Question

Explain how the tracings on an ECG relate to the electrical activity of the heart.

Answer 1

Ans) An electrocardiogram (ECG or EKG) is one of the simplest and fastest procedures used to evaluate the heart. The first short upward notch of the ECG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are contracting to pump out blood.

- The next part of the tracing is a short downward section connected to a tall upward section. This next part is called the "QRS complex." This part indicates that the ventricles (the two lower chambers of the heart) are contracting to pump out blood. The next short upward segment is called the "ST segment." The ST segment indicates the amount of time from the end of the contraction of the ventricles to the beginning of the rest period before the ventricles begin to contract for the next beat. The next upward curve is called the "T wave." The T wave indicates the resting period of the ventricles.

- When the physician views an ECG, he/she studies the size and length of each part of the ECG. Variations in size and length of the different parts of the tracing may be significant. The tracing for each lead of a 12-lead ECG will look different, but will have the same basic components as described above. Each lead of the 12-lead ECG is "looking" at a specific part of the heart, so variations in a lead may indicate a problem with the part of the heart associated with a particular lead.
- During the electrocardiogram (ECG), sticky electrode patches are applied to your chest, arms and legs. Wires connect the electrodes to a computer, which translates the electrical activity in your heart into tracings on a monitor and/or special ECG graph paper. Your doctor will analyze the ECG to learn more about your heart’s rhythm and the overall condition of your heart.

- An ECG shows several types of “waves” of electrical signals.
The “P” wave is the first small peak in the ECG. It indicates the electrical impulse in the upper chambers of your heart.
The “QRS” complex is made up of the “R” wave, which is the tallest peak in the ECG, plus the small notches in the ECG that come before it (the “Q” wave) and after it (the “S” wave). The QRS complex records electrical activity in the lower chambers of your heart.
The “T” wave is the final small peak in the ECG. It reflects the heart’s return to a resting state.
The shape and size of the waves, the time between each wave and the rate and regularity of beating provide valuable information to your doctor. In addition to providing insight into the heart’s rhythm, the ECG helps your doctor determine the size of the heart chambers, detect heart muscle damage and identify abnormal levels of certain minerals in the blood, such as potassium and calcium, which alter the ECG. The results of an ECG can be normal when the patient is in a resting state, which is why many patients also undergo a stress test to evaluate the heart during exercise.