Reading the ECG: The QT Interval

What this deck covers

Reading the ECG: The QT Interval in twelve illustrated clinical cases with worked explanations – case presentations built around clinical images, radiology, teaching illustrations and real laboratory data, with the reference range beside every value a case quotes. This visual, data-interpretation style of practice suits candidates preparing for MRCPCH AKP in particular, alongside Saudi and Gulf licensing examinations such as the Arab Board, DHA and OMSB. Each case gives you a clinical vignette, four options, the correct answer, and an explanation of why each of the other three is wrong.

The twelve cases, in order

1. Measuring an interval end to end
2. Deciding where the T wave ends
3. The same heart at two rates
4. Choosing the cycle for the correction
5. A long value at a very fast rate
6. A second bump after the T wave
7. Choosing the lead to measure in
8. Intervals that differ between beats
9. A borderline value in a well boy
10. A new medicine, and a longer interval
11. A long interval after days of vomiting
12. An interval at the other extreme

What this deck teaches

• Start of the QRS to the end of the T, on one beat. The interval begins at the first deflection of the complex, q wave or R wave, and ends where the T returns to the baseline. Both ends come from the same beat.
• The tangent settles where the T ends. A line along the steepest part of the downslope, extended to the baseline. Eye-balling the tail differs between readers by enough to cross a decision threshold.
• A raw QT without its rate is unusable. Repolarisation takes less time at faster rates, which is why the interval is corrected to what it would be at sixty a minute before it is compared with anything.
• Correct against the cycle the beat actually had. The R to R interval BEFORE the measured beat set the conditions it repolarised under. The interval after it had not happened yet.
• Above about a hundred a minute the correction overestimates. Fever, pain and fear inflate the corrected value in well children, so a high reading taken at speed is repeated once the child is calm before it is acted on.
• The U wave is not part of the T wave. A low rounded deflection after the T, best seen in the mid-praecordial leads. Measuring it in turns a normal interval into an alarming one.

Exam pearls from this deck

• Start of the QRS to the end of the T, on the same beat.
• The tangent removes the argument. Steepest downslope, extended to the baseline.

The twelve worked cases in this deck, with the images and the full explanation of every option, are part of Pediatric Case Review membership. See what is included, or start with the free Pediatric Exam Review Sets.

More from this system: all cardiology illustrated case decks · cardiology board questions for bank-style drilling · the free Pediatric Exam Review Sets · pediatric reference values.