Dual control of relaxation. Its role in the ventricular function in the mammalian heart

Diastolic Heart Failure Mechanisms and Assessment Revisited

The syndrome of heart failure (HF) with preserved ejection fraction (HFpEF) makes up about half of the HF population. The HF mechanisms in these patients are varied and not fully understood. In addition, the term "diastolic HF" was switched to HFpEF because of difficulties in measuring the left ventricular (LV) diastolic performance. In the late stages, HFpEF carries a prognosis that is as bad as or worse than that of HFrEF. Hence, it is important to recognize LV diastolic impairment at an earlier stage so that the causal mechanisms, if any, can be treated to retard its progression. Despite the availability of numerous disease-modifying agents for HFrEF, there are hardly any available treatments for HFpEF. With our aging population, there will be an epidemic of HFpEF and hence this entity needs attention and respect. In this paper, we review the fundamental mechanisms of HFpEF, the physiology of LV filling and how LV diastolic function can be comprehensively measured. We also speculate how this may help with the early recognition of diastolic HF and its treatment.

Study the relationship between left atrial (LA) volume and left ventricular (LV) diastolic dysfunction and LV hypertrophy: Correlate LA volume with cardiovascular risk factors

Heart failure (HF) with normal ejection fraction - the isolated diastolic heart failure, depicts increasing prevalence and health care burden in recent times. Having less mortality rate compared to systolic heart failure but high morbidity, it is evolving as a major cardiac concern. With increasing clinical use of Left atrial volume (LAV) quantitation in clinical settings, LAV has emerged as an important independent predictor of cardiovascular outcome in HF with normal ejection fraction. This article is intended to review the diastolic and systolic heart failure, their association with left atrial volume, in depth study of Left atrial function dynamics with determinants of various functional and structural changes.

Slower shortening kinetics of cardiac muscle performing Windkessel work‑loops increases mechanical efficiency

Conventional experimental methods for studying cardiac muscle in vitro often do not expose the tissue preparations to a mechanical impedance that resembles the in vivo hemodynamic impedance dictated by the arterial system. That is, the afterload in work‑loop contraction is conventionally simplified to be constant throughout muscle shortening, and at a magnitude arbitrarily defined. This conventional afterload does not capture the time‑varying interaction between the left ventricle and the arterial system. We have developed a contraction protocol for isolated tissue experiments that allows the afterload to be described within a Windkessel framework that captures the mechanics of the large arteries. We aim to compare the energy expenditure of cardiac muscle undergoing the two contraction protocols: conventional versus Windkessel loading. Isolated rat left‑ventricular trabeculae were subjected to the two force-length work‑loop contractions. Mechanical work and heat liberation were assessed, and mechanical efficiency quantified, over wide ranges of afterloads or peripheral resistances. Both extent of shortening and heat output were unchanged between protocols, but peak shortening velocity was 39.0 % lower and peak work output was 21.8 % greater when muscles contracted against the Windkessel afterload than against the conventional isotonic afterload. The greater work led to a 25.2 % greater mechanical efficiency. Our findings demonstrate that the mechanoenergetic performance of cardiac muscles in vitro may have been previously constrained by the conventional, arbitrary, loading method. A Windkessel loading protocol, by contrast, unleashes more cardiac muscle mechanoenergetic potential, where the slower shortening increases efficiency in performing mechanical work.

Reduced preload increases Mechanical Control (strain-rate dependence) of Relaxation by modifying myosin kinetics

Rapid myocardial relaxation is essential in maintaining cardiac output, and impaired relaxation is an early indicator of diastolic dysfunction. While the biochemical modifiers of relaxation are well known to include calcium handling, thin filament activation, and myosin kinetics, biophysical and biomechanical modifiers can also alter relaxation. We have previously shown that the relaxation rate is increased by an increasing strain rate, not a reduction in afterload. The slope of the relaxation rate to strain rate relationship defines Mechanical Control of Relaxation (MCR). To investigate MCR further, we performed in vitro experiments and computational modeling of preload-adjustment using intact rat cardiac trabeculae. Trabeculae studies are often performed using isometric (fixed-end) muscles at optimal length (Lo, length producing maximal developed force). We determined that reducing muscle length from Lo increased MCR by 20%, meaning that reducing preload could substantially increase the sensitivity of the relaxation rate to the strain rate. We subsequently used computational modeling to predict mechanisms that might underlie this preload-dependence. Computational modeling was not able to fully replicate experimental data, but suggested that thin-filament properties are not sufficient to explain preload-dependence of MCR because the model required the thin-filament to become more activated at reduced preloads. The models suggested that myosin kinetics may underlie the increase in MCR at reduced preload, an effect that can be enhanced by force-dependence. Relaxation can be modified and enhanced by reduced preload. Computational modeling implicates myosin-based targets for treatment of diastolic dysfunction, but further model refinements are needed to fully replicate experimental data.

What is the clinical significance of ventricular mural antagonism?

Recent morphological studies provide evidence that the ventricular walls are arranged as a 3D meshwork of aggregated cardiomyocyte chains, exhibiting marked local structural variations. In contrary to previous findings, up to two-fifths of the chains are found to have a partially transmural alignment, thus deviating from the prevailing tangential orientation. Upon contraction, they produce, in addition to a tangential force, a radial force component that counteracts ventricular constriction and aids widening of the ventricular cavity. In experimental studies, we have provided evidence for the existence of such forces, which are auxotonic in nature. This is in contrast to the tangentially aligned myocytes that produce constrictive forces, which are unloading in nature. The ventricular myocardium is, therefore, able to function in an antagonistic fashion, with the prevailing constrictive forces acting simultaneously with a dilatory force component. The ratio of constrictive to dilating force varies locally according to the specific mural architecture. Such antagonism acts according to local demands to preserve the ventricular shape, store the elastic energy that drives the fast late systolic dilation and apportion mural motion to facilitate the spiralling nature of intracavitary flow. Intracavitary pressure and flow dynamics are thus governed concurrently by ventricular constrictive and dilative force components. Antagonistic activity, however, increases deleteriously in states of cardiac disease, such as hypertrophy and fibrosis. ß-blockade at low dosage acts selectively to temper the auxotonic forces.

