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
ECG of a heart in normal sinus rhythm
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 12-lead ECG
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.
A 12-lead ECG of a 26-year-old male with an incomplete right bundle branch block (RBBB)
Principle of ECG formation. Note that the red lines represent the depolarization wave, not bloodflow.
A patient undergoing an ECG
Different wave shapes generated by different parts of the heart's action potential
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
A 12-lead ECG of a 26-year-old male with an incomplete right bundle branch block (RBBB)

There is a skeleton of fibrous tissue that surrounds the conduction system which can be seen on an ECG.

- Electrical conduction system of the heart

Dysfunction of the conduction system can cause irregular heart rhythms including rhythms that are too fast or too slow.

- Electrical conduction system of the heart

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

- Arrhythmia

A number of tests can help with diagnosis, including an electrocardiogram (ECG) and Holter monitor.

- Arrhythmia

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

- Electrocardiography

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

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

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

Artificial cardiac pacemaker

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Medical device that generates electrical impulses delivered by electrodes to the chambers of the heart either the upper atria, or lower ventricles to cause the targeted chambers to contract and pump blood.

Medical device that generates electrical impulses delivered by electrodes to the chambers of the heart either the upper atria, or lower ventricles to cause the targeted chambers to contract and 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, the pacemaker regulates the function of the electrical conduction system of the heart.

The rescuer selects the pacing rate, and gradually increases the pacing current (measured in mA) until electrical capture (characterized by a wide QRS complex with a tall, broad T wave on the ECG) is achieved, with a corresponding pulse.

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.