Erwinanto Div. Of Cardiology, Dept. of Internal Medicine Padjadjaran University School of Medicine Hasan Sadikin Hospital Bandung

What medical problems can be diagnosed with an ECG? Enlargement of cardiac chambers Hypertrophy of cardiac muscle Cardiac arrhythmias Insufficient coronary blood flow Death of heart muscle and its location Electrolyte abnormality

What is an Electrocardiogram? An ECG is the recording (“gram”) of the electrical activity (“electro”) of the cells of the heart (“cardio”) that reaches the body surface Initiates the heart muscle to contract, to pump blood to the tissues

What does an ECG actually measure? An ECG records voltage on its vertical axis against time on its horizontal axis Measurement along the vertical axis indicates “summation” of the electrical activation of all of the cardiac cells Measurement along the horizontal axis indicates heart rate, regularity, and the time intervals required for electrical activity to move from one part of the heart to another

– –– ––– ––– ––– – –– ––– ––– – –– – –– +++ ––– – –– +++ ––– – –– +++ ––– – –– +++ ––– – ––

+++ – –– – –– +++ – –– – –– +++ – –– – –– +++ – –– – –– +++ – –– ––– +++ – –– ––– +++ – –– ––– – –– – –– ––– ––– –––

0 + – – –– – –– – –– – –– + –

Systole Diastole ActivationRecovery Electrical ExcitationRecovery DepolarizationRepolarization ShorteningLengthening Mechanical ContractionRelaxation EmptyingFilling Terms describing cardiac cycle

(SAN) (AVN) (BB) (HB) RA LA V V SAN RA LA AVN HB BB V

RECORDING ELECTRODES AND LEADS 1.Bipolar limb leads: record the potential differences between two limbs 2.Unipolar precordial leads: record the absolute electrical potential at each of designated torso sites 3.Augmented unipolar limb leads: is designed to increase the amplitude of the output of limb leads

BIPOLAR LIMBS LEADS Lead ILeft arm Lead IILeft leg Lead IIILeft leg AUGMENTED UNIPOLAR LIMBS LEADS aVRRight arm aVLLeft arm aVFLeft leg PRECORDIAL LEADS V1Right sternal margin, 4 th intercostal space V2Left sternal margin, 4 th intercostal space V3Midway between V2 and V4 V4Left midclavicular line, 5 th intercostal space V5Left anterior axillary line V6Left midaxillary line Positive input Positive input

RRR SQ R QSQS R S R’

Systematic evaluation of the ECG 1.Rate and regularity 2.P-wave morphology 3.PR interval 4.QRS-complex morphology 5.ST-segment morphology 6.T-wave morphology 7.U-wave morphology 8.QTc interval 9.Rythm

Rate and regularity

P waves and QRS complexes are used to determine cardiac rate and regularity Over a particular interval of time, normally, there are same numbers of P waves and QRS complexes Heart rate: * 1500 divided by number of small squares between successive P waves or QRS complexes * 300 divided by number of large squares between successive P waves or QRS complexes Normal heart rate: beats per minute (bpm)

P-wave morphology

1.The contour: is normally smooth and monophasic (entirely positive or negative) in all leads except V1 or occasionally V2 2.Upright or positive P waves are normally seen in leads I, aVL, aVF, V4-V6 and downward in lead aVR. P wave in lead III may be either upright or downward. 3.P-wave duration is normally less than 0.12 seconds 4.The maximal amplitude is normally no more than 0.2 mv

Abnormal P waves

The PR interval

1.The PR interval measures the time required for an electrical impulse to travel from the atrial myocardium adjacent to the SA node to the ventricular myocardium adjacent to the fibers of the Purkinye network 2.The duration is normally from 0.11 to 0.20 seconds 3.PR interval varies with the heart rate. The faster the heart rate, the shorter the PR interval

Abnormal PR interval

Morphology of the QRS complex

1.Q waves. The presence of Q waves in leads V1, V2, and V3 should be consider abnormal. The absence of small Q waves in leads V5 and V6 should be consider abnormal A Q wave of any size is normal in leads III and avR In all other leads, a “normal” Q wave would be very small (less than 0.04 second and its voltage is less than 25% of the R-wave)

Anbormal Q waves

2.R waves The positive R wave normally increases in amplitude and duration from lead V1 to V4 or V5. Loss of normal R-wave progression is considered abnormal 3.S wave S wave should be large in V1 and then progressively smaller to V6 4. Ratio of R/S amplitude in V1 and V2 is normally less than 1

Abnormal R wave in V1

5.Duration of the QRS complex (QRS interval) It normally ranges from 0.07 second to 0.11 second (less than 0.12 second). The QRS interval has no lower limit that indicates abnormality 6. Amplitude of QRS complex There is no arbitrary upper limit for normal voltage of the QRS complex. An abnormally low QRS complex when the amplitude is no more than 0.5 mV in any limb leads and no more than 1.0 mV in any of the precordial leads

Abnormal QRS interval 0.19 s

7.The axis of QRS complex Normal axis: between –30 degrees and +90 degrees Right axis deviation (RAD): between +90 degrees and ± 180 degrees Left axis deviation (LAD): between –30 degrees and –120 degrees

Right axis deviation (RAD)

Left axis deviation (LAD)

Morphology of the ST segment

1.The ST segment represents the period during which the ventricular myocardium remains in an activated or depolarized state 2.ST segment normally located at the same horizontal level with the PR segment 3.Normal variations: Slight upsloping, downsloping, or horizontal depresion Early repolarization: displacement of ST segment by as much as 0.1 mV in the direction of the ensuing T wave 4.ST segment may be altered when there is prolonged QRS complex

Normal ST segment

Normal ST-segment deviation

Morphology of the T and U waves

The T wave The T waves are positively directed in all leads except aVR (negative) and V1 (biphasic) T waves do not normally exceed 0.5 mV in any limb lead or 1.5 mV in any precordial lead The U wave U wave is either absent or present as a small wave following the T wave and is usually most prominent in leads V1 and V2. Increased prominence of the U wave indicates the possibility of hypokalemia

The QTc interval

1.The QT interval measures the duration of electrical activation and recovery of the ventricular myocardium 2.The QT interval decreases as the heart rate increases and therefore should be corrected for cardiac rate (QTc interval) 3.QTc= QT/  RR interval (in seconds) The upper limit of QTc is 0.46 second (slightly longer in in females) 4.QT interval varies among different leads. The longest QT interval measured in multiple leads should therefore be considered the true QT interval