What Are the ECG Characteristics of Sustained Ventricular Tachycardia?

Sustained ventricular tachycardia (VT) is a serious cardiac arrhythmia that originates in the ventricles and can lead to hemodynamic instability if not promptly addressed. The electrocardiogram (ECG) plays a crucial role in identifying this condition and differentiating it from other types of tachyarrhythmias.

Key ECG Features of Sustained Ventricular Tachycardia

1. Rapid Heart Rate with Wide QRS Complexes

One of the hallmark signs of sustained VT is a heart rate typically ranging from 150 to 250 beats per minute. This rapid rhythm is accompanied by wide QRS complexes on the ECG, which reflect abnormal electrical conduction through the ventricles.

2. Atrioventricular Dissociation

In sustained VT, the atria and ventricles beat independently of each other, a phenomenon known as AV dissociation. This means that the P waves, which represent atrial depolarization, are not related to the QRS complexes, which indicate ventricular depolarization. Additionally, the T wave typically appears in the opposite direction of the main QRS deflection, a classic feature of ventricular tachycardia.

3. Normal or Prolonged QT Interval

The QT interval, which represents the time for ventricular depolarization and repolarization, may appear normal or slightly prolonged in patients with sustained VT. This characteristic can help clinicians distinguish VT from other supraventricular tachycardias that may present with a normal QT interval.

4. Presence of Fusion Beats and Ventricular Capture Beats

Another distinguishing ECG feature of sustained VT is the presence of fusion beats and ventricular capture beats. These occur when the normal sinus impulse briefly conducts to the ventricles, resulting in partial or full capture of ventricular activation. A fusion beat represents a mixture of ventricular and sinus-originated activation, providing further evidence of an underlying ventricular tachycardia.

Recognizing these ECG patterns is essential for timely diagnosis and appropriate management of sustained ventricular tachycardia, especially in emergency settings where rapid intervention can be life-saving.