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Duration of the Q-T interval in normal pregnant women
DURATION
OF THE Q-T INTERVAL PREGNANT WOMEN ZACHARY
H. BENJAMIN,
IN NORMAL
M.D.
New York, N. Y.
M
EASUREMENT of the Q-T interval in the electrocardiogram has long been regarded as almost useless for any clinical purpose. It is known to be shortened by digitalis’ and salicylatesz and lengthened by hypocalcemia, quinidine, acute myocardial infarction, and congestive heart failure.3j4 HOWever, since Taran and Szilagyi5 showed that the Q-T interval is abnormally prolonged in all cases of rheumatic carditis which they observed and that it is not prolonged in inactive rheumatic disease or in normal subjects, it has become a measurement of considerable significance in the evaluation of rheumatic carditis. Various studies have been made to determine the normal limits of the Q-T These studies have been used as a base interval in normal healthy individuals. line to determine abnormal prolongation. Inasmuch as it is very important to make an early and correct diagnosis of active rheumatic carditis in pregnant women and in order to use the Q-T interval as one of the criteria for activity, it is first necessary to determine the normal range in healthy pregnant women. It seemed possible that the altered circulatory dynamics during pregnancy. might have some effect on its duration. METHOD
Electrocardiograms were taken on fifty normal women from the prenatal clinic. These covered the entire period of gestation. The electrocardiograms, consisting of the three standard limb leads and CF,, were made with the subjects in the supine position. The instrument used was a Cambridge mobile electric model, with an independent Telechron timer. All measurements were made with the aid of a magnifying lens in all leads in which a clear curve was obtained. The cycle length (R-R) and the Q-T interval were determined from averages of all Q-T leads. Taran’s modification of Bazett’s formula* Q-Tc = = ( d R-R ) was used.“,” This modification instead of using a constant K (= 0.40) to determine the average normal Q-T at any given rate calculates a corrected Q-Tt from any given measured Q-T interval and R-R. This provides an easy method of comparing any. determination with a normal standard. From the Department *Q-T = K 4 R-R. tcorrected to a cycle
of Medicine, length
Beth
Israel
of 1.00 second. 119
Hospital,
New
York,
N.
Y.
120
AMERICAN
HEART
JOURNAL
RESULTS
The results of these measurements and calculations are shown in Table I. Q-Tc ranged from 0.371 to 0.421, with an average value of 0.394. These figures are all below the commonly accepted upper limit of normal of 0.425 for adult women. The measured Q-T intervals were plotted against the R-R intervals on a scatter graph (Fig. 1) on which is shown Ashman and Hull’s7 upper limit of normal and average normal, and Bazett’s” average normal for adult women. It is seen that all the measurements fall below the upper limit of normal and that they follow closely the curves for average normal. Breaking the figures down into the three trimesters of pregnancy gives average Q-Tc values of 0.390, 0.396, and 0.394 for the first, second, and third trimesters, respectively. TABLE =
I.
DURATION
OF PREGNANCY, AGE SPREAD, A&D MEASURED INTERVALS IN FIFTY PREGNANT WOMEN
1
DURA1rION OF PREGNANCY (MO.)
AGE IYEARS:
R-R (SEC.)
Q-T (SEC.)
Q-Tc (SEC.)
CASE
DURAPION 01 PREGIVANCY (MO.1
0.414 0.389 0.397 0.390 0.386 0.387 0.395 0.400 0.396 0.391 0.421 0.382 0.399 0.413 0.371 0.398 0.389 0.402 0.383 0.379 0.407 0.381 0.389 0.403 0.384
3”: 31 32 33 34
3” 3
ii 25 22 27 24 24 26
0.325 0.335 0.340 0.291 0.298 0.338 0.321 0.323 0.319 0.270 0.31B 0.311 0.352 0.320 0.311 0.345 0.280 0.339 0.290 0.325 0.355 0.306 0.303 0.292 0.320
6 4 2
:i 20 21 22 23 24 25
0.620 0.740 0.735 0.564 0.600 0.762 0.660 0.658 0.655 0.480 0.555 0.666 0.776 0.600 0.704 0.74Y 0.521 0.711 0.570 0.739 0.760 0.650 0.611 0.522 0.735
26 27 28
:“4 15 16 17
19 20 20 39 19 23 29 25 21 25 20 23 25 27 20 31 32
CASE
AND CORRECTED Q-T
AGE IYEARS
R-R (SRC.)
