Systolic Phases of the Cardiac Cyclein Children

BY DAvm GOLDE, M.D., AND LuIs BURSTIN, M.D.

SUMMARYThe duration of the systolic phases of the cardiac cycle in 390 normal children

was determined from high-speed simultaneous recordings of the electrocardiogram,phonocardiogram, apexcardiogram, and carotid pulse. Data were obtained on chil-dren 1 mo to 13 years of age and analyzed to define the independent effects ofaging and heart rate on the systolic intervals. Electromechanical systole (Q-II) wasfound to prolong with increasing age in children with the same heart rate. Pre-ejec-tion period was also prolonged in older children and occupied an increased percentageof total systole. The interval from onset of contraction to first sound varied inverselywith heart rate and was independent of age. Electromechanical delay and isometriccontraction time were directly related to age and independent of rate. Ejection timevaried directly with age and inversely with heart rate but occupied a smaller per-

centage of systole in older children. Alterations in systolic phase duration occurringwith maturation reflect the normal functional adaptation of the developing heart.Measurement of these phases can provide useful information relative to cardiac func-tion in children.

Additional Indexing Words:Polycardiography Systolic time intervals Ejection timeIsometric contraction time Pre-ejection periodElectromechanical delay

NONINVASIVE technics have becomeincreasingly important in the study of

cardiovascular disease. With these methodsprecise hemodynamic data may be obtainedwithout risk or discomfort to the patient, andstudies can be repeated frequently and undervarious test conditions. Simultaneous externalpolycardiography is an atraumatic technic thatpermits the measurement of the various

From the Department of Medicine, University ofCalifornia School of Medicine, San Francisco,California, and the Department of Physiopathology,University of Costa Rica School of Medicine, SanJose, Costa Rica.

Presented in part at the 18th Annual ScientificSession, American College of Cardiology, March 1,1969.Address for reprints: David Golde, M.D., Depart-

ment of Medicine, University of Califomia Hospitals,San Francisco Medical Center, San Francisco,California 94122.

Received May 4, 1970; revision accepted forpublication August 25, 1970.

Circulation, Volume XLII, December 1970

PhonocardogramApexcardiogram

phases of cardiac systole. The duration ofthese phases correlates well with the patho-physiology in many abnormal cardiac states,and measurement of the phases can provideuseful clinical information relative to cardiacfunction.

Considerable data have been accumulatedon the normal temporal correlations of thephases of systole in adults.' Specific alterationsin systolic phase duration have been shown tooccur with congestive heart failure,2 thyroiddisease,3 digitalis therapy,4 and hypercal-cemia,5 as well as with various congenital" andvalvular defects.7 Data on the normal tem-poral relationships of the systolic phases inchildren are sparse, however, and age-raterelationships remain ill defined.-10 It isdifficult in children to separate the effects ofage and heart rate on the systolic intervalsbecause of the normal inverse relationshipbetween these variables. Cardiovascular mat-uration presumably involves a series of

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GOLDE, BURSTIN

adaptive processes which are reflected by age-dependent alterations in systolic phase dura-tion.The purpose of the present study was to

determine the independent effects of agingand heart rate on the systolic phases inchildren and to delineate the pattern of phasealteration occurring with normal cardiovascu-lar maturation.

MethodsThree hundred and ninety children (202 male

and 188 female) were studied. The subjectsranged in age from I mo to 13 years and were ingood health and free of heart disease. Each childwas normal on cardiovascular examination whichincluded blood pressure determination (in chil-dren over 2 years), auscultation of the heart andlungs, and a standard 12-lead electrocardiogram.Studies were conducted in the morning with thechildren recumbent and in the postabsorptivestate. Only cooperative subjects were included,and no sedation was used.

