Leads I and II demonstrating complete AV block. Note that the P waves are not related to the QRS complexes (PP interval and QRS interval both constant), demonstrating that the atria are electrically disconnected from the ventricles. The QRS complexes represent an escape rhythm arising from the ventricle. Atrial tachycardia with complete A-V block and resulting junctional escape Many conditions can cause<unk><unk>  heart block, but the most common cause is coronary ischemia. Progressive degeneration of the electrical conduction system of the heart can lead to<unk><unk>  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<unk> . An inferior wall myocardial infarction may cause damage to the AV node, causing<unk><unk>  heart block. In this case, the damage is usually transitory. Studies have shown that<unk><unk>  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. An anterior wall myocardial infarction may damage the distal conduction system of the heart, causing<unk><unk>  heart block. Initially demonstrated by animal studies, this is due to a stark reduction in the Kv β-subunit of the voltage-gated K+ channels in the pacemaker cells of the<unk>  junction, causing significantly decreased propagation of ions across gap junctions between cardiac cells and thus prolonging the PR interval. This is typically extensive, permanent damage to the conduction system, eliciting a necessity for a permanent pacemaker to be placed. The escape rhythm typically originates in the ventricles, producing a wide complex escape rhythm.<unk><unk>  heart block may also be congenital and has been linked to the presence of lupus in the mother. It is thought that maternal antibodies may cross the placenta and attack the heart tissue during gestation. The cause of congenital<unk><unk>  heart block in many patients is unknown. Studies suggest that the prevalence of congenital<unk><unk>  heart block is between 1 in 15,000 and 1 in 22,000 live births. Hyperkalemia in those with previous cardiac disease and Lyme disease can also result in<unk><unk>  heart block.
Third-degree atrioventricular block
Second-degree atrioventricular block
First-degree atrioventricular block
Ventricular escape beat
AV nodal reentrant tachycardia
Wandering atrial pacemaker
Re-entry ventricular arrhythmia
Left bundle branch block