Premature ventricular contraction
Encyclopedia
A premature ventricular contraction (PVC), also known as a premature ventricular complex, ventricular premature contraction (or complex or complexes) (VPC), ventricular premature beat (VPB), or extrasystole, is a relatively common event where the heartbeat
is initiated by the heart ventricle
s rather than by the sinoatrial node
, the normal heartbeat initiator. The electrical events of the heart detected by the electrocardiogram
allow a PVC to be easily distinguished from a normal heart beat.
A PVC may be perceived as a "skipped beat" or felt as palpitations in the chest.
In a normal heartbeat, the ventricles contract after the atria have helped to fill them by contracting; in this way the ventricles can pump a maximized amount of blood both to the lungs and to the rest of the body. In a PVC, the ventricles contract first, which means that circulation is inefficient. However, single beat PVC arrhythmias do not usually pose a danger and can be asymptomatic in healthy individuals.
Some possible causes include:
after exercise. Several PVCs in a row becomes a form of ventricular tachycardia
(VT), which is a dangerous rapid heartbeat.
A physical examination should be conducted after a full history has been taken. This is useful in determining any possible heart defects that might be causing the palpitations. Most cases of premature ventricular contraction have a mitral-valve prolapse which can be determined through the physical examination.
The next step in diagnosis is a 12 lead ECG which can be performed in the doctors’ office over a short period of time however this is often non-conclusive in diagnosis because it is not very sensitive and there is only a small chance of a premature ventricular contraction occurring in the short period of time. Holter monitoring is a far better method for diagnosis as it is continuous recording of the heart’s rhythm over a period of 24 hours, or event monitoring which records noncontinuously for 30 days or indefinitely. This increases the likelihood of a premature ventricular contraction occurring during the recording period and is therefore more useful in diagnosis.
When looking at an electrocardiograph premature ventricular contractions are easily spotted and therefore a definitive diagnosis can be made. The QRS and T waves look very different to normal readings. The spacing between the PVC and the preceding QRS wave is a lot shorter than usual and the time between the PVC and the proceeding QRS is a lot longer. However, the time between the preceding and proceeding QRS waves stays the same as normal due to the compensatory pause.
PVCs can be distinguished from premature atrial contractions because the compensatory pause is longer following premature ventricular contractions.
There are four different named patterns
of regularly occurring PVCs. Depending whether there are 1, 2, or 3 normal beats between each PVC, the rhythm is called bigeminy, trigeminy, or quadrigeminy. A unifocal PVC is where the depolarisation is triggered from the one site in the ventricle causing the peaks on the ECG to look the same. Multifocal PVCs arise when more than one site in the ventricles initiate depolarisation causing each peak on the ECG to have a different shape. If 3 or more PVCs occur in a row it may be called Ventricular tachycardia
.
In healthy individuals, PVCs can often be resolved by restoring the balance of magnesium
, calcium
and potassium
within the body.
The most effective treatment is the elimination of triggers (particularly the cessation of the use of substances such as caffeine
, and certain drugs.)
In the setting of existing cardiac disease, however, PVCs must be watched carefully, as they may cause a form of ventricular tachycardia
(rapid heartbeat).
Recent studies have shown that those subjects who have an extremely high occurrence of PVCs (several thousand a day) can develop dilated cardiomyopathy
. In these cases, if the PVCs are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.
There are two main physiological explanations for premature ventricular contractions: re-entrant signalling and “enhanced automaticity in some ectopic focus”. The enhanced automaticity means that the ectopic centre fires more regularly than usual and is protected from depolarisation that results in premature contractions.
Potassium
ion concentrations are a major determinant in the magnitude of the electrochemical potential of cells, and hypokalemia
makes it more likely that cells will depolarize spontaneously. Hypercalcemia has a similar effect, although clinically it is of less concern. Magnesium
ions affect the flow of calcium
ions, and they affect the function of the Na+/K+ ATPase, and are necessary for maintaining potassium levels. Hypomagnesemia
therefore also makes spontaneous depolarization more likely.
