DESCRIPTION 
- 1st-degree block is prolongation of the PR interval (>200 ms).
- 2nd-degree AV block is classified into 2 subcategories:
- Type I or Mobitz I 2nd-degree atrioventricular (AV) block. Progressive prolongation of the PR interval before a blocked beat (Wenckebach block) usually is associated with a narrow QRS complex.
- Type II or Mobitz II 2nd-degree AV block is the sudden loss of AV conduction without progressive prolongation of the PR interval before the blocked beat. Usually it is associated with a wide QRS complex.
- Advanced AV block refers to the block of
2 consecutive P waves. - 3rd-degree AV block (complete heart block) is defined as absence of AV conduction:
- Patients with abnormalities of AV conduction may be asymptomatic.
- Patients may experience serious symptoms related to bradycardia, ventricular arrhythmias, or both.
- Decisions regarding the need for a pacemaker are importantly influenced by the presence or absence of symptoms directly attributable to bradycardia.
- Synonym(s): Heart block
EPIDEMIOLOGY
Prevalence
Prevalence variable, depends on underlying structural heart disease, and increases with increasing age.
RISK FACTORS
Structural heart disease
ETIOLOGY
- Aging and fibrosis of AV conducting system
- No pathology if AV block is functional and related to drug therapy
- AV node and His–Purkinje system may be damaged due to MI, impingement by calcium from aortic or mitral valve, or the development of fibrosis (Lev and Lenègre diseases).
- Aortic or mitral stenosis, especially following valve replacement; because the mitral valve is close to the AV node, impaired AV conduction often is due to inflammation and resolves. The aortic valve, however, is close to the His–Purkinje system, and when AV block occurs as a consequence of aortic valve disease or surgery. AV block is usually permanent, and pacing is required.
- Not a genetic disease, except in neuromuscular diseases with AV block, such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy (limb-girdle), and peroneal muscular atrophy.
COMMONLY ASSOCIATED CONDITIONS
Structural heart disease
Outline
Signs and symptoms:
- None
- Lightheadedness
- Syncope
- Dyspnea, CHF
- Symptoms may be due to bradycardia itself, or to ventricular arrhythmias precipitated by bradycardia (eg, torsade de pointes ventricular tachycardia).
DIAGNOSTIC TESTS & INTERPRETATION
- EKG most useful
- Ambulatory monitoring (Holter or telemetry):
- Event monitoring for intermittent symptoms
Lab
Generally not applicable; drug level measurement (especially digitalis) is indicated if toxicity suspected.
DIFFERENTIAL DIAGNOSIS
- Junctional rhythm
- Concealed junctional extrasystoles
- When 2:1 AV block is present, the differentiation between Mobitz I and Mobitz II block is difficult because there is no progressive change in the PR interval that can be assessed:
- In general, 2:1 AV block with a narrow QRS is usually due to block in the AV node (eg, Mobitz I) and 2:1 AV block with a wide QRS is often due to block below the AV node (eg, infra-Hissian, Mobitz II).
- Exceptions to these rules do occur.
- The importance of this distinction lies in the indication for pacing in patients with infra His block
Outline
No drugs directly enhance AV conduction. If digitalis is toxic, Digibind antibody is indicated to inhibit digitalis effect on the heart.
ADDITIONAL TREATMENT
General Measures
- For 1st-degree AV block and 2nd-degree Mobitz type I AV block, usually no treatment is recommended. These conduction disturbances are often the result of drug therapy and simply represent drug effects.
- 2nd-degree Mobitz type II AV block, especially if the QRS is wide, reflects infra-Hissian conduction disease, and permanent pacing is usually indicated.
- High-degree and 3rd-degree AV block may be a consequence of drug therapy/toxicity, and a decision on pacing is made on the etiology.
- If a drug causing AV block is not essential, the drug can be stopped. If the drug is essential, permanent pacing is required to support the rate to allow drug administration.
- If there is drug toxicity, the rhythm should be supported by temporary pacing if needed while toxicity resolves.
SURGERY
- The indications for permanent pacing are outlined in the American College of Cardiology/American Heart Association Guidelines referenced below and include the following:
- 3rd-degree AV block at any anatomic level associated with any 1 of the following conditions:
- Bradycardia with symptoms presumed to be due to AV block
- Arrhythmias and other medical conditions that require drugs that result in symptomatic bradycardia
- Documented periods of asystole >3.0 sec or any escape rate <40 bpm in awake, symptom-free patients
- After catheter ablation of the AV junction
- Postoperative AV block that is not expected to resolve
- Neuromuscular diseases with AV block such as myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy (limb-girdle), and peroneal muscular atrophy
- 2nd-degree AV block regardless of type or site of block, with associated symptomatic bradycardia
- Asymptomatic 3rd-degree AV block at any anatomic site with average awake ventricular rates of 40 bpm if cardiomegaly or LV dysfunction is present
- Asymptomatic type II 2nd-degree AV block
- Asymptomatic type I 2nd-degree AV block at intra- or infra-Hissian levels found incidentally at electrophysiologic study for other indications
- 1st-degree AV block with symptoms suggestive of pacemaker syndrome and documented alleviation of symptoms with temporary AV pacing
- Marked 1st-degree AV block (>0.30 sec) in patients with LV dysfunction and symptoms of CHF in whom a shorter AV interval results in hemodynamic improvement, presumably by decreasing left atrial filling pressure
IN-PATIENT CONSIDERATIONS
Admission Criteria
If a patient has symptomatic AV block (especially 3rd-degree or 2:1 AV block with a wide QRS), admission is warranted, usually for pacemaker implantation or treatment of drug toxicity.
Outline
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
- For those without pacemakers, AV conduction should be systematically followed with EKGs or Holter monitors.
- Patients with pacemakers need regular follow-up (trans-telephonic and device clinic).
- Other than avoiding drug toxicity and preventing coronary artery disease, AV block is not preventable.
DIET
No specific diet
PATIENT EDUCATION
- Mostly related pacemaker follow-up in those with pacemakers. If drug toxicity is the cause, counsel to take measures to avoid further toxicity.
- If at risk for falls or syncope, counsel to avoid activities that put the patient or others in danger.
- Activity:
- Depends on hemodynamic consequences and underlying cause of AV block
PROGNOSIS
- Variable and depends on underlying heart disease
- Patients with AV block have a worse prognosis than those with sinus node dysfunction, probably because the former have greater degrees of structural heart disease.
COMPLICATIONS
Complications due to the AV block itself or to its treatment include syncope, injury, and occasionally death.
Outline