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Case study, page T-0048

Missed a statement

Reduced blood flow pattern, bottom and atrial fibrillation

PTB-XL record 4769, a man aged 81. A public research ECG from Germany, printed on A4, photographed by TraceRead's photo simulator and read end to end. Below is the AI first read, next to the original recording and what the dataset's cardiologists recorded.

0.77

median match with the original recording

0.98 after lining up by up to a tenth of a second

1 of 3

cardiologists' statements that TraceRead AI also flagged

9

extra patterns flagged for the doctor to keep or remove

151

heart rate from the photo, beats a minute

150 on the original recording

The AI first read

What the reading doctor gets

Hover a lead to see how closely the red rebuilt line follows the original recording. Untick the box to see the page without it.

Flattened page of PTB-XL record 4769

Numbers under each lead: how closely the rebuilt line follows the original recording, where 1.00 is a perfect match. Median for this page: 0.77.

Photo usable, hold rule version 2AI first read, for a doctor to check

PTB-XL record 4769, a man aged 81. A4 paper, 3x4 with one lead II strip, pulses read 4 of 4.

Measures

MeasureFrom the photoOriginal recording
Heart rate (beats a minute)151150
PR interval (ms)130127
QRS width (ms)8182
QT interval (ms)287279
QTc, corrected for heart rate (ms)390379
Heart axis (degrees)8483

Patterns flagged, with TraceRead AI's score

  • Atrial fibrillation

    an irregular rhythm where the upper heart chambers quiver

    95

  • Unspecific ST changes

    small changes in the middle part of the beat that do not point to one cause

    26

  • ST depression

    the middle part of the beat sits lower than usual

    14

  • Reduced blood flow pattern, front and side

    beat changes over the front and side of the heart that can go with reduced blood flow to the heart muscle

    13

  • Unspecific reduced blood flow pattern

    beat changes that can go with reduced blood flow to the heart muscle, without a clear place

    7

  • Anteroseptal infarct pattern

    a pattern linked to damage to the front wall of the heart muscle and the wall between the lower chambers

    7

  • Low T waves

    the last part of each beat is smaller than usual

    6

  • Left ventricular hypertrophy

    the muscle wall of the main pumping chamber may be thicker than usual

    5

  • Unspecific wide QRS

    the signal spreads slowly inside the lower chambers, so the main spike is wide

    5

  • Pacemaker rhythm

    the heartbeat is set by an artificial pacemaker that is working as expected

    1

Also checked, below the flag line: Minor T wave abnormalities (14).

What the dataset's cardiologists recorded for this ECG

  • Reduced blood flow pattern, bottom
  • Atrial fibrillation
  • Atrial flutter

Against the cardiologists

TraceRead AI and the dataset's cardiologists, side by side

TraceRead AI flagged 10 patterns. 1 of them is also among the dataset's statements (Atrial fibrillation). Not in the dataset's statements: Unspecific ST changes, ST depression, Reduced blood flow pattern, front and side, Unspecific reduced blood flow pattern and 5 more. In the dataset but not flagged: Reduced blood flow pattern, bottom and Atrial flutter.

Found by both 1

  • Atrial fibrillation

    An irregular rhythm where the upper heart chambers quiver.

    95

Recorded by the cardiologists only 2

  • Reduced blood flow pattern, bottom

    Beat changes over the bottom of the heart that can go with reduced blood flow to the heart muscle.

  • Atrial flutter

    A fast, regular rhythm where the upper heart chambers beat very quickly.

Flagged by TraceRead AI only 9

  • Unspecific ST changes

    Small changes in the middle part of the beat that do not point to one cause.

    26

  • ST depression

    The middle part of the beat sits lower than usual.

    14

  • Reduced blood flow pattern, front and side

    Beat changes over the front and side of the heart that can go with reduced blood flow to the heart muscle.

    13

  • Unspecific reduced blood flow pattern

    Beat changes that can go with reduced blood flow to the heart muscle, without a clear place.

    7

  • Anteroseptal infarct pattern

    A pattern linked to damage to the front wall of the heart muscle and the wall between the lower chambers.

    7

  • Low T waves

    The last part of each beat is smaller than usual.

    6

  • Left ventricular hypertrophy

    The muscle wall of the main pumping chamber may be thicker than usual.

    5

  • Unspecific wide QRS

    The signal spreads slowly inside the lower chambers, so the main spike is wide.

    5

  • Pacemaker rhythm

    The heartbeat is set by an artificial pacemaker that is working as expected.

    1

The doctor's review

What the reading doctor would check here

Worked out from this run's own numbers: where the rebuilt line strays, which measures moved, and which flags to keep or remove.