Aortic stiffness, pressure and flow pulsatility, and target organ damage

Measures of aortic stiffness and pressure and flow pulsatility have emerged as correlates of and potential contributors to cardiovascular disease, dementia, and kidney disease. Higher aortic stiffness and greater pressure and flow pulsatility are associated with excessive pulsatile load on the heart, which increases mass and reduces global longitudinal strain of the left ventricle. Excessive stiffness and pulsatility are also associated with microvascular lesions in high-flow organs, such as the brain and kidney, suggesting that small vessels in these organs are damaged by pulsatility. This brief review will summarize evidence relating aortic stiffness to cardiovascular, brain, and kidney disease.

Arterial hypertension and atrial fibrillation: standard and advanced echocardiography from diagnosis to prognostication

: Structural changes in left and right cardiac chambers that occur in arterial hypertension (AH) may lead to an increased risk of atrial fibrillation. Considering that AH is currently the most common cardiovascular disease in the general population, it represents a major risk factor for atrial fibrillation development. This review explores the complex relationship between atrial fibrillation and AH, starting from its pathophysiological basis. It focuses on the role of echocardiography in the management of hypertensive and atrial fibrillation patients, with emphasis on what should be evaluated about left ventricular remodeling, diastolic and systolic function, left atrial (LA) size and function and right ventricular deformation in patients with AH.

Will the real ventricular architecture please stand up?

Ventricular twisting, essential for cardiac function, is attributed to the contraction of myocardial helical fibers. The exact relationship between ventricular anatomy and function remains to be determined, but one commonly used explanatory model is the helical ventricular myocardial band (HVMB) model of Torrent‐Guasp. This model has been successful in explaining many aspects of ventricular function, (Torrent‐Guasp et al. Eur. J. Cardiothorac. Surg., 25, 376, 2004; Buckberg et al. Eur. J. Cardiothorac. Surg., 47, 587, 2015; Buckberg et al. Eur. J. Cardiothorac. Surg. 47, 778, 2015) but the model ignores important aspects of ventricular anatomy and should probably be replaced. The purpose of this review is to compare the HVMB model with a different model (nested layers). A complication when interpreting experimental observations that relate anatomy to function is that, in the myocardium, shortening does not always imply activation and lengthening does not always imply inactivation.

Mechanical Unloading Properties of Axial Flow Pumps and their Effect on Myocardial Stunning

Postischemic myocardial dysfunction affects morbidity and mortality in patients with coronary artery disease. It is known that mechanical unloading of the left heart ventricle can positively influence postischemic myocardial dysfunction. In this respect we tested two miniaturised axial flow pumps, i.e. the 14-F and the 21-F Hemopump®. An experimental study was carried out on 30 open chest sheep where regional myocardial wall motion was followed using sonomicrometry in a preparation of transient coronary artery occlusion. Only the larger 21-F Hemopump® showed hemodynamically significant unloading of the left ventricle. Furthermore, as far as stunning is concerned, systolic wall thickening recovered better when this type of pump was used during reperfusion. Also postejection thickening, which is an indication of diastolic postischemic dysfunction, is reduced significantly in the postischemic area (ANOVA, p<0.05). Thus, the 21F Hemopump®, but not the 14F Hemopump®, provides adequate mechanical unloading in order to beneficially influence myocardial stunning.

Pathophysiological Considerations concerning Uni- and Biventricular Mechanical Cardiac Assist

Mechanical assisted circulation by the means of cardiac assist devices is a routine procedure in modern cardiac surgery and cardiology. We investigated the impact of mechanical unloading on regional myocardial “stunning” and the influence of assisted circulation on left heart and right heart failure persevered by an ultimate addition of pulmonary hypertension in experimental set ups.

We found that mechanical unloading either during ischemia or in the early reperfusion phase attenuates stunning and enhances the return of synchronous heart performance.

In our global dysfunction model we showed that the right heart is dispensable. Sufficient inflow to the left heart is provided unless pulmonary hypertension is present. Also additional left heart support can not overcome the deleterious situation and in select cases only additional right heart support can prevent the “low LVAD output” syndrome.

We conclude that mechanical assisted circulation and mechanical unloading are beneficial in case of regional and global dysfunction persevered by pulmonary hypertension, however, the knowledge about interactions of assist systems and the circulation has to be improved in order to optimize clinical assist device performance.

Myocardial relaxation is accelerated by fast stretch, not reduced afterload

Fast relaxation of cross-bridge generated force in the myocardium facilitates efficient diastolic function. Recently published research studying mechanisms that modulate the relaxation rate has focused on molecular factors. Mechanical factors have received less attention since the 1980s when seminal work established the theory that reducing afterload accelerates the relaxation rate. Clinical trials using afterload reducing drugs, partially based on this theory, have thus far failed to improve outcomes for patients with diastolic dysfunction. Therefore, we reevaluated the protocols that suggest reducing afterload accelerates the relaxation rate and identified that myocardial relengthening was a potential confounding factor. We hypothesized that the speed of myocardial relengthening at end systole (end systolic strain rate), and not afterload, modulates relaxation rate and tested this hypothesis using electrically-stimulated trabeculae from mice, rats, and humans. We used load-clamp techniques to vary afterload and end systolic strain rate independently. Our data show that the rate of relaxation increases monotonically with end systolic strain rate but is not altered by afterload. Computer simulations mimic this behavior and suggest that fast relengthening quickens relaxation by accelerating the detachment of cross-bridges. The relationship between relaxation rate and strain rate is novel and upends the prevailing theory that afterload modifies relaxation. In conclusion, myocardial relaxation is mechanically modified by the rate of stretch at end systole. The rate of myocardial relengthening at end systole may be a new diagnostic indicator or target for treatment of diastolic dysfunction.

Deliberations on Diastolic Heart Failure

Studies of left ventricular diastolic dysfunction and diastolic heart failure (DHF), published during the past 4 decades, include a prodigious number and wide variety of research efforts. This review report considers some of the historical literature and incorporates more recent information supporting the idea that patients with DHF constitute a subgroup of the heterogeneous population of patients with heart failure and a preserved ejection fraction. Clinical investigation, particularly therapeutic trials, should be directed at specific targets within the population of interest, not at the broad heart failure with preserved ejection fraction population. To accomplish this, it is important to stipulate criteria for the diagnosis of DHF and to limit our attention to specific subgroups or phenotypes.

