<Li> The QRS complexes with a regular R - to - R interval represent the second rhythm . The PR interval will be variable, as the hallmark of complete heart block is lack of any apparent relationship between P waves and QRS complexes . </Li> <P> People with third - degree AV block typically experience severe bradycardia (an abnormally low measured heart rate), hypotension, and at times, hemodynamic instability . </P> <P> Many conditions can cause third - degree heart block, but the most common cause is coronary ischemia . Progressive degeneration of the electrical conduction system of the heart can lead to third - degree heart block . This may be preceded by first - degree AV block, second - degree AV block, bundle branch block, or bifascicular block . In addition, acute myocardial infarction may present with third - degree AV block . </P> <P> An inferior wall myocardial infarction may cause damage to the AV node, causing third - degree heart block . In this case, the damage is usually transitory . Studies have shown that third - degree heart block in the setting of an inferior wall myocardial infarction typically resolves within 2 weeks . The escape rhythm typically originates in the AV junction, producing a narrow complex escape rhythm . </P>

Third degree av block with ventricular escape rhythm