Duration of the normal P wave

Duration of the Normal P Wave* Es An A . CACERES, M .D .

and

GEORGE A . KELSER . JR ., M .D .

Washington, D. C .

duration of the P wave is important in correlative studies in clinical electrocardiograph}, in the use of the electrocardiogram to time physiologic events such as heart sounds and vascular pressure curves, and in the measurement of the P-R interval . Al-

T

of first visible downward departure from the top of the baseline for negative waves . The return of the bottom of the trace to the baseline in positive waves, and of the top of the trace in negative waves was considered to be the end of the P wave (Figs . 1 and 2) . Measurements were performed with calipers from images of the tracings

1IE PREaiSE

though the I' wave is usually the simplest of all electrocardiographic waves, the range of normal values for it ; duration, as proposed by different authors, varies considerably, as shown in Table I . The variability of the accepted range limits

magnified ten times utilizing an electrocardiographic enlarger .

Accepted Ranges

the clinical usefulness of the measurement of the P wave duration . The reported variability reflects the difficulty encountered in measurement due to the small size of the wave and the use of different leads in measuring the duration . The present study was performed to determine if it a sere possible to obtain better definition of the duration of the P wave to enhance its

Source Rushmcr' Barker' Bum elm and Winsor'

clinical significance.

American Heart Associations Sodi-Pallares' Whites Grant'

METHODS AND MATERIALS

1'he P'aa'e durations were measured on 50 electrocardiograms recorded on heat-sensitive

Lepeschkin' Katz ,

paper ba direct-writing electrocardiographs, with a paper speed of 25 mm per second . Alt tracings were obtained from males previously found healthy by thorough medical evaluation . The subjects had an average age of 34 years . Twenty si rc between 20 and 30 years, 17 between 30 and 40, 11 between 40 and 50, one was 5_2, And mother, f 2 years of ago .

Gravhiel's

APRIL, 1959

P

Wave Duration in

I

Comment

.

"around 0 .08 sec" "not over 0 .10 sec' "does not normally exceed 0 .11 sec" 206 to 0 .11 we 0 .12 in lead I abnormal

"not over 0 .t sec' in lead 2 0 .12 sec or more considered a prolongation 0 .07 to 0 .12 sec "between 0 .1(1 and 0 .12 see viewed with suspicion . . . over 0 .12 abonrmal" to 0 .12 see

The distribution of the values of the durations of the 600 P waves from the 12 leads of the 50 electrocardiograms are shown in Figure 3 . The range of the P wave duration was 0 .000 to 0-178 sec The zero value refers to five instances when a P wave was not seen in a given lead . Table II presents the range and average

baseline for the positive waves, and as the point of

TABLE I Normal for Adults

RESULTS

F he P was c was measured in each of the three standard leads, the three augmented unipolar leads, and the six routinely taken precordial unipolar leads . The onset of the wave was defined as the point of the first visible upward departure of the trace from the bottom of the

* From the Department

of

Medicine, George Washington University Hospital, w'ashington . D . C . 449



450

Duration of Normal P Wave

`s- • ' dIl .

.'

n

A e

Fig. 1 . Comparison of actual-size electrocardiograms and P waves enlarged 10 times . (A) Lead 2 . The P wave in the center complex, in routine practice, measured 0 .10 second . (B) '1 'he P wave of (A) enlarged 10 times . The first visible upward departure of the trace from the bottom of the baseline occurs 0 .01 sec before the thicker 0.20 time line . The return of the bottom of the trace to the baseline occurs 0 .13 see after the beginning of the wave. (C) Lead aVR . In routine practice the P wave, obscured by the time lines, measured 0 .08 sec . (D) The P wave of (C) enlarged 10 times. Time lines are more clearly seen and the P wave measures 0 .10 sec . values for the duration of the P wave in each lead . The average duration of the 600 P waves was 0 .101 sec . The average of the minimum P wave durations was 0 .071 sec with the shortest P wave duration occurring in aVL . The average of the maximum durations was 0 .130 sec . Of the 50 subjects 44 had a P wave duration of 0 .12 sec or greater in one or more leads . Leads

aVF and V o most often showed the maximum P wave duration (Table III) . Leads a .VR, aVF, and V4 were the leads that most often had a P wave duration of 0 .12 sec or longer (Table IV) . The maximum P wave duration was found in one of the precordial leads in 24 subjects . In 21 of these 24 subjects the maximum duration was 0 .12 sec or greater . In 15 of the latter 21 subjects a P wave of 0 .12 sec or longer appeared in one or more of the limb leads . 130, 120L I10

O

H w so m 0 4 O W 0 f

jI

100` 90L 60', 70 . 60 50 40

2 30

Fig . 2 . (A) Lead V1 from the same subject in Figure 1 . (B) Diphasic P wave from the center camplcx of (A) enlarged 10 times . Measurement of P duration from upward departure of the bottom of the baseline in the positive portion of the wave to the return of the top of the trace to the baseline in the negative portion of the wave is 0 .12 sec .

