What is ventricular tachycardia?
Ventricular tachycardia is an abnormal condition in which the ventricles of the heart beat abnormally fast. This rapid eartbeat is stimulated by electrical signals that arise from within specialized cardiac cells within the ventricles themselves, or it may be caused by electrical signals that do not follow the normal conduction system and stimulate more than one contraction. These are called reentrant signals.
In a normal heart, electrical signals arise from a specialized “natural pacemaker” in the upper right atrium called the sinoatrial node (SA node). These signals first spread through the atria, then into the ventricles. During ventricular tachycardia, however, additional signals arise from the ventricles themselves or are caused by a defect in the heart's conduction system.
Ventricular tachycardias are classified by their duration (e.g., sustained or nonsustained) and whether they occur without cause or because of an underlying condition, such as coronary artery disease. Short, unsustained episodes of VT generally do not produce symptoms and do not require treatment. However, longer, sustained episodes of VT, in the presence of an underlying heart disease, may cause a medical emergency. Over time, VT can lead to heart failure or degenerate into ventricular fibrillation, which can result in cardiac arrest.
The specific types of VT include:
- Nonsustained ventricular tachycardia. An episode of VT that lasts for at least three beats but less than 30 seconds.
- Sustained ventricular tachycardia. An episode of VT that lasts longer than 30 seconds.
- Monomorphic ventricular tachycardia. Fast but regular rhythm.
- Polymorphic ventricular tachycardia. Fast, irregular rhythm.
- Stable ventricular tachycardia. The heart is still pumping enough oxygen-rich blood to meet the body’s needs.
- Unstable ventricular tachycardia. The patient is showing signs of a lack of oxygen-rich blood circulating through the body.
- Torsade de pointes. A particularly rapid, dangerous form of VT that often occurs as a result of certain medications or in patients with congenital long QT syndrome.
- Accelerated idioventricular rhythm (also known as slow ventricular tachycardia). A slower and less dangerous form of VT.
Symptoms of Ventricular tachycardia
Some patients with ventricular tachycardia (VT) have no symptoms. Others experience symptoms such as:
- Shortness of breath
- Fainting (syncope)
- Chest pain
- Feeling like the heart has skipped a beat or is somehow beating abnormally (palpitations)
Ventricular tachycardia may also be implicated when drivers lose consciousness or "fall asleep" behind the wheel. Other heart-related conditions that could lead to loss of consciousness while driving (or near-loss of consciousness and pulling off the road) include syncope, supraventricular tachycardia and/or advanced AV block.
How is it diagnosed?
The first steps that a physician takes when diagnosing ventricular tachycardia (VT) is to obtain a patient’s medical history and to give the patient a physical examination. Next, the physician may order blood tests and an electrocardiogram (EKG). The EKG is a sensitive test that measures the heart's electrical activity and displays it on a computer screen or printout for a physician to analyze.
If the EKG is normal, but the physician still suspects an abnormal heart rhythm, then the patient may need to wear a portable EKG Holter monitor for 24 hours. This device monitors the heart rate for 24 hours, allowing physicians to diagnose nonsustained arrhythmias that occur outside of the physician's office. If the Holter monitor still doesn't record any arrhythmias, the patient may be given a different kind of event recorder that is activated by the patient only when the arrhythmia occurs. This will allow the physician to study the characteristics of their particular arrhythmia.
Depending on the results of these tests, a more invasive test called an electrophysiology (EP) study may be performed. An EP study is a procedure in which a thin tube (catheter) is inserted into a vein or artery (e.g., in the groin) and guided to the heart, where it can perform specific measurements of the heart’s electrical activity and pathways. During the EP study, a physician may or may not be able to reproduce the patient’s VT. If it can be produced, the patient is at particularly high risk of going into cardiac arrest at some point in the future.
EP studies are also an important part of therapy for VT treatment. They are typically performed before surgery or catheter ablation. These precise studies can exactly locate the source of an abnormal rhythm, thus allowing physicians to exactly target the defective area.
How is it treated?
In some cases (e.g. nonsustained ventricular tachycardia [VT] without underlying heart disease), no treatment may be necessary. If treatment is needed, the most common treatment is medication. The goal with medication is to stop the abnormal heart rhythm and prevent it from recurring. Medications used include antiarrhythmics, beta blockers and others.
In recent years, alternative methods have become increasingly common in the management of ventricular tachycardias. These alternative methods include catheter ablation, which is often recommended for patients without underlying heart disease or for patients with certain kinds of arrhythmias (e.g., reentrant ventricular tachycardia). In this procedure, a physician inserts a long, thin tube called a catheter into a blood vessel and guides it into the heart. The catheter is tipped with a special radiofrequency transmitter that is used to destroy selected cardiac cells that are causing the abnormal heart rhythm. So far, ablation has been shown to eliminate certain kinds of VT in between 80 and 100 percent of cases, and its use will likely increase.
Among patients with underlying heart disease, the use of implantable cardioverter defibrillators (ICD) has been steadily growing. This device senses abnormal heart rhythms and delivers a shock to the heart to restore a normal rhythm. In some cases, patients may be treated with medications, catheter ablation and implantation of an ICD.
Surgery is also an option, although to some extent it has become less common since the advent of the ICD. Before surgery for an arrhythmia, the patient's heart will be carefully mapped and areas identified where the abnormal beat is originating. During surgery, these areas are carefully removed. In heart attack patients, this surgery may be accompanied by the placement of bypass grafts to re-establish the flow of oxygen-rich blood. Surgery may also be recommended for patients in whom medications have failed or who are already undergoing surgery to remove a ventricular aneurysm or to repair a defective heart valve.
Because of the risk of fainting associated with ventricular tachycardia, patients may be advised against driving or operating heavy machinery until the condition is under control. American Heart Association has recommended that anyone who has experienced confusion, dizziness or other signs of altered consciousness during a VT episode wait several months before getting behind the wheel again. Once tests have confirmed that treatment has effectively controlled the arrhythmia, then people are generally free to start driving again.
In many cases, an initial episode of VT cannot be prevented. However, once diagnosed, treatment can help prevent future episodes. Furthermore, people can adopt heart-healthy strategies that decrease the likelihood of developing risk factors such as coronary artery disease.
Tenormin (Atenolol), Cordarone (Amiodarone), Betapace (Sotalol)
What might complicate it?
Prognosis depends on the type and degree of underlying heart disease. The outcome is good for individuals who experience ventricular tachycardia as a one-time experience. Complete recovery without lasting adverse reactions may be expected if there is no serious underlying heart disease. Close monitoring of drug therapy in individuals with recurrent episodes usually prevents progression to ventricular fibrillation and death.
Supraventricular tachycardia and aberration is a condition similar to ventricular tachycardia. EKG and rhythm strip may need expert interpretation to differentiate.
Cardiologist and cardio-thoracic surgeon.
Last updated 30 June 2015