The quest for load-independent left ventricular chamber properties: Exploring the normalized pressure phase plane

The pressure phase plane (PPP), defined by dP(t)/dt versus P(t) coordinates has revealed novel physiologic relationships not readily obtainable from conventional, time domain analysis of left ventricular pressure (LVP). We extend the methodology by introducing the normalized pressure phase plane (nPPP), defined by 0 ≤ P ≤ 1 and -1 ≤ dP/dt ≤ +1. Normalization eliminates load-dependent effects facilitating comparison of conserved features of nPPP loops. Hence, insight into load-invariant systolic and diastolic chamber properties and their coupling to load can be obtained. To demonstrate utility, high-fidelity P(t) data from 14 subjects (4234 beats) was analyzed. PNR, the nPPP (dimensionless) pressure, where -dP/dtpeak occurs, was 0.61 and had limited variance (7%). The relative load independence of PNR was corroborated by comparison of PPP and nPPP features of normal sinus rhythm (NSR) and (ejecting and nonejecting) premature ventricular contraction (PVC) beats. PVCs had lower P(t)max and lower peak negative and positive dP(t)/dt values versus NSR beats. In the nPPP, +dP/dtpeak occurred at higher (dimensionless) P in PVC beats than in regular beats (0.44 in NSR vs. 0.48 in PVC). However, PNR for PVC versus NSR remained unaltered (PNR = 0.64; P > 0.05). Possible mechanistic explanation includes a (near) load-independent (constant) ratio of maximum cross-bridge uncoupling rate to instantaneous wall stress. Hence, nPPP analysis reveals LV properties obscured by load and by conventional temporal P(t) and dP(t)/dt analysis. nPPP identifies chamber properties deserving molecular and cellular physiologic explanation.

Effect of exercise training on diastolic function in metabolic syndrome

It has been reported that metabolic syndrome (MetS) impairs left ventricular (LV) diastolic function. The objective of this study was to determine whether exercise training can improve LV diastolic function in individuals with MetS. Twenty-eight individuals with MetS (9 males, aged 60 ± 5 years) underwent a 1-year combined endurance and resistance exercise training program; maximal aerobic capacity (V̇O2max), blood pressure, blood markers, and LV diastolic function were measured at weeks 0, 12, 24, and 52 throughout the training. Pulsed wave Doppler echocardiography across the mitral valve was used to assess peak early flow velocity (E) and peak atrial flow velocity (A) to determine the E/A ratio. Individuals with MetS had a reversed E/A ratio, suggesting impaired LV relaxation, the first stage of LV diastolic dysfunction. Exercise training reduced systolic blood pressure (SBP) (129 ± 14 to 120 ± 12 mm Hg; p < 0.01) and increased V̇O2max (29.2 ± 6.3 to 33.4 ± 6.5 mL·kg−1·min−1; p < 0.01) and high-density lipoprotein cholesterol (1.04 ± 0.21 to 1.12 ± 0.25 mmol·L−1; p = 0.02), but did not improve LV diastolic function. Individuals with an E/A ratio <1 at the start of training had a tendency toward an increased E/A ratio (p = 0.12) accompanied by significant decreases in SBP and increases in V̇O2max with exercise training. Combined resistance and aerobic exercise training improved cardiometabolic health but did not improve the impaired LV diastolic function of individuals with MetS.

Early return of augmented wave reflection impairs left ventricular relaxation in aged Fisher 344 rats

Left ventricular (LV) relaxation is influenced by vascular loads imposed on the heart. The current study investigated the influence of the timing and magnitude of arterial wave reflection on LV isovolumic pressure relaxation, with a specific focus on the aging process. Fisher 344 rats aged 6, 18, and 24 months were anesthetized and thoracotomized. Arterial wave reflection was characterized by wave transit time (τ(w)) and wave reflection factor (R(f)) using the impulse response of the filtered aortic input impedance spectra. Indices of LV pressure relaxation included peak -dP(LV)/dt and the isovolumic relaxation time constant (τ(e)). The vascular dynamic condition in the rats was characterized by (1) a progressive increase in R(f) and decrease in τ(w) associated with age, especially at 24 months; and (2) a decline in aortic compliance (C(m)). Changes in LV relaxation consisted of a fall in peak -dP(LV)/dt and a rise in LV τ(e) with age. Taking LV τ(e) as the dependent variable and arterial R(f) and τ(w) as the two independent variables, multiple linear regression was employed to fit the data. The correlation among the three parameters reached significance (τ(e) =11.885+5.350×R(f)-0.213×τ(w); r=0.5823, p<0.05). This finding indicated that as arterial τ(w) shortened and arterial R(f) was augmented with age, LV τ(e) became more prolonged and late pressure relaxation slowed. Thus, the heavy reflection intensity with early return of the pulse wave reflection might account for the age-related deterioration in LV isovolumic pressure decay.

Cardiac electromechanical models: from cell to organ

The heart is a multiphysics and multiscale system that has driven the development of the most sophisticated mathematical models at the frontiers of computational physiology and medicine. This review focuses on electromechanical (EM) models of the heart from the molecular level of myofilaments to anatomical models of the organ. Because of the coupling in terms of function and emergent behaviors at each level of biological hierarchy, separation of behaviors at a given scale is difficult. Here, a separation is drawn at the cell level so that the first half addresses subcellular/single-cell models and the second half addresses organ models. At the subcellular level, myofilament models represent actin–myosin interaction and Ca-based activation. The discussion of specific models emphasizes the roles of cooperative mechanisms and sarcomere length dependence of contraction force, considered to be the cellular basis of the Frank–Starling law. A model of electrophysiology and Ca handling can be coupled to a myofilament model to produce an EM cell model, and representative examples are summarized to provide an overview of the progression of the field. The second half of the review covers organ-level models that require solution of the electrical component as a reaction–diffusion system and the mechanical component, in which active tension generated by the myocytes produces deformation of the organ as described by the equations of continuum mechanics. As outlined in the review, different organ-level models have chosen to use different ionic and myofilament models depending on the specific application; this choice has been largely dictated by compromises between model complexity and computational tractability. The review also addresses application areas of EM models such as cardiac resynchronization therapy and the role of mechano-electric coupling in arrhythmias and defibrillation.

