|Year : 2009 | Volume
| Issue : 1 | Page : 11-16
The systolic to diastolic duration ratio in children with normal cardiac function and its relation to heart rate, age and body surface area
Roberto Sarnari1, Reema Yousef Kamal1, Mark K Friedberg2, Norman H Silverman3
1 M.D, Pediatric Echocardiography. Division of Pediatric Cardiology. Department of Pediatrics. Stanford University, Stanford, CA, USA
2 M.D, Hospital for Sick Children, Toronto, Ontario, Canada
3 MD, D Sc (Med), FASE, Pediatric Echocardiography. Division of Pediatric Cardiology. Department of Pediatrics. Stanford University, Stanford, CA, USA
|Date of Web Publication||17-Jun-2010|
Norman H Silverman
Division of Pediatric Cardiology, The Roma and Marvin Auerback Scholar in Pediatric Cardiology, Director, Pediatric and Echocardiography Laboratory, Lucile Packard Children's Hospital, Stanford Medical Center, 750 Welch Road - Suite 305, Palo Alto, California 94304
Source of Support: None, Conflict of Interest: None
| Abstract|| |
We have shown the ratio of systole to diastole to be a valuable global index of ventricular dysfunction in pediatric dilated and restrictive cardiomyopathy and also of ventricular function of the single systemic right ventricle in children who have undergone Norwood procedure for hypoplastic left heart. As this index may be a valuable indicator of ventricular performance in other conditions, normal reference values need to be established. The purpose of this study was to establish normal values for the S/D ratio in children and to investigate its relation to heart rate, age and body surface area.
We reviewed 179 echocardiograms of healthy children and young adults (mean: 70.18 months, SD: ± 65.12 months, range 0.02 months to 19 years) and measured the average duration of the holosystolic tricuspid regurgitant jet (systolic interval). The remainder of the cardiac cycle (i.e the period between 2 tricuspid regurgitant jets) was defined as the diastolic interval. We evaluated the relation between the S/D ratio and heart rate, age and body surface area by univariate and multivariate linear regression analysis.
Ranges, mean values and standard deviations are reported from age 0.02 months to 19 years (70.18 ± 65.12 months), BSA 0.11 to 2.51m2 (0.85 ± 0.55) and heart rate 50 to 156 bpm (96.72 ± 23.19). The systolic period ranged between 208.5 to 467 msec (314.08 ± 52.57) and the diastolic period between 166.5 to 809 msec (341.34 ± 129.61) yielding a S/D ratio between 0.397 to 1.62 (0.995 ± 0.23). The S/D ratio correlated positively with heart rate (y = 0.0073x+0.2969, r = 0.72). However, in multivariate analysis there was no significant correlation with age and body surface. Heart rate had a greater effect on shortening the diastolic period, in an exponential fashion (y = 130679x -1.3232, r = -0.88) than on systolic period which responded in linear fashion (y = -1.9228x + 500.05, r = -0.85).
We provide normal reference values for the S/D ratio across a wide range of heart rates in children, adolescents and young adults.
|How to cite this article:|
Sarnari R, Kamal RY, Friedberg MK, Silverman NH. The systolic to diastolic duration ratio in children with normal cardiac function and its relation to heart rate, age and body surface area. Heart Views 2009;10:11-6
|How to cite this URL:|
Sarnari R, Kamal RY, Friedberg MK, Silverman NH. The systolic to diastolic duration ratio in children with normal cardiac function and its relation to heart rate, age and body surface area. Heart Views [serial online] 2009 [cited 2019 May 19];10:11-6. Available from: http://www.heartviews.org/text.asp?2009/10/1/11/63840
| Introduction|| |
We have recently published the ratio of systolic to diastolic duration as a useful index of global and diastolic in children with different phenotypes of heart failure ,, . Although we demonstrated significant differences between heart failure patients and control subjects, normal reference values for the S/D ratio have not previously been established. The objectives of this study were: 1) to establish normal values for the S/D ratio in infants, children and adolescents in order to provide reference values, 2) to determine how the S/D ratio relates to changes in the duration of systole versus diastole and 3) to investigate its relation to heart rate, age and body surface area.
| Methods|| |
We retrospectively reviewed 179 echocardiograms from our database, performed from 2003-2007, of children referred for evaluation of a heart murmur and whose echocardiograms and clinical examinations were reported as normal. All subjects had a trace or a mild degree of holosystolic tricuspid valvar regurgitation  . Echo parameters of systolic and diastolic function including ejection fraction, fractional shortening index, mitral inflow Doppler and left ventricular M-mode, segmental contraction and tissue Doppler evaluation were within normal limits.
