V tach is identified by: wide QRS complexes (>.12 seconds), rate faster than 100 bpm. In MONOMORPHIC V tach, all QRS complexes look alike. There are other mechanisms of wide-complex tachycardia, but they can be difficult to differentiate from a single rhythm strip. All WCT should be treated as V tach until proven otherwise.
This ECG is from a man who was experiencing palpitations and light-headedness with near-syncope. On first look, you will see a wide-complex tachycardia (WTC) with a rate around 240 per minute. It is difficult to assess for the presence of P waves because of the rate and the baseline artifact.
The differential diagnosis of WCT includes ventricular tachycardia and supraventricular tachycardia with aberrant conduction, or interventricular conduction delay (IVCD). We should ALWAYS consider VENTRICULAR TACHYCARDIA first. If the patient is an older adult with structural heart disease, WCT almost always proves to be VT.
ABERRANT SVT? In the setting of SVT with wide QRS, the most common aberrancy is right or left bundle branch block. This ECG could be said to have a “RBBB” type pattern in V1, rSR’ and in Lead I and V6 with a wide S wave. However, the other precordial leads do not have a RBBB pattern.
VENTRICULAR TACHYCARDIA? There are some features of this ECG that favor the diagnosis of VENTRICULAR TACHYCARDIA (VT). They include, but are not limited to:
* Regular, wide QRS complexes, about .14 seconds in this ECG, but varies because of difficulty in measuring the beginning and end of the QRS in each lead. The artifact obscures the exact points of beginning and ending. The QRS complexes, especially from V2 leftward, are very “ugly”, and don’t resemble patterns we would expect with bundle branch block.
* Horizontal plane axis extremely abnormal: Leads II, III, and aVF are negative and aVR and aVL are positive. The biphasic Lead I indicates a nearly vertical axis at around – 90 degrees.
* There is “almost” precordial concordance, but V1 is biphasic.
Unfortunately, we do not see capture beats or fusion beats, which would secure the diagnosis of VT. Disassociated P waves would also be a sure sign of VT, but the artifact in this ECG makes it impossible to say whether there are P waves.
This wide-complex tachycardia is ventricular tachycardia. Along with the wide QRS and the fast rate, features which favor a diagnosis of VT over BBB include: backwards (extreme right) QRS axis, negative QRS in V6, and an apparently monophasic QRS in V1, as opposed to the rSR' pattern of right bundle branch block.
Remember, ALL wide-QRS tachycardias should be treated as V Tach until proven otherwise, as it is a life-threatening arrhythmia. Factors which lower cardiac output during V Tach include: Fast rate, wide QRS, and lack of P wave preceding the QRS. The sudden severe lowering of perfusion that usually accompanies V Tach can lead to rapid deterioraton and ventricular fibrillation.
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.
INTERPRETATION: Ventricular tachycardia (rate about 163/min) presumably originating from the left ventricle (LV).
Overwhelming evidence that this is ventricular tachycardia are as follows:
1.) The ventricular tachycardia is apparently dissociated from a sinus tachycardia at a somewhat slower rate of about 123/min (best seen in leads V1 and aVL; vertical arrows). While not nearly as clinically significant as those types of double tachycardia caused by digitalis intoxication, this example might technically qualify as a form of “double tachycardia” since both the upper and lower chambers of the heart are exceeding a rate of 100/min.
2.) The duration of the QRS interval is so-called “wide-wide” (i.e., > 0.14s) at about 0.19s to 0.20s.
3.) The predominantly negative rS complex in Lead I and wholly negative QS complex in aVF indicate an axis of roughly about -120 and would place it in the right upper quadrant (i.e., “No-Man’s-Land” or “N-M-L”). This is suggestive of an apical origin of the tachycardia.
4.) Brugada criterion # 1: There are no RS complexes in any of the V leads (here they’re either qR or QS complexes.) Brugada pointed out that if none of the V leads contained a diphasic RS complex, then there was no need for any further analysis, the tachycardia was unequivocally ventricular in origin. 2
5.) The presence of a monophasic QS complex in V6 is more diagnostic of ventricular tachycardia than just a rS complex; especially if associated with a QRS complex in V1 that is predominantly positive. By Dr. Marriott’s estimation, this combination only occurs in about 20% of all left ventricular tachycardias (LVT).
6.) Cogent evidence arguing against this being the result of conduction over an accessory pathway are threefold:
a. The wholly negative QS complexes from V4-6 are also suggestive of an apical origin of the tachycardia. Since all accessory pathways enter the ventricles at their base, accessory pathway conduction is effectively excluded; and . . . 1
b. . . . a qR complex in any of the five leads, V2-6 (here in V2-3) also excludes preexcited (W-P-W) tachycardia; and . . . 1
c. . . . the presence of more QRS complexes than P-waves (because in any form of preexcited tachycardia, the atria are involved in every beat). 1
7.) The QRS complex in V1 is not a monophasic R-wave. Rather it is a diphasic qR complex with very subtle notching / slurring on the downstroke (oblique arrow) of the R-wave (i.e., so-called taller left “rabbit-ear” equivalent.)
8.) The q-waves in V1-3 are superficially mimicking the negative component (i.e., nadir) of an atrial flutter wave but right-sided chest leads do not usually show the typical “saw-tooth” pattern so often seen in inferior leads II, III, and aVF. Atrial flutter waves in V1 usually take on the appearance of little positive “P-like” waves. What looks like a retrograde atrial impulse immediately following a QRS complex in V4 is actually part of the QRS complex itself.
References / Sources.
1.) Marriott, HJL. Emergency Electrocardiography. Naples, Fl.: Trinity Press, 1997, p. 60 - 71.
2.) Nelson's EKG Site: http://nelsonsekgsite.com/
All our content is FREE & COPYRIGHT FREE for non-commercial use
Please be courteous and leave any watermark or author attribution on content you reproduce.