Diabetic cardiomyopathy: from the pathophysiology of the cardiac myocytes to current diagnosis and management strategies

Diabetic cardiomyopathy (DCM), although a distinct clinical entity, is also a part of the diabetic atherosclerosis process. It may be independent of the coexistence of ischemic heart disease, hypertension, or other macrovascular complications. Its pathological substrate is characterized by the presence of myocardial damage, reactive hypertrophy, and intermediary fibrosis, structural and functional changes of the small coronary vessels, disturbance of the management of the metabolic cardiovascular load, and cardiac autonomic neuropathy. These alterations make the diabetic heart susceptible to ischemia and less able to recover from an ischemic attack. Arterial hypertension frequently coexists with and exacerbates cardiac functioning, leading to the premature appearance of heart failure. Classical and newer echocardiographic methods are available for early diagnosis. Currently, there is no specific treatment for DCM; targeting its pathophysiological substrate by effective risk management protects the myocardium from further damage and has a recognized primary role in its prevention. Its pathophysiological substrate is also the objective for the new therapies and alternative remedies.

Regional diastolic contour abnormalities during contrast stress echocardiography: improved detection of coronary artery disease

BACKGROUND

Use of contrast improves detection of systolic regional wall motion abnormalities (RWMAs) during stress echocardiography. We evaluated regional diastolic contour abnormalities (RDCAs) that were associated with coronary artery disease (CAD).

METHODS

From August of 2003 to September of 2004, we evaluated 89 patients who underwent contrast stress echocardiography (CSE) and coronary angiography within a 3-month period ("invasive" group) and 17 patients with lower CAD risk who underwent CSE only ("reference" group).

RESULTS

RDCAs were present in 73 patients in the invasive group and were associated with higher Framingham risk scores (relative risk, 3.6; 95% confidence interval, 1.9-6.6). RDCAs were present in 1 patient in the reference group. When combined with RWMA, RDCA improved sensitivity of CSE from 78% to 97% and specificity from 26% to 59% (diagnostic threshold for CAD was 70% stenosis).

CONCLUSION

RDCAs were a novel observation associated with higher CAD risk and improved the diagnostic accuracy of CSE.

Diastolic dysfunction: a link between hypertension and heart failure

Diastolic heart failure is characterized by the symptoms and signs of heart failure, a preserved ejection fraction and abnormal left ventricular (LV) diastolic function caused by a decreased LV compliance and relaxation. The signs and symptoms of diastolic heart failure are indistinguishable from those of heart failure related to systolic dysfunction; therefore, the diagnosis of diastolic heart failure is often one of exclusion. The majority of patients with heart failure and preserved ejection fraction have a history of hypertension. Hypertension induces a compensatory thickening of the ventricular wall in an attempt to normalize wall stress, which results in LV concentric hypertrophy, which in turn decreases LV compliance and LV diastolic filling. There is an abnormal accumulation of fibrillar collagen accompanying the hypertension-induced LV hypertrophy, which is also associated with decreased compliance and LV diastolic dysfunction. There are no specific guidelines for treating diastolic heart failure, but pharmacological treatment should be directed at normalizing blood pressure, promoting regression of LV hypertrophy, preventing tachycardia and treating symptoms of congestion. Preventive strategies directed toward an early and aggressive blood pressure control are likely to offer the greatest promise for reducing the incidence of diastolic heart failure.

Acute pacing-induced dyssynchronous activation of the left ventricle creates systolic dyssynchrony with preserved diastolic synchrony

INTRODUCTION

Patients with heart block have conventionally received a pacemaker that stimulates the right ventricular apex (RVA) to restore heart rate control. While RVA pacing has been shown to create systolic dyssynchrony acutely, dyssynchrony can also occur in diastole. The effects of acute RVA pacing on diastolic synchrony have not been investigated. RVA pacing acutely impairs diastolic function by increasing the time constant of relaxation, decreasing the peak lengthening rate and decreasing peak negative dP/dt. We therefore hypothesized that acute RVA pacing would cause diastolic dyssynchrony in addition to creating systolic dyssynchrony.

METHODS AND RESULTS

Fourteen patients (13 +/- 4 years old) with non-preexcited supraventricular tachycardia underwent ablation therapy with subsequent testing to confirm elimination of the tachycardia substrate. Normal cardiac structure and function were then documented on two-dimensional echocardiography and 12-lead electrocardiography prior to enrollment. Tissue Doppler images were collected during normal sinus rhythm (NSR), right atrial appendage pacing (AAI), and VVI-RVA pacing during the postablation waiting interval. Systolic and diastolic dyssynchrony were quantified using cross-correlation analysis of tissue Doppler velocity curves. Systolic dyssynchrony increased 81% during RVA pacing relative to AAI and NSR (P < 0.01). Diastolic synchrony was not affected by the different pacing modes (P = 0.375).

CONCLUSION

Acute dyssynchronous activation of the LV created by RVA pacing resulted in systolic dyssynchrony with preserved diastolic synchrony in pediatric patients following catheter ablation for treatment of supraventricular tachycardia. Our results suggest that systolic and diastolic dyssynchrony are not tightly coupled and may develop through separate mechanisms.

Curriculum in cardiology: integrated diagnosis and management of diastolic heart failure

Among the general heart failure (HF) population, over half have diastolic HF (DHF). The proportion of DHF increases with age, from 46% in patients younger than 45 years to 59% in patients older than 85 years. The diagnosis of DHF is made by the combination of signs and symptoms of HF with preserved systolic function (left ventricular ejection fraction >50%), and evidence of diastolic dysfunction obtained by echocardiographic Doppler examination, invasive hemodynamic evaluation, or an elevation of serum B-type natriuretic peptide. The most common risk factors for the development of diastolic dysfunction and DHF include long-standing hypertension, older age, female sex, obesity, diabetes, chronic kidney disease, and coronary artery disease. Acute decompensation occurs in the setting of pressure overload, volume overload, or superimposed cardiac ischemia. The cornerstones of in-hospital management include blood pressure and volume control, heart rate control, and correction of precipitating factors. Priorities in the outpatient clinic include optimal blood pressure control, maintenance of euvolemia with minimal or no diuretics, and, potentially, use of disease-modifying drugs including angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, aldosterone receptor blockers, beta-blockers, and digoxin. Long-term regression of left ventricular hypertrophy, improvement in diastolic filling parameters, and sustained reductions in B-type natriuretic peptide may be future treatment targets for this condition.

