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in music, the difference in pitch between two tones. Intervals may be measured acoustically in terms of their vibration numbers. They are more generally named according to the number of steps they contain in the diatonic scale of the piano; e.g., from C to D is a second, C and D being the first two notes of the scale of C. The fourth, fifth, and octave are termed perfect intervals as they have a characteristic sonority quite unlike any other interval. An interval between two natural notes, neither note being a sharp or a flat, is a major interval; if it is reduced by a semitone, it becomes minor. If a perfect or a minor interval is made half a step smaller it is called diminished, and when half a step larger, augmented. An interval may also be expressed by means of the ratio of the frequencies of its two tones. For example, the octave may be expressed by the ratio 2:1 because its upper tone has a frequency twice that of its lower tone.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in music and acoustics, the correlation of two tones according to pitch, that is, the frequency of sound vibration. The lower tone of an interval is known as its foundation, the upper its top. Tones employed in succession form a melodic interval; when used simultaneously, a harmonic interval. Each interval is determined by the volume, or quantitative, magnitude—that is, the number of steps it comprises—and the tonal, or qualitative, magnitude—that is, the number of whole tones or semitones it contains. Intervals formed within the limits of an octave are called simple intervals, and larger ones are called compound intervals. The names of intervals indicate the number of steps each embraces: the tonal size of the intervals determines whether they are minor, major, perfect, augmented, or diminished.

The simple intervals are perfect unison, minor second (a half tone), major second (one tone), minor third (1½ tones), major third (two tones), perfect fourth (2½ tones), augmented fourth (three tones), diminished fifth (three tones), perfect fifth (3½ tones), minor sixth (four tones), major sixth (4½tones), minor seventh (five tones), major seventh (5½tones), and perfect octave (six tones).

Compound intervals are created by adding a simple interval to the octave. They retain the characteristics of the analogous simple intervals; thus, there are ninths, tenths, elevenths, twelfths, thirteenths, fourteenths, and fifteenths (two octaves). Wider intervals are called a second above (or below) two octaves, a third above two octaves, and so on.

The enumerated intervals are known also as fundamental, or diatonic, intervals. Diatonic intervals can be increased or diminished by raising or lowering the foundation or top of the interval one chromatic semitone. If, simultaneously, both steps of an interval are subjected to alteration by a chromatic semitone in different directions, a double-augmented interval results; if one step is altered by one chromatic tone a double-diminished interval is produced. All intervals changed through alteration are called chromatic intervals. Intervals that differ in the quantity of steps they contain but are alike in tonal makeup (sound) are considered enharmonically equal—for example, F to G sharp (an augmented second) and F to A flat (a minor third).

All harmonic intervals are divided into consonant and dissonant intervals. The consonant intervals are the perfect unison and the octave (perfect consonance), the perfect fourth and the perfect fifth (very good consonance), and minor and major thirds and sixths (imperfect consonance). The dissonant intervals are minor and major seconds, the augmented fourth, the diminished fifth, and minor and major sevenths. The transference of the tones of an interval, during which the foundation becomes the upper tone of the interval and the top its lower tone, is called inversion; a new interval results. In inversion all perfect intervals remain perfect, minor intervals become major, major become minor, augmented become diminished, diminished become augmented, double augmented become double diminished, and double diminished become double augmented.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The spacing in pitch or frequency between two sounds; the frequency interval is the ratio of the frequencies or the logarithm of this ratio.
A set of numbers which consists of those numbers that are greater than one fixed number and less than another, and that may also include one or both of the end numbers.
The time separating two events, or the distance between two objects.
In special relativity, the Lorentz invariant quantity c 2t)2-(Δ x)2-(Δ y)2-(Δ z)2, where c is the speed of light, Δ t is the difference in the time coordinates of two specified events, and Δ x, Δ y, and Δ z are differences in their x, y, and z coordinates, respectively.
In general relativity, a generalization of this concept, namely the sum over the indices μ and ν of gμν dx μ dx ν, where dx μand dx νare the differences in the x μand x νcoordinates of two specified neighboring events, and gμνis an element of the metric tensor.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. Music the difference of pitch between two notes, either sounded simultaneously (harmonic interval) or in succession as in a musical part (melodic interval). An interval is calculated by counting the (inclusive) number of notes of the diatonic scale between the two notes
2. the ratio of the frequencies of two sounds
3. Maths the set containing all real numbers or points between two given numbers or points, called the endpoints. A closed interval includes the endpoints, but an open interval does not
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Kleiman et al., "The evaluation and management of drug effects on cardiac conduction (PR and QRS Intervals) in clinical development," The American Heart Journal, vol.
In the present study, we estimated associations between baseline arsenic exposure and subsequent ECG abnormalities, including prolongation of heart rate-corrected QT (QTc), PR, and QRS intervals in 1,715 cohort members.
Figure 8 Bar Chart showing Average QRS Interval in Athletes and Non Athletes QRS Interval Athletes 98 Non Athletes 90 Note: Table made from bar graph.
Since June 2003, CMS has covered ICDs in patients with ischemic dilated car diomyopathy (IDCM), a left ventricular ejection fraction less than 30%, and a QRS interval greater than 120 milliseconds.
At present, based upon data from the pre-SCD-HeFT era, Medicare will pay for an ICD in a patient who has ischemic heart failure, a left ventricular ejection fraction of 30% or less, prior MI, and an electrocardiogram showing a QRS interval or at least 120 milliseconds, regardless of whether the patient has experienced prior cardiac arrest.
Factors such as age, gender, left ventricular ejection fraction, New York Heart Association class, medical therapy, and QRS interval all failed to affect the basic finding that ICDs save lives.
For example, the cost per added life-year remained less than $40,000 whether or not treatment was limited to patients with left ventricular ejection fractions of 30% or less, to patients aged 65 years or older, or to patients with a QRS interval of 120 msec or more.
This means that patients who have the widest QRS interval (greater than 120 mileseconds) will likely have the greatest benefit--the lowest mortality--after ICD implantation.
Since June 2003, CMS has covered ICDs in patients with ischemic dilated cardiomyopathy (IDCM), a left ventricular ejection fraction less than 30%, and a QRS interval greater than 120 milliseconds.
Finally, the outcry over stratification based on QRS interval was unjustified, since previous trials alluded to the importance of the issue in risk stratification.
Those results showed that an implanted resynchronization device could cut the death rate by 27%, and the rate of death or hospitalization for worsening heart failure by 40%, in patients with a left ventricular ejection fraction of less than 35%, a left ventricular end-diastolic volume of at least 55 mm, a QRS interval of at least 130 msec, and a 6-minute walking distance of no more than 450 m.