ECG Review

Why is the Rhythm VT?

By Ken Grauer, MD, Professor Emeritus in Family Medicine, College of Medicine, University of Florida

Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.

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Scenario: The ECG shown above was obtained from a patient whose blood pressure was dropping. How many reasons can you cite to support a diagnosis of ventricular tachycardia (VT)?

Interpretation: The 12-lead ECG in the Figure shows a regular wide complex tachycardia (WCT) rhythm at a rate of ~180/minute. Sinus P waves are absent. The rhythm is sustained VT and the patient is in need of immediate electrical therapy (synchronized cardioversion of defibrillation). Many reasons can be cited to support definitive diagnosis of sustained VT. These include:

1) Statistically, at least 80% of all regular WCT rhythms of uncertain etiology are VT. The likelihood of VT increases to more than 90% if the patient is middle-aged or older (especially if the patient has underlying heart disease).

2) Although on occasion regular WCT rhythms may be due to a supraventricular etiology with either preexisting bundle branch block or aberrant conduction — VT must always be assumed until proven otherwise, because it is a potentially life-threatening arrhythmia.

3) Extreme axis deviation is present. Mild-to-moderate left or right axis deviation may be seen with supraventricular rhythms. However, total negativity in either lead I or lead aVF suggests extreme axis deviation, and is virtually diagnostic of VT.

4) The QRS complex is both markedly widened (to over 0.16 second in many leads) — and the QRS is lacking in organized morphology (which we convey by describing the QRS as “ugly”). Both features are highly suggestive of VT. Aberrant conduction most often manifests a more organized QRS morphology that is consistent with some type of conduction defect (left or right bundle branch block with or without hemiblock).

5) There is ECG evidence of delayed initial ventricular activation. The presence of an r-to-S-nadir of more than 0.10 second in one or more precordial leads is highly suggestive of VT. This is best seen in lead V5.

6) Always assume VT until proven otherwise. Treat the patient accordingly.

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