Cardiac Dysfunction in Heart Failure: The Cardiologist's Love Affair with Time

Translating research into clinical practice has been a challenge throughout medical history. From the present review, it should be clear that this is particularly the case for heart failure. As a consequence, public awareness of this disease has been disillusionedly low, despite its prognosis being worse than that of most cancers and many other chronic diseases. We explore how over the past 150 years since Ludwig and Marey concepts about the evaluation of cardiac performance in patients with heart failure have emerged. From this historical-physiologic perspective, we have seen how 3 increasingly reductionist approaches or schools of thought have evolved in parallel, that is, an input-output approach, a hemodynamic pump approach, and a muscular pump approach. Each one of these has provided complementary insights into the pathophysiology of heart failure and has resulted in measurements or derived indices, some of which still being in use in present-day cardiology. From the third, most reductionist muscular pump approach, we have learned that myocardial and ventricular relaxation properties as well as temporal and spatial nonuniformities have been largely overlooked in the 2 other, input-output and hemodynamic pump, approaches. A key message from the present review is that relaxation and nonuniformities can be fully understood only from within the time-space continuum of cardiac pumping. As cyclicity and rhythm are, in some way, the most basic aspects of cardiac function, considerations of time should dominate over any measurement of cardiac performance as a muscular pump. Any measurement that is blind for the arrow of cardiac time should therefore be interpreted with caution. We have seen how the escape from the time domain-as with the calculation of LV ejection fraction-fascinating though as it may be, has undoubtedly served to hinder a rational scientific debate on the recent, so-called systolic-diastolic heart failure controversy. Lacking appreciation of early relaxation abnormalities and inappropriate degrees of nonuniformities has, indeed, led to some unfortunate misunderstandings about the pathophysiologic time progression of heart failure, in particular, heart failure with compensated hemodynamic pump function (ie, with normal or preserved LV ejection fraction). We have seen that with the introduction of newer powerful diagnostic techniques, as, for example, TDI and MRI, to evaluate ventricular "muscular pump" function, this debate can now be held in a more serene physiologic context. These aspects will be elaborated further in subsequent chapter papers of this symposium. With ongoing stem and other cell-based therapies and future reductionistic insights into cardiac cellular performance, we foresee the emergence of a fourth simple-parallel school of thought viewing the heart as a network of communicating different cell types, that is, cardiomyocytes, endothelial cells, fibroblasts, neurons. In this postgenomic age with the introduction of the rapidly evolving discipline of in vivo molecular imaging techniques, we anticipate that novel measurements of cardiac performance in patients with heart failure will soon become available and complement biopsy and other already available cardiac cellular biomarkers (cardiac troponin I; creatine kinase-MB; myoglobin; BNP). Through the use of these novel biomarkers as a fourth diagnostic track in the evaluation of cardiac performance in patients with heart failure, we will soon be able to increasingly understand the behavior of the heart as a complex biologic system-in other words, how these "low-level" biologic functions and signal transduction pathways at a cellular level contribute to the above "high-level" or system-level approach of cardiac performance at the muscular, the hemodynamic, and the input-output pump system levels and, hopefully, how they could contribute to an early diagnosis of chronic heart failure, in patients.

Improved regional myocardial diastolic function assessed by strain rate imaging in patients with coronary artery disease undergoing percutaneous coronary intervention

This study investigated the effects of percutaneous coronary intervention (PCI) on global and regional left ventricular diastolic function, as assessed by strain rate (SR) imaging. In 27 patients with coronary artery disease, we performed echocardiography before and after PCI to obtain segmental peak systolic SR and peak early diastolic SR (E(SR)). PCI did not significantly change peak systolic SR in the ischemic (1.59 +/- 0.59-1.66 +/- 0.52/s) and nonischemic (1.64 +/- 0.59-1.61 +/- 0.53/s) segments. E(SR) in the ischemic segments was significantly smaller than that in the nonischemic segments at rest (1.82 +/- 0.71 vs 2.03 +/- 0.64/s, P < .01). PCI caused a significant increase in E(SR) from 1.82 +/- 0.71 to 2.29 +/- 0.92/s in the ischemic (P < .001), but not in the nonischemic, segments. The peak early diastolic transmitral flow velocities after PCI were improved in patients with greater extent of improvement of E(SR) in the ischemic segments. These findings suggest that the improvement in left ventricular early diastolic filling after PCI may be associated with the degree of improvement in impaired regional myocardial relaxation.

Effect of weightlifting upon left ventricular function and markers of cardiomyocyte damage

The purpose of this study was to assess left ventricular (LV) function and biochemical markers of myocyte after prolonged weightlifting activity. Seventeen male subjects (age range 20-34 years) performed a 90-min bout of weightlifting exercise consisting of three sets of 8-10 repetitions at 70% one-repetition maximum. Body mass, heart rate, systolic blood pressure (SBP) and echocardiographically determined indices of LV loading (LV internal diameter during diastole, LV meridonial wall stress), systolic function (stroke volume (SV), ejection fraction (EF), end-systolic pressure volume relationship; SBP/ESV) and diastolic filling (ratio of early to late; E:A) were obtained pre-exercise, immediately after and 24 h post-exercise. A 5-ml venous blood sample was obtained for the assessment of cardiac troponin T (cTnT) via third generation electrochemiluminescence assay. Data were assessed via one-way ANOVA and Pearson's correlation. Although SV declined (80.9 +/- 18.3 vs. 66.9 +/- 17.2, p < 0.05) there was no alteration in LV contractility (EF 62 +/- 6 vs. 59 +/- 7; SBP/ESV 3.51 +/- 1.4 vs. 3.51 +/- 1.4, p > 0.05). The E:A ratio was significantly decreased following exercise (1.78 +/- 0.41 vs. 1.33 +/- 0.37, p < 0.05). This decrease was not fully explained by loading conditions (r2 = 0.05 to 0.24). All values returned to baseline 24 h post-exercise. No cTnT was reported in any of the blood samples. In conclusion, there was no significant evidence of any LV contractile depression and no cTnT was observed post exercise. The small reduction in diastolic filling could not be explained by changes in haemodynamic loading or the post-exercise elevation in heart rate.

