The standard ECG uses ten cables to obtain twelve electrical views of the heart. There are three limb leads, three uni-polar leads and six chest leads. For an improved reading the electrodes are placed onto the torso to replace those that are usually placed onto the ankles and wrists. This should minimise any limb interference during the exercise.
METHOD
A twelve lead resting ECG, using suction electrodes was measured with the subject in a supine position. The electrodes are placed on each wrist and ankle making sure that the neutral electrode is placed onto the left ankle. Another six electrodes are placed on the subject making sure that a gel is applied to the electrodes so they stay better on the body. The placement of the electrodes is as follows:
V1 - Fourth intercostal space to the right of the sternum.
V2 – Fourth intercostal space left of the sternum
V3 – between V2 and V4
V4 – fifth intercostal space at the mid clavicular line
V5 – Left auxiliary line, horizontal as V4
V6 – Left mid auxiliary in line with V4
A SERCA ECG machine then calculated the electrical impulses of the heart, making sure that the filter had been switched on to minimise any noise disturbances.
The equipment was later modified by using electrode pads and the Schiller ECG machine which was integrated with a ratchet belt treadmill.
RESULTS
Above is a basic reading of an ECG. The P wave indicates the upper chambers of the heart being stimulated to pump blood into the ventricles. The short downwards section with the sharp upwards section is called the QRS Complex which indicated the chambers of the heart being electrically stimulated to pump the blood out. The next section, the ST segment is the time from the end of contraction to the beginning of the T-Wave which signifies the recovery period of the ventricle.
Above is the copy of the resting ECG achieved from a healthy subject. Although a little unclear, the QRS wave is easy to detect.
DISCUSSION
Over the past few years electrocardiographic (ECG) screening has become increasingly prevalent especially among athletes who compete in competitive sports. However ‘Conducting a 12lead ECG in an exercise test permits mobility.’ Mason (1966)
To overcome this, the limb lead electrodes are placed onto the torso therefore eliminating any resonance that would interfere with the ECG reading.
Normal activation of the heart is directed by the sinus node. Interpretation of the ECG tracing can be occasionally difficult to detect.
Although more prevalent in women, ST-T changes are found to carry the same predictive risk in both sexes.
REFERENCES
De Bacquer D, De Backer G, Kornitzer M, et al. Prognostic value of ischemic electrocardiographic findings for cardiovascular mortality in men and women. Journal of the American Collage of Cardiology.1998; 32:680 –5.
Mason RE, Likar I. A new system of multiple-lead exercise electrocardiography. Am Heart J; 71:196–205.1966
Swallow.EB,Reyes.D,Hopkinson.NS,ManWD,Porcher.R,Cetti.EJ,et al. Quadriceps strength predicts mortality in patients with moderate to severe chronic obstructive pulmonary disease. Thorax 2007; 62:115-20.
