Inferior Infarction: Blocks and Arrhythmias
Report:
Sinus tachycardia 122/min
Second degree AV block, unspecified
Junctional escape beats and rhythm 46/min
Non-phasic aberrant conduction
Acute inferior infarction
Comment:
It is said that the presence of 2o AV block in inferior infarction denotes additional, independent disease of the LAD artery57. This was certainly the case here: the left circumflex (infarct-related) artery was completely occluded, with 80% lesion in the LAD artery; the RCA was small, non-dominant, and had only a 30% narrowing. This anatomy was subsequently deemed inoperable.
The AV block is reported as unspecified only because there are no consecutive conducted P waves; the three conducted (with 1o AV block) sinus beats could be described as capture beats in AV dissociation with interference. They are the interference. In this setting, however, the block is almost certainly AV nodal (rather than ventricular) and would show Wenckebach periodicity at another time. It did that, in the tracing below (Fig 80a), with bigeminy due to 3:2 conduction.
The junctional beats are slightly different (short and stubby in the rhythm strip, terminating long cycles), presumably due to a different activation front from a junctional focus. This constitutes what Schamroth called non-phasic aberrant conduction â non-phasic because it des not depend on long-short cycle sequences.
In the next 8 pages, included here for teaching purposes, the patient shows typical blocks and rhythms of inferior infarction: 3o AV block, 2:1 AV block, 1o AV block, AF and flutter with 3o AV block and conducted, and eventual sinus rhythm with only borderline 1o block.
80a. Wenckebach bigeminy.
80b. AV dissociation due to 3o AVB. Junctional rhythm is slightly accelerated at 69/min, but sinus tachycardia would still be expected to make some captures if it could. AVB, not AJR, stops it.
80c. 1o AVB with PR interval 0.40â. This is where Bix rule should be considered: is another P wave hiding half-way, in the QRS complex? Unlikely in this case: the atrial rate would have to be 168/min if 2:1 AVB were present. 80d. 2:1 AVB. 80e. Atrial flutter about 280/min with 3o AVB and junctional escape rhythm 45/min. There is no fixed F-QRS relationship..
80f. Atrial fibrillation with 3o AVB and junctional escape rhythm 52/min.
80g. Atrial flutter 280/min with 4:1 AVB. The F-QRS relationship is constant.
80h. Atrial fibrillation with ventricular response 65/min. The injured AV node plays the role normally reserved for digitalis in controlling the ventricular rate.
80i. Sinus rhythm 73/min with PR interval just over 0.20â 13 days after admission.
81. 66 year old lady with chest pain.
Collections
Tags
sinus tachycardia second degree av block AV block unspecified junctional escape beats Myocardial infarction left anterior descending artery disease markers av block in inferior mi AV dissociation with interference Bigeminy 3-2 av block Aberrant conduction non-phasic inferior mi Atrial flutter AF
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