| QR | <abbreviation> Origin: L quantum rectum, however much is correct. (05 Mar 2000) |
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| QRS complex | <cardiology> The deflections in an electrocardiographic tracing and represent ventricular activity of the heart. (13 Nov 1997) |
| QRS interval | The duration of the QRS complex in the electrocardiogram. (05 Mar 2000) |