Impaired left ventricular relaxation is an early manifestation of diastolic dysfunction: can noninvasive indices be of help?

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Abstract

Diastolic dysfunction of the left ventricle is characterized by two major components, impaired relaxation and decreased compliance. Impaired relaxation is often the first abnormality noted in diastolic dysfunction. Traditionally, invasive indices have been used as gold standards, in accurate detection of relaxation abnormalities of the left ventricle. Earlier noninvasive indices of relaxation, had some inherent limitations e.g. load-dependency. More recently newer noninvasive indices have been described, that accurately track changes in relaxation, detected by invasive indices. By utilizing an integrative approach and combining the use of traditional, noninvasive indices with the newer ones, it will be possible to detect abnormalities in relaxation, which could previously be detected only by invasive measurements.

Introduction

Over the past several years there has been a growing interest in understanding the diastolic properties of the heart in children. In adults, numerous studies have tried to unravel the complexity shrouding diastolic properties and in the process, the field of "diastology" has been established. However, perhaps due to a lower incidence of diastolic dysfunction in children, the field of diastology has made slower progress than that in adults. Traditionally diastole has been subdivided into four components: (1) isovolumic relaxation, (2) rapid filling phase, (3) slow filling phase (diastasis) and (4) atrial contraction. Although this subdivision provides an elegant physiologic model, from the practical standpoint a more realistic subdivision of diastole consists of two major components: (1) relaxation and (2) diastolic filling.

Left ventricular (LV) relaxation starts with the closure of the aortic valve and continues until the mitral valve opens. As both the aortic and mitral valves remain closed during relaxation, the LV volume remains unchanged and filling of the LV does not occur. However, relaxation prepares the LV for the process of filling. It causes myocardial fibers to decompress and untwist and results in recoil of the fibers like an unloaded spring. At the subcellular level, relaxation occurs during detachment of actin-myosin cross-bridges as a result of removal of Ca2+ from troponin-C, by the sarcoplasmic reticulum. During the process of relaxation the LV pressure declines extremely rapidly. Therefore, a slower decline in LV pressure results from impaired relaxation. Although relaxation is an isovolumic event and actual filling of the LV does not take place during this phase, it prepares the LV for the event of filling. Therefore, a continuation of the process of relaxation is necessary for early filling period of diastole [1] , a period during which the majority of cardiac filling occurs.

Section snippets

Invasive indices of LV relaxation

The process of relaxation has been studied extensively both in the research as well as in the clinical setting. Invasive indices derived by high-fidelity micromanometric catheters positioned in the LV, have been used as gold standards. In order to interpret noninvasive indices of relaxation, we need to first understand the principles behind the invasive indices. This is especially important as some noninvasive indices of relaxation are used as surrogates for the invasive ones. Two invasive

Isovolumic relaxation time (IVRT)

IVRT has been used as a noninvasive index of relaxation. It differs from tau, in the sense that tau describes the rate of drop of LV pressure during relaxation, whereas IVRT measures the duration of relaxation. IVRT can be calculated by various techniques, including a combination of a phonocardiogram, to detect the closure of the aortic valve and M-mode echocardiogram, to detect opening of the mitral valve. In the present era phonocardiograms are used somewhat infrequently. However, the Doppler

Transmitral Doppler profile

The mitral inflow Doppler profile is characterized by an E and an A wave. The deceleration time of the E wave is the time interval from the peak of the E-wave to the actual or extrapolated baseline crossing of the decelerating E wave. In children and young adults the mean deceleration time is 100 ms (range: 48–139 ms) [11] (Table 1). The phenomenon of E and A wave reversal that has been described in adults, consists of a lower E wave velocity and a higher A wave velocity with prolonged

Pulmonary venous Doppler profile

When the mitral inflow Doppler has a ‘normal’ appearance, pulmonary vein Doppler can provide additional insight into diastolic function. Pulmonary vein Doppler waves can be obtained in younger children quite easily by transthoracic echocardiogram from the upper pulmonary veins using a foreshortened apical 4-chamber view, with the sample volume placed one cm inside the mouth of the pulmonary vein [15]. However, since the pulmonary veins are in the far field of the ultrasound beam, optimal

Non-invasive determination of minimum dP/dt and tau

In adults mitral regurgitation jet as well as aortic regurgitation jet has been used to calculate tau. Chen et al. [18] have evaluated tau by the Doppler technique and compared it with invasive measurement of tau, using a micromanometric catheter, in a canine model of mitral regurgitation. By digitizing the Doppler profile of the regurgitant jet, the instantaneous pressure gradient between the LV and LA throughout systole, was calculated using the simplified Bernoulli equation. This resulted in

Future directions

In order for noninvasive indices to be successful in predicting abnormalities of relaxation and diastolic dysfunction in the clinical arena, they should be simple to use and offer the same specificity as that offered by invasive gold standards. Two noninvasive indices, color M-mode Doppler and Tissue Doppler imaging (TDI) have shown considerable promise in studies performed in adults. However, in children further studies need to be performed.

Conclusions

Diastolic dysfunction of the LV is characterized by two major components, impaired relaxation and decreased compliance. Impaired relaxation is often the first abnormality noted in diastolic dysfunction. Noninvasive indices of relaxation are often dependent on age, heart rate and loading conditions. Therefore, accurate interpretation of each of these indices is necessary, especially when applied to children. However, by utilizing a combined approach, integrating many of the noninvasive indices

References (32)

  • T. Oki et al.

    Clinical application of pulsed Doppler tissue imahing for assessing abnormal left ventricular relaxation

    Am J Cardiol

    (1997)
  • J. Rychik et al.

    Quantitative assessment of myocardial tissue velocities in normal children with Doppler tissue imaging

    Am J Cardiol

    (1996)
  • W.C. Little et al.

    Clinical evaluation of left ventricular diastolic performance

    Prog Cardiovasc Dis

    (1990)
  • T.W. Riggs et al.

    Respiratory influence on right and left ventricular diastolic function in normal children

    Am J Cardiol

    (1989)
  • M.L. Weisfeldt et al.

    Hemodynamic determinants of maximum negative dP-dt and periods of diastole

    Am J Physiol

    (1974)
  • J.L. Weiss et al.

    Hemodynamic determinants of the time-course of fall in canine left ventricular pressure

    J Clin Invest

    (1976)
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