Echocardiography-Guided Arrhythmic Risk Prediction in the Long QT Syndrome.

A 31-year old man presented to the cardiology emergency department with palpitations. An electrocardiogram (ECG) obtained showed polymorphic ventricular tachycardia [Figure 1a]. The patient developed cardiac arrest in the ER and was resuscitated with synchronized direct current cardioversion. A baseline ECG showed prolonged QT (corrected QTc 641 msec by Bazett's formula) [Figure 1b].

Figure 1

(a) ECG showing VT; (b) Baseline ECG showing Long QT; (c) Electromechanical Window on Echocardiography

Echocardiography revealed no structural abnormality. However, the electromechanical window (EMW) was found to be negative with a value of − 49 ms [Figure 1c]. Coronary angiography and cardiac magnetic resonance imaging were normal. An implantable cardioverter-defibrillator was implanted and the patient was discharged for routine follow-up.

The electromechanical window refers to the difference between mechanical and electrical systole in the same heart beat. Normally, mechanical systole is longer than electrical systole, resulting in the EMW being a positive number. In patients with long QT syndrome (LQTS), the EMW is negative as the electrical systole becomes prolonged.[1]

Mechanical systole is calculated from beginning of QRS to aortic valve closure. Electrical systole is calculated as the QT interval from the ECG for the same beat. EMW has been shown to outperform QTc in predicting symptomatic patients. Furthermore, the measurement has shown good reliability among different operators. Exercise-induced greater negativity of the EMW and drug response as judged by reduced negative values (i.e., more positive values) may provide assessment of arrhythmic risk in patients with LQTS.[23]

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Conflicts of interest

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