Simultaneous recordings were taken of theelectrocardiogram (lead II), phonocardiogram,apexcardiogram, and carotid pulse. Tracings were

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recorded on a Siemens Cardirex-6 direct-writingapparatus (linear frequency response 0.07 to 500Hz, 30% amplitude reduction at 650 Hz) utilizingthe Maass-Weber filter system. Boucke-Brechttype transducers were used for the carotid pulsepickup and apexcardiogram. The phonocardio-gram was recorded with an electromagneticmicrophone placed over the left ventricle at alocation giving the clearest reception of the firstand second heart sounds. All wave forns weredisplayed oscillographically, and recordings weretaken at paper speeds of 200 mm/ sec whenoptimal reception was achieved. The phases weremeasured by hand (with the aid of magnifica-tion) in five consecutive cycles at end expiration,and the average was recorded. Only tracings withclear wave forms and inflection points wereutilized. Though the usual limit of readingaccuracy for these types of recordings was takenas 5 msec,2 smaller units were interpolated inestimating phases of extremely short duration.

Six phases of cardiac systole were studied (fig.1) . Total electromechanical systole (hereafterreferred to as systole) was taken to comprise theQ-second sound interval (Q-II). The Q-first soundperiod (Q-I) was separated into two phases,electromechanical delay (EMD) and the intervalfrom the onset of contraction to the first sound

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phonocardiogram, carotid pulse, and apex-systolic phase duration (paper speed, 200

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CARDIAC CYCLE IN CHILDREN

Table 1Mean Values for Phase Duration in Five Age Groups (30 Children in Each)

HeartSex Yr/mo rate Q-II PEP Q-I EMD C-I ICT ET SQ

F 1/7 120 0.220 0.034 0.021 0.002 0.018 0.014 0.186 5.48M 1/6 119 0.220 0.034 0.021 0.002 0.018 0.014 0.186 5.43F 5/3 106 0.256 0.048 0.031 0.006 0.026 0.018 0.207 4.21M 5/6 104 0.257 0.050 0.031 0.006 0.026 0.018 0.207 4.15F 6/8 105 0.265 0.056 0.036 0.011 0.025 0.020 0.209 3.70M 6/7 90 0.294 0.063 0.043 0.014 0.029 0.021 0.232 3.71F 8/7 94 0.321 0.(060 0.035 0.012 0.023 0.025 0.260 4.30M 8/6 92 0.320 0.061 0.037 0.014 0.023 0.024 0.260 4.28F 13/8 84 0.367 0.093 0.060 0.029 0.031 0.033 0.274 2.97M 13/6 87 0.357 0.089 0.057 0.028 0.029 0.032 0.268 3.01

Abbreviations: Yr/mo = mean age in years and months; heart rate = beats/min; Q-II =

electromechanical systole; PEP = pre-ejection period; Q-I = transformation time; EMD =electromechanical delay; C-I = onset of contraction to 1st sound; ICT = isometric contraction;ET = ejection time; SQ = systolic quotient.

(C-I).1 EMD was measured from the Q wave ofthe electrocardiogram (lead II) to the onset ofthe systolic wave of the apexcardiogram (Cpoint). Q-I was read directly from the Q wave ofthe ECG to the first high frequency vibrations ofthe first heart sound, and C-I was calculated bysubtracting EMD from Q-I. Isometric contractiontime (ICT) was determined by measuring theinterval from the first heart sound to the onset ofthe upstroke of the carotid pulse wave andcorrecting for pulse transmission delay." Pulsedelay time was taken as the interval between thesecond heart sound and the trough of the carotidincisura. The pre-ejection phase (PEP) was

calculated by summing Q-I and ICT. Ejectiontime (ET) was measured from the onset of thecarotid upstroke to the trough of the incisura.12The systolic quotient (SQ) was calculated as theratio of ET and PEP. The data were stored on

magnetic tape and analyzed with the aid of an

IBM 360-50 computer. Preliminary plots were

made directly from taped data using the Cal-Comp apparatus.* Standard computer programswere used for regression analysis and tests ofstatistical significance. To determine possible sex

differences in systolic phase duration, t-tests were

performed on the entire population, on datacomparing children of various ages with the same

heart rate, and on children of the same age withvarious heart rates.

