Ventricular fibrillation (VF) showing disorganized electrical activity producing a spiked tracing on an electrocardiogram (ECG)
Heart; conduction system. 1. SA node. 2. AV node. 3. Bundle of His. 8. Septum
Broad classification of arrhythmias according to region of heart required to sustain the rhythm
Overview of the system of electrical conduction which maintains the rhythmical contraction of the heart
Normal sinus rhythm, with solid black arrows pointing to normal P waves representative of normal sinus node function, followed by a pause in sinus node activity (resulting in a transient loss of heartbeats). Note that the P wave that disrupts the pause (indicated by the dashed arrow) does not look like the previous (normal) P waves – this last P wave is arising from a different part of the atrium, representing an escape rhythm.
Principle of ECG formation. Note that the red lines represent the depolarization wave, not bloodflow.

Dysfunction of the conduction system can cause irregular, fast, or slow heart rhythms.

- Electrical conduction system of the heart

Arrhythmias are due to problems with the electrical conduction system of the heart.

- Arrhythmia
Ventricular fibrillation (VF) showing disorganized electrical activity producing a spiked tracing on an electrocardiogram (ECG)

5 related topics

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St. Jude Medical single-lead pacemaker with ruler (released in 2005 )

Artificial cardiac pacemaker

Medical device that generates electrical impulses delivered by electrodes to cause the heart muscle chambers (the upper, or atria and/or the lower, or ventricles) to contract and therefore pump blood.

Medical device that generates electrical impulses delivered by electrodes to cause the heart muscle chambers (the upper, or atria and/or the lower, or ventricles) to contract and therefore pump blood.

St. Jude Medical single-lead pacemaker with ruler (released in 2005 )
An ECG in a person with an atrial pacemaker. Note the circle around one of the sharp electrical spikes in the position where one would expect the P wave.
An ECG of a person with a dual chamber pacemaker
ECG rhythm strip of a threshold determination in a patient with a temporary (epicardial) ventricular pacemaker. The epicardial pacemaker leads were placed after the patient collapsed during aortic valve surgery. In the first half of the tracing, pacemaker stimuli at 60 beats per minute result in a wide QRS complex with a right bundle branch block pattern. Progressively weaker pacing stimuli are administered, which results in asystole in the second half of the tracing. At the end of the tracing, distortion results from muscle contractions due to a (short) hypoxic seizure. Because decreased pacemaker stimuli do not result in a ventricular escape rhythm, the patient can be said to be pacemaker-dependent and needs a definitive pacemaker.
Right atrial and right ventricular leads as visualized under x-ray during a pacemaker implant procedure. The atrial lead is the curved one making a U shape in the upper left part of the figure.
Single-chamber VVIR/AAIR pacemaker
Dual-chamber DDDR pacemaker
Three leads can be seen in this example of a cardiac resynchronization device: a right atrial lead (solid black arrow), a right ventricular lead (dashed black arrow), and a coronary sinus lead (red arrow). The coronary sinus lead wraps around the outside of the left ventricle, enabling pacing of the left ventricle. Note that the right ventricular lead in this case has two thickened aspects that represent conduction coils and that the generator is larger than typical pacemaker generators, demonstrating that this device is both a pacemaker and a cardioverter-defibrillator, capable of delivering electrical shocks for dangerously fast abnormal ventricular rhythms.
Posteroanterior and lateral chest radiographs of a pacemaker with normally located leads in the right atrium (white arrow) and right ventricle (black arrowhead), respectively.
Two types of remote monitoring devices used by pacemaker patients
In 1958, Arne Larsson (1915–2001) became the first to receive an implantable pacemaker. He had 26 devices during his life and campaigned for other patients needing pacemakers.
Illustration of implanted cardiac pacemaker showing locations of cardiac pacemaker leads
The first lithium-iodide cell-powered pacemaker. Invented by Anthony Adducci and Art Schwalm. Cardiac Pacemakers Inc. 1972

By doing so, this device replaces and/or regulates the function of the electrical conduction system of the heart.

Any events that were stored since the last follow-up, in particular arrhythmias such as atrial fibrillation. These are typically stored based on specific criteria set by the physician and specific to the patient. Some devices have the availability to display intracardiac electrograms of the onset of the event as well as the event itself. This is especially helpful in diagnosing the cause or origin of the event and making any necessary programming changes.

Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.

Cardiac pacemaker

Initiated by electrical impulses known as action potentials.

Initiated by electrical impulses known as action potentials.

Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.
Schematic representation of the sinoatrial node and the atrioventricular bundle of His. The location of the SA node is shown in blue. The bundle, represented in red, originates near the orifice of the coronary sinus, undergoes slight enlargement to form the AV node. The AV node tapers down into the bundle of HIS, which passes into the ventricular septum and divides into two bundle branches, the left and right bundles. The ultimate distribution cannot be completely shown in this diagram.

Sometimes an ectopic pacemaker sets the pace, if the SA node is damaged or if the electrical conduction system of the heart has problems.

Cardiac arrhythmias can cause heart block, in which the contractions lose any useful rhythm.

Cardiac muscle

One of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

One of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

3D rendering showing thick myocardium within the heart wall.
The swirling musculature of the heart ensures effective pumping of blood.
Cardiac muscle
Illustration of a cardiac muscle cell.
Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.
Dog cardiac muscle (400X)

Each cardiomyocyte needs to contract in coordination with its neighboring cells - known as a functional syncytium - working to efficiently pump blood from the heart, and if this coordination breaks down then – despite individual cells contracting – the heart may not pump at all, such as may occur during abnormal heart rhythms such as ventricular fibrillation.

Other potential roles for fibroblasts include electrical insulation of the cardiac conduction system, and the ability to transform into other cell types including cardiomyocytes and adipocytes.

ECG of a heart in normal sinus rhythm

Electrocardiography

Process of producing an electrocardiogram , a recording of the heart's electrical activity.

Process of producing an electrocardiogram , a recording of the heart's electrical activity.

ECG of a heart in normal sinus rhythm
Normal 12-lead ECG
A 12-lead ECG of a 26-year-old male with an incomplete right bundle branch block (RBBB)
A patient undergoing an ECG
An EKG electrode
Proper placement of the limb electrodes. The limb electrodes can be far down on the limbs or close to the hips/shoulders as long as they are placed symmetrically.
Placement of the precordial electrodes
The limb leads and augmented limb leads (Wilson's central terminal is used as the negative pole for the latter in this representation)
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Diagram showing the contiguous leads in the same color in the standard 12-lead layout
QRS is upright in a lead when its axis is aligned with that lead's vector
Schematic representation of a normal ECG
Measuring time and voltage with ECG graph paper
Animation of a normal ECG wave
Formation of limb waveforms during a pulse
An early commercial ECG device (1911)
ECG from 1957
Use of real time monitoring of the heart in an intensive care unit in a German hospital (2015), the monitoring screen above the patient displaying an electrocardiogram and various values of parameters of the heart like heart rate and blood pressure

Symptoms such as shortness of breath, murmurs, fainting, seizures, funny turns, or arrhythmias including new onset palpitations or monitoring of known cardiac arrhythmias

Interpretation of the ECG is fundamentally about understanding the electrical conduction system of the heart.

Image showing the conduction system of the heart. The AV node is labelled 2.

Atrioventricular node

Image showing the conduction system of the heart. The AV node is labelled 2.
Isolated heart conduction system showing atrioventricular node

The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart.

This also protects the ventricles from excessively fast rate response to atrial arrhythmias (see below).