Monomorphic Ventricular Tachycardia (MVT) is a serious, rapid heart rhythm originating in the ventricles, the lower chambers of the heart. The term “monomorphic” refers to the uniform appearance of electrical signals on an electrocardiogram, indicating the rhythm comes consistently from a single, abnormal focus. This fast, regular rhythm prevents the ventricles from filling properly, severely reducing the heart’s ability to pump blood effectively.
The underlying cause of MVT is often scar tissue from previous heart events, such as a heart attack, or conditions like cardiomyopathy. This damaged tissue creates an electrical short-circuit, or re-entry loop, that triggers the sustained, fast heartbeat. Because MVT can quickly degenerate into ventricular fibrillation—a chaotic, deadly rhythm—treatment is urgently required and stratified based on the patient’s immediate stability and long-term risk of recurrence.
Acute Stabilization and Emergency Care
Immediate treatment for an active MVT episode depends entirely on the patient’s hemodynamic status. Patients experiencing unstable MVT show signs of cardiovascular collapse, such as low blood pressure, altered mental status, or acute heart failure. For these individuals, the most effective treatment is immediate electrical cardioversion, which delivers a synchronized electrical shock to reset the heart’s rhythm. If the patient is conscious but unstable, sedation is administered quickly before the shock, but treatment must not be delayed.
If MVT recurs shortly after the initial electrical conversion, intravenous antiarrhythmic medications like amiodarone may be administered to prevent further episodes. In contrast, patients with stable MVT are conscious and maintain adequate blood pressure and organ perfusion. For stable MVT, physicians often attempt chemical conversion using intravenous antiarrhythmic drugs before resorting to an electrical shock.
The first-line pharmacological agent for stable MVT is typically intravenous procainamide, infused slowly over 10 to 20 minutes. Amiodarone is a common alternative, especially for patients with underlying impaired heart function or heart failure, as procainamide can sometimes exacerbate these conditions. Electrical cardioversion remains the most efficacious option and is used if drug therapy fails to convert the rhythm.
Long-Term Pharmacological Management
Long-term pharmacological management focuses on preventing future MVT events using oral antiarrhythmic drugs (AADs). Beta-blockers are the initial treatment choice, particularly for patients with structural heart disease, because they slow the heart rate and reduce the risk of sudden death. These maintenance medications work to suppress the electrical irritability in the heart muscle that causes the arrhythmia.
If beta-blockers are insufficient or not tolerated, other AADs are introduced. Amiodarone, a Class III agent, is frequently chosen as a second-line option because it is highly effective at suppressing MVT, even in patients with structural heart disease. Long-term use of amiodarone requires careful monitoring due to serious side effects, including pulmonary toxicity, thyroid dysfunction, and liver issues.
Other AADs, such as Class I agents like flecainide or propafenone, may be used for MVT in patients whose hearts are otherwise structurally normal. These medications are generally avoided in patients with coronary artery disease or structural damage due to the risk of proarrhythmia. Proarrhythmia is the unpredictable risk that the drug itself can create a new, potentially more dangerous heart rhythm, necessitating a carefully tailored regimen.
Catheter Ablation Procedures
Catheter ablation is an interventional procedure that aims to eliminate the source of the MVT. The procedure begins with the insertion of thin, flexible wires, called catheters, into a blood vessel, usually in the groin, which are then guided up to the heart. Specialized catheters create a detailed three-dimensional electrical map of the heart’s interior, known as electroanatomical mapping.
This mapping process identifies the precise location of the abnormal electrical focus or slow-conducting pathway, often within scar tissue. Once the target site is pinpointed, the tip of the ablation catheter is positioned against the tissue. Energy, most commonly radiofrequency energy that heats the tissue, is then delivered to create a tiny, controlled scar.
This intentional scar tissue blocks the abnormal electrical signals, preventing the MVT from initiating. If the MVT originates deep within the heart muscle or on the outer surface, a different approach or cryotherapy, which uses extreme cold, may be necessary. Catheter ablation is often considered when medications have failed or are not tolerated, with success rates ranging from 65% to over 90%.
Implantable Cardioverter-Defibrillators (ICD)
For patients at high risk of sudden cardiac death due to MVT, an Implantable Cardioverter-Defibrillator (ICD) is a device-based therapy. The ICD is a small, battery-powered unit implanted beneath the skin, typically near the collarbone, with wires extending into the heart chambers. Its primary function is to continuously monitor the heart’s electrical activity.
If the device detects a sustained, life-threatening MVT or deterioration into ventricular fibrillation, it delivers therapy to terminate the arrhythmia. Treatment is delivered either as anti-tachycardia pacing (ATP)—rapid electrical pulses that attempt to interrupt the rhythm—or as a high-energy electrical shock (defibrillation). ICDs are strongly indicated for patients who have survived a sudden cardiac arrest or those with severe structural heart disease, such as a very low left ventricular ejection fraction.
While the ICD is a life-saving device, it does not prevent the arrhythmia from occurring, meaning patients may still experience MVT episodes. Because receiving a high-energy shock can be painful and psychologically distressing, AADs or catheter ablation are often combined with ICD implantation to reduce MVT frequency. The decision to implant an ICD is based on a comprehensive risk assessment, ensuring the patient’s anticipated survival is more than one year.