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.
IDIOPATHIC POSTERIOR FASCICULAR TACHYCARDIA? This tracing also has features of Posterior Fascicular Tachycardia, a type of ventricular tachycardia sometimes called Belhassen-type Tachycardia. These include:
* Borderline QRS width. Fascicular tachycardia usually has a QRS duration of .10 - .14 seconds. (100-140 ms), narrower than other types of VT.
* Short RS interval in the precordial leads. The time from onset of the r wave to the nadir of the S wave appears to be between .04 sec. and .06 sec. The RS interval is usually .10 sec. (100 ms) or more in other types of VT.
* A RBBB pattern, with additional left anterior fascicular block (LAFB or LAHB) pattern. While not typical for RBBB in all the precordial leads, V1, V6 and Lead I suggest a RBBB pattern.
* Left axis deviation, indicating that, if this is fascicular tachycardia, it is arising from the posterior fascicle.
Fascicular tachycardia is an idiopathic tachycardia usually occurring in young, healthy patients, most often male. There is a lack of structural heart disease, and the tachycardia usually occurs at rest. The mechanism is re-entry of an ectopic beat from the left ventricle. It often responds to the use of Verapamil, rather than the usual drugs used for SVT and VT.
BOTTOM LINE When faced with a patient with wide-complex tachycardia, the more information you have, the better. That includes patient history, family history, medications, signs and symptoms. A 12-lead ECG may prove to be invaluable, unless the patient is so severely unstable that there is no time. It can be very difficult to diagnose a WCT from these tools, and electrophysiology studies may prove beneficial.
ALWAYS TREAT WCT AS VENTRICULAR TACHYCARDIA UNTIL IT IS PROVEN TO BE SOMETHING ELSE.
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