Editing Heart (section)

====Electrocardiogram====
{{main|Electrocardiography}}
[[File:2028 Cardiac Cycle vs Electrocardiogram.jpg|thumb|Cardiac cycle shown against ECG]]
Using surface electrodes on the body, it is possible to record the electrical activity of the heart. This tracing of the electrical signal is the electrocardiogram (ECG) or (EKG). An ECG is a [[bedside test]] and involves the placement of ten leads on the body. This produces a "12 lead" ECG (three extra leads are calculated mathematically, and one lead is [[Ground (electricity)|electrically ground]], or earthed).{{sfn|Davidson's|2010|pp=528–530}}

There are five prominent features on the ECG: the [[P wave (electrocardiography)|P wave]] (atrial depolarisation), the [[QRS complex]] (ventricular depolarisation){{efn|Depolarisation of the ventricles occurs concurrently, but is not significant enough to be detected on an ECG.{{sfn|Davidson's|2010|pp=528–530}}
}} and the [[T wave]] (ventricular repolarisation).<ref name="CNX2014"/> As the heart cells contract, they create a current that travels through the heart. A downward deflection on the ECG implies cells are becoming more positive in charge ("depolarising") in the direction of that lead, whereas an upward inflection implies cells are becoming more negative ("repolarising") in the direction of the lead. This depends on the position of the lead, so if a wave of depolarising moved from left to right, a lead on the left would show a negative deflection, and a lead on the right would show a positive deflection. The ECG is a useful tool in detecting [[arrythmia|rhythm disturbances]] and in detecting insufficient blood supply to the heart.{{sfn|Davidson's|2010|pp=528–530}} Sometimes abnormalities are suspected, but not immediately visible on the ECG. [[Cardiac stress test|Testing when exercising]] can be used to provoke an abnormality or an ECG can be worn for a longer period such as a 24-hour [[Holter monitor]] if a suspected rhythm abnormality is not present at the time of assessment.{{sfn|Davidson's|2010|pp=528–530}}