eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology
Atrioventricular Block, Second Degree: Treatment & Medication
Updated: Sep 19, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Treatment
Medical Care
Presentation of second-degree atrioventricular (AV) block varies. In general, patients with Mobitz I (Wenckebach) AV block are asymptomatic. However, when bradycardia is present, intravenous medications such as isoproterenol and atropine may be helpful. These agents must be administered in a hospital setting with cardiac monitoring. Patients with Mobitz I (Wenckebach) AV block secondary to increased vagal tone may respond to theophylline, glycopyrrolate, or scopolamine. Pacemaker therapy is rarely required when medications fail to control symptoms.
Asymptomatic patients with Wenckebach or non-Wenckebach AV block do not require immediate pacemaker therapy. However, they should be monitored periodically because of the possibility of cardiovascular syncope or Stokes-Adams attacks in cases of a very slow escape rhythm. Because these patients may be at risk for sudden death, pacemaker therapy is indicated. Pacemaker therapy is also indicated in asymptomatic patients who have AV block within the His bundle (demonstrated by electrophysiologic study) and in those whose Wenckebach AV block persists for more than 7 days after cardiac surgery.
- In symptomatic patients, initiation of short-term therapy with a chronotropic agent, such as isoproterenol, is reasonable. However, isoproterenol may exacerbate the condition by accelerating the atrial rate, which results in a higher grade of AV block by increasing myocardial oxygen demand, by reducing diastolic and coronary perfusing pressure, or by initiating ventricular dysrhythmias. If a vagal mechanism is suspected as the cause of acute symptomatic heart block, atropine may also be used. Arrangements for a stable temporary pacing system are necessary because drug therapy is usually only a temporizing measure for symptomatic heart block.
- Temporary pacing may be initiated using a noninvasive transcutaneous pacing system; however, the potential for discomfort in all patients and skin burns in newborns must be recognized, and arrangements for transvenous (or epicardial) pacing are usually initiated simultaneously. If the cause of the symptomatic second-degree AV block is unlikely to be reversible, permanent pacing can be initiated. However, in most patients, permanent pacing is reserved for those who do not demonstrate resolution of their conduction disorder after a reasonable period of observation.
- Until the heart rate has improved, second-degree AV block related to transient phenomena, such as myocardial infarction, infections, or toxins, should be supported with temporary pacing if the patient is symptomatic. Heart block occurring above the His bundle, most commonly in a Wenckebach pattern, is usually more benign than heart block occurring below the His bundle (most commonly in a non-Wenckebach pattern).
- Second-degree AV block occurring in the hemifascicles of the specialized conduction system may have a very low escape pacemaker rate if it progresses to complete AV block. Prophylactic pacemaker placement may be warranted in conditions such as Kearns-Sayre syndrome, a mitochondrial genetic disorder characterized by external ophthalmoplegia and progressive fascicular block.
- Before the decision is made regarding whether to treat patients with a permanent pacing system, posttraumatic second-degree AV block should usually be monitored and supported for 7-10 days to assess whether the condition is resolving or progressing.
- A unique and rare cause of second-degree AV block is a severe infantile form of long-QT syndrome. The prognosis in such long-QT syndromes is very guarded, even if patients are treated with beta blockers, pacing, and stellate ganglionectomy. It has been suggested that the prognosis of patients with high-grade AV block is similar to that of patients with complete AV block and that management should be the same for the two.
Consultations
Patients with a second-degree AV block should be evaluated by a cardiologist even when they are asymptomatic, to assess for any associated congenital heart disease, to identify sinus node dysfunction, and to determine whether it may progress to worrying symptoms, such as low heart frequency and syncope.
Activity
Activity should be tailored to the patient's physical capabilities. A 24-hour Holter monitor and an exercise stress test may aid in determining recommendations in this regard. In addition, an exercise stress test helps determine who likely requires a pacemaker; in patients who already have a pacemaker, it helps reprogram the device according to the patient's needs.
Medication
In general, patients with second-degree atrioventricular (AV) block with symptomatic bradycardia may be medicated with intravenous isoproterenol or atropine acutely. However, these agents must be administered in a hospital setting with cardiac monitoring available. Patients with Mobitz I (Wenckebach) AV block secondary to increased vagal tone may respond to theophylline, glycopyrrolate, or scopolamine. Pacemaker therapy is required when medications fail to control symptoms.
