Wide QRS complex tachycardias

Associate Editor-In-Chief Jiwon Kim

Differential Diagnosis of Tachycardia with Wide QRS Complex

 * 1) A regular tachycardia with a rate of 120 to 200 BPM with a QRS duration of .12 seconds or longer may be due to:
 * 2) * Paroxysmal VT
 * 3) * Supraventricular tachycardia with abnormally wide QRS
 * Sinus tachycardia
 * SA nodal reentrant tachycardia
 * Paroxysmal atrial tachycardia
 * Intraatrial reentrant tachycardia
 * Atrial flutter with 2:1 conduction and occasional 1:1 conduction
 * AV nodal reentrant tachycardia
 * Automatic junctional tachycardia
 * AV reentrant tachycardia using a bypass tract

Differential Diagnosis of Wide QRS Complexes

 * 1) Aberrant ventricular conduction
 * 2) Preexisting left or right bundle branch block
 * 3) Preexisting nonspecific IVCD
 * 4) Antegrade conduction through the bypass tract in patients with WPW

Clues to the Diagnosis of VT

 * 1) Morphology of Premature Beats During Sinus Rhythm:
 * 2) * Previous EKG may show preexisting IVCD.
 * 3) * If PVCs are present, and if the morphology of the arrhythmia is the same, then it is likely to be ventricular in origin.
 * 4) * If there are PACs with aberrant conduction, then the origin of the arrhythmia may be supraventricular.
 * 5) Onset of the Tachycardia:
 * 6) * Diagnosis of SVT made if the episode is initiated by a premature P wave.
 * 7) * If the paroxysm begins with a QRS then the tachycardia may be either ventricular or junctional in origin.
 * 8) * If the first QRS of the tachycardia is preceded by a sinus p wave with a PR interval shorter than that of the conducted sinus beats, the tachycardia is ventricular.
 * 9) AV Dissociation:
 * 10) * Although is highly suggestive of VT, it may also be seen in junctional tachycardias with retrograde block.
 * 11)  Morphology of the QRS Complexes and QRS Axis:
 * 12) * 80 to 85% of aberrant beats have a RBBB pattern, but ectopic beats that arise from the LV have a similar morphology.
 * 13) * The finding of a positive or negative QRS complex in all precordial leads is in favor of ventricular ectopy.
 * 14) * A QRS duration of > .14 seconds (A Wellens criterion)
 * 15) * Left axis deviation (A Wellens criterion)
 * 16) * A monophasic or biphasic RBBB QRS complex in V1. But none of their patients with SVT had a preexisting RBBB. Therefore, this finding is of limited importance. (A Wellens criterion)
 * 17) Akhtar studied 150 patients with a wide complex tachycardia. The following were helpful in the diagnosis of VT:
 * 18) * all patients with VT had a QRS duration > 120 msecond.
 * 19) * QRS > .14 with a RBBB, QRS > .16 with LBBB.
 * 20) * V1 - V6 all show a positive deflection.
 * 21) * QRS axis between -90 and + 180 degrees.
 * 22) * The QRS complexes have a LBBB but the QRS axis is rightward.
 * 23) * In patients with preexisting bundle branch block, there is a change in the QRS pattern during the tachycardia.
 * 24) Capture beats:
 * 25) * Rare, but one of the strongest pieces of evidence in favor of VT.
 * 26) * Aberrancy rarely follows a beat of such short cycle length.
 * 27) Fusion beats:
 * 28) * Rare but also strongly suggests VT.
 * 29) Vagal Stimulation:
 * 30) * VT is not affected by vagal stimulation.
 * 31) * May terminate reentrant arrhythmias
 * 32) Atrial pacing:
 * 33) * A pacing wire is placed in the RA and the atrium is stimulated at a rate faster than the tachycardia.
 * 34) * If ventricular capture occurs and the QRS is normal in duration, then one can exclude the possibility of aberrant conduction.
 * 35) His bundle recording:
 * 36) * In SVT, each QRS is preceded by a His bundle potential.
 * 37) * In VT there is no preceding His deflection.
 * 38) * The retrograde His deflection is usually obscured by the much larger QRS complex.

Differential Diagnosis of Wide QRS Complex Tachycardia

 * 1) The following favor the diagnosis of VT:
 * 2) * AV dissociation
 * 3) * RBBB with QRS > .14, or LBBB with QRS > .16
 * 4) * QRS axis in RUQ between -90 and +180 degrees
 * 5) * Positive QRS in all the precordial leads (V1-V6)
 * 6) * LBBB with a rightward axis
 * 7) * LBBB with the following QRS morphology
 * R wave in V1 or V2 > 0.03 second
 * any Q wave in V6
 * Onset of the QRS to nadir of the S wave in V1 > 0.06 seconds
 * Notching of the S wave in V1 or V2
 * 1) * Capture beats, fusion beats
 * 2) * QRS morphology identical to that of premature ventricular beats during sinus rhythm

Clinical Correlation

 * 1) Most patients with VT have organic heart disease.
 * 2) Post MI VT is associated with a doubling of the risk of death.
 * 3) This was an a risk factor independent of poor LV function.
 * 4) VT can be seen with reperfusion, but an accelerated idioventricular rhythm is more common.
 * 5) Digoxin intoxication is a common cause. Other antiarrhythmics, phenothiazines, TCAs, and pheochromocytoma may also cause this.
 * 6) Cardiac catheterization, DC countershock, following repair of congenital lesions, and the hereditary QT prolongation are all associated with VT.