Echocardiography was performed using Sequoia and Philips IE-33 ultrasound systems. Probes of appropriate frequency were used and simultaneous ECG tracings were recorded. Doppler flow signals of atrioventricular regurgitation were recorded from the apical four-chamber view, parasternal short or long axis view of the tricuspid valve. Systolic duration was defined as the duration of holosystolic tricuspid regurgitation. Patients with less than holosystolic regurgitation were excluded from analysis. Diastolic duration was measured as the interval from the end of the tricuspid regurgitant jet to the onset of the subsequent regurgitant jet [Figure 1]. Images were obtained with a simultaneous electrocardiogram tracing on the ultrasound image. The heart rate was recorded in the same frame where Doppler flow measurement of systole and diastole was obtained. Demographic data including age, sex, and body surface area, were also recorded.
Measurements of systolic and diastolic duration were made offline by two observers from digitally stored images using commercially available software (KinetDx, Acuson, Mountain View). Three cardiac cycles were examined and the results averaged.
Repeated measurement of the S/D ratio was performed in 20 subjects to identify the inter- and intra-observer variability. Systolic and diastolic intervals were measured by an observer on two separate occasions to determine intra observer variability and inter observer variability. Observers were blinded to the results of previous measurements.
| Statistical analysis|| |
Statistical Software for Social Sciences (SPSS) ® and Excel® were used for statistical analysis.
We evaluated relationships between the systolic and diastolic periods with heart rate, age and body surface area using univariate and multivariate regression analysis. Results are expressed as the mean ± standard deviation and 95% confidence intervals. Age is reported in months, cardiac intervals in milliseconds and the S/D ratio as a decimal fraction.
Using Working-Hotelling analysis we calculated the upper and lower limit expected values for new observations on normal hearts (95% limits)  .
The study was approved by the Stanford University institutional review board (IRB number: 4947, Protocol ID:98253).
| Results|| |
We analyzed echocardiograms of 179 patients, age 70.18 ± 65.12 months (range: 0.02-228), BSA 0.85 ± 0.55 m2 (range: 0.11 - 2.51) and heart rate 96.72 ± 23.19 bpm (range: 50-156) [Table 1]. The S/D ratio was 0.995 ± 0.23 (range: 0.397-1.62). The systolic and diastolic durations were 314.08 ± 52.57 msec (range: 208.5-467) and 341.34 ± 129.61 msec (range 166.5-809) respectively [Table 2].
On univariate analysis we found a weak correlation between age and body surface area to S/D ratio [Figure 5],[Figure 6]; however, on multivariate linear regression analysis only heart rate demonstrated a significant and strong linear relationship with the S/D ratio y = 0.0072x +0.2969, r = 0.72, p < 0.0001; [Figure 2].
Systolic duration showed a negative linear relationship to heart rate y = -1.9228x+500.05, r = -0.85, p < 0.001; [Figure 3] while diastolic duration shortens in an exponential fashion with increasing heart rate y=130679x-1.3232, r=-0.88, p < 0.0001; [Figure 4]
| Intra and inter-observer variability|| |
We evaluated 20 patients to assess intra- and inter-operator variability for measurement of the S/D ratio. There was high inter and intra observer reliability at less than 5% each.
| Discussion|| |
The main objective of this paper was to determine normal reference values for the ratio of the duration of systole to diastole in infants, children and adolescents across a wide range of ages and heart rates. Our results also provide useful insight into the physiology of the cardiac cycle, the influence of heart rate on systole and diastole and how these might be affected in cardiac dysfunction.
Our results show that in children, on average, systole and diastole occupy roughly equal parts of the cardiac cycle with a resultant S/D ratio approximating one. Although we found an average systolic duration that is somewhat higher than the 40% systolic duration found in an early study  and although the resultant S/D ratio of 1 is somewhat higher than the 0.8 we found in a normal control population in a previous study, these are likely not substantially different and may be attributable to the different methodology used in the first instance and the larger sample size in the second.
