Reading the ECG: The PR Interval and the Blocks

What this deck covers

Reading the ECG: The PR Interval and the Blocks 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. Where the interval is measured from
2. One interval, two different verdicts
3. Every beat conducts, but slowly
4. A dropped beat with a warning
5. A dropped beat with no warning
6. Alternate beats, and an honest answer
7. Where in the system the delay sits
8. A slow regular unrelated rhythm
9. A pause with something hidden in it
10. An irregular rhythm that is normal
11. A long interval that disappears
12. An interval that cannot be reported

What this deck teaches

• Start of the P wave to the start of the QRS. The interval contains the P wave itself as well as the flat segment after it. Peaks are not used, because a peak is not where conduction begins or ends.
• There is no single normal PR. The upper limit rises with age and shortens as the rate rises, so an interval is read against a table for that child at that rate.
• Delay is not block. In a first degree pattern every P wave still conducts and no beat is lost. It is a measurement rather than an event.
• Lengthening before the drop, or no warning at all. Progressive lengthening then a dropped beat is nodal and usually benign. A constant interval and a beat that simply fails is lower, and is referred.
• Two to one conduction cannot be typed. With only one conducted beat between the dropped ones there is no sequence of intervals to compare. A longer strip, or a faster rate, settles it.
• The QRS width says where the block sits. Narrow means the impulse is using the normal system below the node; broad means the conducting tissue itself is diseased.

Exam pearls from this deck

• The interval includes the P wave. The flat part after it is a different thing.
• The interval is judged against the age and the rate, never against one number.

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.