Existing damage to the myocardium can also provoke PVCs. The myocardial scarring
that occurs in myocardial infarction
and also in the surgical repair of congenital heart disease can disrupt the conduction system of the heart and may also irritate surrounding viable ventricular myocytes, make them more likely to depolarize spontaneously. Inflammation of the myocardium (as occurs in myocarditis
) and systemic inflammation cause surges of cytokines, which can affect the electrical properties of myocytes and may be ultimately responsible for causing irritability of myocytes.
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
is initiated by the heart ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
s rather than by the sinoatrial node
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...
, the normal heartbeat initiator. The electrical events of the heart detected by the electrocardiogram
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
allow a PVC to be easily distinguished from a normal heart beat.
A PVC may be perceived as a "skipped beat" or felt as palpitations in the chest.
In a normal heartbeat, the ventricles contract after the atria have helped to fill them by contracting; in this way the ventricles can pump a maximized amount of blood both to the lungs and to the rest of the body. In a PVC, the ventricles contract first, which means that circulation is inefficient. However, single beat PVC arrhythmias do not usually pose a danger and can be asymptomatic in healthy individuals.
Causes
Premature ventricular contractions can occur in a healthy person of any age, but are more prevalent in the elderly and in men. They frequently occur spontaneously with no known cause.Some possible causes include:
- IschemiaIschemiaIn medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
; - Certain medicines such as digoxinDigoxinDigoxin INN , also known as digitalis, is a purified cardiac glycoside and extracted from the foxglove plant, Digitalis lanata. Its corresponding aglycone is digoxigenin, and its acetyl derivative is acetyldigoxin...
, which increases heart contraction - MyocarditisMyocarditisMyocarditis is inflammation of heart muscle . It resembles a heart attack but coronary arteries are not blocked.Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi or Trypanosoma cruzi, or as a...
; - CardiomyopathyCardiomyopathyCardiomyopathy, which literally means "heart muscle disease," is the deterioration of the function of the myocardium for any reason. People with cardiomyopathy are often at risk of arrhythmia or sudden cardiac death or both. Cardiomyopathy can often go undetected, making it especially dangerous to...
, hypertrophic or dilated; - Myocardial contusion;
- HypoxiaHypoxia (medical)Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
; - HypercapniaHypercapniaHypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...
(CO2 poisoning); - SarcoidosisSarcoidosisSarcoidosis , also called sarcoid, Besnier-Boeck disease or Besnier-Boeck-Schaumann disease, is a disease in which abnormal collections of chronic inflammatory cells form as nodules in multiple organs. The cause of sarcoidosis is unknown...
; - Mitral valve prolapse;
- Smoking;
- Alcohol;
- Drugs such as cocaine;
- Caffeine;
- Theobromine;
- Tricyclic antidepressantTricyclic antidepressantTricyclic antidepressants are heterocyclic chemical compounds used primarily as antidepressants. The TCAs were first discovered in the early 1950s and were subsequently introduced later in the decade; they are named after their chemical structure, which contains three rings of atoms...
s; - Magnesium and potassium deficiency;
- Calcium excess;
- Thyroid problems;
- Chemical (electrolyte) problems in the blood;
- Heart attack;
- Adrenaline excess;
- Lack of sleep/exhaustion;
- Stress
Symptoms
A PVC may be perceived as a skipped heart beat, a strong beat, or a feeling of suction in the chest. They may also cause chest pain, a faint feeling, fatigue, or hyperventilationHyperventilation
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
after exercise. Several PVCs in a row becomes a form of ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...
(VT), which is a dangerous rapid heartbeat.
