A patient after thrombolysis for MI develops missed beats. ECG shows?
Correct Answer: Mobitz II heart block
Description: Ans. (b) Mobitz II heart block.In 30 seconds you get in the examination for this rhythm strip compare the PR interval preceding the missed/arrow marked qRS complex with the subsequent one. If both the preceding and subsequent PR intervals are equal then, it is diagnostic of Mobitz II heart block. This usually occurs secondary to septal MI and needs pacing.In case the PR interval preceding the missed beat is longer in duration than the PR interval subsequent to the missed beat, it is diagnostic of Mobitz 1 heart block.* Mobitz II is usually due to failure of conduction at the level of the His-Purkinje system (i.e. below the AV node).* While Mobitz I is usually due to a functional suppression of AV conduction (e.g. due to drugs, reversible ischemia), Mobitz II is more likely to be due to structural damage to the conducting system (e.g. infarction, fibrosis, necrosis).* Patients typically have a pre-existing LBBB or bifascicular block, and the 2nd degree AV block is produced by intermittent failure of the remaining fascicle ("bilateral bundle-branch block").* In around 75% of cases, the conduction block is located distal to the Bundle of His, producing broad qRS complexes.* In the remaining 25% of cases, the conduction block is located within the His Bundle itself, producing narrow qRS complexes.* Unlike Mobitz I, which is produced by progressive fatigue of the AV nodal cells, Mobitz II is an "all or nothing" phenomenon whereby the His-Purkinje cells suddenly and unexpectedly fail to conduct a supraventricular impulse.* Ihere may be no pattern to the conduction blockade, or alternatively there may be a fixed relationship between the P waves and qRS complexes, e.g. 2:1 block, 3:1 block.
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