Diabetic cardiomyopathy: mechanisms, diagnosis and treatment

Independent of the severity of coronary artery disease, diabetic patients have an increased risk of developing heart failure. This clinical entity has been considered to be a distinct disease process referred to as 'diabetic cardiomyopathy'. Experimental studies suggest that extensive metabolic perturbations may underlie both functional and structural alterations of the diabetic myocardium. Translational studies are, however, limited and only partly explain why diabetic patients are at increased risk of cardiomyopathy and heart failure. Although a range of diagnostic methods may help to characterize alterations in cardiac function in general, none are specific for the alterations in diabetes. Treatment paradigms are very much limited to interpretation and translation from the results of interventions in non-diabetic patients with heart failure. This suggests that there is an urgent need to conduct pathogenetic, diagnostic and therapeutic studies specifically in diabetic patients with cardiomyopathy to better understand the factors which initiate and progress diabetic cardiomyopathy and to develop more effective treatments.

Late systolic onset of regional LV relaxation demonstrated in three-dimensional space by MRI tissue tagging

Left ventricular (LV) relaxation entails myocardial deformation that induces LV filling. Yet, the precise mechanisms of the earliest changes in tissue properties that characterize myocardial relaxation remain incompletely understood. Ten healthy volunteers (seven males), 25–43 yr, underwent tagged and cine MRI with high temporal resolution (25–35 ms). Normal strains including radial ( Err), circumferential ( Ecc), and longitudinal ( Ell) strains, shear strains including Ecl (circumferential-longitudinal), Ecr (circumferential-radial), and Erl (radial-longitudinal), and principal strains ( E1, E2, and E3) were calculated using a displacement field-fitting method. Temporal changes in angular strains indicative of shear and torsion release and normal strains were studied during late systole and early relaxation. The onset of individual relaxation strains was heterogeneous relative to LV filling. Shear strains ( Ecr, Erl, and Ecl) and radial thinning were first to develop. Times of onset of Ecr, Erl, Ecl, and Err occurred 108, 93, 67, and 73 ms before aortic valve closure, respectively. Ell, Ecc, and LV volume change commenced significantly later after the onset of diastolic shear strains and radial thinning. The onset of Ecc, Ell, and LV volume change was noted 38 ms before aortic valve closure ( P ≤ 0.05 relative to the onset of shear strains and Err). Myocardial relaxation is characterized by a three-dimensional unfolding deformation that includes release of torsion, shear, and radial thinning beginning before aortic valve closure. This unfolding pattern precedes longitudinal and circumferential elongation and may facilitate early diastolic filling.

Early and subtle abnormalities of left ventricular function in clinically stable coronary artery disease patients with normal ejection fraction

BACKGROUND

It has been reported that, in the initial phase of ischemic cardiomyopathy, the earliest alterations of left ventricular function are detected during the relaxation phase. The aim of this study was to look for precocious abnormalities in the early stage of ischemic cardiomyopathy in both left ventricular systolic and diastolic phases.

METHODS AND RESULTS

Using simultaneous left ventricular catheterization and echo-Doppler techniques, we studied both systolic and diastolic function in 44 (37 males and 7 females, mean age 55.7+/-8) normotensive, clinically stable, coronary artery disease patients with normal left ventricular ejection fraction in comparison to 9 age- and sex-matched normal control subjects (7 males and 2 females, mean age 54.7+/-9). Mean values of E deceleration time, tau, left ventricular end-diastolic volume and pressure, and end-systolic volume and lowest diastolic pressure were significantly higher (from P<.05 to P<.01), whereas mean dP/dt/P values significantly lower (P<.05) in coronary artery disease patients than in controls. A strict relationship (P<.001) between dP/dt/P and tau, left ventricular lowest and end-diastolic pressure was found in all subjects studied.

CONCLUSION

Early and subtle abnormalities in parameters of both systolic and diastolic function can be found in the majority of coronary artery disease patients with normal ejection fraction.

Left ventricular diastolic dysfunction and diastolic heart failure

Thirty to fifty percent of patients presenting with signs and symptoms of heart failure have a normal left ventricular (LV) systolic ejection fraction. The clinical examination cannot distinguish these patients (diastolic heart failure) from those with a depressed ejection fraction (systolic heart failure), but echocardiography can. The management of diastolic heart failure has two major objectives. The first is to reverse the consequences of diastolic dysfunction (e.g., venous congestion), and the second is to eliminate or reduce the factors responsible for diastolic dysfunction (e.g., myocardial hypertrophy, fibrosis, and ischemia).

The forces generated within the musculature of the left ventricular wall

OBJECTIVES

To test the hypothesis that two populations of myocardial fibres-fibres aligned parallel to the surfaces of the wall and an additional population of fibres that extend obliquely through the wall-when working in concert produce a dualistic, self stabilising arrangement.

METHODS

Assessment of tensile forces in the walls of seven porcine hearts by using needle probes. Ventricular diameter was measured with microsonometry and the intracavitary pressure through a fluid filled catheter. Positive inotropism was induced by dopamine, and negative inotropism by thiopental. The preload was raised by volume load and lowered by withdrawal of blood. Afterload was increased by inflation of a balloon in the aortic root. The anatomical orientation of the fibres was established subsequently in histological sections.

RESULTS

The forces in the fibres parallel to the surface decreased 20-35% during systolic shrinkage of the ventricle, during negative inotropism, and during ventricular unloading. They increased 10-30% on positive inotropic stimulation and with augmentation in preload and afterload. The forces in the oblique transmural fibres increased 8-65% during systole, on positive inotropic medication, with an increase in afterload and during ventricular shrinkage, and decreased 36% on negative inotropic medication. There was a delay of up to 147 ms in the drop in activity during relaxation in the oblique transmural fibres.