Diagnosis
PVCs are usually diagnosed after the patient has described “skipped beats”, pauses or palpitations. Typically the palpitations felt by PVC patients are very irregular and less sustained than patients with other types of arrhythmia. They are likely to have “flip flopping” sensations where it feels like the heart is flipping over or pounding due to there being a pause after the premature contraction and then a powerful contraction after the pause. There is a possibility that they might feel a ‘fluttering’ in their chest or a pounding in their neck but these two types of palpitations aren’t very common in PVC patients.A physical examination should be conducted after a full history has been taken. This is useful in determining any possible heart defects that might be causing the palpitations. Most cases of premature ventricular contraction have a mitral-valve prolapse which can be determined through the physical examination.
The next step in diagnosis is a 12 lead ECG which can be performed in the doctors’ office over a short period of time however this is often non-conclusive in diagnosis because it is not very sensitive and there is only a small chance of a premature ventricular contraction occurring in the short period of time. Holter monitoring is a far better method for diagnosis as it is continuous recording of the heart’s rhythm over a period of 24 hours, or event monitoring which records noncontinuously for 30 days or indefinitely. This increases the likelihood of a premature ventricular contraction occurring during the recording period and is therefore more useful in diagnosis.
When looking at an electrocardiograph premature ventricular contractions are easily spotted and therefore a definitive diagnosis can be made. The QRS and T waves look very different to normal readings. The spacing between the PVC and the preceding QRS wave is a lot shorter than usual and the time between the PVC and the proceeding QRS is a lot longer. However, the time between the preceding and proceeding QRS waves stays the same as normal due to the compensatory pause.
PVCs can be distinguished from premature atrial contractions because the compensatory pause is longer following premature ventricular contractions.
There are four different named patterns
Numbering aberrant rhythms
Bigeminy is a descriptor for a heart arrhythmia in which abnormal heart beats occur every other concurrent beat. A typical example is with bigeminal premature ventricular beats, also known as a premature ventricular contractions/complexes . Following the PVC there is a pause and then the normal...
of regularly occurring PVCs. Depending whether there are 1, 2, or 3 normal beats between each PVC, the rhythm is called bigeminy, trigeminy, or quadrigeminy. A unifocal PVC is where the depolarisation is triggered from the one site in the ventricle causing the peaks on the ECG to look the same. Multifocal PVCs arise when more than one site in the ventricles initiate depolarisation causing each peak on the ECG to have a different shape. If 3 or more PVCs occur in a row it may be called Ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...
.
Treatment
Isolated PVCs with benign characteristics require no treatment.In healthy individuals, PVCs can often be resolved by restoring the balance of magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
within the body.
The most effective treatment is the elimination of triggers (particularly the cessation of the use of substances such as caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
, and certain drugs.)
- Pharmacological agents
- Antiarrhythmics: these agents alter the electrophysiologic mechanisms responsible for PVCs
- Beta blockerBeta blockerBeta blockers or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications. They are particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction ,...
s - Calcium channel blockers
- Electrolytes replacement
- Magnesium supplements (e.g. magnesium citrate, orotate, Maalox, etc.)
- Potassium supplements
- Radiofrequency catheter ablation treatment
- Lifestyle modification
- Frequently stressed individuals should consider therapy, or joining a support groupSupport groupIn a support group, members provide each other with various types of help, usually nonprofessional and nonmaterial, for a particular shared, usually burdensome, characteristic...
. - Heart attacks can increase the likelihood of having PVCs.
- Frequently stressed individuals should consider therapy, or joining a support group
In the setting of existing cardiac disease, however, PVCs must be watched carefully, as they may cause a form of ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...
(rapid heartbeat).
Recent studies have shown that those subjects who have an extremely high occurrence of PVCs (several thousand a day) can develop dilated cardiomyopathy
Dilated cardiomyopathy
Dilated cardiomyopathy or DCM is a condition in which the heart becomes weakened and enlarged and cannot pump blood efficiently. The decreased heart function can affect the lungs, liver, and other body systems....
. In these cases, if the PVCs are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.