  1. 1The rebuilt line strays from the original recording in I (0.71), aVR (0.75), V1 (0.76), V4 (0.67) and aVL (0.74) and 6 more. Compare those leads with the paper first.
  2. 2Every measure from the photo is close to the same measure on the original recording.
  3. 3The cardiologists recorded reduced blood flow pattern, bottom and atrial flutter, which TraceRead AI did not flag.
  4. 4TraceRead AI flagged 9 patterns the cardiologists did not record: unspecific ST changes, ST depression, reduced blood flow pattern, front and side, unspecific reduced blood flow pattern, anteroseptal infarct pattern, low T waves, left ventricular hypertrophy, unspecific wide QRS and pacemaker rhythm. The doctor keeps or removes each one.
  5. 5The calibration pulse looks wider than expected, which would mean a paper speed of about 31.1 millimetres a second. TraceRead still reads the page at 25 millimetres a second, the usual speed, so timings could be a little off if that reading were right.

An AI first read is not the last word.

  • A qualified doctor reviews every AI first read. Nothing reaches a patient until a doctor signs it.
  • Do not rely on TraceRead alone in an emergency.
  • A normal AI first read does not rule out heart disease.
  • For adults, 18 and over.

Stage by stage

How TraceRead read this page

Every step of this run, with what went in and what came out.

Step 1: the photo

On the phone

What went in: one photo of a printed ECG

PTB-XL record 4769, a public research ECG from Germany, was printed as page T-0048 on A4 at 25 mm a second and 10 mm per millivolt. TraceRead's photo simulator then took a photo of it: tilted, lit unevenly, slightly blurred, with sensor noise and JPEG compression, the way a phone camera would.

This record was in PTB-XL's test set, so TraceRead AI never saw it during training. The person was a man aged 81. Age and sex are all TraceRead keeps.

Photo made by computer of the printed PTB-XL record 4769
Shown at 1600 by 1200 pixels.

Step 2: page finder

TraceRead AI

Find the paper and how it is turned

TraceRead AI looks at the whole photo and marks the four corners of the page, and which way up it is. Fixed code then measures the printed millimetre grid to correct the scale and the tilt, and makes the page flat.

Page found
yes
Turned
0 degrees
Paper
A4
The photo with the four page corners TraceRead AI found
The four corners TraceRead AI found, in red.

Step 3: layout reader

TraceRead AI

Work out where each lead sits

Every row of a printout starts with a calibration pulse, a small square step that is 10 mm tall for 1 millivolt. TraceRead AI finds the pulses, and fixed code matches them against 14 known page layouts to work out where each of the 12 leads sits and how long it runs.

Layout
3x4 with one lead II strip
Calibration pulses read
4 of 4
Height of 1 millivolt
10 mm
Paper speed used
25 mm a second
Pulse width suggested
31.1 mm a second
Layout match
0.977

Warnings this step raised

  • The calibration pulse looks wider than expected, which would mean a paper speed of about 31.1 millimetres a second. TraceRead still reads the page at 25 millimetres a second, the usual speed, so timings could be a little off if that reading were right.

Step 4: trace rebuild

TraceRead AI

Rebuild every lead as a digital signal

TraceRead AI marks which pixels are trace ink. Fixed code then follows the ink of each lead, column by column, and turns it into millivolts, 500 points a second. The rebuilt line is drawn back over the paper so a doctor can see at a glance if a lead was misread.

Because this ECG is public, we can check the rebuilt signal against the original recording. 1.00 would be a perfect match; the second number allows the two to be lined up by up to a tenth of a second.

LeadSeconds shownInk foundMatchLined up
I0 to 2.5100%0.710.82
aVR2.5 to 5100%0.750.99
V15 to 7.5100%0.761.00
V47.5 to 10100%0.670.91
II0 to 2.5100%0.930.98
aVL2.5 to 5100%0.740.98
V25 to 7.5100%0.781.00
V57.5 to 10100%0.810.98
III0 to 2.5100%0.940.98
aVF2.5 to 5100%0.780.99
V35 to 7.5100%0.730.99
V67.5 to 10100%0.800.98
II, rhythm strip0 to 100.820.97

Median match for this page: 0.77.

The flattened page with every rebuilt lead drawn over it in red
The flat page with every rebuilt lead drawn over it in red.

Step 5: coverage map

Fixed code

Mark which seconds the paper shows

A 3x4 printout shows each lead for only 2.5 of the 10 seconds the machine recorded. The coverage map tells the pattern finder exactly which seconds of each lead it has, so a part that is not on the paper is never read as a flat line.