CONCLUSION

Although the two populations of myocardial fibres are densely interwoven, it is possible to distinguish their functions with force probes. The delayed drop in force during relaxation in obliquely oriented fibres indicates that they are hindered in their shortening to an extent that parallels any increase in mural thickness. The transmural fibres, therefore, contribute to stiffening of the ventricular wall and hence to confining ventricular compliance.

Systolic and diastolic properties of univentricular hearts in children: insights from physiologic indices that reflect calcium cycling

Physiologic indices that reflect intracellular Ca2+ cycling were chosen to evaluate contraction and relaxation properties of the univentricular heart. We hypothesized that these indices would be impaired in univentricular hearts. With advances in surgical palliation, an increasing number of children are surviving with univentricular hearts supporting the systemic circulation. Similar to the adult failing heart, single ventricles may also manifest impaired Ca2+ cycling, which may have important therapeutic implications. In our study, we did not actually measure Ca2+ uptake or transients in the cardiac myocyte. Rather, we used previously validated physiologic indices that are known to reflect Ca2+ cycling. Sixteen children were studied, eight with single ventricles (SV) and eight as matched control subjects. Systolic properties were studied using maximal derivative of ventricular pressure (dP/dtmax), force-frequency relationship, and mechanical restitution. Diastolic properties were assessed using time constant of relaxation (tau) and the relaxation-frequency relationship. The critical HR (HRcrit) was assessed from the force-frequency relationship and relaxation-frequency relationship. DP/dtmax and tau were calculated from micromanometric tracings at increasing HRs, generated by right atrial pacing. In SV patients, dP/dtmax was lower than in the control group at each matched HR, and the force-frequency relationship was shifted downward. Restitution of contractility was slower in patients with SV. Tau was similar in both groups at lower HRs but significantly prolonged in the SV group at faster HRs. In the SV, HRcrit was significantly shifted to the left. These findings indicate impaired systolic and diastolic properties of univentricular heart, especially at increased HRs. Because these physiologic indices reflect Ca2+ cycling, it is speculated that the phenomenon of Ca2+ cycling may be impaired in the myocytes of univentricular hearts.

Post-endsystolic active shortening in the non-ischemic region impairs left ventricular pressure fall in acute ischemic heart

To investigate the relation between the impairment of isovolumic relaxation and the regional wall motion in acute ischemia, the left ventricular pressure fall and regional myocardial motion were examined in the relaxation phase in dogs during both acute coronary artery occlusion (n = 12) and a regional coronary flow reduction (n = 6). Fifteen to 40 seconds after complete coronary artery occlusion or in the stable state after a regional coronary flow reduction by 70 to 90% of the control state, a shortening of the non-ischemic region at the early isovolumic relaxation phase (the post-endsystolic shortening) appeared, combined with lengthening of the ischemic region. In these situations, the logarithmic plots of the left ventricular pressure fall was composed of two components (time constant of early part [Ta] and at latter part [Tb]). Ta was greater than Tb (64.3 +/- 13.8 milliseconds vs. 36.6 +/- 10.4 milliseconds at 15 seconds after coronary occlusion, p < 0.01; 67.6 +/- 22.9 milliseconds vs. 45.1 +/- 17.5 milliseconds at flow reduction, p < 0.01) and the time constant at control (p < 0.01). These findings suggested that post-endsystolic shortening in the non-ischemic region played a role in a the non-uniformity of the left ventricular contraction and contributed to the impairment of the left ventricular pressure fall in acute regional ischemia, especially in early isovolumic relaxation.

Echocardiography-derived variables predict outcome in patients with nonischemic dilated cardiomyopathy with or without a restrictive filling pattern

BACKGROUND

Despite recent therapeutic advances, patients with heart failure caused by dilated cardiomyopathy (DCM) still have high morbidity and mortality rates. In this study, we sought to assess the prognostic value of echocardiographic variables in patients with DCM and to assess the impact of a restrictive left ventricle filling pattern.

DESIGN

We conducted a retrospective cohort study of 337 patients with DCM, using the Royal Brompton Hospital Echocardiography database for the years 1994 to 1998.

METHODS AND RESULTS

There were 337 patients with a mean age of 53 +/- 15 years. One hundred ninety-five patients (58%) had a restrictive left ventricle filling pattern (RFP). There was a total of 74 deaths (22%) during the follow-up period (43 +/- 25 months). RFP more than tripled the risk of death (adjusted hazard ratio 3.2, 95% CI 1.8-5.7, P =.003). RFP is correlated with isovolumic relaxation time, incoordinate wall-motion, amplitude of right ventricular long axis excursion on M-mode echocardiography, and mitral regurgitation.

CONCLUSION

RFP is a powerful independent predictor of mortality in patients with nonischemic DCM. The risk associated with RFP is greatest among patients who had short isovolumic relaxation time, mitral regurgitation, incoordinate wall-motion, and depressed amplitude of right ventricular long axis excursion. Thus, echocardiography-derived variables may stratify patients with heart failure with DCM who are at high risk, for whom aggressive medical treatment or heart transplantation should be considered early.

[Contraction-relaxation coupling of skeletal muscle in patients susceptible to malignant hyperthermia]

OBJECTIVE

To assess whether halothane exposure could influence contraction-relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility. STUDY DESIGNED: Laboratory investigation.

MATERIAL AND METHODS

Muscle biopsies from 14 patients, including six classified as susceptible to MH (MHS) and eight as classified as non-susceptible (MHN) according to criteria of the European MH group. Mechanical parameters of strips were obtained before and after 3 vol% halothane exposure. The contraction and relaxation parameters were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (respectively maxVc and maxVr); peak of the positive (+dP/dtmax) and negative (-dP/dtmax) twitch tension derivative; ratio R1 = maxVc/maxVr and ratio R2 = (+dP/dtmax) (-dp/dtmax).

RESULTS

In MHN muscle, halothane markedly increased maxVc and maxVr, so that the ratio R1 was unchanged. Both +dP/dtmax and -dP/dtmax increased such that the ratio R2 did not vary. In MHS muscle, halothane induced a significant decrease in maxVr (p < 0.05) without changes in maxVc, so that the ratio R1 increased significantly. +dP/dtmax remained unchanged whereas -dP/dtmax decreased significantly; the ratio R2 increased (p < 0.05).

