In the complex world of heart rhythm disturbances (“arrhythmias”), the word “tachycardia” simply means a rapid heartbeat. In general, any heart rate over 100 beats per minute (bpm) is considered “tachycardia.” People who exercise get tachycardia, but in that case the heartbeats are still coming from the normal electrical system. When rapid, abnormal heartbeats arise from the bottom chambers of the heart (the ventricles), we can diagnose a ventricular tachyarrhythmia, though there are several different types. This article will serve to help you understand what the different types of ventricular tachyarrhythmias are, why they can happen and what (if anything) may need to be done about them.
How Is The Normal Heartbeat Controlled?
A normal resting heart rate for adults is anywhere from 60 to 80 beats per minute (bpm), depending on age, level of fitness, and other factors. Therefore, the normal heart beats approximately once every second. The electrical signal that controls the heart beat arises from a specialized structure in the top of the right atrium. This electrical structure is known as the sinus node or sinoatrial node. The signal generated by the sinus node stimulates the top chambers (atria) to contract. The atrial signal then enters another electrical structure called the AV (atrioventricular) node, which serves as the “main wire” connecting the top and bottom chambers. The AV node delays the signal for a fraction of a second and then passes it down to the ventricles through a complex network of branching cells called Purkinje Fibers, which stimulate the ventricular heart muscle cells to contract. The Purkinje fibers branch like a tree, with a main “trunk” known as the Bundle of His that is continuous with the AV Node, and two major branches known as the Right Bundle Branch (that stimulates the right ventricle) and a much larger Left Bundle Branch, which stimulates the left ventricle. The electrical system is designed to keep the heart beating at an appropriate rate to meet our body’s needs. When the rate is between 60 and 100 bpm, we refer to the rhythm as a “Normal Sinus Rhythm.” If the sinus node drops below 60 bpm, the rhythm is referred to as “Sinus Bradycardia.” If we are exercising or angry or upset, the sinus node can start firing at rates over 100 bpm, which is referred to as “Sinus Tachycardia.”
What is Ventricular Tachycardia?
It turns out that every cell in the heart is capable of generating an electrical impulse. If a group of cells in the ventricle decides to “fire” prematurely, it causes the bottom chambers to contract earlier than the top chamber. A single premature beat that arises from the bottom chamber is known as a PVC or premature ventricular contraction. A PVC disturbs the normal timing of the heart chambers for one beat, which can give rise to symptoms like palpitations, fluttering or flipping of the heart, or give the sense that the heart “skipped” a beat. Sometimes every other beat or every third beat is a PVC, giving rise to annoying symptoms that can go on for a minute or even longer.
If that spot in the ventricle were to fire repeatedly, then several ventricular beats can occur in a row, giving rise to “ventricular tachycardia” or VT. Generally, we consider 3 or more PVCs in a row to meet the definition of VT, provided that the rate of these beats is at least 100 bpm. Since this kind of ventricular tachyarrhythia starts and stops, we refer to it as “non-sustained” ventricular tachycardia or NSVT. Sometimes NSVT can last three beats but it can go on for longer… 5, 10, 20 beats, and so on. But what if the spot in the heart keeps firing and firing… this can give rise to “sustained” ventricular tachycardia, which is defined as any VT run that lasts for more than 30 seconds.
Although the description of sustained VT above describes a single spot in the ventricle giving rise to the rapid arrhythmia, sustained VT more commonly arises from an electrical “short circuit” in the bottom chambers that allows the electrical signal to get stuck going round and round a pathway, like a car that keeps driving around a traffic circle. The electrical signal chases its own tail within a set “reentry” circuit and may cause such a rapid heart rate that the person’s blood pressure can drop precipitously. Extreme cases can cause sudden loss of consciousness. When a very low blood pressure occurs, the heart cannot provide sufficient oxygen to all the vital organs and cardiac arrest ensues. If the heart itself suffers from a lack of oxygen, it stops pumping altogether and sudden cardiac death occurs.
Another type of lethal ventricular tachyarrhythmia is known as ventricular fibrillation (VF). In this case, the electrical signals in the bottom chamber become extremely rapid and disorganized. The signal becomes chaotic, with rates usually above 300 bpm, which causes the heart muscle to simply quiver without actually pumping in any effective manner. This usually causes cardiac arrest within seconds and is universally fatal unless the person is rescued with a shock from an external device known as a defibrillator.
PVCs and non-sustained VT can cause symptoms of palpitations and even lightheadedness, but many patients have these arrhythmia and do not notice anything. PVCs can occur in normal people. However, NSVT may be a sign of serious heart disease and should always be evaluated by a cardiac specialist (cardiologist) or heart rhythm specialist (cardiac electrophysiologist).
What Are the Causes of Ventricular Tachycardia?
Sustained ventricular tachycardia and ventricular fibrillation are nearly always associated with serious underlying heart disease. Generally, the heart muscle has been weakened by a prior heart attack due to the presence of severe coronary artery disease, or it may be weak from longstanding valvular heart disease, hypertension, heavy alcohol use, or possibly even genetic reasons. Heart muscle disease is known as Cardiomyopathy, and over 96% of patients with sustained VT or VF have some form of cardiomyopathy.
Non-sustained VT, on the other hand, may be due to tiny areas within the ventricular heart muscle that are simply “acting up.” The reason for the electrical irritability is sometimes unknown, but it can occur in people with no underlying heart disease at all. At times, NSVT can be a sign of heart failure, coronary insufficiency and a lack of oxygen delivery to the heart (known as ischemia), or it may even occur in the setting of electrolyte imbalances like a low potassium or low magnesium level in the blood.
Sometimes we cannot determine the cause of NSVT, especially in younger people with normal hearts. However, as mentioned previously, the majority of cases stem from an existing heart condition.