Q-T (SEC.)
23 29 23 21 31 29 27 21 20 31 22 26 26 38 23 26 21 24 23 24 30 29 2c 21 20
0.706 0.619 0.850 0.721 0.770 0.763 0.705 0.680 0.635 0.750 0.819 0.570 0,710 0.626 0.854 0.521 0.715 0.634 0.509 0.666 0.615 0.635 0.520 0.795 0.673
0.329 0.311 0.361 0.323 0.333 0.337 0.325 0.330 0.319 0.350 0.360 0.295 0.349 0.331 0.351 0.280 0.327 0.302 0.283 0.318 0.310 0.309 0.287 0.340 0.320
0.391 0.398 0.392 0.381 0.379 0.385 0.387 0.399 0.400 0.405 0.399 0.392 0.415 0.416 0.383 0.389 0.387 0.390 0.397 0.391 0.395 0.389 0.397 0.383 0.392
0.656
0.320
0.394
.1 i 5” 6 7 8 1,” :;
Q-TC (SEC.) _----
ii 37 38 39 40 41 42 :i 45 46 47 48 5”:
i 9 5% 3
6% 5% i 5 4 8
8% 8% 7 8 9 3% 5
--Average
COMMENT
Despite alterations in the circulatory dynamics during pregnancy, there is no significant variation in the duration of electrical systole from the average normal. This knowledge enables one to make use of the Q-T interval in determining the presence and the duration of active rheumatic carditis. Abnormally
BENJAMIN:
Q-T
INTERVAL,
NORMAL
PREGNANT
WOMEN
121
prolonged Q-T intervals were found throughout the entire period of activity in three pregnant women admitted to Beth Israel Hospital with acute rheumatic carditis during the past year. Electrocardiograms before and after activity had normal Q-T intervals.
Fig.
I.--Measured
Q-T intervals plotted and normal curves for
against cycle adult woman.
length
in seconds,
122
AMERICAN
HEART
JOURNAL
CONCLUSIONS
1. Measurements of the Q-T interval of fifty pregnant women.
were done on the electrocardiograms
2. LU measurements were found to fall within the normal limits as determined by previous studies done on normal adult women.
3. Making use of Q-Tc (the corrected Q-T interval),” furnishes a simple means of determining whether a given measurement is above or below the normal range. 4. All corrected Q-T intervals accepted upper limit of 0.425.
in this series were below the commonly
REFERENCES 1.
Cheer,
2. 3.
Taran, Pardee,
4.
Stroud,
5.
Taran,
6.
Bazett,
7.
Ashman,
S. N., and Dieuaide, F. R.: Studies on Electrical Systole (“Q-T” Interval) of the Heart; Its Duration in Cardiac Failure, J. Clin. Investigation 10:889, 1931. L. M.: Personal communication. H. E. B.: Clinical Aspects of the Electrocardiogram, ed. 4, New York, 1941, Harper ct Brothers. W. D.: The Diagnosis and Treatment of Cardiovascular Disease, ed. 3, Philadelphia, 1945, F. A. Davis Company. The Duration of the Electrical Systole (Q-T) in Acute L. M., and Szilagyi, Nelly: Rheumatic Carditis in Children. AM. HEART 1. 33:14. 1947. H. C.: An Analysis of the Time Relations”of the Electrocardiogram, Heart 7:353, 1920. R., and Hull, I?.: Essentials of Electrocardiography, ed. 2, New York, 1941, The Macmillan Company.
