| RSR | regular sinus rhythm; relative survival rate; right superior rectus [muscle] |
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| SMR | senior medical resident; sensorimotor rhythm; severe mental retardation; sexual maturity rating; ske... |
| SR | sarcoplasmic reticulum; saturation recovery; scanning radiometer; screen; secretion rate; sedimentat... |
| UHR | underlying heart rhythm |
| VR | right arm [electrode]; valve replacement; variable ratio; vascular resistance; venous reflux; venous... |
| trigeminal rhythm | A cardiac arrhythmia in which the beats are grouped in trios, usually composed of a sinus beat followed by two extrasystoles. Synonym: trigeminy. (05 Mar 2000) |
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| triple rhythm | A triple cadence to the heart sounds at any heart rate, due to the easy audibility of a third (usually) or fourth heart sound, or at faster rates a summation sound due to coincidence of the third and fourth heart sounds. (05 Mar 2000) |
| escape rhythm | Three or more consecutive impulses at a rate not exceeding the upper limit of the inherent pacemaker; extreme range of impulse formation at the sinoatrial node is between 40 to 180 impulses per minute, that of the atrioventricular junction is normally 40 to 60 impulses per minute, and the normal rate of the ventricular myocardium (idioventricular rhythm) is 20 to 40 impulses per minute. (05 Mar 2000) |
| junctional rhythm | Rhythms originating anywhere within the A-V junction. Formerly, "A-V nodal" or simply "nodal" rhythms. (05 Mar 2000) |
| ultradian rhythm | See: ultradian. (05 Mar 2000) |