ECG Basics to Brilliance



ECG interpretation for nurses- including common ED presentations

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)

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

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Normal T waves

◙ Upright in leads I, II, V3-V6

◙ Negative (inverted/flipped) in aVR

◙ Variable (may be upright or inverted) in III, aVF, aVL, V1-V2

Sinus rhythm The normal rhythm of the heart

Pacemaking impulses arise from the sino-atrial node and are transmitted to the ventricles via the Atrio-ventricular node and the His-Purkinje system.

Think of this as the electrical system of the heart.

• This results in a regular, narrow-complex heart rhythm at 60-100 bpm.

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Characteristics of normal sinus rhythm

• Regular rhythm at a rate of 60-100 bpm

• There is a normal P wave before each QRS complex.

• Normal P waves- upright in leads I and II (inferior leads), inverted (flipped P wave) in aVR.

• The PR interval remains constant.

4 zones of heart that can produce their own heart beats

SA node, atrial cells, AV node, ventricular cells

Premature complexes

(Intrinsic pacemaker cell fires at a rate faster than the SA node.

Hence, complex occurs early compared to where it should have occurred along the strip.

(Can be sinus, atrial, junctional or ventricular in origin.

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Sequential repetitive occurrence of the premature complex:

(Bigeminy- premature complex arrives every 2nd beat.

(trigeminy- premature complex arrives every 3rd beat.

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Escape complexes

(Occurs late compared to where it should have occurred along the strip.

(The pacemaker that is setting the main rhythm fails & next intrinsic pacemaker site that is functional takes over.

(Can occur for 1 complex or for many.

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What is the significance of “extra beats” (premature or escape complexes)

(The patient may feel palpitations

(Check the electrolytes (aim for potassium to be 4-4.5)

(If bigeminy, feel the pulse- the ectopic beats may not actually pump the heart enough to cause an adequate pulse (eg in ventricular bigeminy, monitor may say 80bpm, but pulse is actually 40 bpm)

Atrial Fibrillation

SA node not working. Disorganised atrial electrical activity (lots of different atrial cells firing away) which means the atrium of the heart does not contract properly, so this reduces cardiac output.

Complications of AF including embolic stroke (a clot forms in the heart as it isn’t beating properly, and a bit flicks off and stops blood supply to a part of the brain).

People with AF should be on anticoagulants to reduce the risk of stroke (doctors will do a CHADS-VASc score).

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ECG criteria

• No P waves visible

• Irregularly irregular rhythm (the intervals between each QRS complex are different)

Management of AF

• If in AF but heart rate is normal (60-100 bpm) nothing needs to be done acutely in ED.

• The problem is if they are in rapid AF (when heart rate > 100 bpm).

This is when we need to check electrolytes, and slow the rate down (eg with beta blocks, calcium channel blockers, or cardiovert if BP low).

SVT = supraventricular tachycardia (=rhythm starting above the ventricles and heart rate > 100bpm)

This term encompasses many quick rhythms.

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ECG criteria (criteria is for typical AVNRT)

• Fast heart rate (140-280 bpm)

• No P waves before each QRS (if there was, this would be a sinus tachycardia)

How do people with SVT present to ED?

Usually with palpitations

How do we treat it?

Vagal manouvres

iv adenosine

Quick guide to identifying concerning ECG features in someone presenting with chest pain

A “healthy” patient should be in sinus rhythm, and T waves should be upright in I, II, V3-V6.

If cardiac ischemia occurs (lack of blood flow to a part of the heart causing angina or a heart attack), ECG changes can occur as well. Note- a normal ECG does not exclude cardiac ischemia.

1. Look for Q waves

Pathological Q waves indicates a heart attack (new or old).

Any Q wave in V1-V3

0.03 seconds or wider (0.03 seconds is ¾ width of one little square)

Depth of the Q wave is equal to or greater than 25% of the height of the R wave.

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Above: Anterior (V1-V3) Q waves with associated ST segment elevation indicating an anterior STEMI

2. Check the ST segment

◙ The ST segment may elevate above the isoelectric baseline (eg STEMI)- the overall “look” of the ST elevation is variable.

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◙ OR The ST segment may go below the isoelectric baseline (ST depression)

3. Check the T waves

T waves should be upright (in I, II, V3-V6), T waves usually inverted only in aVR, III and V1.

Look for

◙ T wave flattening

◙ Inverted T waves (flip/negative T wave)

Occur in multiple leads based on the anatomical location of the area of ischaemia/infarction:

• Inferior =  II, III, aVF

• Lateral =  I, aVL, V5-6

• Anterior =  V2-6

[pic]

Above: T wave inversion in the inferior leads (II, III, aVF). T wave upright in aVL indicating the high lateral leads (aVL) not affected.

◙Hyperacute T waves (look “peaky”)

• Broad, asymmetrically peaked T-waves are seen in the early stages of ST-elevation MI (STEMI) and often precede the appearance of ST elevation and Q waves.

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4. Look for abnormal rhythms

Is the patient in heart block? Are there any dropped beats?

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The 4th complex is a premature atrial contraction

4th complex is a ventricular escape beat

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