Ectopic pacemaker
Encyclopedia
An ectopic pacemaker or ectopic focus is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the human heart
. Acute occurrence is usually non-life threatening, but chronic occurrence can progress into tachycardia
, bradycardia
or ventricular fibrillation
. In a normal heart beat rhythm, the SA node usually suppresses the ectopic pacemaker activity due to the higher impulse rate of the SA node. However, in the instance of either a malfunctioning SA node or an ectopic foci bearing an intrinsic rate superior to SA node rate, ectopic pacemaker activity may rule over the heart rhythm.
They can also occur within unhealthy hearts, caused by:
, or within the muscle cells of the atria or ventricles
. When an ectopic pacemaker initiates a beat, premature contraction occurs. A premature contraction will not follow the normal signal transduction pathway, and can render the heart refractory or incapable of transmitting the normal signal from the SA node. Location of the pacemaker can also change its effect on the SA node and its rhythm. An ectopic pacemaker located in the atria is known as an atrial pacemaker and can cause the atrial contraction to be faster. An ectopic pacemaker situated near the AV node and the septum
is known as a junctional pacemaker. The pacemaker that is operating in the ventricles is known as the ventricular. Other such ectopic pacemakers can even lie within the pulmonary vein
and thoracic vein walls.
will be abnormally shaped when looking at ventricular ectopic activity, often it occurs earlier with an absent P wave. It can be perceived as a skipped beat on both the ECG and through normal pulse-taking.
During atrial ectopic activity where the P wave is normally rounded can be inverted or peaked. However the QRS complex and T waves appear relatively normal.
Conversely, during junctional ectopic activity the P wave is frequently absent or can be hidden in the QRS complex
Clinical cardiac electrophysiology
Electrical conduction system of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. Acute occurrence is usually non-life threatening, but chronic occurrence can progress into tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
, bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
or ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...
. In a normal heart beat rhythm, the SA node usually suppresses the ectopic pacemaker activity due to the higher impulse rate of the SA node. However, in the instance of either a malfunctioning SA node or an ectopic foci bearing an intrinsic rate superior to SA node rate, ectopic pacemaker activity may rule over the heart rhythm.
Etiology
Ectopic pacemakers can occur within healthy hearts in response to various stimulating events, such as:- Increased local parasympathetic nervous systemParasympathetic nervous systemThe parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
activity - Elevated sympathetic nervous systemSympathetic nervous systemThe sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
output - Overstimulation from drugs 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...
, digitalisDigitalisDigitalis is a genus of about 20 species of herbaceous perennials, shrubs, and biennials that are commonly called foxgloves. This genus was traditionally placed in the figwort family Scrophulariaceae, but recent reviews of phylogenetic research have placed it in the much enlarged family...
and catecholamines. - Cardiac 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...
(particularly ventricular ischemia) - The membranes of apoptotic (dying) cells become "leaky" and cause surrounding tissue to become hyperkalemic or hypercalcemic (high concentration of potassium/calcium), causing random excitation.
They can also occur within unhealthy hearts, caused by:
- Infection
- Disease, such as sinus venosis and atrial defects.
- SA node dysfunction, (1st degree block) which can cause the rate of impulse to slow.
- SA node blockage so that impulses never leave the atria.
- AV node blockage (3rd degree block) prevents normal conduction across ventricles.
Physiology
An ectopic pacemaker can reside within a part of the electrical conduction system of the heartElectrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...
, or within the muscle cells of the atria or ventricles
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...
. When an ectopic pacemaker initiates a beat, premature contraction occurs. A premature contraction will not follow the normal signal transduction pathway, and can render the heart refractory or incapable of transmitting the normal signal from the SA node. Location of the pacemaker can also change its effect on the SA node and its rhythm. An ectopic pacemaker located in the atria is known as an atrial pacemaker and can cause the atrial contraction to be faster. An ectopic pacemaker situated near the AV node and the septum
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
is known as a junctional pacemaker. The pacemaker that is operating in the ventricles is known as the ventricular. Other such ectopic pacemakers can even lie within the pulmonary vein
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...
and thoracic vein walls.
Diagnosis
On an ECG, the QRS complexQRS complex
The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...
will be abnormally shaped when looking at ventricular ectopic activity, often it occurs earlier with an absent P wave. It can be perceived as a skipped beat on both the ECG and through normal pulse-taking.
During atrial ectopic activity where the P wave is normally rounded can be inverted or peaked. However the QRS complex and T waves appear relatively normal.
Conversely, during junctional ectopic activity the P wave is frequently absent or can be hidden in the QRS complex
See also
Cardiac ectopyCardiac ectopy
Ectopic beat is a disturbance of the cardiac rhythm frequently related to the electrical conduction system of the heart, in which beats arise from fiber or group of fibers outside the region in the heart muscle ordinarily responsible for impulse formation, i.e., the Sinus node...
Clinical cardiac electrophysiology
Clinical cardiac electrophysiology
Cardiac Electrophysiology , is a branch of the medical specialty of clinical cardiology and is concerned with the study and treatment of rhythm disorders of the heart. Cardiologists with expertise in this area are usually referred to as electrophysiologists...
Electrical conduction system of the heart
Electrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...