Heart Block Management

Introduction to Heart Block Treatment

• The American College of Cardiology recommends a stepwise approach for treating heart block, based on the type of block, symptoms, and hemodynamic stability, with permanent pacing indicated for symptomatic second-degree or third-degree AV block that is not due to reversible causes 1

Medications for Heart Block

• The American Heart Association suggests that atropine 0.5-1 mg IV is reasonable for patients with second-degree or third-degree AV block at the AV nodal level with symptoms or hemodynamic compromise 1
• Beta-adrenergic agonists, such as isoproterenol, dopamine, dobutamine, and epinephrine, may be considered for symptomatic second-degree or third-degree AV block with low likelihood for coronary ischemia, as recommended by the American College of Cardiology 1, 2
• Theophylline/Aminophylline may be effective for bradycardia after inferior MI, cardiac transplant, or spinal cord injury 3
• Glucagon, high-dose insulin therapy, and IV calcium are reasonable to increase heart rate in patients with beta-blocker or calcium channel blocker overdose, with a strength of evidence of Class IIa 1

Pacing for Heart Block

• The American College of Cardiology recommends transcutaneous pacing for patients with second-degree or third-degree AV block and hemodynamic compromise refractory to medical therapy, as a bridge until transvenous pacing or permanent pacemaker is placed 1
• Temporary transvenous pacing is reasonable for patients with symptomatic second-degree or third-degree AV block refractory to medical therapy, according to the American College of Cardiology 1
• Transcutaneous pacing is indicated when medications fail, with a Class IIa and Level of Evidence B, and may be considered as initial therapy in unstable patients with high-degree AV block when IV access is not available, with a Class IIb and Level of Evidence C 4
• Transvenous pacing is indicated if the patient does not respond to drugs or transcutaneous pacing, with a Class IIa and Level of Evidence C, and should be considered early for patients likely to require ongoing pacing 4, 5

Indications for Permanent Pacing

• The American College of Cardiology indicates that symptomatic second-degree or third-degree AV block is a Class I indication for permanent pacing, as well as persistent second-degree AV block in the His-Purkinje system with bilateral bundle branch block 1, 2, 6
• Symptomatic AV block attributable to a known reversible cause that does not resolve despite treatment is also a reasonable indication for permanent pacing, as recommended by the American College of Cardiology 1
• Permanent pacemaker implantation is recommended for patients with symptomatic first-degree AV block, particularly when the PR interval exceeds 0.3 seconds, as stated by the European Society of Cardiology, with the following indications:

7, 8, 9, 10, 6

• Permanent pacing is indicated in patients with heart rate <50 beats/min, prolonged QT interval, or structural heart disease, as recommended by the European Heart Journal 11

Special Considerations

• The American College of Cardiology suggests that permanent pacing may be reasonable for patients with symptomatic AV block associated with cardiac sarcoidosis, and for patients with second-degree or third-degree AV block associated with thyroid function abnormalities without clinical myxedema 1
• For patients with Lyme carditis, medical therapy with antibiotics and supportive care, including temporary pacing if necessary, is recommended, according to the Infectious Diseases Society of America 1, 12
• The European Society of Cardiology recommends that permanent pacing may be reasonable when PR interval exceeds 0.3 seconds and causes symptoms similar to pacemaker syndrome 13
• Echo guidance or electro-anatomic navigation can be used to avoid fluoroscopy during pacemaker implantation, as suggested by the European Society of Cardiology 14
• Dual-chamber pacing (DDD) is recommended for patients in sinus rhythm, according to the American Heart Association and the American College of Cardiology, while single-chamber ventricular pacing is recommended for patients in permanent atrial fibrillation 9, 15

Medication Management

• Medications that can worsen AV conduction, such as digitalis, beta blockers, and calcium channel blockers, should be identified and discontinued if possible in patients with AV block 16
• Tricyclic antidepressants have significant cardiac conduction effects and can worsen AV block, and beta-blockers can further slow AV conduction and worsen heart block 17, 18
• Selective serotonin reuptake inhibitors (SSRIs) are the safest first-line anxiety medications for patients with second-degree heart block, particularly Mobitz type II, due to their minimal cardiac conduction effects, as recommended by the American College of Cardiology 2
• Non-dihydropyridine agents, such as verapamil and diltiazem, are more likely to cause bradycardia, while dihydropyridines, such as amlodipine and nifedipine, are less likely to cause significant bradycardia, as reported by the European Society of Cardiology 19

Assessment and Evaluation

• The American Heart Association recommends assessing for signs of hemodynamic compromise, including altered mental status, hypotension, chest pain, acute heart failure, shortness of breath, and syncope or pre-syncope, in patients with bradycardia 20
• The American College of Cardiology recommends evaluating all patients receiving permanent pacemakers for ICD indications 15
• AV nodal block is more likely to respond to atropine and is often transient, according to the European Society of Cardiology 21
• Infranodal block is associated with extensive myocardial damage, higher mortality risk, and is less responsive to atropine, as stated by the European Society of Cardiology 21
• In patients with inferior MI, AV block is usually at the level of the AV node, and atropine may be effective, as reported by the European Heart Journal 21, 11
• In patients with anterior MI, AV block is usually infra-nodal, associated with extensive myocardial damage, and has a higher mortality risk, requiring permanent pacing, as stated by the European Heart Journal 21, 11