OF THE Q-T INTERVAL PREGNANT WOMEN ZACHARY
H. BENJAMIN,
IN NORMAL
M.D.
New York, N. Y.
M
EASUREMENT of the Q-T interval in the electrocardiogram has long been regarded as almost useless for any clinical purpose. It is known to be shortened by digitalis’ and salicylatesz and lengthened by hypocalcemia, quinidine, acute myocardial infarction, and congestive heart failure.3j4 HOWever, since Taran and Szilagyi5 showed that the Q-T interval is abnormally prolonged in all cases of rheumatic carditis which they observed and that it is not prolonged in inactive rheumatic disease or in normal subjects, it has become a measurement of considerable significance in the evaluation of rheumatic carditis. Various studies have been made to determine the normal limits of the Q-T These studies have been used as a base interval in normal healthy individuals. line to determine abnormal prolongation. Inasmuch as it is very important to make an early and correct diagnosis of active rheumatic carditis in pregnant women and in order to use the Q-T interval as one of the criteria for activity, it is first necessary to determine the normal range in healthy pregnant women. It seemed possible that the altered circulatory dynamics during pregnancy. might have some effect on its duration. METHOD
Electrocardiograms were taken on fifty normal women from the prenatal clinic. These covered the entire period of gestation. The electrocardiograms, consisting of the three standard limb leads and CF,, were made with the subjects in the supine position. The instrument used was a Cambridge mobile electric model, with an independent Telechron timer. All measurements were made with the aid of a magnifying lens in all leads in which a clear curve was obtained. The cycle length (R-R) and the Q-T interval were determined from averages of all Q-T leads. Taran’s modification of Bazett’s formula* Q-Tc = = ( d R-R ) was used.“,” This modification instead of using a constant K (= 0.40) to determine the average normal Q-T at any given rate calculates a corrected Q-Tt from any given measured Q-T interval and R-R. This provides an easy method of comparing any. determination with a normal standard. From the Department *Q-T = K 4 R-R. tcorrected to a cycle
of Medicine, length
Beth
Israel
of 1.00 second. 119
Hospital,
New
York,
N.
Y.
120
AMERICAN
HEART
JOURNAL
RESULTS
The results of these measurements and calculations are shown in Table I. Q-Tc ranged from 0.371 to 0.421, with an average value of 0.394. These figures are all below the commonly accepted upper limit of normal of 0.425 for adult women. The measured Q-T intervals were plotted against the R-R intervals on a scatter graph (Fig. 1) on which is shown Ashman and Hull’s7 upper limit of normal and average normal, and Bazett’s” average normal for adult women. It is seen that all the measurements fall below the upper limit of normal and that they follow closely the curves for average normal. Breaking the figures down into the three trimesters of pregnancy gives average Q-Tc values of 0.390, 0.396, and 0.394 for the first, second, and third trimesters, respectively. TABLE =
I.
DURATION
OF PREGNANCY, AGE SPREAD, A&D MEASURED INTERVALS IN FIFTY PREGNANT WOMEN
1
DURA1rION OF PREGNANCY (MO.)
AGE IYEARS:
R-R (SEC.)
Q-T (SEC.)
Q-Tc (SEC.)
CASE
DURAPION 01 PREGIVANCY (MO.1
0.414 0.389 0.397 0.390 0.386 0.387 0.395 0.400 0.396 0.391 0.421 0.382 0.399 0.413 0.371 0.398 0.389 0.402 0.383 0.379 0.407 0.381 0.389 0.403 0.384
3”: 31 32 33 34
3” 3
ii 25 22 27 24 24 26
0.325 0.335 0.340 0.291 0.298 0.338 0.321 0.323 0.319 0.270 0.31B 0.311 0.352 0.320 0.311 0.345 0.280 0.339 0.290 0.325 0.355 0.306 0.303 0.292 0.320
6 4 2
:i 20 21 22 23 24 25
0.620 0.740 0.735 0.564 0.600 0.762 0.660 0.658 0.655 0.480 0.555 0.666 0.776 0.600 0.704 0.74Y 0.521 0.711 0.570 0.739 0.760 0.650 0.611 0.522 0.735
26 27 28
:“4 15 16 17
19 20 20 39 19 23 29 25 21 25 20 23 25 27 20 31 32
CASE
AND CORRECTED Q-T
AGE IYEARS
R-R (SRC.)
