theta rhythm

rhythm (rithm) a measured movement; the recurrence of an action or function at regular intervals.rhyth´micrhyth´mical

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alpha rhythm  electroencephalographic waves having a uniform rhythm and average frequency of 10 per second, typical of a normal person awake in a quiet resting state.

atrial escape rhythm  a cardiac dysrhythmia occurring when sustained suppression of sinus impulse formation causes other atrial foci to act as cardiac pacemakers.

atrioventricular (AV) junctional rhythm  the heart rhythm that results when the atrioventricular junction acts as pacemaker.

atrioventricular (AV) junctional escape rhythm  a cardiac rhythm of four or more AV junctional escape beats at a rate below 60 beats per minute.

beta rhythm  electroencephalographic waves having a frequency of 18 to 30 per second, typical during periods of intense activity of the nervous system.

circadian rhythm  the regular recurrence in cycles of approximately 24 hours from one stated point to another, e.g., certain biological activities that occur at that interval regardless of constant darkness or other conditions of illumination.

coupled rhythm  heart beats occurring in pairs, the second beat usually being a ventricular premature beat; see also bigeminal pulse.

delta rhythm  rhythm on the electroencephalogram consisting of delta waves.

ectopic rhythm  a heart rhythm initiated by a focus outside the sinoatrial node.

escape rhythm  a heart rhythm initiated by lower centers when the sinoatrial node fails to initiate impulses, when its rhythmicity is depressed, or when its impulses are completely blocked.

gallop rhythm  an auscultatory finding of three (triple r.) or four (quadruple r.) heart sounds; the extra sounds occur in diastole and are related either to atrial contraction (S), to early rapid filling of a ventricle (S), or to concurrence of both events (summation gallop) .

idioventricular rhythm  a sustained series of impulses propagated by an independent pacemaker within the ventricles, with a rate of 20 to 50 beats per minute.

infradian rhythm  the regular recurrence in cycles of more than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

nodal rhythm  atrioventricular junctional r.

pendulum rhythm  alternation in the rhythm of the heart sounds in which the diastolic and systolic sounds are nearly identical and the heartbeat resembles the tick of a watch.

quadruple rhythm  the gallop rhythm cadence produced when all four heart sounds recur in successive cardiac cycles.

reciprocal rhythm  a cardiac dysrhythmia established by a sustained reentrant mechanism in which impulses traveling back toward the atria also travel forward to reexcite the ventricles, so that each cycle contains a reciprocal beat, with two ventricular contractions.

reciprocating rhythm  a cardiac dysrhythmia in which an impulse initiated in the atrioventricular node travels toward both the atria and ventricles, followed by cycles of bidirectional propagation of the impulse alternately initiating from those impulses traveling up and those traveling down.

reentrant rhythm  an abnormal cardiac rhythm resulting from reentry.

sinoatrial rhythm , sinus rhythm the normal heart rhythm originating in the sinoatrial node.

supraventricular rhythm  any cardiac rhythm originating above the ventricles.

theta rhythm  rhythm on the electroencephalogram consisting of theta waves.

triple rhythm  the cadence produced when three heart sounds recur in successive cardiac cycles; see also gallop r.

ultradian rhythm  the regular recurrence in cycles of less than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

ventricular rhythm 

1. idioventricular r.

2. any cardiac rhythm controlled by a focus within the ventricles.

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rhythm [rith´m]

a measured movement; the recurrence of an action or function at regular intervals. adj., adj rhyth´mic, rhyth´�mical.

accelerated idiojunctional rhythm a junctional rhythm, without retrograde conduction to the atria, at a rate exceeding the normal firing rate of the junction; it is an ectopic rhythm located in the bundle of His and controlling ventricles at a rate of 60 to 100 beats per minute.

accelerated idioventricular rhythm a rhythm of ectopic ventricular origin, faster than the normal rate of the His-Purkinje system but slower than 100 beats per minute, without retrograde conduction to the atria.

accelerated junctional rhythm a rhythm emanating from a focus in the AV junction at a rate greater than its normal rate of 60 but less than 100 beats per minute; it may be due to altered automaticity secondary to disease or to triggered activity secondary to digitalis toxicity. There may or may not be retrograde conduction to the atria.

alpha rhythm uniform rhythm of waves in the normal electroencephalogram, showing an average frequency of 10 per second, typical of a normal person awake in a quiet resting state. Called also Berger rhythm. See also electroencephalography.

atrioventricular junctional rhythm a junctional rhythm originating in the bundle of His, with a heart rate of 40 to 60 beats per minute; called also nodal rhythm.

automatic rhythm spontaneous rhythms initiated by the sinoatrial node, or by subsidiary atrial or ventricular pacemakers; in practice this refers to a normal sinus rhythm at a rate of 60 to 100 beats per minute.

