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Electrocardiography is the process of producing an electrocardiogram (ECG or EKG [a]), a recording of the heart's electrical activity through repeated cardiac cycles. [4] It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart [ 5 ] using electrodes placed on the skin.
Unlike standard basal ECG recording, which requires only a few seconds, SAECG recording requires a few minutes (usually about 7-10 minutes), as the machine must record multiple subsequent QRS potentials to remove interference due to skeletal muscle and to obtain a statistically significant average trace. For this reason, it is important for the ...
In a healthy heart all activities and rests during each individual cardiac cycle, or heartbeat, are initiated and orchestrated by signals of the heart's electrical conduction system, which is the "wiring" of the heart that carries electrical impulses throughout the body of cardiomyocytes, the specialized muscle cells of the heart.
Another important ion is calcium (Ca 2+), which can be found inside the cell in the sarcoplasmic reticulum (SR) where calcium is stored, and is also found outside of the cell. Release of Ca 2+ from the SR, via a process called calcium-induced calcium release , is vital for the plateau phase of the action potential (see phase 2, below) and is a ...
Cardiac muscle has some similarities to neurons and skeletal muscle, as well as important unique properties. Like a neuron, a given myocardial cell has a negative membrane potential when at rest. Stimulation above a threshold value induces the opening of voltage-gated ion channels and a flood of cations into the cell.
Schematic representation of a normal sinus rhythm ECG wave. Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the heart's electrical axis in the frontal plane. The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually ...
ECG would be abnormal in 75 to 95% of the patients. Characteristic ECG changes would be large QRS complex associated with giant T wave inversion [4] in lateral leads I, aVL, V5, and V6, together with ST segment depression in left ventricular thickening. For right ventricular thickening, T waves are inverted from V2 to V3 leads.
Each Holter system has hardware (called monitor or recorder) for recording the signal, and software for review and analysis of the record. There may be a "patient button" on the front that the patient can press at specific instants such as feeling/being sick, going to bed, taking pills, marking an event of symptoms which is then documented in the symptoms diary, etc.; this records a mark that ...