Use of ECG for Diagnostic Purposes



diagnostic information can be obtained from the ECG waveform, by analysis of the amplitude and relative timing of the various segments. In general, cardiac muscle damage, or infarcts, are correlated with loss of amplitude. Abnormal heart rates (arrhythmias) can be observed and treated; for examples slow rhythms (bradycardia) can be treated with stimulants or a pacemaker whilst in the case of fast (tachycardia) depressants can be prescribed. Ectopic beats are beats which originate from a region of the heart other than the SA node. An ectopic beat in the ventricle causes an extra R−wave, indicative of a premature ventricular contraction (PVC).

These abnormal conditions are usually identified by one of two means:

• Ambulatory monitoring for up to 24 hours of patients who have been identified as being at risk of heart attacks. Data compression techniques (eg beat−to−beat interval histograms) are often used although advances in memory technology is reducing the need for these.

•  Exercise stress ECGs in which the patient is taken close to maximum heart rate by exercising, for example on a tread mill. Changes in the ECG waveform during this process give the cardiologist indications as to the efficiency and capacity of the heart’s pumping action. PVCs may only occur when the body is under physical stress, as this makes demands for higher cardiac output. Exercise testing can also be used to assess the effectiveness of therapeutic and surgical treatments.

A more specialised application of ECG analysis is the detection of foetal distress prior to and during labour. An additional problem here is the separation of the maternal and foetal ECGs (adaptive filtering techniques are usually required in addition to careful positioning of the ecletrodes).

All the above applications involve the analysis of the ECG waveform and the extraction of

various features of the waveform. In each case, the heart rate provides information of value

and needs to be calculated. There are two types of heart rate meters (also known as

cardiotachometers):

• the averaging heart rate meter which calculates the average heart rate from a count or estimate of the number of beats over a period of time.

• the beat−to−beat heart rate meter which computes the reciprocal of the time interval between two consecutive heart beats and updates the information with each heart beat.( this method will be use in this project )