J. ELECTROCARDIOLOGY 12 (3), 1979, 279-281

The Effect of Pregnancy on the Frontal Plane QRS Axis BY DAVID B. SCHWARTZ, M.B.B.CH. (RAND), DIP. MID. C.O.G. (S.A.), M.R.C.O.G., F.G.O.G. (S.A.) AND LEO SCHAMROTH, M.D., D.SC. (WITS), F.R.C.P. (EDIN. & GLASC.), F.A.C.C., F.R.S. (S.A.)t

SUMMARY The electrical axis of the heart is an important parameter in graphic assessment. Slight degrees of left axis deviation have been horizontal heart position resulting from the mechanical effects distension, such as the physiological event of pregnancy. 1,2 This dertaken to establish the validity of this concept.

MATERIALS AND METHODS

electrocardioattributed to a of abdominal study was un-

the n o r m a l r a n g e of 0 ~ to + 90 ~ The exception w a s one w o m a n w i t h a n axis of + 1000. c) The m e a n axis w a s +47.33 w i t h a S.D. 18.2 ~ (Table I, Fig. 1.). 2. The post-delivery Q R S axes. a) T h e r a n g e w a s - 1 0 ~ to +900. b) F o r t y - n i n e o u t of t h e 50 a x e s w e r e w i t h i n the n o r m a l r a n g e of 0 ~ to +900. The exception was one w o m a n w i t h a n axis of - 1 0 ~. c) The m e a n axis w a s + 4 2 . 2 ~ w i t h a S.D. 21.60. (Table I Fig. 1.). 3. The change of Q R S axis. a) I n 29 of t h e 50 p a t i e n t s (58%) t h e r e was no s i g n i f i c a n t c h a n g e of QRS axis in the pre- a n d post-delivery tracings. (Table I a n d P a n e l A of Fig. 1.) b) I n five of t h e 50 p a t i e n t s (10%) t h e r e w a s a s l i g h t r i g h t w a r d s h i f t in t h e post-delivery ECG. This c h a n g e r a n g e d b e t w e e n + 10 ~ a n d + 2 0 ~ w i t h a m e a n of + 12 ~ (Table I a n d P a n e l C of Fig. 1). I n o t h e r words, t h e r e w a s a slight leftward shift (within t h e n o r m a l r a n g e ) d u r i n g t h e p r e g n a n c y itself. c) I n 16 of the 50 p a t i e n t s (32%) t h e r e w a s a s l i g h t l e f t w a r d s h i f t in t h e p o s t delivery ECG which ranged between 10 ~ and 40 ~ w i t h a m e a n of 220. (Table I a n d P a n e l B of Fig. 1.) I n o t h e r words, there was a slight rightward shift (within the n o r m a l r a n g e ) d u r i n g the p r e g n a n c y itself. 4. T wave axis/pre-delivery. T h e p r e - d e l i v e r y T w a v e axes r a n g e d be-

The study was performed on 50 pregnant women. All patients were screened to exclude cardiovascular disease. All patients were confined at full term. All laboured uneventfully and normally, and were delivered spontaneously of live infants. An electrocardiogram (ECG) was recorded antenatally within 10 days of delivery. A repeat ECG was recorded w i t h i n 12 h o u r s a f t e r delivery. The parameters tested were pre-and post-delivery QRS axes, T wave axes, QRS-T angles and heart rates. Axes were determined according to the method of Grant. 3 The normal range of QRS axis is taken as 0~ clockwise to +90 ~ Right axis deviation is considered for axes greater than +90 ~. Slight left axis deviation is considered as axes from - 1 ~ to - 2 9 ~ Marked left axis deviation is considered for axes of - 3 0 ~ and further leftward.

RESULTS These are depicted in Table I a n d Fig. 1. 1. The pre-delivery QRS axes. a) T h e axes r a n g e d from 09 to + 100 ~ b) F o r t y - n i n e of the 50 axes were w i t h i n

*The University of Wisconsin Center for Health Sciences, Department of Gynecologyand Obstetrics, Madison, Wisconsin. tThe Department of Medicine, Baragwanath Hospital and the University of the Witwatersrand, Johannesburg. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. w 1734 solely to indicate this fact. Reprint requests to: David B. Schwartz, University of Wisconsin, Center for Health Sciences, Department of Gynecologyand Obstetrics, 1300 University Ave., Madison, Wisconsin, 53706.

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SCHWARTZ AND SCHAMROTH

TABLE I: Tabulation of Pre- and Post-delivery QRS and T wave axes and heart rates. Pre-delivery

Post-delivery

Heart Rates/minute Post-delivery

Case

QRS axis

T wave axis

QRS-T angle

QRS axis

T wave axis

QRS-T angle

Pre-delivery

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

+20 +60 +60 +50 +60 +50 +50 +40 +45 +45 +40 +50 0 +30 +60 +60 +40 +45 +30 +40 +30 +80 +40 +40 +45 +60 +45 +60 + 10 +50 +30 +10 +20 +30 +60 +30 +50 +60 +45 +50 +60 +70 +70 +60 +50 +60 "100 +20 +60 +45

+60 +60 +30 +45 +40 +30 0 +30 +40 +50 +50 +30 +30 +45 +30 +20 +30 +20 +30 +30 +45 +45 +30 +30 +30 +80 +30 +20 +40 +30 +40 +20 +20 +30 +45 +30 +30 +50 +45 +20 +40 +30 +60 +60 +60 +30 +40 +40 +30 +30

