, which can lead to palpitations, dyspnea, and other symptoms 5, 7.