Beta-adrenergic agonists
Isoproterenol has beta1-adrenergic and beta2-adrenergic receptor activity. It binds beta receptors of the heart, smooth muscle of bronchi, skeletal muscle, vasculature, and alimentary tract. Isoproterenol has positive inotropic and chronotropic actions.
Isoproterenol (Isuprel)
Usually given as continuous IV infusion for rate support. Usually a temporizing measure, initiated during organization of temporary or permanent pacing system placement for symptomatic patients with bradycardia from heart block or sinus node disease.
Adult
2-20 mcg/min IV
Pediatric
0.01-0.04 mcg/kg/min IV infusion
Bretylium increases action of vasopressors on adrenergic receptors, which may in turn result in arrhythmias; guanethidine may increase effect of direct-acting vasopressors, possibly resulting in severe hypertension; tricyclic antidepressants may potentiate pressor response of direct-acting vasopressors
Documented hypersensitivity; tachyarrhythmias; tachycardia or heart block caused by digitalis intoxication; ventricular arrhythmias, which require inotropic therapy; angina pectoris
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
Difficult to titrate in patients requiring rate support for bradycardia (easy to overshoot and provide excessive dose, resulting in tachycardia, dysrhythmias, or hemodynamic compromise); pacemaker rate support should usually be arranged for patients who may require isoproterenol for bradycardia; increasing myocardial oxygen requirements while decreasing effective coronary perfusion may have a deleterious effect on injured or failing heart; in some patients, presumably with organic disease of the AV node and its branches, may paradoxically worsen heart blocks or precipitate Adams-Stokes attacks; caution in coronary artery disease, coronary insufficiency, diabetes mellitus, or hyperthyroidism and sensitivity to sympathomimetic amines; if heart rate >110 bpm, may be advisable to decrease infusion rate or temporarily discontinue infusion
Anticholinergics
The goal is to improve AV node conduction by reducing vagal tone via the muscarinic receptor blockade. This is only effective if the site of block is within the AV node. Anticholinergic therapy is ineffective for patients with infranodal block.
Atropine
To increase heart rate through vagolytic effects, causing an increase in cardiac output.
Adult
0.5-1 mg IV q3-5min up to 3 mg total (0.04 mg/kg)
Pediatric
0.02 mg/kg/dose IV, use a minimum of 0.1 mg/dose; not to exceed 0.5 mg/dose (children) or 1 mg/dose (adolescents); may repeat q5min not to exceed a total cumulative dose of 1 mg (children) or 2 mg (adolescents)
Coadministration with other anticholinergics have additive effects; may cause pharmacologic effects of atenolol and digoxin to increase; antipsychotic effects of phenothiazines may decrease; tricyclic antidepressants with anticholinergic activity may increase effects
Documented hypersensitivity; thyrotoxicosis, narrow-angle glaucoma, and tachycardia
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Caution in persons with Down syndrome and/or children with brain damage to prevent hyperreactive response; caution in coronary heart disease, tachycardia, congestive heart failure, cardiac arrhythmias, hypertension, peritonitis, ulcerative colitis, hepatic disease, and hiatal hernia with reflux esophagitis; in prostatic hypertrophy, prostatism can have dysuria and may require catheterization
More on Atrioventricular Block, Second Degree |
| Overview: Atrioventricular Block, Second Degree |
| Differential Diagnoses & Workup: Atrioventricular Block, Second Degree |
 Treatment & Medication: Atrioventricular Block, Second Degree |
| Follow-up: Atrioventricular Block, Second Degree |
| Multimedia: Atrioventricular Block, Second Degree |
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References
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Further Reading
Keywords
atrioventricular, AV, second-degree atrioventricular block, second-degree AV block, Mobitz I AV block, Wenckebach AV block, Mobitz II AV block, non-Wenckebach AV block, heart block, third-degree atrioventricular block, dilated cardiomyopathy, syncope, presyncope, irregular pulse, heart failure, hepatomegaly, peripheral edema, neonatal lupus erythematosus, myocarditis, endocarditis, Lyme disease, rheumatic fever, hyperthyroidism, thyroid disease, corrected transposition of the great arteries, atrial septal defect, Duchenne muscular dystrophy, rhabdomyoma, acute rheumatic heart disease, Lyme carditis, cardiac dystrophies, lipodystrophies, premature aging syndromes, Kearns-Sayre syndrome, sickle cell disease, drug-induced torsade de pointes
