Preksha Meditation & Human Health: 1.5 Cardiac Conduction Pathway

The cardiac cycle is regulated by the electrical activity of the myocardium. Cardiac muscle cells have the ability to contract spontaneously; that is; nerve impulses are not required to cause contraction. The heart generates its own beat, and the electrical impulses follow a very specific route throughout the myocardium. The natural pacemaker of the heart is the sinoatrial (SA) node, a specialized group of cardiac muscle cells located in the wall of the right atrium just below the opening of the superior vena cava (Fig. 1-5). The SA node is considered specialized because it has the most rapid rate of contraction, that is, it depolarizes more rapidly than any other part of the myocardium (60 to 80 times per minute). From the SA node, impulses for contraction travel to the atrioventricular (AV) node, located in the lower interatrial septum. The transmission of impulses from the SA node to the AV node and to the rest of the atrial myocardium brings about atrial systole. The pathway for impulses from the atria to the ventricles, is the atrioventricular bundle (AV bundle), also called the bundle of His. The AV bundle is within the upper interventricular septum; it receives impulses from the AV node and transmits them to the right and left bundle branches. From the bundle branches, impulses travel along Purkinje fibres to the rest of the ventricular myocardium and bring about ventricular systole. The electrical activity of the atria and ventricles is depicted by an electrocardiogram (ECG) (Scanlon, 2007).