Complete heart block

Complete heart block, also referred to as third-degree heart block, or third-degree atrioventricular (AV) block, is a disorder of the cardiac conduction system, where there is no conduction through the AV node. Therefore, complete disassociation of the atrial and ventricular activity exists. The ventricular escape mechanism can occur anywhere from the AV node to the bundle-branch Purkinje system. It is important to realize, however, that not all patients with AV dissociation have complete heart block. For example, patients with accelerated junctional rhythms have AV dissociation, but not complete heart block, if the escape rate is faster than the intrinsic sinus rate. Electrocardiographically, complete heart block is represented by QRS complexes being conducted at their own rate and totally independent of the P waves.

Physical

• The physical examination will be notable for bradycardia, which can be quite severe.
• Signs of congestive heart failure as a result of decreased cardiac output may be present and include the following:

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• Tachypnea or respiratory distress
• Rales
• Jugular venous distention
• Patients may have signs of hypoperfusion, including the following:

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• Altered mental status
• Hypotension
• Lethargy
• In patients with concomitant myocardial ischemia or infarction, corresponding signs may be evident on examination:

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• Signs of anxiety such as agitation or unease
• Diaphoresis
• Pale or pasty complexion
• Tachypnea
• Regularized atrial fibrillation is the classic sign of complete heart block due to digitalis toxicity. This rhythm occurs because of the junctional escape rhythm.

Prehospital Care

• All patients should be rapidly transported to the nearest available facility, applying advanced life support (ACLS) with continuous cardiac monitoring, as per local protocols.
• For any symptomatic patient, transcutaneous pacing is the treatment of choice.
• In all patients, oxygen should be administered and intravenous access should be established.
• Maneuvers that are likely to increase vagal tone (eg, Valsalva maneuvers, painful stimuli) should be avoided.
• Atropine can be administered but should be given cautiously, because it is likely to be ineffective in a wide complex QRS rhythm and can be dangerous if the patient is having a concurrent MI.

Date: 2015-01-12; view: 840