Some of the most common causes of sustained VT are:
- Cardiomyopathy, where the heart muscle is weakened
- Heart failure, which means your heart isn’t able to pump blood adequately
- Ischemic heart disease, due to insufficient blood flowing to your heart
- Structural heart disease, which may occur due to damage caused by a heart attack
- Diseases that create abnormal areas in the heart muscle, such as amyloidosis or sarcoidosis
- Medication side effects
- Excessive use of cardiac stimulants like caffeine or alcohol
- Recreational drug abuse, e.g. cocaine
- Abnormal electrical activity of the heart that may have been inherited
Inherited forms of ventricular tachyarrhythmias, including the long QT syndrome, arrhythmogenic right ventricular cardiomyopathy, or catecholaminergic polymorphic ventricular tachycardia, are rare causes of VT/VF in patients with otherwise normal hearts. VT or VF with no obvious cause is known as “idiopathic” VT or VF.
What Are the Symptoms of Ventricular Tachycardia?
A brief episode of non-sustained VT might not result in any symptoms, but you may experience:
- Dizziness / Lightheadedness
- Palpitations (the sensation that your heart is racing or fluttering)
- Shortness of breath
- Chest pain
If you experience any of these symptoms, you should visit your doctor for an evaluation.
Sustained ventricular tachyarrhythmias result in more severe symptoms such as fainting, seizures (due to lack of oxygen to the brain cells), collapse, and even sudden death. In some cases of sustained VT, especially if the VT rate is below 170 bpm or so, patients will be able to maintain an adequate blood pressure and may present to an emergency room with weakness, rapid heart palpitations, lightheadedness, difficulty breathing, or possibly chest pain. VT can be diagnosed with an electrocardiogram (ECG or EKG) if it’s happening at the time. In patients with NSVT, the ECG may have to be observed for a longer period of time to diagnose the problem. The use of a heart monitor for 1 to 30 days may be necessary to determine the exact nature of the arrhythmia.
Once ventricular tachycardia is diagnosed, patients generally need to have a series of tests to determine why they have it. An electrocardiogram (ECG), a stress test, an echocardiogram, and sometimes a cardiac MRI are necessary to determine the cause of the arrhythmia. The exact cause of the VT will affect how a person is treated, since some cases of NSVT do not require any treatment. Sustained VT or VF virtually always require an intervention to avoid recurrences and prevent sudden cardiac death.
How Can Ventricular Tachycardia Be Treated?
The type of treatment recommended for you will depend on how severe your VT is and what is causing the arrhythmia. In patients with non-sustained VT, a normal heart, and no symptoms, generally no treatment is needed. On the other side of the spectrum, someone with sustained VT/VF will need aggressive therapy to reduce their risk of sudden cardiac death.
Therefore, the goal of the physician evaluating the patient is to assess the risk of sudden death and to also determine the impact of the arrhythmia on quality of life. Treatment is based on these two factors and must be individualized for each patient. Most patients should obtain a consultation from a heart rhythm specialist or cardiac electrophysiologist for the best care and access to the most options for therapy.
If recurrent runs of non-sustained VT are causing intolerable symptoms, medications known as antiarrhythmic drugs can be used to suppress the abnormal beats and improve a patient’s quality of life. However, some of these drugs can actually make the rhythm problems worse in patients with a history of heart muscle damage. This “Pro-Arrhythmic” effect can actually worsen survival in patients after a heart attack. Therefore, the choice of antiarrhythmic medication should be left to the heart rhythm specialist.
Obviously, a patient with sustained VT or VF is a life-threatening emergency. If unconscious, CPR must be performed to maintain circulation to the vital organs like the brain, and a defibrillator must be used to shock the heart back into a normal rhythm. Taking care of patients under these circumstances require someone trained in Advanced Cardiac Life Support (ACLS) and immediate transport to a hospital emergency room. Most large buildings, businesses, schools, and even shopping malls are equipped with “Automatic External Defibrillators” or AEDs, which can be applied by a trained staff member or experienced onlooker, and can successfully shock someone out of VT or VF and save their life. Antiarrhythmic medication may be administered to help stabilize the rhythm, and patients need to be evaluated to see if they have suffered any further heart damage from the event.
Long-term treatments of sustained VT/VF include:
- An Implantable Cardioverter Defibrillator (ICD): This device is implanted under the skin and monitors the heart continuously. It is able to automatically restore a normal heart rhythm if sustained VT or VF occurs.
- Antiarrhythmic drugs: Drugs do not always work, but they can reduce the frequency and severity of these arrhythmias. Generally an ICD is needed as a back up in patients with sustained VT or VF, in case the drug fails.
- Revascularization: In cases where the arrhythmia is due to an insufficient supply of blood to the heart muscle, improving the blood supply can help treat the arrhythmia. These treatments include opening a blocked artery with a balloon and inserting a coronary stent to keep the vessel open. In patients with extensive coronary blockages, coronary bypass surgery can be used to correct the circulation problem and may reduce the risk of recurrent arrhythmias.
- Radiofrequency or catheter ablation: This procedure destroys the heart tissue that’s responsible for the ventricular arrhythmia. It is used in patients with recurrent sustained VT who are refractory to medications, especially if they have been receiving repeated shocks from their ICD. Ablation can also be recommended in patients with frequent, highly symptomatic non-sustained VT when it is coming from a small spot in the ventricle that can be reached with a long wire (catheter) through an artery or a vein. Ablating the spot that is causing the arrhythmia can cure the problem completely in some patients.
The prognosis and treatment needs of patients with ventricular tachycardia can vary dramatically. If you have any history of this arrhythmia or ongoing symptoms related to arrhythmia, you should seek advice from a heart rhythm specialist who can put things in perspective, provide you with expert recommendations, and deliver state of the art therapy.