I
aVR
V1
V4
II
aVL
V2
V5
III
aVF
V3
V6
II strip
0 s5 s10 s

Step 6: hold for retake

Fixed code

Decide whether the photo can be read

Before any pattern is read, a fixed hold rule decides whether the rebuild can be trusted. Version 1 looked only at how well the page matched a known layout and how unsure the AI was about the five main groups. Version 2 also checks the calibration, the page shape, how much trace was found, whether the overlapping lead II pieces agree, and clipped or flat parts. If the rebuilt trace looks unreliable, it asks for a new photo instead of giving a first read. Both versions' decisions for this page are shown below.

Version 1Photo usable

The layout match score was 0.977 (a photo is held back when the score is below 0.888) and 4 of 4 calibration pulses were read. The AI's own uncertainty about the five main heart groups was 0.327 (a photo is held back above 0.497). Neither check fired, so the photo is used.

Version 2Photo usable
  • Every check passed, so the rebuilt trace is used.
CheckValueLimitResult
page_foundpassed
gain_standard0.0090.05passed
paper_speed31.112434passed
layout_match0.9770.889passed
page_shape1.0011.7passed
ink_median10.9passed
coverage11passed
lead_ii_agree0.9970.49passed
lead_ii_amplitude0.0090.5passed
goldberger0.1071.45passed
edge_clipping00.027passed
flat_run0.0180.34passed
lead_ii_raw0.9940.2passed

Step 7: measures

Fixed code

Measure the heartbeat

Fixed code finds every beat, lines the leads up and measures them together. The same code run on the original recording shows how much the photo changed each number, and a reference ECG program from the PTB-XL+ dataset gives a second opinion.

MeasureFrom the photoOriginal recordingReference program
Heart rate (beats a minute)151150151
PR interval (ms)130127not measured
QRS width (ms)818296
QT interval (ms)287279302
QTc, corrected for heart rate (ms)390379410
Heart axis (degrees)848382
PR 124 msQRS 80 msQT 312 ms
The median heartbeat of lead II, from the photo, with the points the PR, QRS and QT measures start and end at.

Step 8: pattern finder

TraceRead AI

Score 71 patterns and flag the ones that pass their line

TraceRead AI reads the 12 rebuilt leads and the coverage map together and scores 71 patterns of rhythm, conduction, thickened heart muscle and ST and T changes. A pattern is flagged when its score passes a line set in advance on other ECGs, never on this one. The lines are set so that patterns are not missed, which is why a pattern can be flagged with a low score, and why some flags are wrong: the doctor decides.

What the dataset's cardiologists recorded for this ECG

  • Reduced blood flow pattern, bottom
  • Atrial fibrillation
  • Atrial flutter

TraceRead AI flagged 10 patterns. 1 of them is also among the dataset's statements (Atrial fibrillation). Not in the dataset's statements: Unspecific ST changes, ST depression, Reduced blood flow pattern, front and side, Unspecific reduced blood flow pattern and 5 more. In the dataset but not flagged: Reduced blood flow pattern, bottom and Atrial flutter.

TraceRead AI's score for each pattern, from 0 to 100. The thin line is where that pattern gets flagged.

  • Atrial fibrillation

    flagged

    an irregular rhythm where the upper heart chambers quiver

    95

  • Unspecific ST changes

    flagged

    small changes in the middle part of the beat that do not point to one cause

    26

  • Minor T wave abnormalities

    below the line

    small changes in the last part of the beat that are not enough to point to a cause

    14

  • ST depression

    flagged

    the middle part of the beat sits lower than usual

    14

  • Reduced blood flow pattern, front and side

    flagged

    beat changes over the front and side of the heart that can go with reduced blood flow to the heart muscle

    13

  • Unspecific reduced blood flow pattern

    flagged

    beat changes that can go with reduced blood flow to the heart muscle, without a clear place

    7

  • Anteroseptal infarct pattern

    flagged

    a pattern linked to damage to the front wall of the heart muscle and the wall between the lower chambers

    7

  • Low T waves

    flagged

    the last part of each beat is smaller than usual

    6

  • Left ventricular hypertrophy

    flagged

    the muscle wall of the main pumping chamber may be thicker than usual

    5

  • Unspecific wide QRS

    flagged

    the signal spreads slowly inside the lower chambers, so the main spike is wide

    5

  • Pacemaker rhythm

    flagged

    the heartbeat is set by an artificial pacemaker that is working as expected

    1

More case studies

Previous, T-0046

Unspecific wide QRS and anterolateral infarct pattern

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Normal ECG

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