ECG PERFORMANCE AND INTERPRETATION DR FRANCIS AGYEKUM CARDIOLOGIST

OBJECTIVES TO DESCRIBE HOW TO PERFORM ECG TO DESCRIBE THE ECG NOMENCLATURE TO INTRODUCE THE NORMAL ECG TO DESCRIBE THE STEP-WISE APPROACH TO ECG INTERPRETATION

What is ECG An electrocardiogram (ECG) is a recording of cardiac electrical activity made from the body surface and displayed on graph paper Each millimeter on the horizontal axis represents 40 ms (0.04 s) of elapsed time and each millimeter on the vertical axis represents 0.1 mV of electrical force. Each 5 millimeter mark on the paper is scored with a heavier line representing 200 ms or 0.20 s on the horizontal axis or time line and 0.5 millivolt on the vertical axis or amplitude line.

Leads placement 6 Limb leads: 6 horizontal or chest leads (unipolar) 3 bipolar 3 unipolar (augmented leads) 6 horizontal or chest leads (unipolar) V1 – 4th ICS RSB V2 – 4th ICS LSB V4 – 5th ICS MCL V3 – between V2 and V4 V5, 6 – 5th ICS anterior and mid axillary line respectively.

Conventional electrode placement

WHICH PART OF THE HEART?

Einthoven’s triangle

THE HEXAXIAL REFERENCE SYSTEM

Cardiac events on the ECG

NOMENCLATURE Complexes and intervals. a: P wave amplitude, b: R wave amplitude, c: Q wave amplitude, d: T wave amplitude, e: S wave amplitude.

ECG and the Cardiac Cycle

NOMENCLATURE

12-Lead Shows 2.5 Sec View of Each Lead The 12-lead ECG only provides a 2.5-second view of each lead. When first introduced to the 12-lead ECG, these 2.5 seconds may seem prohibitively short. However, when looking for evidence of infarction, most of the information is obtained from analyzing a single, representative complex in each lead. It is assumed that 2.5 seconds is long enough to capture at least one representative complex. A 2.5-second view is not long enough to properly assess rate and rhythm, so at least one continuous rhythm strip is usually included at the bottom of the tracing.

SYSTEMATIC INTERPRETATION Systematic approach with careful examination of each of the 12 leads. 9-step approach

9-STEP APPROACH 1. Calibration 2. Rate 3. Rhythm 4. Axis 5. Waves and segments 6. Chamber enlargement 7. Ischaemia and infarction 8. Miscellaneous 9. Synthesis

The ECG Paper

RATE 300/BIG BOXES 1500/SMALL BOXES IRREGULAR RHYTHMS: RHYTHM STRIP (10secs) then multiply by 6 Note: each big box = 0.2secs; small box = 0.04 secs

What is the heart rate?

RHYTHM Start from rhythm strip then look at all 12: What is the rate: tachy; brady? QRS: Narrow or wide complexes? Do you see P waves? Is it regular, regularly irregular or irregularly irregular? What is the relationship b/n P and QRS? Vagal maneuvers (CSM, Valsalva)

AXIS DETERMINATION QRS axis: normal = -30 to +90 Shortcut and approximate axis

QUICK LOOK METHOD NORMAL: positive in leads I, II and/or aVF, aVL LAD: Positive in I but negative in II and aVF RAD: negative in I but positive in II and aVF If negative in both I and II = extreme RAD

ISOELECTRIC LEAD METHOD the hexa-axial system Identify the most isoelectric lead Axis is perpendicular to this lead

QRS AXIS

WAVES AND SEGMENTS P WAVE PR INTERVAL QRS COMPLEX Q WAVE R WAVE ST SEGMENT J POINT U WAVE QT INTERVAL

P WAVE Represents atrial depolarization Best seen in leads II, aVF and V1 Normal: 120msec and 0.25mV Sinus P wave: Upright in I, II, aVF and V2-6 Biphasic in V1 Variable in III and aVL P-pulmonale and P-mitrale

P MITRALE

P-Pulmonale

PR INTERVAL Represents the time interval between the onset of atrial depolarization and the onset of ventricular depolarization Normal: 120 – 200msec Prolonged and short PR PR depression: normal variant, pericarditis, COPD.

24 yo lady, routine ECG during med screening

QRS complex Represents ventricular depolarization Measured in the lead with the widest QRS complex Normal duration: 60-110msec Widening: BBB, Aberrancy, Ventricular source, severe hyperkalaemia Amplitude: large or low voltages

RBBB

LBBB

Large voltages Ventricular hypertrophy Thin chest wall Alternating QRS height (electrical alternans) is highly suggestive of pericardial effusion, when it occurs in sinus rhythm.

Low voltages Cardiomyopathy Myocarditis Pericardial effusion Obesity Pneumothorax Hypothyroidism

Q WAVES Pathological Q wave defined as >0.02s in leads V2-3 or QS complex in leads V2-V3 >0.03s and >0.1mV deep or QS complex in leads I, II, aVL or V4-6

RVH Frontal plane leads: • Right axis deviation of at least +110 degrees. Horizontal plane leads: • R:S ratio in V1 greater than 1.0 • R wave in V1 = 7 mm • S wave in V1 is less than 2 mm • qR or qRS pattern in V1 • S wave in V5 or V6 = 7 mm • rSR′ in V1 with R′ wave greater than 10 mm • R in V1 + S in V5 or V6 greater than 10.5 mm (SOKOLOW-LYON)

RVH

LVH Many criteria; all are specific but insensitive Sokolow-Lyon index: SV1 + RV5 or 6 > 3.5mV RaVL > 1.1mV Cornell Voltage Criteria: RaVL + SV3 > 2.0mV (women) or 2.8mV (men) Romhilt-Estes : 5-points or 4-points score Other criteria

OTHER LVH CRITERIA R wave in aVL = 11 mm R wave in aVF = 20 mm. Horizontal plane leads: S wave in V1 + R wave in V5 or V6 = 35 mm R wave in V5 or V6 = 26 mm Largest S wave + largest R wave = 45 mm Secondary ST segment and T wave abnormalities Prolonged QR interval in V6.

LVH

TO BE CONTINUED THANK YOU