ResultsThe mean values obtained for the phases of

systole in five age groups are presented in

table 1. All phases of systole were found toprolong with increasing age, and the heartrate was progressively slower in older chil-dren. Linear regression equations relatingphase duration to age and heart rate are givenin table 2. F values for all equations weresignificant at P < 0.001. No significant differ-ences (P <0.05) were found between malesand females in the complete population forthe phases studied. In the group of 6 yearolds, however, systole (Q-II), PEP, and ETwere significantly shorter in girls (table 1).This was accounted for by the higher meanheart rate in girls in that age group ( 105 vs.90). In comparing boys and girls of similar

Table 2Regression Equations for Calculating SystolicPhase Duration* Based on Data from 390 Children1 Month to 13 Years of Age

Equation r SE

Systole (Q-II) = 0.65 M - 1.66 R + 402 0.97 14PEP = 0.30 M - 0.32 R + 65 0.94 6ET = 0.35 M- 1.35 R + 337 0.94 13EMD = 0.21 M-5.6 0.90 4C-I = 47-0.23 R 0.77 5Q-I = 0.18 M-0.31 R + 53 0.91 5ICT = 0.12 M + 11 0.89 3SQ = 5.47 - 0.015 M 0.78

*Interval in milliseconds.Abbreviations: M = age in months; R = rate in

beats per minute; r = correlation coefficient; SE =standard error.

*CaifoniaComputer Products, Inc., Anaheim,California.Circulation, Volume XLII, December 1970

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GOLDE, BURSTIN

heart rates, no differences were present forany of the phases.

Systole

A direct and linear relationship was foundto exist between the duration of systole (Q-II)and age for all of the children studied (fig. 2).Though a linear regression equation withacceptable fit may be written for this relation-ship, age and rate effects cannot be separatedfrom these data. When systole is plottedagainst heart rate for 13-year-old children (fig.3), the expected inverse relationship is seen.To determine possible independent effects ofage, duration of systole was compared for allchildren in the study (48) who coincidentlyhad a heart rate of 100 + 2.5 beats/min.Systole was found to prolong with increasingage apart from any rate considerations (fig.

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Duration of systole (Q-II) vs. age for entire population(390 children).

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Duration of systole (Q-II) vs. age for all children inthe study with a heart rate of 100 ± 2.5 beats/min.

4). The regression equation for calculatingtotal systole, therefore, contains two vanrablesand reflects the independent relationship ofsystole to age. This type of analysis wasapplied to all of the phases studied.

Electromechanical DelayEMD was found to prolong with increasing

age (fig. -5) but was relatively independentof heart rate (fig. 6). The regression equationfor EMD contains only one variable. When thephases are expressed as a percentage of totalsystole (table 3), EMD is seen to occupy anincreasing percentage of total systole in older

Table 3Mean Duration of Systolic Phases for Each AgeGroup Expressed as a Percentage of Systole (Q-II)

Age (yr) EMD C-I Q-I ICT PEP ET

<1 8.8 6.9 15.8 84.21 0.8 8.2 9.0 6.5 15.6 84.42 0.8 8.7 9.5 6.5 15.9 84.13 0.9 9.6 10.6 6.6 16.8 83.24 2.1 9.8 11.9 6.8 18.7 81.35 2.3 9.9 12.3 7.0 19.3 80.76 4.4 9.6 14.0 7.3 21.3 78.77 4.6 8.5 13.2 7.6 20.7 79.38 4.1 7.2 11.3 7.6 19.1 80.99 5.2 7.8 12.9 7.6 20.5 79.510 5.1 7.8 12.9 7.5 20.4 79.711 7.7 7.0 14.5 7.4 21.9 78.112 8.5 7.5 15.9 8.5 24.4 75.713 7.8 8.4 16.2 9.0 25.1 75.9

Abbreviations: Same as in table 1.

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CARDIAC CYCLE IN CHILDREN

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is dependent on both age and heart ratealterations and was found to prolong withboth increasing age and decreasing rate. Thecomposition of the Q-I period also changedmarkedly with aging. In children 1 to 3 yearsold the Q-I interval largely reflected theduration of C-I, whereas in 13 year olds EMDaccounted for approximately half of Q-I.

Isometric Contraction Time

ICT was found to prolong with increasingage and was independent of heart rate withinthe range studied. The duration of isometriccontraction increased approximately two anda half times between the ages of 1 and 13years and occupied a slightly increasedpercentage of systole in older children.

CHILDREN EIGHT YEARS OLD

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children. EMD was not measurable in chil-dren under 1 year with our technics and is lessthan 5 msec through the first 4 years of life.Approximately a sixfold increase in EMD isnoted between 4 and 13 years.