Q-T (SEC.)
23 29 23 21 31 29 27 21 20 31 22 26 26 38 23 26 21 24 23 24 30 29 2c 21 20
0.706 0.619 0.850 0.721 0.770 0.763 0.705 0.680 0.635 0.750 0.819 0.570 0,710 0.626 0.854 0.521 0.715 0.634 0.509 0.666 0.615 0.635 0.520 0.795 0.673
0.329 0.311 0.361 0.323 0.333 0.337 0.325 0.330 0.319 0.350 0.360 0.295 0.349 0.331 0.351 0.280 0.327 0.302 0.283 0.318 0.310 0.309 0.287 0.340 0.320
0.391 0.398 0.392 0.381 0.379 0.385 0.387 0.399 0.400 0.405 0.399 0.392 0.415 0.416 0.383 0.389 0.387 0.390 0.397 0.391 0.395 0.389 0.397 0.383 0.392
0.656
0.320
0.394
.1 i 5” 6 7 8 1,” :;
Q-TC (SEC.) _----
ii 37 38 39 40 41 42 :i 45 46 47 48 5”:
i 9 5% 3
6% 5% i 5 4 8
8% 8% 7 8 9 3% 5
--Average
COMMENT
Despite alterations in the circulatory dynamics during pregnancy, there is no significant variation in the duration of electrical systole from the average normal. This knowledge enables one to make use of the Q-T interval in determining the presence and the duration of active rheumatic carditis. Abnormally
BENJAMIN:
Q-T
INTERVAL,
NORMAL
PREGNANT
WOMEN
121
prolonged Q-T intervals were found throughout the entire period of activity in three pregnant women admitted to Beth Israel Hospital with acute rheumatic carditis during the past year. Electrocardiograms before and after activity had normal Q-T intervals.
Fig.
I.--Measured
Q-T intervals plotted and normal curves for
against cycle adult woman.
length
in seconds,
122
AMERICAN
HEART
JOURNAL
CONCLUSIONS
1. Measurements of the Q-T interval of fifty pregnant women.
were done on the electrocardiograms
2. LU measurements were found to fall within the normal limits as determined by previous studies done on normal adult women.
3. Making use of Q-Tc (the corrected Q-T interval),” furnishes a simple means of determining whether a given measurement is above or below the normal range. 4. All corrected Q-T intervals accepted upper limit of 0.425.
in this series were below the commonly
REFERENCES 1.
Cheer,
2. 3.
Taran, Pardee,
4.
Stroud,
5.
Taran,
6.
Bazett,
7.
Ashman,
S. N., and Dieuaide, F. R.: Studies on Electrical Systole (“Q-T” Interval) of the Heart; Its Duration in Cardiac Failure, J. Clin. Investigation 10:889, 1931. L. M.: Personal communication. H. E. B.: Clinical Aspects of the Electrocardiogram, ed. 4, New York, 1941, Harper ct Brothers. W. D.: The Diagnosis and Treatment of Cardiovascular Disease, ed. 3, Philadelphia, 1945, F. A. Davis Company. The Duration of the Electrical Systole (Q-T) in Acute L. M., and Szilagyi, Nelly: Rheumatic Carditis in Children. AM. HEART 1. 33:14. 1947. H. C.: An Analysis of the Time Relations”of the Electrocardiogram, Heart 7:353, 1920. R., and Hull, I?.: Essentials of Electrocardiography, ed. 2, New York, 1941, The Macmillan Company.