PRACTICAL 2 : ELECTROCARDIOGRAM (ECG/EKG) By.Mohamad Azmir bin Azizan Medical lab technologist Faculty of Medicine UiTM

What is an electrocardiogram? An electrocardiogram or 'ECG' records the electrical activity of the heart. The heart produces tiny electrical impulses which spread through the heart muscle to make the heart contract. These impulses can be detected by the ECG machine. You may have an ECG to help find the cause of symptoms such as palpitations or chest pain. Sometimes it is done as part of routine tests, for example, before you have an operation. The ECG test is painless and harmless. (The ECG machine records electrical impulses coming from your body - it does not put any electricity into your body

How is it done? Small metal electrodes are stuck onto your arms, legs and chest. Wires from the electrodes are connected to the ECG machine. The machine detects and amplifies the electrical impulses that occur each heartbeat and records them onto a paper or computer. A few heartbeats are recorded from different sets of electrodes. The test takes about five minutes to do.

What does an ECG show? The electrodes on the different parts of the body detect electrical impulses coming from different directions within the heart. There are normal patterns for each electrode. Various heart disorders produce abnormal patterns. The heart disorders that can be detected include: Abnormal heart rhythms. If the heart rate is very fast, very slow, or irregular. There are various types of irregular heart rhythm with characteristic ECG patterns. A heart attack, and if it was recent or some time ago. A heart attack causes damage to heart muscle, and heals with scar tissue. These can be detected by abnormal ECG patterns. An enlarged heart. Basically this causes bigger impulses than normal.

Understanding ECG recording Each conventional ECG tracing records from : bipolar leads (2 opposite points) consisting of lead I, II, III and (ii) unipolar leads i.e. aVR, aVL, aVF, V1, V2, V3, V4, V5 and V6. Bipolar leads All the bipolar leads measure the potential difference between 2 points namely : lead I between right arm (RA) and the left arm (LA). lead II between RA and left leg (LL). lead III between LA and LL.

Procedure Students are to be chosen as subjects for ECG recording. Ask the subject to lie on the couch/table. Clean the skin of the arms and legs with alcohol provided. Apply electrolyte or electrode cream/jelly on the surface of the electrodes and to the skin where electrodes will be placed. Secure the electrodes to the arms or legs using rubber straps.

Recording standard lead I, II and III Set up the electrodes on the subject’s arms and legs as follows (see Figure) –RA electrode on the right arm. –LA electrode on the left arm. –LF/LL electrode on the left leg. –Earth/ground electrode on the right leg. Set up the physiograph using channel II with paper speed of 2.5 cm/second and calibrate the recording pen at 1.0 mV/cm. Record 5 heart beats from each lead : I, II and III. Without changing the position of the electrodes, change the knob on the physiograph to record unipolar lead aVR, aVL and aVF. Record 5 heart beats from each lead : aVR, aVL and aVF. To do the chest lead, ask the subject to undress the upper body to expose the chest. Locate the anatomical parts of the subject’s chest and place the cup suction one at a time as follows

V1 – right margin of the sternum at the 4th intercoastal space. V2 – left margin of the sternum at the 4th intercoastal space. V3 – midway between V2 and V4. V4 – 5th intercostals space at left midclavicular line. V5 – 5th intercoastal space at left midaxillary line. V6 – 5th intercoastal space at left midaxillary line.

Mid-Clavicular line

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RIGHT ARM LEFT ARM RIGHT LEG LEFT LEG

Locations of standard lead I, II, III and chest leads for ECG recording Lead I Lead IILead III - Lead I + Lead II - +Lead III - +

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How to interpret ECG tracing

The normal ECG Drawing of the EKG, with labels of intervals P=P wave, PR=PR segment, QRS=QRS complex, QT=QT interval, ST=ST segment, T=T wave. Electrocardiogram of a healthy man, A typical ECG tracing of a normal heartbeat consists of a P wave, a QRS complex and a T wave. A small U wave is not normally visible.

Axis The axis is the general direction of the electrical impulse through the heart. It is usually directed to the bottom left, although it can deviate to the right in very tall people and to the left in obesity. Extreme deviation is abnormal and indicates a bundle branch block, ventricular hypertrophy or (if to the right) pulmonary embolism. It also can diagnose dextrocardia or a reversal of the direction in which the heart faces, but this condition is very rare and often has already been diagnosed by something else(such as a chest x-ray).obesitybundle branch blockventricular hypertrophy pulmonary embolism dextrocardiachest x-ray P wave The P wave is the electrical signature of the current that causes atrial contraction. Both the left and right atria contract simultaneously. Irregular or absent P waves may indicate arrhythmia. Its relationship to QRS complexes determines the presence of a heart block.contraction atriaarrhythmiaheart block

QRS The QRS complex corresponds to the current that causes contraction of the left and right ventricles, which is much more forceful than that of the atria and involves more muscle mass, thus resulting in a greater ECG deflection.leftright The Q wave, when present, represents the small horizontal (left to right) current as the action potential travels through the interventricular septum. Very wide and deep Q waves do not have a septal origin, but indicate myocardial infarction.myocardial infarction The R and S waves indicate contraction of the myocardium. Abnormalities in the QRS complex may indicate bundle branch block (when wide), ventricular origin of tachycardia, ventricular hypertrophy or other ventricular abnormalities. The complexes are often small in pericarditis.. myocardiumbundle branch blockventricular origin of tachycardiaventricular hypertrophypericarditis

T wave The T wave represents the repolarization of the ventricles. The QRS complex usually obscures the atrial repolarization wave so that it is not usually seen. Electrically, the cardiac muscle cells are like loaded springs. A small impulse sets them off, they depolarize and contract. Setting the spring up again is repolarization (more at action potential).action potential In most leads, the T wave is positive. Negative T waves can be signs of disease, although an inverted T wave is normal in V1 (and V2-3 in black people). The ST segment connects the QRS complex and the T wave. It can be depressed in ischemia and elevated in myocardial infarction, and downslopes in digoxin use.ischemiamyocardial infarctiondigoxin T wave abnormalities may indicate electrolyte disturbance, such as hyperkalemiaelectrolytehyperkalemia

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