ecg and sounds

7/28/2019 Ecg and Sounds

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ELECTROCARDIOGRAM

&

HEART SOUNDS

Learning Objectives

• By the end of today's laboratory you will:

• Explain the time relationships between the electrical activity

of the heart (as recorded in the ECG) and the mechanical

activity of the heart (as judged from the heart sounds)

HEART SOUNDS

The closure of the heart valves is responsible for the

characteristic sound produced by the heart, usually referred

to as a ‘lub-dup’ sound.

The lower-pitched ‘lub’ sound occurs during the early phase of ventricular contraction. This is produced by closing

of the atrioventricular (mitral and tricuspid) valves.

These valves prevent blood from flowing back into the

atria. When the ventricles relax, the blood pressure drops

below that in the artery, and the semilunar valves (aortic and

pulmonary) close, producing the higher-pitched ‘dup’ sound.

Malfunctions of these valves often produce an audible

murmur, which can be detected with a stethoscope.



A Wiggers' diagram.

Standard Connection

Attach the positive electrode to

the left wrist,the negative to the right wrist,

and the ground to the right

leg.V

Alternative Electrode Connection

Alternative connection:

• positive electrode to the left upper

arm

•negative electrode to the right upper arm

• ground to either wrist

*Do not place the electrodes over the major muscles of the

upper arm, because muscle activity interferes with the signal



recorded from the heart.

Exercise 3

You will measure and correlate the ECG and heart sounds in aresting volunteer.

Using a Stethoscope

• It is generally better to use the bell

than the diaphragm because it

reduces room noise.• The earpieces should point slightly

forward to match the direction of the

external auditory canal.

• Tap on the bell; if you do not hear

sounds clearly, rotate the bell 180° on

its endpiece.

• PROCEDURE

• The volunteer should place the bell of the stethoscope on the

left side of their chest, using the right hand. (It is easy

enough to do this under one's shirt.) The stethoscope should

be moved to different positions until the student listening to

the stethoscope hears clear heart sounds. The sounds are

soft, and room noise must be kept low. Once clear heart

sounds are heard, the volunteer should hold the stethoscope

in place with the right hand while the student listening to the

stethoscope listens and records.



• Click Start to record the ECG, and press the push-button

switch on hearing 'lub' and release it on 'dub'.

• After a few heart beat cycles, click Stop.

Channel Trace Buttons

• Normally each channel only

displays a single data trace.

Sometimes, however, it is more

convenient to be able to overlay

the traces, like shown on the left.

• The vertical scale only applies to

one of the traces.

• Click on either of the buttons to see how the vertical scale on

the left becomes the one belonging to the data trace of the

same color as the button.Analysis

• To make it easier to compare the recordings in the two

channels, the LabTutor panel has been set up to display the

recordings overlaid. With the Channel Trace buttons you can

select which of the two channels is 'active' in the panel.

• Note the correlation between Event and ECG signals.

• Using the Marker and Waveform Cursor, follow the

instructions below to measure the time between the peak of



the R wave and the Event signal going high.

– Select the ECG channel as active

–Place the Marker on the R wave

– Select the Event channel as active

– Use the waveform cursor and select the Event signal

going high

– Insert this time into the table

• Now measure the time between the peak of the T wave andthe Event signal going low.

– Select the ECG channel as active

– Place the Marker on the T wave

– Select the Event channel as active

–Use the waveform cursor and select the Event signalgoing low

– Insert this time into the table

Troubleshooting

• Make sure students check the electrode connections and

placement.

• Artifacts can result from movement of the Bio Amp cable

and leads.



• If the electrodes are connected backwards (i.e. positive

electrode on right arm), the ECG signal will appear inverted.

Reattach the cables the in the proper configuration.

• Make sure students are not wearing metal jewelry.

• Make sure that electrode cream is used on the reusable ECG

electrodes.

• Weak heart sounds signal

• The bell of the stethoscope may not be placed firmly enough

over the apex of the heart.

• The head piece of the stethoscope may be turned so that the

diaphragm is connected. Rotate the stethoscope head piece

and try again.

ECG and heart sounds

1. Explain why ventricular contraction (systole) and the ‘lub’

sound occur immediately after the QRS complex.

• QRS complex represents the upstroke of the ventricular

action potential, with ventricular contraction startingsoon after. The ‘lub’ sound is generally thought to be due

to the closure of the AV valves but part of the sound may

derive from mechanical events in ventricular muscle.



2. Explain why ventricular relaxation (diastole) and the ‘dup’

sound occur after the T wave.

• The T wave represents ventricular repolarization, with

ventricular relaxation following soon after. The ‘dup’

sound is associated with closure of the aortic and

pulmonary valves.

THANK YOU

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