PAT with Block: Pacemaker Lead
Report:
Atrial tachycardia 138/min
Second degree AV block, Möbitz 1; 2:1 & 3:2 block
Right atrial electrode recording (bottom strips)
Comment:
The question is a "trick" one, designed to implicate the spurious change in the heart rate in the patient's progressive hypotension. The tachycardia is in fact virtually unchanged throughout, as is the degree of AV block and the consequent ventricular rate. The relative size of the atrial and ventricular complexes is reversed in the atrial (pacemaker) lead.
The tachycardia shown is an autonomous one, not abolished by atrial pacing (the presence of AV block alone is usually sufficient evidence against a reentry mechanism). The atrial pacemaker was inserted for episodes of junctional bradycardia observed on admission. The patient was later given temporary AV sequential pacing (Fig 15a). It did not work as such during the PAT with block and later the patient did not need any pacing at all.
The real reason for âprogressive hypotensionâ should be familiar to all those working in critical care areas: the patient was given extra sedation for the procedure! It should rarely be necessary, butâ¦
Fig 15a. Temporary AV sequential pacing, several hours later. Not a great idea with PAT with block. There is no evidence of atrial capture in the top strip; there may be occasional one in the lower strips, hæmodynamically worthless. Right ventricular pacing in the two lower strips did improve the cardiac output through increased heart rate without concomittant rise in pulmonary pressure.
Fig 16b. Reversion to sinus tachycardia 110/min, with variable Wenckebach block and pacemaker escape beats and rhythm taking over when AV block increases beyond 2:1. Top strips also, incidentally, demonstrate the diagnostic value of narrow capture beats proving the fat beats are of ventricular origin. Such proof is of course de trop in this case.
Fig 16. 73 year old man with acute inferior infarction. The ectopic beats present are different from sinus beats, but less so than they look.
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