Xylocaine Tachycardia

Report:

Sinus tachycardia 114/min (middle strip)

SVEBs

Blocked, in bigeminy (top)

Aberrantly conducted, in bigeminy (bottom)

Comment:

Xylocaine has some atropinic effect and may have facilitated AV conduction, impairing at the same time the intraventricular conduction. Thus the blocked atrial ectopics are now conducted across the AV node, but with incomplete and complete LBBB aberrancy in the ventricles. More graded variation in the degree of aberrancy is seen below (Fig 32a). This case is in some ways obverse to other cases in this collection where Xylocaine abolished the intraventricular conduction altogether, causing bradycardia24 or asystole25. Xylocaine is thus one of the agents that can, however rarely, either double or halve the ventricular rate in the presence of bigeminal SVEBs in a steady state. True sinus rate without the SVEBs is seen at the beginning of the strip in Fig 32a: about 116/min. The SVEBs, being premature, slow it down.

Fig 32a. The fourth P wave is a P’, initiating bigeminy with variable aberrancy. The patient eventually reverted to blocked SVEBs in bigeminy. Fig 33. Asymptomatic 60 year old man admitted with ECG evidence of “subendocardial” infarction (as noted on the strip, many years ago) and treated with propranolol and nitrates.