Ventricular tachycardia (VTach) is generally a regular rhythm, but the answer depends on the type. Monomorphic VTach, the most common form, produces a steady, regular pattern on an ECG with identical-looking beats. Polymorphic VTach, a less common and more dangerous form, is irregular. Understanding which type you’re looking at changes the clinical picture significantly.
Monomorphic VTach: Regular Rhythm
The classic form of VTach is monomorphic, meaning every heartbeat originates from the same abnormal spot in the lower chambers of the heart. Because there’s a single source generating each beat, the electrical signal follows the same path every time. On an ECG strip, this produces wide QRS complexes (the tall spikes representing each heartbeat) that look identical from beat to beat, marching along at a regular, predictable interval. The heart rate is typically 100 beats per minute or faster.
This regularity is one reason VTach can be tricky to distinguish from another rhythm called supraventricular tachycardia (SVT) with aberrant conduction, which can also appear as a regular wide-complex tachycardia. The general rule in emergency medicine is that any wide-complex tachycardia (QRS of 0.12 seconds or wider) should be treated as VTach until proven otherwise, since VTach is far more dangerous and far more common in adults with heart disease.
Polymorphic VTach: Irregular Rhythm
Polymorphic VTach breaks the regularity rule. Instead of one abnormal focus firing in the heart’s ventricles, multiple sites are generating electrical signals. The result is a rhythm where the QRS complexes change shape from beat to beat and the intervals between them vary. This is an irregular rhythm, and it signals much more unstable electrical activity in the heart.
The most well-known form of polymorphic VTach is torsades de pointes, French for “twisting of the points.” On an ECG, the peaks of the heartbeat complexes appear to rotate around the baseline, creating a distinctive twisting pattern. Torsades is associated with a prolonged QT interval, which is a measurement of how long the heart’s electrical system takes to reset between beats. This form of VTach can rapidly deteriorate into ventricular fibrillation, a completely chaotic rhythm that causes cardiac arrest.
How to Tell Them Apart on an ECG
The key visual difference is consistency. In monomorphic VTach, the beats look like carbon copies of each other. Wide, uniform, evenly spaced. In polymorphic VTach, the beats shift in height, shape, and spacing, giving the strip a chaotic, undulating appearance.
Several other ECG features help confirm a VTach diagnosis regardless of type:
- Very wide QRS complexes. VTach typically produces beats wider than 0.12 seconds, and monomorphic VTach often exceeds 0.16 seconds.
- AV dissociation. The upper chambers (atria) and lower chambers (ventricles) beat independently of each other. When visible, this is one of the strongest confirmations of VTach. It’s only seen in a small percentage of ECG tracings because the fast ventricular rate makes the atrial signals hard to spot.
- A dominant R wave in lead aVR. A diagnostic algorithm using just this single ECG lead has a reported accuracy of about 91.5% for distinguishing VTach from SVT with aberrancy.
Why the Distinction Matters
Monomorphic VTach, while serious, can sometimes be tolerated briefly. Some people remain conscious and hemodynamically stable, experiencing palpitations or lightheadedness without immediately collapsing. When stable, this rhythm can be treated with a controlled electrical shock (cardioversion) delivered under sedation.
Polymorphic VTach is far less forgiving. The unstable electrical activity means the heart is pumping inefficiently or barely pumping at all. It frequently degenerates into ventricular fibrillation. Someone in polymorphic VTach is much more likely to lose consciousness quickly and require immediate defibrillation.
Both types can cause symptoms ranging from palpitations to full cardiac arrest. Sustained VTach of either form, meaning it lasts more than 30 seconds or causes hemodynamic collapse before that point, is almost always symptomatic and requires urgent treatment. Pulseless VTach, where the heart is beating too fast to actually move blood, is treated the same as ventricular fibrillation: immediate defibrillation.
The Short Answer
If someone asks whether VTach is regular or irregular without specifying the type, the standard answer is regular. That’s because monomorphic VTach is the more common form and the one most people encounter in textbooks, exams, and clinical practice. But the complete answer is that it depends on the subtype. Monomorphic VTach is regular with uniform beats. Polymorphic VTach is irregular with constantly changing beats. Knowing which one you’re dealing with changes both the urgency and the treatment approach.