DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Heart disease. Electrocardiogram (ECG) showing the heartbeat during atrial fibrillation in an 80- year-old man. An ECG records the pumping of the heart's chambers, tracing electrical waves (blue) that are the output from 12 external electrodes (I-III, V1-V6 and aVR, aVL and aVF). In atrial fibrillation, the heart muscle fibres of the atria (two of the heart chambers) fail to contract in a co-ordinated way, leading to a rapid, irregular beat. This case may have been caused by myocardial ischaemia, inadequate blood flow to the heart muscle due to blocked blood vessels. Abnormalities in this ECG include changes (e.g. trough in trace V4) in the T wave after the main heartbeat peak.
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