Contraction to First Sound (C-I)The C-I period was found to prolong with

decreasing heart rate but was largely inde-pendent of age. Rate-dependent alterations inthe C-I period roughly approximated those ofsystole; C-I, therefore, occupied a relativelyconstant percentage of systole in all agegroups (table 3).

Q-I IntervalThe Q-I interval (transformation time)

comprises both the EMD and C-I periods. It

Circulation, Volume XLII, December 1970

Pre-ejection PeriodPEP comprises the Q-I and ICT phases and

therefore relates twice to age and once to rate.PEP was prolonged in older children due to adirect relationship with age and indirectrelationship with rate. PEP occupied a pro-gressively greater percentage of systole withmaturation.

Ejection TimeET was found to relate independently to

age and heart rate. Though ET prolongedwith increasing age, it occupied a progressive-ly smaller percentage of total systole (table3).

Systolic QuotientThe systolic quotient was inversely related

to age and relatively independent of rate (fig.7). The quotient reflects the relative durationof PEP and ET and decreases with aging.

DiscussionThe duration of the various systolic phases

in children differs markedly from thoseobserved in adults.-10 Though some of thesedifferences may be explained by the morerapid heart rates of childhood, age per se is animportant determinant of phase duration. Thisis illustrated (table 4) by comparing valuesfor systolic phase duration in adults (based ondata from 121 normal males studied byWeissler and associates2) with values derived

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CHILDREN NINE YEARS OLD

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Systolic quotient vs. heart rate for 9-year-old children.

GOLDE, BURSTIN

Rate Age % Systole

Systole tElectromechanical

Delay - t 1C-1 -_Isometric

Contraction - tEjection time i t ISystolic Quotient - I

Figure 8Relationship of systolic phase duration, age, andheart rate; absolutely and as a percentage of systole.f = Direct relationship; 4 = inverse relaionship.

in this study for 3-year-old children, bothassuming a heart rate of 100 beats/min. Inorder to define the relative contribution ofage and heart rate to systolic phase duration,a large sample was studied permitting a com-parison of children of different ages withsimilar heart rates and children with varyingheart rates within a single age group. Usingthis type of analysis, a consistent pattern ofphase alteration was observed with matura-tion. The precise maturation factors responsi-ble for these alterations were not identified,though it seems likely that heart size, bloodpressure, and blood volume, are importantin this regard. Theoretically, some of the ob-served changes in phase duration could relateto extracardiac factors such as thoracic de-velopment. Autonomic activity must also beconsidered a significant factor.'3 Figure 8summarizes the relationships among the

Table 4Comparison of Systolic Phase Duration in Adultsand 3-Year-Old Children Based on a Heart Rateof 100 Beats/Min: Adult Values Calculated fromthe Regression Data of Weissler and Associates2

Adults Children (3 yr old)msec % of systole msee % of systole

Cycle 600 600Diastole 264 341Systole (Q-II) 336 259PEP 91 27 44 17ET 243 72 215 83Q-I 50 15 28 11ICT 38 11 16 6

Abbreviations: Same as in table 1.

duration of the systolic phases and age andrate.

Systole (Q-II) was found to relate inverselyto heart rate and indirectly to age. For a givenrate, systole was prolonged in older childrenand diastole was abbreviated. Diastole, there-fore, occupied a smaller percentage of thecardiac cycle, though in absolute terms itsduration increased in older children becauseof a slower heart rate. Interestingly, aprolongation of systole has been reported tooccur in old age.14 In our study, theprolongation of systole with age was largelydue to a long PEP, and ET, though alsolengthened, occupied a progressively smallerpercentage of systole in older children. Thelong systole found in old age was thought tobe due primarily to an increase in PEP.14 Arecent study,'5 however, has shown that ETalso is prolonged in old age independently ofchanges in heart rate and blood pressure. Theobserved alterations in systole, PEP, and EToccurring with maturation in children are,

therefore, qualitatively similar to those seen inold age.The duration of PEP has been taken as an

index of myocardial contractility and iscorrelated with ejection fraction,16 17 leftventricular end-diastolic pressure,18 cardiacoutput, and stroke volume.19' 20 Weissler hasshown that congestive heart failure in adultsresults in a prolongation of PEP and an

abbreviated ET.2 Digitalis will reverse theseeffects and cause a shortening of total systole.4The changes in PEP and ET which occur with

