Ventricular tachycardia (VT)
Three or more consecutive ventricular ectopic beats - a run of wide, bizarre QRS complexes faster than, and dissociated from, the underlying sinus rhythm.
Key ECG features
- ✓Three or more consecutive ventricular beats
- ✓Wide, bizarre QRS complexes
- ✓Fast rate
- •T wave deflected opposite the QRS
- ±AV dissociation: sinus P waves march through
- ±Fusion or capture beats at the edges of the run
✓ required · • typical · ± may be present
ECG characteristics
Wide QRS complexes at a fast rate, uniform or varying in shape, with T waves usually deflected opposite to the QRS. Sinus P waves continue independently and march through the run (AV dissociation), and fusion or capture beats may appear at its edges.
This illustration is schematic. Dashed line is a normal rhythm. The grid is not drawn to scale.
Common causes
Primary myocardial disease, but equally myocardial hypoxia, trauma, gastric dilatation-volvulus, splenic disease, sepsis, and electrolyte disturbance. In some breeds it is inherited or breed-associated: arrhythmogenic right ventricular cardiomyopathy in the Boxer, dilated cardiomyopathy in the Doberman Pinscher, and the inherited ventricular arrhythmia of young German Shepherd Dogs. In cats it is less common and usually accompanies cardiomyopathy.
Why it matters
It ranges from brief, non-sustained paroxysms to sustained runs, and at extreme rates degenerates toward ventricular flutter and fibrillation. Fast rates can compromise cardiac output and carry a risk of sudden deterioration, making it one of the more urgent rhythm diagnoses. R-on-T beats within a run add to the concern mainly when there is underlying myocardial disease.
Differentiate from
- Accelerated idioventricular rhythmMuch the same picture at a slower rate. Counting the rate is usually what distinguishes them, and it changes the urgency.
- Supraventricular tachycardiaA supraventricular rhythm conducted with bundle branch block is also wide. Look for a P wave in front of every complex.
- Ventricular escape rhythmEscape complexes are equally wide but arrive late and slowly, rescuing a failed pacemaker; ventricular tachycardia arrives early and fast.
- Bundle branch blockA supraventricular rhythm conducted with a blocked bundle branch is equally wide. When the underlying rhythm is sinus, a P wave before every complex settles it; in atrial fibrillation with bundle branch block there is no P wave to find, and the irregularly irregular spacing is the clue.