Electrical conduction pathway of the heart. Normal ECG tracing for a single contraction of the heart. The synchronized contraction of the heart occurs through a well-coordinated electrical signal pathway. The initial electrical signal originates from the SA node located in the upper portion of the right atrium. The electrical signal then travels through both the right and left atrium and causes the two atria to contract at the same time. This simultaneous contraction results in the P wave seen in an ECG tracing. The electrical signal then travels to the AV node located on the lower portion of the interatrial septum. At the AV node there is a delay in the electrical signal, which allows the atria to contract and blood to flow from the atria to the ventricles. This delay accounts for the ECG period between the P wave and the QRS complex, and creates the PR interval. From the AV nodes, the electrical signal travels through Bundle of His and divides into the right bundle and left bundle, which are located within the interventricular septum. Finally, the electrical signal travels into the Purkinje fibers. The division of the signal into a right and left bundle and then into the Purkinje fibers allows for a simultaneous depolarization and contraction of the right and left ventricles. The contraction of the ventricles results in the QRS complex seen on an ECG tracing.ECG tracing in relation to normal depolarization and contraction of the heart. Red tracing indicates pathway of electrical depolarization. Blue tracing indicates resulting ECG tracing. After contraction, the ventricles must repolarize, or reset themselves, in order to allow for a second depolarization and contraction. The repolarization creates the T wave in the ECG tracing.
Atrioventricular block
Left bundle branch block
Right bundle branch block
Sinoatrial block
Ectopic beat
Bundle branch block
Sinus arrhythmia
Junctional tachycardia