Systolic time intervals in atrial fibrillation

Age- and sex-based normal reference ranges of the cardiac time intervals: the Copenhagen City Heart Study

BACKGROUND

Color tissue Doppler imaging (TDI) M-mode can be used to measure the cardiac time intervals including the isovolumic contraction time (IVCT), the left ventricular ejection time (LVET), the isovolumic relaxation time (IVRT), and the combination of all the cardiac time intervals in the myocardial performance index (MPI) defined as [(IVCT + IVRT)/LVET]. The aim of this study was to establish normal age- and sex-based reference ranges for the cardiac time intervals.

METHODS AND RESULTS

A total of 1969 participants free of cardiovascular diseases and risk factors from the general population with limited age range underwent an echocardiographic examination including TDI. The median age was 46 years (25th-75th percentile: 33-58 years), and 61.5% were females. In the entire study population, the IVCT was observed to be 40 ± 10 ms [95% prediction interval (PI) 20-59 ms], the LVET 292 ± 23 ms (95% PI 248-336 ms), the IVRT 96 ± 19 ms (95% PI 59-134 ms) and MPI 0.47 ± 0.09 (95% PI 0.29-0.65). All the cardiac time intervals differed significantly between females and males. With increasing age, the IVCT increased in females, but not in males. The LVET did not change with age in both sexes, while the IVRT increased in both sexes with increasing age. Furthermore, we developed regression equations relating the heart rate to the cardiac time intervals and age- and sex-based normal reference ranges corrected for heart rate.

CONCLUSION

In this study, we established normal age- and sex-based reference ranges for the cardiac time intervals. These normal reference ranges differed significantly with sex.

The significance of left ventricular ejection time in heart failure with reduced ejection fraction

Left ventricular ejection time (LVET) is defined as the time interval from aortic valve opening to aortic valve closure, and is the phase of systole during which the left ventricle ejects blood into the aorta. LVET has been used for several decades to assess left ventricular function and contractility. However, there is a recent interest in LVET as a measure of therapeutic action for novel drugs in patients with heart failure with reduced ejection fraction (HFrEF), since LVET is shortened in these patients. This review provides an overview of the available information on LVET including methods of measuring LVET, mechanistic understanding of LVET, association of LVET with outcomes, mechanisms behind shortened LVET in HFrEF and the potential implications of drugs that affect and normalize LVET.

Investigating the estimation of cardiac time intervals using gyrocardiography

OBJECTIVE

Assessment of cardiac time intervals (CTIs) is essential for monitoring cardiac performance. Recently, gyrocardiography (GCG) has been introduced as a non-invasive technology for cardiac monitoring. GCG measures the chest's angular precordial vibrations caused by myocardium wall motion using a gyroscope sensor attached to the sternum. In this study, we investigated the accuracy and reproducibility of estimating CTIs from the GCG recordings of 50 adults.

APPROACH

We proposed five fiducial points for the GCG waveforms associated with the opening and closure of aortic and mitral valves. Two annotators annotated the suggested points on each cardiac cycle. The points were compared to the corresponding opening and closing of cardiac valves delineated on Tissue Doppler imaging (TDI) recordings. The fiducial points were annotated on seismocardiography (SCG) and impedance cardiography (ICG) signals recorded simultaneously.

MAIN RESULTS

For estimating the timing of mitral valve closure, aortic valve opening, aortic valve closure, and mitral valve opening, 40%, 67%, 75%, and 70% of GCG annotations fell in the corresponding echocardiography ranges, respectively. The results showed moderate-to-excellent (r = 0.4-0.92; p-value < 0.01) correlation between the measured and the reference CTls. A myocardial performance index (Tei index) adapted using joint GCG and SCG resulted in a moderate correlation (r = 0.4; p-value < 0.001).

SIGNIFICANCE

The findings showed that the CTIs can be easily measured using GCG. Also, we found that using SCG and GCG recordings together could provide an opportunity to estimate CTIs more accurately, and make it possible to calculate the Tei index as an indicator of myocardial performance.

Automatic Identification of Systolic Time Intervals in Seismocardiogram

Continuous and non-invasive monitoring of hemodynamic parameters through unobtrusive wearable sensors can potentially aid in early detection of cardiac abnormalities, and provides a viable solution for long-term follow-up of patients with chronic cardiovascular diseases without disrupting the daily life activities. Electrocardiogram (ECG) and siesmocardiogram (SCG) signals can be readily acquired from light-weight electrodes and accelerometers respectively, which can be employed to derive systolic time intervals (STI). For this purpose, automated and accurate annotation of the relevant peaks in these signals is required, which is challenging due to the inter-subject morphological variability and noise prone nature of SCG signal. In this paper, an approach is proposed to automatically annotate the desired peaks in SCG signal that are related to STI by utilizing the information of peak detected in the sliding template to narrow-down the search for the desired peak in actual SCG signal. Experimental validation of this approach performed in conventional/controlled supine and realistic/challenging seated conditions, containing over 5600 heart beat cycles shows good performance and robustness of the proposed approach in noisy conditions. Automated measurement of STI in wearable configuration can provide a quantified cardiac health index for long-term monitoring of patients, elderly people at risk and health-enthusiasts.

