Ectopic pacemaker
(Redirected from
Ectopic focus
)| Ectopic pacemaker | |
|---|---|
| Other names | Ectopic focus, ectopic foci |
left ventricle | |
| Specialty | Electrophysiology, Cardiology |
| Symptoms |
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An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a
SA node of the heart. It is thus a cardiac pacemaker that is ectopic, producing an ectopic beat. Acute occurrence is usually non-life-threatening, but chronic occurrence can progress into tachycardia,[1] bradycardia or ventricular fibrillation.[2] 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 focus bearing an intrinsic rate superior to SA node rate, ectopic pacemaker activity may take over the natural heart rhythm.[3]
This phenomenon (an intrinsically slower pacemaker activity being unmasked by failure of faster pacemaker tissue 'upstream') is called an escape rhythm, the lower rhythm having escaped from the dominance of the upper rhythm. As a rule, premature ectopic beats (i.e. with a shorter than the prevailing preceding R-R' interval) indicate increased myocyte or conducting tissue excitability, whereas late ectopic beats (i.e. with a prolonged preceding R-R' interval) indicate proximal pacemaker or conduction failure with an escape 'ectopic' beat.
Signs and symptoms
- Isolated ectopic beats frequently cause no symptoms, although the most common symptom is the perception of a 'missed beat'. This occurs because the person notices the prolonged gap between the early (ectopic) beat and the next normal beat.
- Palpitations
- Feeling faint[4]
Cause
Ectopic pacemakers can occur within healthy hearts in response to various stimulating events, they can be caused by
automaticity
or triggered activity, such as:
- Increased local parasympathetic nervous system activity[3]
- Elevated sympathetic nervous system output[3]
- Overstimulation from drugs such as catecholamines[6]
- Cardiac hypercalcemic (high concentration of potassium/calcium), causing random excitation.[7]
They can also occur within unhealthy hearts, caused by:
- Infection
- Disease, such as sinus venosus and atrial defects[8][9]
- SA node dysfunction (1st degree block) which can cause the rate of impulse to slow[1]
- SA node blockage so that impulses never leave the atria[1]
- AV node blockage (3rd degree block) prevents normal conduction across ventricles[1]
Physiology
An ectopic pacemaker can reside within a part of the
AV node and the septum is known as a junctional pacemaker.[11] The pacemaker that is operating in the ventricles is known as the ventricular.[12] Other such ectopic pacemakers can even lie within the pulmonary vein and thoracic vein walls.[13][14]
Diagnosis
On an
ECG, the QRS complex 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.[12]
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.[10]
Conversely, during junctional ectopic activity the P wave is frequently absent or can be hidden in the QRS complex.[11]
See also
- Cardiac ectopy
- Clinical cardiac electrophysiology
- Electrical conduction system of the heart
References
- ^ PMID 14079200.
- PMID 18539188.
- ^ PMID 2035673.
- ^ Abbott, Louise (December 2012). "Atrial Fibrillation – information, symptoms and treatment". Bupa. Archived from the original on 2009-01-24. Retrieved 2009-02-04.
- ISBN 978-0-7817-4988-6.
- PMID 17325650.
- ^ Keller-Wood, Maureen. "Electrical Activity in the Heart." Lecture at the University of Florida College of Pharmacy, 23-Oct-2007.[verification needed]
- PMID 11712295.
- PMID 17473172.
- ^ ISBN 978-1-58255-701-4.
- ^ ISBN 978-1-58255-701-4.
- ^ ISBN 978-1-58255-701-4.
- PMID 17599474.
- PMID 18539751.