Monomorphic ventricular tachycardia is a fast heart rhythm that originates in the lower chambers of the heart (the ventricles) and produces the same electrical pattern with each beat. The heart rate typically falls between 150 and 200 beats per minute, and what makes it “monomorphic” is that every heartbeat looks identical on an ECG recording. This distinguishes it from polymorphic ventricular tachycardia, where the electrical pattern shifts and changes from beat to beat. Monomorphic VT can be a brief, well-tolerated episode or a life-threatening emergency, depending on what’s causing it and how long it lasts.
How It Looks on an ECG
On an electrocardiogram, monomorphic VT has four hallmark features: wide QRS complexes (the spiky waveforms that represent each heartbeat are broader than normal), a rate above 100 beats per minute, a regular or near-regular rhythm with only slight beat-to-beat variation, and a consistent electrical axis, meaning the direction of each heartbeat’s electrical signal stays the same. That consistency is the defining trait. In polymorphic VT, the QRS complexes continuously shift in shape and direction, often signaling a more chaotic and immediately dangerous electrical disturbance that can quickly deteriorate into cardiac arrest.
One additional clue doctors look for is atrioventricular dissociation, where the upper and lower chambers of the heart beat independently of each other. When present, this essentially confirms the rhythm is coming from the ventricles rather than from a fast rhythm originating higher up in the heart that merely looks wide on the tracing. In practice, though, this sign can be difficult to spot on a standard ECG.
What Causes It
The most common cause of monomorphic VT is scar tissue in the heart muscle from a previous heart attack. When heart muscle dies and heals, it leaves behind patches of fibrous tissue interspersed with surviving muscle cells. Electrical signals can loop around and through these patches in a self-sustaining circuit, a process called reentry. Think of it like a car stuck in a roundabout with no exit: the electrical impulse keeps circling the scar, firing the ventricles rapidly with each pass. Because the circuit follows the same path every time, each heartbeat looks identical.
Other forms of structural heart disease can create the same kind of scar-based circuits. These include arrhythmogenic right ventricular cardiomyopathy (where heart muscle is replaced by fatty or fibrous tissue), cardiac sarcoidosis (an inflammatory condition that scars the heart), Chagas disease, and repaired congenital heart defects. Any condition that produces fibrosis in the ventricles can set the stage for monomorphic VT through the same reentry mechanism.
Beyond reentry, two other electrical mechanisms can trigger this rhythm. Enhanced automaticity occurs when a group of cells in the ventricles starts firing on its own, faster than the heart’s normal pacemaker. Triggered activity happens when an abnormal electrical aftershock following a normal heartbeat reaches a threshold that sparks a new beat, which then sparks another, creating a rapid chain reaction.
Idiopathic VT in Structurally Normal Hearts
Not all monomorphic VT comes from a damaged heart. In younger, otherwise healthy people, it can arise from specific spots in an apparently normal heart. The most common origin is the right ventricular outflow tract (RVOT), the muscular tunnel that directs blood from the right ventricle into the lungs. People with this form typically experience palpitations, sometimes with short bursts of rapid heartbeats during exercise or stress.
Other recognized sites include the left ventricular outflow tract, the area near the aortic valve, the papillary muscles (small muscular pillars inside the ventricles that anchor the heart valves), and the moderator band, a muscular cord that runs across the inside of the right ventricle. One well-known subtype, called fascicular or verapamil-responsive VT, originates along the heart’s internal wiring (the left bundle branch fascicles) and responds to a specific calcium channel blocker. These idiopathic forms generally carry a much better prognosis than scar-related VT, though they can still cause significant symptoms.
Why It Matters: Risk and Prognosis
Monomorphic VT is not just an electrical curiosity. In people with weakened hearts, it is a strong predictor of serious outcomes. A large study of patients with non-ischemic dilated cardiomyopathy found that a prior episode of sustained VT was independently associated with a more than fourfold increase in the risk of death or need for heart transplantation, and a sevenfold increase in the risk of sudden cardiovascular death, even after accounting for other risk factors like age and ejection fraction.
For context, annual sudden cardiac death rates in patients with reduced ejection fraction have fallen to roughly 2.7 to 3.3 per 100 patient-years thanks to modern heart failure medications. But within that population, those who develop sustained VT face a markedly higher risk. Key factors that independently predict worse outcomes include older age, lower ejection fraction, reduced kidney function, and the occurrence of sustained VT itself.
How It Feels
Symptoms depend on the heart rate, how long the episode lasts, and how well the heart pumps during the episode. Brief runs may cause nothing more than a fluttering sensation in the chest. Longer or faster episodes can produce lightheadedness, chest pain, shortness of breath, or near-fainting. If the heart rate is very fast or the heart muscle is already weak, VT can cause a dangerous drop in blood pressure, loss of consciousness, or cardiac arrest. Some people tolerate episodes surprisingly well, particularly those with idiopathic VT and normal heart function, while others become hemodynamically unstable within seconds.
Treatment Options
Medications
Antiarrhythmic drugs are a mainstay of treatment for preventing recurrent episodes. Amiodarone is the most widely used, typically given at a higher dose initially and then reduced to a daily maintenance dose. Sotalol, a beta-blocker with additional antiarrhythmic properties, is another common choice, though it requires dose adjustment in people with kidney disease and careful monitoring. For the idiopathic fascicular form, a calcium channel blocker can be effective on its own. The choice of medication depends on the underlying cause, heart function, and how well a given drug is tolerated over time.
Catheter Ablation
Catheter ablation is a procedure where a thin wire is threaded through a blood vessel to the heart, and targeted energy (usually radiofrequency heat) is applied to destroy the small area of tissue responsible for the abnormal circuit. For idiopathic monomorphic VT, success rates are high. Studies report successful elimination of the arrhythmia in about 84% of patients, with recurrence rates ranging from 9% to 19% over follow-up periods averaging around two and a half years. For scar-related VT, ablation is more complex because the circuits can be larger and more numerous, but it remains an important option, especially when medications alone don’t control the rhythm.
Implantable Defibrillators
An implantable cardioverter-defibrillator (ICD) doesn’t prevent VT, but it can terminate dangerous episodes within seconds by delivering a shock or a rapid burst of pacing. Current guidelines recommend ICD implantation for patients with ischemic or non-ischemic cardiomyopathy whose ejection fraction is 35% or below. ICDs are also considered for patients who have survived hemodynamically significant VT, meaning episodes that caused dangerously low blood pressure, fainting, or other serious symptoms, regardless of their ejection fraction. In people with structurally normal hearts and idiopathic VT, ICDs are generally not needed because the arrhythmia responds well to ablation or medication and rarely causes sudden death.