ECG Basics to Brilliance- initial pre-reading



ECG interpretation- The basics but in depth

ECG paper

(Passes under the pen at rate of 25mm/sec (so each little box is 1/25 of a second = 0.04 sec)

(1 Little box = 0.04sec

(1 Big box (5 little boxes) = 0.2 sec

(5 big boxes = 1 sec

Calibration box should be 10 mm high (2 big boxes) & 0.20 sec wide (1 big box)

Lead placement

(Limb leads I, II & III must be placed at least 10cm from the heart

Machine does vector manipulation to come up with aVR, aVF & aVL.

(Precordial leads (V1-V6)

Anatomy refresher- Angle of Louis (below manubrium) is next to the 2nd rib.

The space beneath 2nd rib is 2nd intercostal space. Space beneath 4th rib is 4th intercostal space.

|V1 |In the 4th intercostal space just to the right of the sternum |

|V2 |In the 4th intercostal space just to the left of the sternum. |

|V3 |Between leads V2 and V4. |

|V4 |In the 5th intercostal space in the mid-clavicular line. |

|V5 |Horizontally even with V4, in the left anterior axillary line. |

|V6 |Horizontally even with V4 and V5 in the midaxillary line. |

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Do right sided and posterior leads if patient presents with chest pain and any evidence of STEMI pattern in inferior leads, or ST depression in leads V1-V3.

Right ventricular leads placement

Place the standard leads V1-V6 in a mirror image position on the right side of the anterior chest.

V4R, at 5th right intercostal space in mid-clavicular line, is most useful lead to detect RV ST elevation.

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Isoelectric baseline

(Line between the T wave of previous complex & start of the P wave of the next complex

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Waves

(= Deflections from the baseline

(Tall or deep waves/deflections in QRS complexes are given capital letters, small waves/deflections are given small letters.

Q wave- 1st negative wave after P wave

R wave- 1st positive deflection after the P

S wave- 1st negative component after an R wave

If another upward component- R’, next negative component is S’.

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Conduction ratio P:QRS

Number of atrial contractions to ventricular contractions

Eg 3:2 conduction means that for every 3 P waves created, 2 are conducted, and 1 is blocked.

Block ratio P:QRS is different to conduction ratio

Eg 3:2 block means that for every 3 P waves created, 2 are blocked, and only one is conducted.

P waves- in depth

●Ascending limb is RA (right atrium) depolarisation, descending limb is LA (left atrium) depolarisation.

Normal Duration 0.08-0.11sec (so < 3mm in width)

Amplitude 2.5mm), peaked P waves (esp II, III, aVF)

Causes: lung disease eg COPD

P mitrale

Left atrial enlargement

●Double peaked apex. Distance between 2 peaks is > 0.04 sec (> 1 little square)

Most prominent I, aVL, V5/V6 (the leftward leads)

●Duration > 0.11 sec

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|P wave present & upright in I, II, III, aVF, |P wave present but may be upright OR inverted|P wave may be present but always inverted |

|V5 & V6 | | |

|Sinus brady, SR, sinus tachy, sinus arrythmia|Ectopic atrial rhythm |Junctional rhythm |

| |(rate 100 bpm) | |

| |Wandering atrial pacemaker |Junctional tachycardia |

| |(rate < 100 bpm) | |

| |Multifocal atrial tachycardia |AVNRT |

| |(rate > 100 bpm) | |

| |Premature atrial complexes |AVRT |

| |Escape atrial complexes | |

|PR segment |The line between the end of P wave & start of QRS. |

| |Normally at baseline or depressed (line below baseline) < 0.8mm (< 1 small square) |

| |Pathologically depressed in pericarditis. |

|PR interval |Start of P wave to start of QRS. |

| |From initiation of SA node impulse up to start of ventricular depolarisation. |

| |Normal: 0.12-0.2 sec (3-5 little boxes) |

| | |

| |Short PR: 0.2 sec |

| |●If each PR interval is the same, and followed by a QRS complex- 1st degree AV block |

| | |

| |If PR interval varies (of any duration): |

| |(1) wandering atrial pacemaker (rate < 100) OR multifocal atrial tachycardia (rate > 100) |

| |(2) premature atrial contractions |

| |(3) 2nd degree heart block, 3rd degree block |

|QRS |Indicates ventricular depolarisation |

| |Determined by the widest complex, usually V2/V3. |

| |Normal ................
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