Previous work has shown that heart rate and age are the two major determinants affecting the duration of systole and diastole. Our results show that in normal physiology, heart rate is the single most important determinant of diastolic duration and the effects of age and body surface area are likely related to changes in heart rate. In our study, the effect of increasing heart rate on shortening of the diastolic duration was striking. Although this fundamental relationship has been well known for many years, our results in normal children are, nevertheless, important in that we have previously shown that in systolic dysfunction, the S/D ratio is elevated due to diastolic shortening beyond the expected decrease related to heart rate. Systolic time intervals have been previously evaluated and isovolumic contraction time was demonstrated being constant for a wide range of heart rate variations , . In this relatively large group of children we found, as others have previously, that systolic duration is linearly related to heart rate  , due to an inverse correlation between ejection time and heart rate ,,, . In contrast, diastolic duration has a more complex relation with heart rate. Our results, again in keeping with previous findings, show that diastole has a strong logarithmic relationship to heart rate, becoming progressively shorter at faster heart rates, due to a shortened diastasis , . This strong physiologic effect of heart rate on diastolic duration, more than systolic duration, in addition to the heart-rate independent diastolic shortening found in cardiomyopathy, may explain the susceptibility of diastolic filling in cardiac dysfunction. Children may be especially susceptible to these effects due to naturally faster heart rates. In addition, diastolic dysfunction and elevated ventricular end-diastolic pressures may delay atrioventricular valve excursion further shortening diastole. The compound effect of these factors is to shorten diastole, compromise ventricular filling and decrease coronary perfusion. This may explain, at least in part, the importance of diastolic function as a prognostic factor in dilated cardiomyopathy.
The average systolic duration varied between 60% of the diastolic duration at low heart rates, to 120% of the diastolic duration at high heart rates. The implications of this result is that in infants who physiologically have heart rates of 100-140 bpm, the ventricle has to fill in a very short period of time. This presents a mechanistic conundrum given the low compliance of the immature myocardium and invokes the question of how the infantile ventricle achieves adequate filling. It is taught that infants increase cardiac output by increasing heart rate rather than by increasing stroke volume  . Our results suggest that this premise must be limited in scope, at least at high heart rates, as high heart rates limit diastolic filling thus limiting stroke volume and cardiac output.
The strong and different relations that exist between heart rate and systolic and diastolic durations make the S/D ratio a simple, yet strong indicator of global cardiac function. However, despite the widespread use of indices that utilize isovolumic intervals such as the myocardial performance index  and systolic time intervals as indicators of cardiac function ,, the S/D ratio has not been widely used. Measurement of the S/D ratio from the Doppler signal of atrioventricular regurgitation is simple and the onset and termination of atrioventricular regurgitation, emphasized by the valve click, is usually readily discernable. The establishment of normal reference values in this paper will hopefully facilitate clinical use of this readily available and reproducible index. The obvious limitation of this technique is that some degree of atrioventricular regurgitation is needed. Most children in need of cardiac function assessment by echocardiography will have at least a trivial degree of tricuspid or mitral regurgitation, adequate for assessment of the S/D ratio. In a previous study we did not find significant differences in the duration of left versus right atrioventricular regurgitation and we believe that either may be used to determine the S/D ratio; based on its characteristics, this index may also result particularly useful in single ventricle anatomy (e.g. HLHS) evaluation, where, at the present time, right ventricular function is assessed most commonly by qualitative visual evaluation on echo studies  .
Different definitions of what constitutes systole and diastole may be used. Our use of atrioventricular flow to define systole includes the isovolumic contraction and ventricular ejection, but not the electro-mechanical delay. Although this leads to a shorter systolic interval, we believe that this is not clinically significant. On the other hand, our definition of diastole incorporates isovolumic relaxation. This is different from the myocardial performance index which does not address diastole in its entirety.
| Study limitations|| |
In this retrospective study we did not examine the effect of exercise or pharmacological agents on the S/D ratio. These may have effects independent of heart rate. In addition, while we demonstrate the effect of heart rate on systolic and diastolic durations, we did not investigate which components of systole and diastole are affected.
| Conclusion|| |
We provide normal reference data for the S/D ratio in children and adolescents and demonstrate the profound effects of heart rate on the duration of systole and especially the duration of diastole.
Acknowledgements: We would like to thank Dr. Alex McMillan for his valuable contribution to the statistical analysis.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]