An Atrioventricular Block occurs when the signal is delayed or blocked while transiting through the heart. This is generally due to damage to the heart's conduction system and can be idiopathic, or the result of damage from ischemic heart disease (heart attacks) or diseases (cardiomyopathies) or inflammation (myocarditis).
A First Degree Atrioventricular block occurs when the PR Interval is longer than .2 seconds (a normal PR Interval is between .12 and .2 seconds), but each P-wave (atrial contraction) has a following QRS complex (ventricular contraction).
A Second Degree Type I Atrioventricular Block occurs when the PR Interval becomes progressively longer until the signal does not pass, resulting in a dropped beat. The rhythm then returns to a short PR interval, lengthening again until dropped.
A Second Degree Type II Atrioventricular Block occurs when the PR interval is consistent, but beats are dropped irregularly.
A Third Degree Atrioventricular Block occurs occurs when there is no pattern between P-waves and ventricular contractions. P-waves occur at their regular rate, with ventricular escape beats interspersed.
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