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Depending on the duration and severity of the heart block, patients with AV block may be asymptomatic or complain of syncope, near syncope, sudden cardiac death, palpitations, angina, or transient ischemic attacks.


  1. Secondary to conduction abnormalities in the AV node, bundle of His, or bundle branches impairing transmission from atria to the ventricles.

  2. The disturbance may be intermittent or permanent.

  3. Classification (Table 31-5)

    1. In first-degree AV block, all of the sinus impulses (P waves) are conducted but the PR interval is prolonged.

    2. In second-degree block, some of the impulses are conducted. There are 2 subtypes: Mobitz type I and Mobitz type II (Table 31-5).

    3. In third-degree AV block, none of the P waves are conducted (Figure 31-8).

    4. In second- or third-degree AV block, the ventricular rate slows and may depend on lower intrinsic pacemakers residing within the ventricle. The bradycardia can cause dyspnea, angina, hypotension, syncope, or death.

  4. AV nodal disease should also be suspected in patients with atrial fibrillation who have a slow ventricular response and are not taking medications that slow AV conduction (eg, digoxin, beta-blockers, verapamil, or diltiazem).

  5. Etiology

    1. Fibrosis of the conduction system

    2. Ischemic heart disease

    3. Medications (eg, beta-blockers, verapamil, diltiazem, digoxin, adenosine, amiodarone)

      image Most patients with AV block attributed to verapamil, diltiazem, or beta-blockers also have conduction disease and are likely (> 80%) to experience AV block even off medications.

    4. Sarcoidosis is a common cause of unexplained second- or third-degree AV block in patients younger than 60 years (34%) and should be considered even if there is no prior diagnosis of sarcoidosis. 27% of such patients subsequently suffer from VT of HF.

    5. Hyperkalemia

    6. Valvular heart disease (due to extension of calcification into the conduction system)

    7. Increased vagal tone

    8. Miscellaneous other causes (hypothyroidism, Lyme disease, amyloidosis, etc)

    9. Cardiac procedures (ie, transcathetic aortic valve implantation)

Table 31-5.Classification of heart block.
Figure 31-8.

Third-degree atrioventricular block.

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