Premature ventricular contractions are abnormally early contractions of the heart’s ventricles, then a brief interruption in the normal rhythm followed by a strong beat due to the ventricle contracting more forcefully on the subsequent beat. Premature ventricular contractions symptoms are variously experienced as:
• a skipped beat
• a strong beat
• or a sucking sensation in the chest
Infrequently, premature ventricular contractions will cause chest pain, weakness and dizziness or hyperventilation after exercise.
In otherwise healthy individuals, PVCs are usually completely asymptomatic and occasional premature ventricular contractions are common. Dangers of premature ventricular contractions are minimal and living with premature ventricular contractions remains unproblematic if the condition is mild. However, a potentially fatal abnormal heart rhythm, a form of ventricular tachycardia (VT), can develop when a series of PVCs occur in a short period of time.
Causes Of Premature Ventricular Contractions
The heart has four chambers, two atria and two ventricles that beat in response to electrical stimulation coming from the heart’s electrical pacemaker, the sinoatrial (SA) node. The causes of premature ventricular contractions are disorders to this system.
The primary cause of premature ventricular contractions is an abnormally originating (ectopic) electrical discharge that stimulates the ventricle to contract prematurely. The ectopic stimulation starts directly in the Purkinje fibers innervating in the ventricles rather than originating from the SA node. The action potential (electrical signal) does not travel along the normal ventricular conduction system but directly from one myocyte (cardiac cell) to another and thereby propagates more slowly. This results in a slower contraction and longer interval.
While the abnormal electrical discharge is the direct cause of premature ventricular contractions, the cause of the discharges is heightened sensitivity of the heart muscle of the ventricles to contract in response to electrical stimulation. The cellular cause of premature ventricular contractions that is most directly responsible for the heightened sensitivity seen in ectopic stimulation is an excess of cellular calcium: the muscle cells of the heart’s ventricles have an increased flow of calcium ions into the cells, thereby lowering their firing threshold. This lowered firing threshold can be the result of numerous physiological conditions, including:
• stimulation of the sympathetic nervous system and an abundance of adrenaline in the body due to anxiety or exercise,
• injury to the myocardium (e.g. due to earlier infarct),
• electrolyte imbalances, especially potassium or magnesium deficiency,
• lack of proper oxygenation,
• certain drugs including caffeine and tobacco,
• medications such as digoxin, tricyclic antidepressants and decongestants,
• High blood pressure (hypertension).
These are the primary risk factors associated with premature ventricular contractions.
The medical causes of premature ventricular contractions can develop in healthy individuals of any age, however the elderly population and males experience symptoms at a greater rate
Diagnosis and tests
Patients usually go to their doctors because they are experiencing some premature ventricular contraction symptoms. Diagnosis relies on the careful assessment of the symptoms, which are often transient and infrequent. The characteristic skipped heartbeat is easily detectable upon a basic physical examination. But premature ventricular contractions are irregular and may not present during the examination.
An occasional skipped beat is common and poses no major health risks to healthy individuals. However, those with pre-existing cardiac conditions need to be more closely assessed. In these cases, the diagnostician can turn to electrocardiography (ECG) to acquire a more extensive picture. On an ECG the heart’s electrical impulses during a heartbeat are measured. If observed, the premature ventricular contractions will appear as a high voltage QRS wave which is also abnormally wide (revealing slow propagation of ectopic electrical signal).
Another option is for the patient to remain normally active and wear a portable ECG, a Holter monitor. This is a method of 24-hour monitoring using a portable, battery-operated ECG. Holter monitors gather data about cardiac electrical activity continuously over the course of a complete day. This increases the chance of seeing the premature ventricular contraction.
Exercise stress testing is an ECG taken during periods of physical activity such as running on a treadmill. This exercise stress can induce a premature ventricular contraction in vulnerable cardiac tissue.
Echocardiography (the uses ultrasonic sound waves to visualize the physiology and structure of the heart) can reveal abnormal contractions as well as myocardial injury.
There are many individuals living with premature ventricular contractions without any ill effects. While some will feel an occasional heart flutter or a skipped beat, there are many who live without any premature ventricular contractions symptoms and do not know they have it. With infrequent premature ventricular contractions there is no risk for complications.
The medically significant dangers of premature ventricular contractions occur when the premature contractions occur with high frequency or in quick succession. When this occurs, there is an increased risks of developing ventricular tachycardia. Ventricular tachycardia consists of fast ventricular contractions and is life-threatening because it can very quickly progress into ventricular fibrillation( rapid, erratic beats with ventricles that pulsate without pumping blood).
Beyond the immediate risks of ventricular fibrillation, high rates of premature ventricular contractions are associated with an increased risk for developing arrhythmias or cardiomyopathy.
Additionally, there is an association between the onset of premature ventricular contractions symptoms and exercise. Exercise appears to increase the chances of some types of premature ventricular contractions, those with symptoms or without. Exercise is linked to key risk factors such as high blood pressure, reduced oxygenation and increased adrenaline.
Treatment and Management
With many types of premature ventricular contractions, symptoms are transient and require no medical treatment especially if the premature ventricular contraction is a singular event in a healthy adult. If the premature ventricular contractions persist, drug treatment, changes in lifestyle as well as surgical ablation are indicated to reduce the complications.
To reduce the risk of premature ventricular contractions progressing to VT, antiarrhythmics, beta-blockers and calcium channel blockers are used to lower action potential thresholds and electrically stabilize the myocardium. For the majority of patients, simple lifestyle changes are the only required treatment.
• reducing the intake of stimulants such as caffeine and tobacco,
• careful management of medications
• as well as reducing hypertension.
In healthy adults, there is no risk of complications from occasional premature ventricular contractions when taking exercise, which is recommended to reduce the risk factors.
However, in cases of frequent recurring premature ventricular contractions with pre-existing cardiomyopathy and an increased risk for developing complications, surgical ablation of the electrical focal point has been recognized as a safe option for treating premature ventricular contractions.
In patients without underlying heart disease, the long-term prognosis is excellent. There is no effect on life quality or duration from infrequent premature ventricular contractions. Those that suffer from frequent premature ventricular contractions are at an increased risk to develop cardiomyopathy and ventricular fibrillations as well as twice the risk of sudden death.