Question

Given above is the ECG of a normal human. Which one of its components is correctly interpreted below?

• A. Complex QRS-One complete pulse
• B. Peak P and Peak R together - systolic and diastolic blood pressures
• C. Peak T - Initiation of total cardiac contraction
• D. Peak P - Initiation of left atrial contraction only

Answer 1

Answer: (A)

The P wave in the ECG represents atrial depolarization, which results in atrial contraction. The largest wave in the QRS complex is the R wave. The R wave represents the electrical stimulus as it passes through the main portion of the ventricular walls. The wall of the ventricles are very thick due to the amount of work they have to do, consequently, more voltage is required. This is why the R wave is by far the biggest wave generated during normal conduction. Diastole represents the period of time when the ventricles are relaxed (not contracting). Systole represents the time during which the left and right ventricles contract and eject blood into the aorta and pulmonary artery, respectively. The cardiac cycle is usually divided into seven phases. The first phase begins with the P wave of the electrocardiogram, which represents atrial depolarization, and is the last phase of diastole. Phases 2-4 represent systole, and phases 5-7 represent early and mid-diastole. The last phase of the cardiac cycle ends with the appearance of the next P wave, which begins a new cycle.