Summary of ECG QRS transition
Transcript for ECG QRS transition
ECG QRS transition
An electrocardiogram is also known as an ECG; the Dutch and German version of the word, elektrokardiogram, is shortened to EKG. It is a tool used to visualize, or “gram,” the electricity, or “electro,” that flows through the heart, or “cardio.” Specifically, an ECG tracing shows how the depolarization wave, which is a wave of positive charge, moves during each heartbeat by providing the perspectives of different sets of electrodes. This particular set of electrodes is called lead II; one electrode is placed on the right arm and the other on the left leg. Essentially, when the wave’s moving toward the left leg electrode, you get a positive deflection. This big, positive deflection corresponds to the wave moving down the septum. To read an ECG, there are a few key elements to keep in mind; one is to figure out the QRS transition.
The chest leads will have a mostly positive deflection, if a depolarization wave is moving towards them. The QRS transition zone refers to where the QRS complex switches from being mostly negative to mostly positive, from the point of view of the chest leads, V1 through V6, which “view” the heart through the horizontal plane. The QRS transition usually happens in lead V3 or V4, depending on factors such as chest lead placement and the exact anatomy of a person’s heart. So, the QRS transition tells us when the overall QRS vector is aligned in the direction of the chest leads; it’s a way of understanding what’s happening to the QRS axis in the horizontal plane.
If something alters the heart’s overall QRS vector, then the QRS transition zone can shift to the right, towards V1 and V2, or to the left, towards V5 and V6. For example, a myocardial infarction leads to the formation of scar tissue that can’t depolarize. Generally speaking, the QRS transition zone will shift away from a region of scar tissue, because it no longer contributes to the overall QRS vector. Consider the following: a blockage in the left circumflex artery can cause infarction of the posterior wall of the left ventricle, which would lead to a rightward rotation of the QRS transition zone, toward V1 and V2. Another example would be cardiac hypertrophy, because a thicker muscular wall contributes more to the overall QRS vector. If it’s right ventricular hypertrophy, it would lead to a rightward rotation of the QRS transition zone, towards V1 and V2, similar to the result of an infarction of the posterior wall of the left ventricle. In contrast, a right ventricular infarction or a left ventricular hypertrophy would lead to a leftward rotation of the QRS transition zone, towards V5 and V6.