History
The degree atrioventricular (AV) block is generally associated with the severity of symptoms and clinical history. Common presentations and symptoms are outlined below for the different types of AV block.
Any level of AV block leading to profound bradycardia may also lead to life-threatening torsade de pointes (TdP). This is due to the inverse relationship between bradycardia and repolarization time; it may prolong the QT interval and predispose a patient to TdP especially if there is a long short interval.
First-degree AV block
History
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High vagal tone
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Acute inferior myocardial infarction (MI)
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Use of antiarrhythmic medication(s)
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Being a conditioned athlete
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Hypokalemia, hypomagnesemia
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Degeneration of the AV node
Symptoms
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None
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Shortness of breath
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Exercise intolerance
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Fatigue
Second-degree AV Block
History
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Inflammatory disease
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Infiltrative disease
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Hyperkalemia
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Catheter ablation of the slow pathway
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Valve replacement surgery
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Acute MI
Symptoms
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Fatigue
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Shortness of breath
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Exercise intolerance
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Dizziness
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Syncope
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Chest pain
Third-degree AV Block
History
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Degenerative disease
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Infiltrative disease
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Myocarditis
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Neuromuscular disease
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Ischemia/infarction
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Hypoxia
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Hyperkalemia
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Use of antiarrhythmic medication(s)
Symptoms
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Fatigue
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Shortness of breath
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Exercise intolerance
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Lightheadedness, dizziness
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Syncope
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Chest pain
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Neck palpitations
Physical Examination
Routine physical examination does not lead to the diagnosis of first-degree atrioventricular (AV) block. Second-degree AV block may manifest as bradycardia (Mobitz II), irregularity of the heart rate (Mobitz I), or a variable pulse and variable neck vein distention.
Third-degree AV block may be associated with profound bradycardia. In cases of concomitant structural heart disease, pulmonary edema and jugular venous distention may be noted. Cannon A-waves may be observed intermittently due to right atrium contraction against a closed tricuspid valve. A variable S2 and variable strength of the pulse is noted.
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Atrioventricular Block. This rhythm strip shows first-degree atrioventricular block with a PR interval of 0.360 sec. Note the fixed prolonged PR interval.
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Atrioventricular Block. First-degree atrioventricular block. PR interval is constant and is 0.280 sec.
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Atrioventricular Block. Second-degree Mobitz type I atrioventricular block. Note the prolongation of the PR interval preceding the dropped beat and the shortened PR interval following the dropped beat.
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Atrioventricular Block. Second-degree atrioventricular block, Mobitz type I (Wenckebach). Note the prolongation of the PR interval preceding the dropped beat and the shortened PR interval following the dropped beat.
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Atrioventricular Block. Second-degree Mobitz II atrioventricular block. Note the fixed PR interval, but after the third beat, an atrial impulse fails to conduct to the ventricle. Courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Second_degree_heart_block.png).
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Atrioventricular Block. Second-degree atrioventricular block, Mobitz type II. A constant PR interval in conducted beats is present. Intraventricular conduction delay is also present.
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Atrioventricular Block. A constant PP interval and normal PR interval in conducted beats is present. This progresses to 2:1 atrioventricular (AV) block. A 2:1 AV block can be present with conduction delay in the AV node or His-Purkinje system, but it is more likely to be in the AV node for all patients (with a greater chance of AV block in the His-Purkinje system if there is a bundle branch block). Review extended monitoring strips because Mobitz I or Mobitz II may be present at other times, and this might help to determine the level of the block.
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Atrioventricular Block. High-degree atrioventricular block is demonstrated with a 4:1 atrial-to-ventricular conduction ratio. Note the P wave prior to the QRS conducts whereas the others do not. Courtesy of Life in the Fast Lane (https://lifeinthefastlane.com/ecg-library/basics/high-grade-block/), Edward J Burns, MD, Sydney, Australia.
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Atrioventricular Block. This rhythm strip shows third-degree atrioventricular block (complete heart block). The atrial rate is faster than the ventricular rate, and no association exists between the atrial and ventricular activity. Courtesy of Life in the Fast Lane (https://lifeinthefastlane.com/ecg-library/basics/complete-heart-block/), Edward J Burns, MD, Sydney, Australia.
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Atrioventricular Block. Third-degree atrioventricular block (complete heart block). The atrial rate is faster than the ventricular rate, and no association exists between the atrial and ventricular activity.
