It is important to recognize that not every QRS complex will contain Q, R, and S waves. As with the P wave, the QRS complex starts just before ventricular contraction. The QRS complex represents the electrical impulse as it spreads through the ventricles and indicates ventricular depolarization. These three waves occur in rapid succession. It will be positive in leads I, II, aVF and V1 through V6.Īs the name suggests, the QRS complex includes the Q wave, R wave, and S wave. In most cases, the P wave will be smooth and rounded, no more than 2.5 mm tall, and no more than 0.11 seconds in duration. Because it is so small, atrial repolarization is usually not visible on ECG.
Strictly speaking, the atria contract a split second after the P wave begins. The P wave represents the depolarization of the left and right atrium and also corresponds to atrial contraction. Studying these electrical impulses allows us to understand how the heart is functioning. This electrical impulse causes the four chambers of the heart to contract and relax in a coordinated fashion. Under normal circumstances, an electrical impulse will travel from the sinoatrial node, spread across the atrium, to the atrioventricular node and through the ventricular septum of the heart. Fortunately, basic ECG interpretation can be rather straightforward, as long as you know the basics.Īn electrocardiogram is a tracing of the electrical activity that is taking place within the heart.
Learning how to interpret the subtle differences in characteristic changes that can arise is a specialized skill that can take years to learn. The information contained within a single 12-lead electrocardiogram can be extensive.