Paroxysmal Ventricular Tachycardia

What paroxysmal ventricular tachycardia is

The heartbeat normally starts in the sinus node, the heart's natural pacemaker in the upper right chamber. The signal travels through the upper chambers, then down a specialized wiring system that makes the ventricles squeeze in a coordinated way.

In ventricular tachycardia (VT), an abnormal electrical circuit or an irritable spot in the ventricle takes over and fires rapidly. The ventricles beat so fast that they do not have time to fill properly, so the heart pumps less blood with each beat. "Paroxysmal" means the rhythm comes in sudden bursts with normal rhythm between them.

Nonsustained vs sustained VT

Monomorphic vs polymorphic VT

On an ECG, monomorphic VT has identical-looking beats from one circuit, often around scar tissue. Polymorphic VT has beats that change shape and is less stable. A special type called torsades de pointes twists around the baseline and is linked to a prolonged QT interval. Polymorphic VT more readily degenerates into ventricular fibrillation, which causes cardiac arrest within seconds.

Symptoms

Symptoms depend on how fast and how long the VT is, and how strong the heart is to begin with.

• Palpitations: a sudden pounding or racing heartbeat. See heart palpitations.
• Lightheadedness or dizziness, and blurred or graying vision.
• Shortness of breath.
• Chest pain or pressure.
• Fainting (syncope), sometimes with no warning.
• Cardiac arrest: collapse, no pulse and no normal breathing.

Short runs of nonsustained VT are often found by chance on a Holter monitor, exercise test or smartwatch in someone with no symptoms at all.

Causes and risk factors

Structural heart disease (most cases)

• Scar from a previous heart attack: the commonest cause in adults. Electrical circuits form around the border of the scar, sometimes years later. See heart attack.
• Cardiomyopathy: dilated, hypertrophic and arrhythmogenic types. See cardiomyopathy.
• Heart failure with a low ejection fraction.
• Myocarditis, cardiac sarcoidosis and congenital heart disease after surgical repair.
• Acute ischemia: VT during a heart attack in progress.

Inherited rhythm disorders (a structurally normal heart)

• Long QT syndrome, which predisposes to torsades de pointes. See long QT syndrome.
• Brugada syndrome.
• Catecholaminergic polymorphic VT (CPVT), triggered by exercise or emotion, often in children and young adults.

Idiopathic VT

Some VT happens in people with a structurally normal heart. The most common types start in the outflow tract of the right ventricle or in the left ventricle's conduction fibers. They are often triggered by exercise, stress or caffeine, have a good outlook, and frequently respond to medicines or ablation.

Triggers and reversible causes

• Low potassium or magnesium, often from diuretics, vomiting or diarrhea
• Medicines that prolong the QT interval: some antibiotics, antifungals, antipsychotics, antidepressants and anti-nausea drugs
• Digoxin toxicity
• Stimulants: cocaine, amphetamines and, in susceptible people, high doses of caffeine
• Severe hypoxia, acidosis or thyroid overactivity

How it is diagnosed

• ECG during symptoms: the key test. VT shows a fast, wide-complex rhythm.
• Holter or event monitor: records the heart for 24 hours to several weeks. An implantable loop recorder can monitor for up to 3 years when episodes are rare.
• Echocardiogram: measures heart pumping strength (ejection fraction) and valves.
• Cardiac MRI: detects scar, inflammation and cardiomyopathy.
• Blood tests: potassium, magnesium, calcium, thyroid function and troponin.
• Coronary angiography or CT: looks for blocked arteries.
• Exercise stress test: shows exercise-triggered VT or ischemia.
• Electrophysiology study: catheters inside the heart map the circuit and test whether VT can be triggered. It is often combined with ablation.
• Genetic testing when an inherited syndrome is suspected, with screening of family members.

A wide-complex tachycardia should be treated as VT until proven otherwise. It is sometimes confused with supraventricular tachycardia with abnormal conduction.

Treatment

Stopping an episode

• Unstable VT (low blood pressure, chest pain, collapse): immediate electrical cardioversion. Pulseless VT is treated as cardiac arrest with CPR and defibrillation.
• Stable sustained VT: intravenous antiarrhythmic medicines such as amiodarone, or a planned shock under sedation.
• Torsades de pointes: intravenous magnesium, correcting potassium and stopping the drug responsible.

Preventing further episodes

• Fix triggers: correct electrolytes, stop QT-prolonging drugs, treat ischemia and thyroid disease, and avoid stimulants.
• Beta-blockers: first-line for many people, including those with heart failure, long QT syndrome and CPVT.
• Other antiarrhythmics: amiodarone, sotalol, mexiletine and others, chosen by a cardiologist with ECG monitoring.
• Catheter ablation: thin catheters map and burn or freeze the tissue that sustains the circuit. It can cure idiopathic VT and reduces recurrences and ICD shocks in scar-related VT.
• Implantable cardioverter-defibrillator (ICD): a device under the skin that detects VT and ends it with rapid pacing or a shock. It is recommended for people who survived cardiac arrest or sustained VT with heart disease, and for many with a weak heart muscle (ejection fraction 35% or lower) despite treatment.
• Treating the underlying disease: heart failure medicines, revascularization with stents or bypass surgery, and treatment of myocarditis or sarcoidosis.

Outlook and living with VT

The outlook depends mostly on the heart underneath. Idiopathic VT in a normal heart rarely threatens life. Sustained VT with scarring or cardiomyopathy carries a real risk of sudden cardiac death, which an ICD largely reduces.

Practical points:

• Driving is usually restricted for a period after sustained VT, syncope or an ICD shock. Local rules vary.
• Most people with an ICD can exercise. Your cardiologist will advise on intensity, especially with inherited syndromes.
• Teach family members CPR.
• Check every new medicine, including over-the-counter and herbal products, for interactions and QT effects.

Frequently asked questions

What is paroxysmal ventricular tachycardia?

It is a fast heart rhythm that starts in the ventricles and occurs in sudden episodes that begin and end abruptly. Episodes can last a few beats or many minutes. It ranges from a harmless finding in a normal heart to a dangerous rhythm in people with heart disease.

What does PVT mean in heart medicine?

In cardiology, PVT usually means paroxysmal or polymorphic ventricular tachycardia, depending on context. Both are fast rhythms from the ventricles. In resuscitation, "pulseless VT" is also abbreviated as pVT and is treated like ventricular fibrillation with CPR and defibrillation.

Is nonsustained ventricular tachycardia dangerous?

In a structurally normal heart, brief runs of nonsustained VT are usually low risk. In someone with a prior heart attack, cardiomyopathy or a weak heart, they can signal a higher risk of sustained VT and sudden death, so a cardiologist will usually order an echocardiogram and further tests.

What triggers ventricular tachycardia episodes?

Common triggers include low potassium or magnesium, certain medicines that prolong the QT interval, stimulants such as cocaine and amphetamines, intense exercise or emotional stress in some inherited conditions, and acute reduced blood flow to the heart during a heart attack.

Can ventricular tachycardia be cured?

Idiopathic VT in a normal heart can often be cured by catheter ablation. VT related to scarring or cardiomyopathy is usually controlled rather than cured, using medicines, ablation and an ICD that stops dangerous episodes if they occur.

How is ventricular tachycardia different from supraventricular tachycardia?

Supraventricular tachycardia starts above the ventricles and is rarely life-threatening. Ventricular tachycardia starts in the ventricles, produces wide complexes on an ECG and can lead to cardiac arrest. Because they can look alike, doctors treat any uncertain wide-complex rhythm as VT.