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Day 8: The Differential Diagnosis of Wide-QRS Tachycardias

  1. Basic considerations

    1. Wide QRS tachycardias represent either VT or SVT with aberrant conduction.

    2. VT and SVT represent vastly different clinical situations as far as etiology, extent of underlying cardiac disease, treatment, and prognosis.

    3. The following discussion applies to hemodynamically stable patients; unstable patients should have emergent electrocardioversion.

  2. Brugada’s criteria

    1. In 1991, Brugada published a landmark paper on this problem, and his algorithm will be followed here (Brugada P, et al., A New Approach to the Differential Diagnosis of a Regular Tachycardia with a Wide QRS Complex. Circulation, Vol. 83, No. 5, May 1991).

    2. Brugada’s criteria is based on the standard 12-lead ECG, but additional leads and techniques may aide in diagnosis.

  3. Application of Brugada’s criteria (see tree diagram)

    1. The presence and duration of an RS complex in the precordial leads

      1. Any initial R wave followed by an S wave in the precordial leads qualifies for analysis.

      2. Lack of an RS in any precordial lead is highly specific for VT.

      3. An RS interval (defined as the interval between the onset of the R wave and the nadir of the S wave in any precordial lead) greater than 100 msec is highly specific for VT.




    2. AV dissociation

      1. The presence of AV dissociation is highly specific for VT.

      2. AV dissociation can be detected on the standard ECG in about 20% of VT.

      3. Methods for detection of AV dissociation

        1. Examination of the patient may reveal irregular cannon A waves, in the neck veins caused by coincidental simultaneous atrial and ventricular systole.

        2. Standard ECG leads II, III, aVF, and V2 are best for detecting P waves.

        3. Moving one of the chest leads to the V3R position may reveal P waves.

        4. An S5 or "Lewis’ leads" is obtained by placing the right arm lead in the second right interspace and the left arm lead in the suprasternal notch with the ECG machine set to Lead I.




        5. A transesophogeal or intraatrial lead may be necessary to make a definitive diagnosis

        6. Another evidence of AV dissociation is the presence of occasional narrow complex beats in the midst of a wide complex tachycardia. These so-called "capture beats" result from AV nodal transmission of a fortuitously timed supraventricular beat that "captures" the ventricle.

    3. The morphology of the QRS complexes in V1–V2 and V6 (see table)

      1. The first determination is whether the QRS morphology in the precordial leads is a RBBB or a LBBB

      2. If the QRS complexes in V1–V2 and V6 both meet criteria for VT (see diagram), VT is confirmed.

      3. If there is discordance between the criteria for VT in V1–V2 and V6, SVT is strongly implicated. (Day 8-01) (Day 8-02) (Day 8-03) (Day 8-04) (Day 8-05) (Day 8-06) (Day 8-07) (Day 8-08) ...

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