Electrocardiogram (ECG or sometimes known as EKG) offers two types of information. It measures the length it takes for electrical waves to travel through the heart and the amount of electrical activity that is generated and passes through the heart muscles. ECG can determine whether the waves are slow, fast or irregular.

In the heart, pacemaker cells are specialized cells that produce electricity by rapid change of their electrical charges from positive to negative and vise versa. This electrical current begins from the top of the heart and spreads quickly to the end. The heart beat produces makes the heart muscles contract. The contracting of the heart muscles work to pump blood from the heart.

As electrical waves tend to get weaker when it travels through bone and skin, the ECG has electrodes sensitive enough to detect these waves non-invasively through the skin. These electrical waves is recorded in millivolts by an electrocardiograph and translated to recordings in paper by the ECG machine. The 12 electrodes are connected to the machine through wires called leads. ECG procedure is generally painless and not harmful. The area of skin for electrode attachment needs to be cleaned before the electrodes are hooked up.

Electrocardiogram primarily is used to diagnosis heart conditions and records small electric waves generated during heart activity. 12 lead ECG is as effective as cardiac catheterization for diagnosing right ventricular myocardial infarction (RVMI). Cardiac catheterization visualizes vessels and pumping action of the heart. ECG is also used for diagnosis of left ventricular hypertrophy (Levy et al 1997). Together with echocardiogram, ECG can improve the diagnosis of ischemic stroke. (Kohsaka et al 2005). 24 hour electrocardiographic monitoring (holter) is used to detect initial tendency for arrhythmias for patients with unexplained syncope (Sarasin et al 2005)

ECG measurement is also used during a cardiovascular stress test. A stress test is done to indicate whether adequate blood flow is getting to the heart when a person is stressed or during exercise. During a cardiopulmonary stress test, ECG measures the cardiac capability while gas exchange in the lungs is measured to indicate the respiratory limitations. A thallium stress test is done to find out whether exercise induces a decreased blow flow to the heart. Exercise electrocardigraphy is a cost effective screening for coronary artery disease. A study done on asymptomatic diabetic patients found that exercise electrocardiography and exercise echocardiography are best early detection methods for these patients (Hayashino et al 2004)

Electrocardiogram has also been incorporated into a PDA for portable access. A study has shown that the program had excellent accuracy making it a good potential for quick and regular screening (Rodriguez et al 2005).

(12 Lead Ekg Placement Information)

REFERENCES
Levy D.; Salomon M.; D'Agostino R.B.; Belanger A.J.; Kannel W.B. (1997). Prognostic implications of baseline electrocardiographic features and their serial changes in subjects with left ventricular hypertrophy. Framingham Heart Study USA, EMBASE
Kohsaka S, Sciacca RR, Sugioka K, Sacco RL, Homma S, Di Tullio MR. (2005). Additional impact of electrocardiographic over echocardiographic diagnosis of left ventricular hypertrophy for predicting the risk of ischemic stroke. Am Heart J.: 149(1);181-6
Sarasin FP, Carballo D, Slama S, Louis-Simonet M. (2005). Usefulness of 24-h Holter monitoring in patients with unexplained syncope and a high likelihood of arrhythmias. Int J Cardiol.:101(2);203-7.
Hayashino Y, Nagata-Kobayashi S, Morimoto T, Maeda K, Shombo T, Fukui T. (2004). Cost-effectiveness of screening for coronary artery disease in asymptomatic patients with Type 2 diabetes and additional risk factors. J. Gen Intern Med. 19(12); 1181-91
Rodriguez J, Goni A, Illarramendi A. (2005). Real-time classification of ECGs on a PDA. IEEE Trans Inf Technol Biomed.: 9(1);23-34