40 0 30 15 20 20 50 10 5 5 10 20 30 15 30 40 10 25 0 10 15 35 10 10 15 10 15 40 30 20 10 10 50 0 15 0 30 10 0 30 20 40 10 0 10 30 60 20 30 15

+30 +60 +60 +40 +60 +50 +30 +40 +45 +60 +50 +30 0 +30 +60 +60 +40 +45 +30 +20 +30 +80 +30 +40 +20 +60 +30 +60 +40 +50 -10 +10 +20 +30 +60 0 +70 +60 +45 +60 +30 +60 +50 +30 +10 +60 + 90 +20 +20 +45

+50 +50 +30 +30 +40 +20 0 +30 +40 +50 +50 0 +30 +45 +60 +20 +30 +40 +30 +30 +45 +20 +30 +30 +20 +40 +30 +20 +40 +30 +40 +20 +20 +20 +45 +30 +30 +30 +45 +45 +30 +30 +45 +40 +20 +35 +40 +30 +40 +20

20 10 30 10 20 30 30 10 5 10 0 30 30 15 0 40 10 5 0 10 15 60 0 10 0 20 0 40 30 20 50 10 0 10 15 30 40 30 0 15 0 30 5 10 10 25 50

90 110 90 90 105 105 75 75 90 100 105 90 110 90 90 85 90 9O 90 90 90 95 90 90 90 90 95 95 110 110 120 100 90 85 85 115 100 75 90 85 120 115 9O 116 120 120 75 85 IO0 115

tween 0~ and 60 ~ (mean +36~ 5. The T wave axis/post-delivery. The p o s t - d e l i v e r y T w a v e axes r a n g e d bet w e e n 0 ~ a n d 60 ~ ( m e a n 32.6~

10 20 25

90 110 90 90 100 100 75 75 90 90 95 110 90 90 90 85 90 9O 110 90 85 110 90 85 90 95 85 105 90 110 65 90 90 85 85 90 90 90 85 85 100 95 105 100 110 90 85 85 70 110

DISCUSSION Pregnancy with a comparison of pre-and post-delivery ECGs probably constitutes the ideal model for the study of mechanical disJ. ELECTROCARDIOLOGY, VOL 12, NO. 3, 1979

PREGNANCY AND THE ORS AXIS

281

9 = Pre -delivery QRS oxes x : Post-delivery QRS exes

A :

.

. . . .

:

.

: :

x "-

:

:

,

x

X

B X

X

C Fig. 1. Graphic representation of pre- and post-delivery frontal plane QRS axes.

9 X

+ldo o + 9 o o

tension on the ECG, since the change from m a x i m u m distension to normal is sudden following parturition. It is evident from this study t h a t the QRS axes during pregnancy are distributed within the normal range. Ninety-eight per cent of cases were in the range of 0 ~ to + 90 ~ the only exception being one case w i t h an axis of +100 ~ Thus, it is clear t h a t the abdominal distension of pregnancy does not cause a left axis deviation. In one case the post-delivery tracing showed a slight left axis deviation of the QRS to -100, while the pre-delivery trac, ing was +30 ~ The only deviation which could possibly be considered outside the normal range d u r i n g the pregnancy was one case with a slight right axis deviation of + 100 ~ in the pre-delivery tracing. It is further evident t h a t the abdominal distension does not cause any significant change in QRS axis. Thus, in 50% of cases there was no change at all in the pre- and post-delivery axes. In the 42% of cases w h e r e a c h a n g e was observed, the change was slight, and occurred within the normal range. Of the patients who exhibited a change, most (16 patients or 32% of the total sample) reflected a rightward shift during the pregnancy, whereas only five patients or 10% of the total sample reflected a leftward change. Furthermore, the rightward shift was more marked and ranged from 10 ~ to 40 ~ (mean of 22~ whereas the leftward shift ranged from 10 ~ to 20 ~ with a m e a n of 12 ~ The QRS-T angles did not exceed the normal limit of 60 ~ in either the pre-or postdelivery tracings. There was no significant change in QRS-T angles between the pre- and post-delivery tracings (Table I). Although the increases in rate m a y cause a slight right axis J. ELECTROCARDIOLOGY, VOk 12, NO. 3, 1979

X

o +7bo +do ~ +s'o o + 4 0 ~ + i o o + g o ~

o

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-I() ~

Frontal Plone Degrees

shift, there was no significant change in rate between the pre- and post-delivery tracings.

CONCLUSIONS The following conclusions m a y be drawn from this study 1. The frontal plane QRS and T wave axes are distributed within the normal range during maximal abdominal distension at full term. 2. No significant shift of axis occurs during the maximal distension at full term. 3. Where a shift (within the normal range) does occur, most cases actually reflect a slight rightward shift during full term. It is evident from this study t h a t abdominal distension does not cause a leftward deviation of the frontal plane QRS axis, and thus contradicts pre-existing concepts. If, therefore, a left axis shift does occur even w i t h i n the range of slight left axis deviation, i.e. within the range of 0 ~ to - 3 0 ~ it probably reflects early or slight left anterior hemiblock - - an intraventricular conduction defect. Acknowledgments: We wish to thank the Photographic Unit, Department of Medicine, University of the Witwatersrand, for the photographic reproductions. REFERENCES 1. WOOD, P.: Diseases of the Heart and Circulation. Eyre and Spottiswood, London, 1956, p 95 2. SODI-PALLARES D AND CALDERR M: New Bases of Electrocardiography. C V MOSBYAND Co, ST LOUIS, 1956 p 90 3. GRANT,R P: Spatial vectorelectrocardiography. A method for calculating the spatial electrical vectors of the heart from conventional leads. Circulation 2:676, 1950