ECG 1.BIPOLAR LEADS I II III 2.UNIPOLAR LIMB LEADS aVR aVL aVF 3.UNIPOLAR CHEST LEADS C1………..C6 4.RECORDING OF THE ECG

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Ground electrode Limb leads Lead I: Right arm to left arm aVR: right arm aVL: left arm Lead II: Right arm to left leg Lead III: Left arm to left leg aVF: left leg FIGURE 9-13: Electrocardiogram leads. (a) Limb leads. The six limb leads include leads I, II, III, aVR, aVL, and aVF. Leads I, II, and III are bipolar leads because two recording electrodes are used. The tracing records the difference in potential between the two electrodes. For example, lead I records the difference in potential detected at the right arm and left arm. The electrode placed on the right leg serves as a ground and is not a recording electrode. The aVR, aVL, and aVF leads are unipolar leads. Even though two electrodes are used, only the actual potential under one electrode, the exploring electrode, is recorded. The other electrode is set at zero potential and serves as a neutral reference point. For example, the aVR lead records the potential reaching the right arm in comparison to the rest of the body. Ground electrode Fig. 9-13a, p. 253

Einthoven ----------------- Einthoven’s law Einthoven’s triangle

2)Chest leads (precordial leads): 14

2 1 6 3 5 4 FIGURE 9-13: Electrocardiogram leads. (b) Chest leads. The six chest leads, V1 through V6, are also unipolar leads. The exploring electrode mainly records the electrical potential of the cardiac musculature immediately beneath the electrode in six different locations surrounding the heart. Fig. 9-13b, p. 253

ECG 1.ECG WAVES P, QRS AND T 2.ECG SEGMENTS PR AND ST 3.ECG INTERVAL PR, QT AND TP

The shape of the ECG 17

SINGLE VENTRICULAR ACTION POTENTIAL ENDOCARDIAL FIBER ATRIAL FIBER EPICARDIAL FIBER R 1 mV ECG T P Repolarization of ventricles Q S Depolarization of ventricles Depolarization of atria

EKG Waves and Intervals QRS length R T P Q S Normal: PR interval: 0.12-0.2 sec QRS length: <0.10 sec QT interval: 0.3-0.4 sec Abnormalities in: QRS – ventricular depolarizaton problems P-R interval – A/V conduction problems P-R interval Q-T interval

EKG Reading 0.2 sec 0.04 sec 1.0 mV Test pulse HR = 1500/ small boxes between QRS complexes

3)Augmented unipolar limb leads: 21

Relationship between No. of large squares & HR ….. Heart rate (beat/min) R-R interval (large squares) 300 1 150 2 100 3 75 4 60 5 50 6 23

Times & speed…. Normal duration (s) Range Average intervals 0.12-0.20 0.18 PR interval 0.07-.10 0.08 QRS duration 0.33-.43 0.40 QT interval … 0.32 ST interval 24