20 10 NCI

co a 0e n9 m 1 • 1c am on . Fig . 3 . P wave durations in 50 normal electrocardiograms (600 measurements) . omoxo.. .0' ors 0] 0a 05

ME AMERICAS JOURNAL. OF CARDtOL0GY



Caceres and Kelser TABLE It Duration of the P Wave in 50 Electrocardiograms Time in sceonds Leads

Maximum

Average

Minimum

I 2 3 aVR aVL aVF V,

0 .160 0 .130 0 .142 0 13 .5 0 130 0 .178 0 .134 0 .146 0 .160 0 .150 0 140 0 135

0 .096 0 .108 0 .098 (1 .110 (1 .088 0 .109 0 .091 0 .094 0 .100 0_109 0 .108 0 .105

0 .054 0 .060 0 .048 0_074 0_038 0 .056 0_050 0 .044 0 .048 0 .070 0_070 0_062

V4 V;

TABLE III Frequency of Occurrence of Maximum P Wave Duration Lead 1 > 3 aVR aVI . a'sF V V V, V, V,.

Subjects 4 2 5 6 4 12

4 8 6

Age did nut affect the values . Since the rate in the electrocardiograms studied was within normal limits it was not a consideration in P wave duration . DISCUSSION AND CONCLUSIONS

Values of P wave duration obtained from averages of P waves in all leads or in specific leads did not representt the maximal P wave duration found in a normal subject's electrocardiogram . The maximal duration encountered in the 12-lead electrocardiogram was considered the measurement most accurately representing atrial electrical activity, although it is conceivable that the entire P wave may not be represented in any of the conventionally recorded 12 leads . The lead in which the maximal duraAPRIL, 195(9

451

TABLE I\7 Frequency of Occurrence of P Wave Duration of 0 .12 Second or Greater Lead 1 2 3 nVR aVL aVF V, V, V .: V4 V, V6

I

Stthjrca

I 6 21

14

tion is encountered could not be predicted (Tables Ill and IV) . Leads in which the P wave measures less than the maximal duration should not be considered representative of atrial electrical activity and should not be used for electrocardiographic measurement or to rime physiologic events. Forty-four of 5(1 normal subjects had P wave durations of 0 .12 sec or greater in one or more leads . The average maximum P wave duration was (1 .13 sec . These measurements reflect the precision gained by magnification of the tracings with consequent better definition of the waves and improved determination of the points of departure and return of the trace from and to the baseline. These findings suggest that the P wave duration generally exceeds that accepted as normal' -r' and that P waves of less than 0 .12 sec may not be representative of atrial electrical activity . SUMMARY

Accurate use of the P wave in electrocardiographic measurement and in electroeardiographic timing of physiologic events requires prior study in each individual to determine the lead with the maximal P wave duration . Magnification of electrocardiographic waves is useful to determine their duration . The duration of the P wave in the electrocardiograms of 50 normal males was found to exceed the accepted normal . Criteria for normal P wave duration based on average values of the duration in all leads or average values of



452

Duration

of

the duration in specific leads arc nor representative

of

maximal

P

wave duration in the electro-

cardiogram . Maximal P wave duration must be considered most representative of atrial electrical activity .

I'

waves

of

less than

0 .12

sec in duration should

not generally be considered representative

of

atrial electrical activity in normal subjects . REFERENCES 1 . RUSHMER,

R . F. :

Cardiac Diagnosis. Saunders, Philadelphia, 1955 . 2 . BARKER, J . M . : The Umpolar Electrocardiogram . Appleton-Century-Crofts, New York, 1952 . 3 . BURCH, G . E . and WINSnR, T . : A Primer of Eleairocardiograpley . Lea, Philadelphia, 1949 .

Normal

P

Wave

4 . Electrocardiographic Test Book . American Heart Association, New York, 1956 . 5 . Som-P.AI .5.AREs, D . : New B,,,esof Iilea?ocnrdiography . Moshy .. St . Louis, 1956 . 6 . WHITE, P . D . : Heart Disease, ed . 4. .illan, . Mac Now York, 1951 . 7 . CRAW', R. P. : C'Ivueal Electroeardiography . McGrawHill, New York, 1957 . S . 1 .EPESCHRIN, P. . : ifodern Electrocardiography, Vol . 1 . William, & Wilkins, Baltimore, 1951 . 9 . KATZ, L . N . : IYectroeardiography . Lea, Philadelphia, 1946 . GRAS BILL . A ., MCFARLAND, R . A ., GATES, D . C ., and Weasr'ER, F . A . : Analysis of the electrocardiograms obtained from 1000 young healthy aviators . Am . Heart .1 . 2' : 524, 1944 . 11 . BRAD, or, S. M . and MARRIOTT, H. J . T, . : Intraatrial block. Circalaliov 14 : 1073, 1956 -

10 .

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