What the numbers on your ECG report mean: PR, QRS, QT and QTc

Almost every 12-lead ECG machine prints a row of measurements above the squiggles: ventricular rate, PR interval, QRS duration, QT and QTc, and three axis numbers. These are the machine's own measurements, and understanding them makes the report far less mysterious.

Ventricular rate

How many times the main chambers beat per minute. Roughly 60 to 100 at rest is the textbook normal band, but fit people commonly sit in the 40s and 50s, and anxiety, fever, caffeine, or pain push it higher. The number alone rarely means much without the rhythm line next to it.

PR interval (normal 120-200 ms)

The time the electrical signal takes to travel from the top chambers to the bottom ones. A long PR is first-degree heart block, often benign and common in athletes and on beta-blockers. A short PR can point toward pre-excitation pathways such as WPW, which is worth showing to a clinician.

QRS duration (normal under 120 ms)

How long the main chambers take to depolarise. A wide QRS suggests a conduction delay such as a bundle branch block, or a ventricular origin for the rhythm. Machines flag this well; interpreting why it is wide is a human job.

QT and QTc: the one worth understanding

The QT interval is how long the bottom chambers take to recharge. It shortens naturally as heart rate rises, so machines print QTc, the rate-corrected version. The common correction (Bazett) over-corrects at high heart rates, which is why Fridericia's formula is often preferred. As a rough guide, QTc above about 450 ms in men and 470 ms in women counts as prolonged, and above 500 ms is clearly abnormal and deserves medical review, especially if you take medicines known to prolong QT, such as sotalol, some antiarrhythmics, certain antibiotics, or some antipsychotics.

The axis numbers

P, QRS, and T axes describe the average direction of each electrical wavefront in degrees. A QRS axis between about minus 30 and plus 90 is normal for most adults. Axis shifts matter mainly in patterns alongside other findings, not as standalone numbers.

A word about machine interpretations

The sentence the machine prints, normal ECG, borderline, possible this or that, is a first-pass algorithm, not a reading. Studies consistently show machine interpretations miss and overcall abnormalities, which is why most machines print unconfirmed diagnosis under their own verdict. Photograph the whole report, keep the numbers, and let a clinician read the tracing itself. CardioTrack's ECG import extracts exactly these printed values so you can track QTc and rate over time; it deliberately does not interpret the waveform.

The numbers on an ECG are measurements with normal ranges. The sentence beneath them is a machine's guess. Neither replaces a clinician reading the actual tracing.