ECG Heart Sounds Protocol

Teaching Experiment 

Electrocardiogram and Heart Sounds An introduction to the recording and analysis of electrocardiograms, and the sounds of the heart. Written by Staf o ADInstruments

Introduction  The beating of the heart is is accompanied accompanied by both electrical electrical activity activity and sound. sound. The pattern pattern of electrical activity produced by each heart beat cycle is called the electrocardiogram electrocardiogram or  or ECG.  The aim of this this session is is to record record and analyze analyze an ECG ECG from a student volunteer, volunteer, and to examine the relationship between the ECG and the characteristic sounds of the heart.

Background  The heart is is a dual pump that pushes pushes blood around around the body and and through the lungs. lood enters the atrial atrial chambers  chambers of the heart at a low pressure and leaves the ventricles ventricles at  at a higher pressure! it is this high arterial pressure that provides the energy to force blood through the circulatory system. "igure # shows #  shows the organization of the human heart and the circulatory system, in schematic form. lood returning from the body arrives at the right side of the heart and is pumped through the lungs to pic$ up oxygen and release carbon dioxide. This oxygenated blood then arrives at the left side of the heart, from where it is pumped bac$ to the body.

Lungs

Right atrium

Left atrium

AV valves

Rig Right ve ventric ricle

Left ventric ricle

Semilunar valves

Tissues

Figure 1. A schematic diagram of the human heart and circulatory system.

Cardiac contractions are not dependent upon a nerve supply. A group of wea$ muscle cells %sinoatrial %sinoatrial or sinuatrial sinuatrial node, &A node' acts as the pacema$er pacema$er for the heart % "igure ('. ( '. These cells rhythmically produce action potentials that spread through the )bers of the atria. The resulting resulting contraction pushes blood into the ventricles. The only electrical connection between the atria and the ventricles is via the atrioventricular %A*' node. The action potential spreads SPB08c

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Teaching Experiment  slowly through the A* node %thus giving a time delay for ventricular )lling' and then rapidly through the A* bundle and +ur$ine )bers to excite both ventricles. The large muscle mass of the ventricles allows powerful contractions. SA node

Atrial muscle

AV node AV bun dl e

Purkinje fibres

Ventri cular muscle

Figure 2. Components of the human heart involved in conduction.

Each side of the heart is provided with two valves, to convert rhythmic contractions into a unidirectional pumping. The valves close automatically whenever there is a pressure di-erence across the valve that would cause bac$ow of blood. Closure gives rise to audible vibrations %heart sounds'. Atrioventricular (AV) valves between the atrium and ventricle on each side of the heart prevent bac$ow from ventricle to atrium. Semilunar valves are located between the ventricle and the artery on each side of the heart, and prevent bac$ow of blood from artery to ventricle. The cardiac cycle involves a se/uential contraction of the atria and the ventricles. The combined electrical activity of the di-erent myocardial cells produces electrical currents that spread through the body uids. These currents are large enough to be detected by recording electrodes placed on the s$in. The regular pattern of pea$s produced by each heart beat cycle is called the electrocardiogram or ECG % "igure 0'. R

1.0

0.5 T

P

Time Q S – 0.5

Figure 3. A typical ECG showing the fundamental parts that make up the signal.

 The action potentials recorded from atrial and ventricular )bers are di-erent from those recorded from nerves and s$eletal muscle. The cardiac action potential is composed of three phases1 a rapid depolarization, a plateau depolarization %which is very obvious in ventricular )bers', and a repolarization bac$ to resting membrane potential.  The components of the ECG can be correlated with the electrical activity of the atrial and ventricular muscle1 the P-wave is produced by atrial depolarization •

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Teaching Experiment  •

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the QRS complex is produced by ventricular depolarization! atrial repolarization also occurs during this time the T-wave is produced by ventricular repolarization.

 The characteristic sound produced by the heart is usually referred to as a 2lub3dup4 sound. The lower3pitched 2lub4 sound occurs during the early phase of ventricular contraction and is produced by closing of the atrioventricular valves %the mitral valve and tricuspid valve', which prevent blood from owing bac$ into the atria. 5hen the ventricles relax, the blood pressure drops below that in the artery and the semilunar valves %aortic and pulmonary' close, producing the higher3pitched 2dup4 sound.

Required Equipment  The experiment has been designed for and tested on a +ower6ab 78(9T system, although it can easily be adapted for other +ower6ab systems.  This general setup is used for all the exercises in this experiment. The +ower6ab 78(9T should already be connected up to your computer and turned on. The e/uipment re/uired for these exercises is1 A computer system Chart software version :.9 or later +ower6ab %with built3in io Amp or +ower6ab and io Amp front3end' "ive3lead &hielded io Amp Cable ; snap3connect 6ead 5ires  Three reusable clamp electrodes or disposable adhesive electrodes Electrode cream %for use with the clamp electrodes' Alcohol swabs %