Electrocardiography is the detection of cardiac contraction. The electrocardiogram is a recording on paper of potential changes. The contraction of the myocardial fibers is caused by electrical changes. Wanting to study this phenomenon of the heart may be used for both electrodes attached directly sull'epicardio, both electrodes placed in various regions of the body, in fact, patterns of myocardial action spread throughout the body. The currents that reach the skin, however, are very weak and require highly sensitive recording equipment. The electrocardiographs work almost exclusively by batteries placed in battery using electronic amplification circuits and sophisticated writing systems. The electrical signal comes from the heart through the electrode at the junction and then switch to the pre-amplifier which is amplified for the first time, then moves on to the final stages of amplification and is then sent to the instrument detection, and writing. L ' ECG is a representative curve of the waves of change of cardiac action potential in the various phases of the cardiac cycle,
whose interpretation makes a thorough knowledge of the state of the myocardium. waves in a fixed position, which compose it are called P - Q - R - S - T . Measurement of heart rate
When reading an ECG is important to quickly go back to the heart rate in beats per minute (bpm).
The following is the mathematical rule and also a mnemonic rule of considerable interest
F (bpm) = 1 / T (min) = 60 / T (sec)
From the ECG of a cardiac cycle period T is detectable in mm. For the standard paper speed of 25 mm / sec, an inch of track match:
1 mm = 1 / 25 sec = 0.04 sec = 40 msec
For example: a period of 20 mm corresponds to a frequency:
F = 60 / T = 60/20 = 0.04 x 60 / 0.8 = 75 bpm
More simply the distance traveled by the pen in one minute divided by a time T in mm:
F = 1500 mm/20 mm = 75 bpm
(200 words ... a bit more ...)
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