Berger rhythm alpha rhythm.

beta rhythm a rhythm in the electroencephalogram consisting of waves smaller than those of the alpha rhythm, having an average frequency of 25 per second, typical during periods of intense activity of the nervous system. See also electroencephalography.

biological r's the cyclic changes that occur in physiological processes of living organisms; these rhythms are so persistent in nature that they probably should be considered a fundamental characteristic of life, as are growth, reproduction, metabolism, and irritability. Many of the physiological processes that recur in humans about every 24 hours (with circadian rhythm) have been known for centuries. Examples include the peaks and troughs seen in body temperature, vital signs, brain function, and muscular activity. Biochemical analyses of urine, blood enzymes, and plasma serum also have demonstrated circadian rhythms. Called also biorhythms.



It has long been believed that the cyclic changes observed in plants and animals were totally in response to environmental changes and, as such, were exogenous or of external origin. This hypothesis has now been rejected by most chronobiologists, who hold that the biological rhythms are intrinsic to the organisms, and that the organisms possess their own physiological mechanism for keeping time. This mechanism has been called the “biological clock.” An example of adjustment of the biological clock in humans is recovery from “jet lag.” This phenomenon, also known as jet syndrome, occurs when humans are transported by jet plane across time zones. It is characterized by fatigue and lowered efficiency, which persist until the biological clock adjusts to the new environmental cycle.

Biological rhythms are responsive to, or synchronous with, environmental cycles, but it is generally agreed among chronobiologists that the rhythmic changes in environmental factors do not create biological rhythms, even though they are capable of influencing them. Even in the absence of such environmental stimuli as light, darkness, temperature, gravity, and electromagnetic field, biological rhythms continue to maintain their cyclic nature for a period of time.

circadian rhythm the regular recurrence in cycles of about 24 hours from one point to another, such as certain biological activities that do this regardless of long periods of darkness or other changes in environmental conditions.

circamensual rhythm recurrence in cycles of about one month (30 days).

circannual rhythm recurrence of a phenomenon in cycles of about one year.

circaseptan rhythm that which occurs in cycles of about seven days (one week).

coupled rhythm heart beats occurring in pairs, the second beat of the pair usually being a ventricular premature beat.

delta rhythm

1. electroencephalographic waves having a frequency below 3½ per second, typical in deep sleep, in infancy, and in serious brain disorders. See also electroencephalography.

2. delta waves.

escape rhythm a heart rhythm initiated by lower centers when the sinoatrial node fails to initiate impulses, its rhythmicity is depressed, or its impulses are completely blocked.

gallop rhythm an auscultatory finding of three or four heart sounds, created by gushes of blood entering resistant or stiffened ventricles. This can happen at two different times during ventricular diastole: either at initial filling or at the time of ventricular contraction. Therefore, gallops occur during early and late ventricular diastole.

gamma rhythm a rhythm in the waves in the electroencephalogram having a frequency of 50 per second. See also electroencephalography.

idiojunctional rhythm a rhythm emanating from the atrioventricular junction but without retrograde conduction to the atria.

infradian rhythm the regular recurrence in cycles of more than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination or other environmental conditions.

junctional rhythm an arrhythmia caused by an abnormality in the atrioventricular junction; see accelerated junctional rhythm and atrioventricular junctional rhythm.

rhythm method old popular name for natural family planning.

nodal rhythm

1. atrioventricular junctional rhythm.

2. junctional rhythm.

nyctohemeral rhythm a day and night rhythm.

pendulum rhythm alternation in the rhythm of the heart sounds in which the diastolic sound is equal in time, character, and loudness to the systolic sound, the beat of the heart resembling the tick of a watch.

sinus rhythm normal heart rhythm originating in the sinoatrial node, with a normal rate of 60 to 100 beats per minute.

theta rhythm electroencephalographic waves having a frequency of 4 to 7 per second, occurring mainly in children but also in adults under emotional stress. See also electroencephalography.

ultradian rhythm the regular recurrence in cycles of less than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination or other environmental conditions.

ventricular rhythm the ventricular contractions which occur in cases of complete heart block.

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theta rhythm

a rhythmic hippocampal electrical discharge correlated with movement and locomotion.