Question

What is the purpose of using a 6-lead ECG as opposed to only 1 lead?

Describe the cascade of electrical activity through the heart with a normal sinus rhythm. What controls HR?

What changes are anticipated in an ECG recording in the transition from rest to exercise? What abnormal or pathological changes may occur in the transition from

rest to exercise?

How does body position affect HR? What is occurring physiologically to cause these changes?

Answer 1

An ECG is a representative of condition of all the wall of heart based on recording its conduting electrical stimuli.

1)A 6 lead ECG records the electrical stimuli from 6 direction, while a single lead ECG records only the anterior wall conduction. Hence, to know about condition of all the walls, it is important to get a 6 lead ECG.

2) Electrical stimuli is generated by the Pacemaker SA node located in the Right atrium and it travels through three internodal pathway to AV node from here Bundle of His to Left and right bundle branch which further travels into purkinje fibers supplyinh the ventricles and then to the ventricular myocytes.

Heart rate is under controle of pacemaker SA node.

3) While transition from rest to exercising the PR interval may reduce to increase heart rate. The amplitude of left ventricular wall QRS may increase due to increased contractility of heart.

4) Pathological change - If the person is having some problem and not able to maintain COP to meet the demand of exercising myocardium. Then there may occur acute ishemia notice by Tall T waves followed by elevation of ST segment.

5) Heart rate increase from supine to sitting position.

When we suddenly get up from supine position to standkng position there is peripheral pooling of blood to venous sytem that lead to decreased venous return and BP. This is sensed by baro-, receptors and this increase sympthetic and decreses Parasympathetic outflow. Hencr, HR Increases from supine to sitting position.