Cardiograms

Cardiograms are graphical records of the heart's activity, produced by noninvasive monitoring techniques. The most widely used form is the electrocardiogram (ECG or EKG), which records the heart's electrical impulses as they propagate through the atria and ventricles.

An ECG is typically obtained with electrodes placed on the arms, legs, and chest, and often displayed as a set of 12 leads. It provides a snapshot of electrical activity over time and can be repeated to monitor changes.

ECG tracings show waves and intervals that reflect events in the cardiac cycle. The P wave indicates atrial depolarization; the QRS complex represents ventricular depolarization; the T wave corresponds to ventricular repolarization. Measurements include heart rate, rhythm, PR interval, QRS duration, and QT interval. The axis of electrical activity and the presence of ST-segment or T-wave abnormalities are also evaluated for signs of ischemia or injury.

Cardiograms are used to diagnose or assess arrhythmias, conduction disorders, myocardial infarction or ischemia, electrolyte disturbances, and drug effects. They are also used in preoperative evaluation, during acute care, and in routine health screening. Ambulatory versions (Holter monitors) or event recorders extend monitoring over days to weeks, and exercise tests assess ECG changes with physical activity.

While highly informative, cardiograms primarily reflect electrical activity and do not directly measure heart muscle pumping function; findings require clinical context. Artefacts from movement or poor contact can affect interpretation, and abnormal results are often followed by additional imaging or testing. The notion of cardiograms also includes related recordings, such as phonocardiograms that graphically represent heart sounds.