Pathophysiology
Normally impulses pass through both ventricles almost simultaneously, the depolarisation waves of the two ventricles partially cancel each other out in the ECG. However, when a PVC occurs the impulse nearly always travels in one direction therefore there is no neutralisation effect which results in the high voltage QRS wave in the electrocardiograph.There are two main physiological explanations for premature ventricular contractions: re-entrant signalling and “enhanced automaticity in some ectopic focus”. The enhanced automaticity means that the ectopic centre fires more regularly than usual and is protected from depolarisation that results in premature contractions.
Molecular Basis
There are a number of different molecular explanations for PVCs. One explanation is most basically due to an increased amount of cyclic AMP(cAMP) in the ventricular cardiac myocytes leading to increased flow of calcium ions into the cell. This may happen for the following reasons:- Activation of the sympathetic nervous system, due to anxiety and/or physiological stress, for example hypovolemiaHypovolemiaIn physiology and medicine, hypovolemia is a state of decreased blood volume; more specifically, decrease in volume of blood plasma...
caused by dehydrationDehydrationIn physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
or hemorrhage. This activation can cause a release of catecholamines such as epinephrineEpinephrineEpinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
(adrenaline) which can bind to beta-1 adrenergic receptorBeta-1 adrenergic receptorThe beta-1 adrenergic receptor , also known as ADRB1, is a beta-adrenergic receptor, and also denotes the human gene encoding it...
(β1 receptors) on cardiac myocytes, activating a type of guanosine nucleotide-binding protein called Gs proteinGS-Places:* South Georgia and the South Sandwich Islands ** .gs, an Internet country code top-level domain-Science:* g-force , multiples of the acceleration due to gravity* Guanosine synthetase-Technologies:* Glideslope* Ground Speed...
. This type of protein stimulates the production of cAMP, ultimately increasing the flow of calcium ions from the extracellular space and from the sarcoplasmic reticulum into the cytosol.
This has the effect of (1) increasing the strength of contraction (inotropy) and (2) depolarizing the myocyte more rapidly (chronotropy). The ventricular myocytes are therefore more irritable than usual, and may depolarize spontaneously before the SA node depolarizes. Other sympathomimetic molecules such as amphetamines and cocaineCocaineCocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
will also cause this effect. - Phosphodiesterase inhibitors such as caffeineCaffeineCaffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
directly affect the G-coupled signal transduction cascade by inhibiting the enzyme that catalyzes the breakdown of cAMP, again leading to the increased concentration of calcium ions in the cytosol.
Potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
ion concentrations are a major determinant in the magnitude of the electrochemical potential of cells, and hypokalemia
Hypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
makes it more likely that cells will depolarize spontaneously. Hypercalcemia has a similar effect, although clinically it is of less concern. Magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
ions affect the flow of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
ions, and they affect the function of the Na+/K+ ATPase, and are necessary for maintaining potassium levels. Hypomagnesemia
Hypomagnesemia
Hypomagnesemia is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Usually a serum level less than 0.7 mmol/L is used as reference. The prefix hypo- means low . The middle 'magnes' refers to magnesium...
therefore also makes spontaneous depolarization more likely.
Existing damage to the myocardium can also provoke PVCs. The myocardial scarring
Myocardial scarring
Myocardial scarring is fibrous tissue that replaces normal tissue destroyed by injury or disease pertaining to the muscular tissue of the heart....
that occurs in myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
and also in the surgical repair of congenital heart disease can disrupt the conduction system of the heart and may also irritate surrounding viable ventricular myocytes, make them more likely to depolarize spontaneously. Inflammation of the myocardium (as occurs in myocarditis
Myocarditis
Myocarditis is inflammation of heart muscle . It resembles a heart attack but coronary arteries are not blocked.Myocarditis is most often due to infection by common viruses, such as parvovirus B19, less commonly non-viral pathogens such as Borrelia burgdorferi or Trypanosoma cruzi, or as a...
) and systemic inflammation cause surges of cytokines, which can affect the electrical properties of myocytes and may be ultimately responsible for causing irritability of myocytes.