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aging in children could reflect alterations inmyocardial contractility or primarily relate tochanges in preload and afterload consequentto increased ventricular volume and highermean aortic pressures. The relative duration ofET and PEP is reflected by the SQ which islargely independent of rate and decreaseswith aging in childhood.9 In adults thequotient is constant over a wide age and raterange and is reported to be decreased inpatients with congestive failure2 and coronaryartery disease.21No significant sex differences in phase

duration were found in our study, though bothsystole (Q-II) and ET have been found to belonger in adult females than in males.2 Thissex differential may only become apparentafter puberty. Galstian9 reported ET to beshorter and the heart rates more rapid in girls7 to 15 years old. The decreased ET seems tobe a rate phenomenon, as no significantdifferences were found in our study for theentire population or when children withsimilar heart rates were compared. In the onlyage group in which a sex differential existed(6 year olds) there was also a marked differ-ence in heart rate between boys and girls.The shortened PEP found in young children

was due largely to decreased duration ofEMD and ICT. These two phases wereindependent of heart rate and directly relatedto age. ICT has been reported to beindependent of rate in both adults22 andchildren.4 EMD represents the time intervalbetween excitation and the onset of precordialmovement as measured from the Q wave ofthe electrocardiogram (lead II) to the onsetof the systolic wave of the apexcardiogramand is less than 5 msec in children under 4years. EMD prolongs with aging in childrenbut is relatively constant in adults, with 38msec frequently taken as a mean value.23Since EMD and ICT do not alter with ratechanges, they occupy an increased percentageof systole at more rapid heart rates. Thesephases would appear to be theoretically rate-limiting; however, our study includes onlyphysiologic rate changes and different phaserelationships may be operative with markedCirculation, Volume XLII, December 1970

bradycardia or tachycardia. Willems andKesteloot,24 for example, found ET to relatelinearly to heart rate, but exponential orpolynomial relationships existed in paroxysmalatrial tachycardia or with complete A-Vblock.The C-I interval was not related to age and

varied inversely with heart rate. This periodparalleled rate changes both absolutely and asa percentage of systole. Some of the difficultyin utilizing the Q-I interval clinically mayrelate to the disparity in the physiologiccorrelations of its component phases, EMDand C-I. For example, C-I has been found tobe a good index of the severity of mitralstenosis, whereas Q-I is poorly correlated.7The measurement of the systolic phases in

children by external graphic recordings can bepotentially useful in the diagnosis and quanti-tation of congenital defects, assessment ofmyocardial function, and screening for pediat-ric heart disease. Clinical application, how-ever, is predicated on an understanding of thenormal phase relationships in childhood.External recordings lend themselves to com-puter applications in which wave forms can bedigitized and phase duration calculateddirectly.25 Such a system could provideinstantaneous data on phase alterations andwould eliminate the subjective errors inherentin determining phase duration by handreading.The changes in systolic phase duration

occurring with maturation presumably repre-sent the normal functional adaptation of thedeveloping heart. This is manifested by anorderly redistribution of systolic intervalsresulting in a characteristic phase structure foreach age group and heart rate. Further studyof the precise maturation factors responsiblefor these changes is necessary. Measurement ofthe systolic phases in various childhood diseasestates can provide valuable information rela-tive to the effect of these diseases on cardiacfunction.

AcknowledgmentThe authors wish to express their appreciation to

Dr. Carlos Brenes Pereira for assistance with theclinical studies and Mr. George Shakargi for statisticalconsultation.

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The left ventricular ejection time in elderlysubjects. Circulation 42: 37, 1970

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Correlation of left ventricular pre-ejectionperiod with left ventricular ejection fraction inpatients with heart disease. (Abstr) Proc CentSoc Clin Res 42: 70, 1969

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DAVID GOLDE and LUIS BURSTINSystolic Phases of the Cardiac Cycle in Children

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1970 American Heart Association, Inc. All rights reserved.

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