Systolic time intervals as simple echocardiographic parameters of left ventricular systolic performance: correlation with ejection fraction and longitudinal two-dimensional strain

AIMS

Conventionally, the evaluation of left ventricular (LV) systolic function is based on ejection fraction assessment, which may be supplemented by other echocardiographic techniques, such as tissue Doppler imaging, 3D evaluation, and speckle tracking strains. However, these imaging modalities have a high technicity and are time-consuming, while being associated with reproducibility limitations. In this context, the usefulness of simpler measurements such as systolic time intervals (STI) by pulsed Doppler echocardiography must be emphasized.

METHODS AND RESULTS

In this multicentre study, left ventricular ejection fraction (LVEF), dP/dt(max), LV stroke volume, myocardial longitudinal deformation, aortic pre-ejectional period (PEP, ms), and left ventricular ejection time (LVET, ms) were prospectively investigated and compared in 134 consecutive heart failure (HF) patients and 43 control subjects. Feasibility of STI measurements was 100%. Intra-observer reproducibility was 98% for PEP, 96% for LVET, 87% for LVEF, and 93% for global longitudinal strain (GLS). By subgroup analyses, with increasingly altered LVEF or GLS, PEP significantly increased, whereas significantly LVET decreased, resulting in a significantly increased PEP/LVET ratio (P < 0.001). In the HF patients group, a correlation between LVEF and PEP/LVET was found, with r = 0.55 (y = -0.0083x + 0.75, P < 0.001). Based on receiver operating curve analyses, the area under the curve was 0.91 for PEP/LVET > 0.43, which allowed us to detect LVEF < 35% with a sensitivity of 87%, and a specificity of 84%.

CONCLUSION

STI can be easily and accurately measured in clinical practice, and may be used for detecting alterations in LV systolic function. Moreover, this method is likely to have potential applications in the management of HF patients.

Adaptive left ventricular ejection time estimation using multiple peripheral pressure waveforms

An adaptive approach is proposed for the problem of left ventricular ejection time (LVET) estimation using peripheral pressure waveform signals. The proposed algorithm, which makes use of 2 peripheral pressure measurements, makes it possible to adaptively estimate the LVET in response to different cardiovascular physiologic states. The algorithm builds on features obtained from global and branch-specific characterization of the cardiovascular circulation as well as waveform features to dramatically improve the accuracy of LVET estimation. The performance of the proposed approach is evaluated with respect to its heart-rate-based conventional counterpart, which shows approximately 40% improvement of estimation accuracy in terms of R²values &#9633; from 0.6655 for the conventional waveform-based approach to 0.9222 for the proposed approach.

Effect of coronary vasodilating drug on myocardial work

The purpose of this paper is to show, by noninvasive measurements, previously undocumented effects on cardiac work of the nitrate coronary vasodilator Pentaerythritol Tetranitrate (Peritrate). The chew-and-swallow 40-mg tablets of this drug were given to 10 patients of type II AHA classification. The Diastolic Time Tension Index/Systolic Time Tension Index Ratio increased significantly from 1.15 (+/- 0.11 SEM) to 1.46 (+/- 0.13), p less than 0.05. The Double Product decreased significantly from 9813 (+/- 606) to 8336 (+/- 497), p less than 0.01. The Triple Product also decreased significantly from 3223 (+/- 235) to 2425 (+/- 206), p less than 0.01. The percent diastole of the R-R interval increased significantly from 65% (+/- 2.44) to 70% (+/- 1.73) p less than 0.05, while no significant change in heart rate occurred (63.2 bts/min to 62.4 bts/min). Correspondingly, there was a decrease of systolic time interval, from 0.33 second (+/- 0.2) to 0.29 second (+/- .01) p less than 0.01. A significant decrease in blood pressure was also noted. Systolic BP dropped from 155 (+/- 8.0) to 134 (+/- 7.2), p less than 0.01. Diastolic BP dropped from 89.2 (+/- 2.8) to 79.2 (+/- 2.2), p less than 0.01. This study shows that Peritrate produced significantly favorable changes in all the cited indicators of cardiac work.