![]() ![]() Other causes include hypothyroidism, Lyme disease, endocarditis, sarcoidosis, systemic inflammatory diseases, and genetic channelopathies.Īsymptomatic, low grade AV block (1st degree or type I second degree) is often an incidental finding, usually reflecting prior ischemic disease or myocyte damage. Medications such as beta-blockers, calcium channel blockers, digoxin, and antiarrhythmic agents such as amiodarone may also be responsible for conduction delays. However, it is important to remember that any AV block may be due to myocardial ischemia or infarction, particularly of the inferior or anterior walls. Additionally, 1st degree AV block may be the result of high vagal tone in healthy individuals and is not necessary pathologic. Lenegre-Lev syndrome, also known as senile degeneration, is an age related fibrosis of the conduction system leading to AV block. The etiology of AV block is quite variable. Conversely, a wide QRS complex suggests the block is infranodal. If the escape rhythm has a narrow QRS complex, again the origin is at or near the AV node. In this case the atrial and ventricular impulses are not synchronous, and the atrial rate is faster than the independent ventricular rate. Third degree AV block occurs when P waves are not conducted to the ventricles and an ectopic, slow escape rhythm is present. A narrow QRS complex suggests nodal arrhythmia and likely type I block, while a wide complex indicates an infranodal location and type II block. This block is commonly infranodal.īe mindful of 2:1 block, which may be either type I or type II second degree AV block. Type II second degree AV block may present as a single nonconducted P wave or a repetitive pattern of nonconduction (2:1, 3:1, etc.). Type II second degree AV block occurs in the setting of a constant PR interval with sudden nonconduction of a P wave. Type I second degree AV block involves progressive PR lengthening until the QRS “drops out,” indicating the previous P wave was not conducted to the ventricles. It is not a true block but instead is just a delay in conduction of the atrial impulse, resulting in an increased PR interval of greater than 200 msec. First degree AV block is a bit of a misnomer. ![]()
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