The Effect of Temperature on the Growth and Survival of Micro-Organisms.

The electrical activity of the

heart: the electrocardiogram

Electrical activity is a basic characteristic of the heart and is the stimulus for cardiac contraction. Disturbances of electrical function are common in heart disease. Their registration as an electrocardiogram (ECG) plays an essential role in the diagnosis and management of heart disorders.

THE GENESIS OF THE ELECTROCARDIOGRAM Pathways of conduction and the electrocardiogram

The sinus node is situated in the right atrium close to the entrance of the superior vena cava. The atrioventricular node lies in the right atrial wall immediately above the tricuspid valve. The fibres of the AV bundle (of His) arise from the atrioventricular node and run along the posterior border of the septum between the ventricles (Fig. 1.1). On reaching the muscular part of the septum, they split into right and left bundle branches and then spread out in the subendocardium of the ventricles as the Purkinje system. The right bundle is a slender, compact structure. The left bundle soon splits into two or more divisions or fascicles, one of which proceeds anteriorly, sharing