ECG Review

A WCT with 'P' Waves?

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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.

Scenario: Interpret the 12-lead ECG shown above obtained from a hemodynamically stable patient with underlying heart disease and new-onset palpitations. Despite the apparent QRS widening — is this sinus tachycardia (arrow pointing to 'P waves' in lead II)?

Interpretation: The most important consideration in this case is that the patient is hemodynamically stable despite the tachycardia. This means that there is at least a moment of time to contemplate what the rhythm is likely to be. There looks to be a regular wide complex tachycardia (WCT) at a rate of about 150/minute. Although it is possible that a WCT may be supraventricular, the diagnosis of ventricular tachycardia (VT) is statistically far more likely. Despite the arrow in lead II, there are no definite P waves on this tracing. Instead, simultaneously obtained lead I suggests that the pseudo-P upright deflection under the arrow corresponds to the initial portion of the QRS complex. This is confirmed by the markedly widened QRS complexes present in all other leads. The rhythm is ventricular tachycardia.

Important points to emphasize from this case include the following:

• VT is by far the most common cause of a WCT when there is either no atrial activity or uncertain atrial activity. Statistical odds that a WCT without P waves is VT rather than supraventricular tachycardia with preexisting bundle branch block or aberrant conduction exceed 90% when the patient in question has underlying heart disease.

• Not all patients in VT immediately decompensate. Some may remain hemodynamically stable despite ongoing VT for hours, or even days.

• Obtaining a 12-lead tracing during tachycardia may be invaluable for honing in on the etiology of a tachycardia. In this case, there are a number of clues that overwhelmingly suggest VT as the diagnosis. These include: 1) marked QRS widening in all other leads; 2) bizarre QRS axis during the tachycardia (extreme left axis deviation); 3) bizarre QRS morphology (not resembling any form of organized bundle branch block); 4) markedly negative QRS complex in lead left-sided V6 (which virtually always has more than a tiny r wave of positive activity); and 5) concordance of the QRS in precordial leads (all precordial lead QRS complexes are predominantly negative). Bottom line: 12 leads are better than one — and a WCT without definite P waves should always be presumed to be VT until proven otherwise, regardless of whether the patient is hemodynamically stable.