Thread by @DFyenbo

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Time for a #tweetorial on simple #ECG interpretation

When I learned to read ECGs, my biggest fear was to miss an important finding!
To avoid that: Be systematic❗️

My simple approach to ECGs with 8 steps 🪜👇

#medicalstudent #education #cardiotwitter #medtwitter #EPeeps

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‼️ All following ECGs are with paper speed of 25 mm/s and a signal gain of 10 mm/mV ‼️

Therefore:
1 small square = 40 ms
1 big square = 200 ms

Now we are ready to read the ECG systematically

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1⃣ Rhythm

Sinus rhythm or abnormal rhythm?
(Also note if regular or irregular)

Normal: One P-wave precedes each QRS complex (sinus rhythm)

Interpret from the lead that shows the P-wave most clearly (usually lead II)

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2⃣ Frequency

Regular rhythm: 300 divided by number of big squares between QRS complexes

Irregular rhythm: Number of QRS complexes per 3s multiplied by 20

Assess both atrial and ventricular frequency if dissimilar

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3⃣ P-wave morphology
👉 assess the width and height

Normal: ≤3 mm wide and ≤3 mm tall

>3 mm tall ➡️ enlargement of the RA (P-pulmonale?)
>3 mm wide ➡️ enlargement of the LA (P-mitrale?)

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4⃣ PR interval
👉 assess the length

Normal: 120-220 ms

If abnormal, AV-block may be present

Check out the tweetorial about AV node physiology by @AvrahamCooperMD here: bit.ly/3CbBZg0

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5⃣ QRS complex
👉assess the width, axis, amplitude and Q-waves

Let's take them one by one 👇

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Length of the QRS complex
Normal: ≤120 ms

If >120 ms, several causes exist: LBBB/RBBB, ventricular arrhythmia, pre-excitation, ventricular pacing, aberrant conduction, PVCs, electrolyte derangement etc.

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Axis: Fast and simple approach: Look at lead I and aVF:
Normal: Positive QRS in I and aVF

Left⏪: Positive QRS in I, negative in aVF
Right⏩: Negative QRS in I, positive in aVF

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Amplitude of the QRS complex
Normal: 5-30 mm (rule of thumb – several criteria exist)

>30 mm: May be due to ventricular hypertrophy
<5 mm (low voltage): May be due to pericardial effusion, hyperthyroidism, obesity etc.

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Q-waves present?
Normal: <1 mm wide and <2 mm deep

If wider/deeper: Pathological – may be due to necrotic tissue (electrically dead) and the lead therefore record a current running from endocardium to epicardium in the opposite myocardial wall (➡️ negative deflection)

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6⃣ ST segment
👉 deviations from the J-point?
Normal: Isoelectric

>1 mm elevation (except in V2-3, elevation should be higher): May be #STEMI
>0.5 mm depression: May be #NSTEMI

Note, deviations may also be due to several other conditions than #AMI‼️

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7⃣ T-wave morphology
👉assess deflection, symmetry and height

Normal: Upright in all leads except aVR and V1, asymmetric, <5mm in limb leads and <10mm in precordial leads

If abnormal: Ischemia, electrolyte derangement, structural heart disease, PE etc. may be considered!

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8⃣ QT interval
👉assess the length

Rule of thumb: Normal QT is less than half the preceding RR interval

However, QTc are more precise and may be applied

QTc is prolonged if >440ms in 👨 or >460ms in 👩 and shortened if <350ms

QTc >500 ms ➡️ increased risk of TdP

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💥Summary💥

Be systematic and use the 8 simple steps 🪜

Once you have seen multiple normal ECGs it may be easier to spot an abnormality

If you are in doubt 👉 seek expert help as even minor ECG abnormalities may be due to severe pathology

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Thank you for reading the #tweetorial

Please re-tweet, like, and tag peers who may find it useful 🙏

@EmilHolckMD @TanjaCharlotteF @arnelasaljic @Dominik_Linz @ThomasJesperse6 @DCAcademyDK @AUHCardio @MedTweetorials