Dawn's picture

This ECG was donated to the ECG Guru by Brent Dubois, and was originally published on the FaceBook page, Paramedic Tips & Tricks.  We published it to this site three years ago, but believe it should be shown again, as it is somewhat rare to catch a good-quality 12-Lead ECG of an implanted cardioverter-defibrillator pacemaer using overdrive pacing to terminate a ventricular tachycardia.  Most of our examples have been rhythm strips.

In this strip, we see the patient in ventricular tachycardia (V tach) at a rate of about 190 / minute.  The ICD, in response to the fast rate, delivers a short burst of even faster paced beats.  The physological rule in the heart is, "the fastest pacemaker controls the heart".  Once the pacemaker has terminated the V tach, it paces at a much slower rate.  It is pacing the atria, and the conduction system is intact, allowing the impulse to travel normally through the ventricles.  If the sinus node is able to "outpace" the slower paced rhythm, the heart will resume a sinus rhythm.

This is called "overdrive pacing" and is done automatically by an ICD that is programmed to do so.  Overdrive pacing can also be accomplished by a temporary transvenous pacer or transcutaneous pacemaker.  

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ekgpress@mac.com's picture

     NIce description by Dawn of AntiTachycardia Pacing to convert VT in this patient with an ICD. Since Dawn described functioning of the Anti-Tachycardia device  I'll just comment briefly on the rhythm before the device was activated. 

  • We can be 100% certain that the initial rhythm is VT. It is RARE that one is able to be this certain about anything  but reasons why I am so certain are: i) There is a very wide and "ugly" QRS complex in the 6 limb leads (being "ugly" is another way of saying not resembling any morphology consistent with aberration); ii) There is extreme axis deviation (ALL negative QRS in each of the inferior leads); iii) the QRS is ALL upright in lead aVR (virtually 100% specific for VT!); and iv) Knowing this patient has an ICD and is in a regular and very wide tachycardia without P waves makes the odds >>90% that this is VT even before you look at the tracing.

For those wanting review of the criteria to distinguish between SVT vs VT - Please check out my ECG Blog #42 -


Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

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