CONCLUSION

Our results indicated that, in MHN muscle the contractility property is improved with halothane exposure. In MHS muscle, halothane caused an impairment of relaxation. The mechanical abnormalities observed in this study might be related to sarcoplasmic reticulum dysfunction in MH diseases.

Does the progression of myocardial fibrosis lead to atrial fibrillation in patients with hypertrophic cardiomyopathy?

The majority of left ventricular (LV) inflow volumes in hypertrophic cardiomyopathy (HCM) depend on atrial contraction because of impaired LV relaxation. If HCM is complicated by atrial fibrillation (AF), heart failure can develop because of the loss of atrial contraction. The purpose of this study was to determine the relationship between the development of AF and myocardial fibrosis or intramyocardial small artery (IMSA) stenosis in autopsied hearts with HCM. Studies were performed in five HCM hearts with AF (AF group) and five HCM hearts without AF (non-AF group). LV specimens were divided into the inner (IT), middle (MT), and outer (OT) thirds. We selected at random 120 fields and 20 IMSAs from each layer and assessed them quantitatively using an image analyzer. We determined the extent of fibrosis (%F) and the degree of stenosis of each IMSA (%L). The %F in the AF group was greater than in the non-AF group (P<.01). In the AF group, the %F of the IT was greater than in the MT and the OT (P<.01). In the non-AF group, the %F of the IT was greater than in the MT (P<.05), and the %F of the MT was greater than in the OT (P<.01). The %L was similar in the AF and non-AF groups. In both groups, the %L of the IT was lower than in the MT (P<.01), which was lower than that of the OT (P<.05). LV fibrosis is more severe in patients with HCM and AF than in those without AF. Therefore, myocardial fibrosis might impair LV relaxation, resulting in hemodynamic intolerance to AF.

Cardiac responses to insulin-induced hypoglycemia in nondiabetic and intensively treated type 1 diabetic patients

Insulin-induced hypoglycemia occurs commonly in intensively treated patients with type 1 diabetes, but the cardiovascular consequences of hypoglycemia in these patients are not known. We studied left ventricular systolic [left ventricular ejection fraction (LVEF)] and diastolic [peak filling rate (PFR)] function by equilibrium radionuclide angiography during insulin infusion (12 pmol. kg(-1). min(-1)) under either hypoglycemic (approximately 2.8 mmol/l) or euglycemic (approximately 5 mmol/l) conditions in intensively treated patients with type 1 diabetes and healthy nondiabetic subjects (n = 9 for each). During hypoglycemic hyperinsulinemia, there were significant increases in LVEF (DeltaLVEF = 11 +/- 2%) and PFR [DeltaPFR = 0.88 +/- 0.18 end diastolic volume (EDV)/s] in diabetic subjects as well as in the nondiabetic group (DeltaLVEF = 13 +/- 2%; DeltaPFR = 0.79 +/- 0.17 EDV/s). The increases in LVEF and PFR were comparable overall but occurred earlier in the nondiabetic group. A blunted increase in plasma catecholamine, cortisol, and glucagon concentrations occurred in response to hypoglycemia in the diabetic subjects. During euglycemic hyperinsulinemia, LVEF also increased in both the diabetic (DeltaLVEF = 7 +/- 1%) and nondiabetic (DeltaLVEF = 4 +/- 2%) groups, but PFR increased only in the diabetic group. In the comparison of the responses to hypoglycemic and euglycemic hyperinsulinemia, only the nondiabetic group had greater augmentation of LVEF, PFR, and cardiac output in the hypoglycemic study (P < 0.05 for each). Thus intensively treated type 1 diabetic patients demonstrate delayed augmentation of ventricular function during moderate insulin-induced hypoglycemia. Although diabetic subjects have a more pronounced cardiac response to hyperinsulinemia per se than nondiabetic subjects, their response to hypoglycemia is blunted.

Evaluation of diastolic function

Abnormalities of diastolic function are increasingly recognized as important components of the abnormal physiology in many patients with heart failure. In order to better understand the role of abnormalities of individual parameters or diastolic function affecting filling of the left ventricular a broader understanding of the relationship of systolic and diastolic performance on overall left ventricular pump performance should be considered. While measurement of diastolic function noninvasively has become the predominant way of assessing diastolic performance, invasive evaluation remains important. Moreover, understanding the physiology of diastolic performance remains essential to proper diagnosis and management.

Enhanced external counterpulsation improves exercise tolerance, reduces exercise-induced myocardial ischemia and improves left ventricular diastolic filling in patients with coronary artery disease

OBJECTIVES

We examined whether enhanced external counterpulsation (EECP) improves myocardial ischemia, exercise tolerance and cardiac function in patients with coronary artery disease (CAD).

BACKGROUND

Enhanced external counterpulsation reduces angina and improves exercise tolerance in patients with CAD. Some objective improvements of ischemia by EECP have been reported, but they should be confirmed further. Detailed hemodynamic effects of EECP have been less well documented.

METHODS

Enhanced external counterpulsation was performed for a total of 35 h in patients with stable CAD (n = 12) who showed evidence of exercise-induced myocardial ischemia despite conventional medical or surgical therapies. All patients had significant stenotic lesions in major coronary arteries.

RESULTS

Enhanced external counterpulsation improved all exercise test parameters (p < 0.05): exercise duration, time to 1-mm ST segment depression, rate-pressure product at peak exercise and rate-pressure product at 1-mm ST segment depression. Moreover, the prevalence of exercise-induced reversible perfusion defects by thallium scintigraphy decreased after treatment (p < 0.01). Enhanced external counterpulsation did not alter systolic function but improved diastolic filling, left ventricular (LV) end-diastolic pressure (p < 0.05) by cardiac catheterization and LV peak filling rate end-diastolic volume/s (p < 0.01) and time to peak filling rate (p < 0.05) by radionuclide scintigraphy. These hemodynamic improvements were associated with decreased plasma brain natriuretic peptides levels after EECP (p < 0.05).

CONCLUSIONS

Thus, EECP treatment improves exercise tolerance and reduced myocardial ischemia by thallium scintigraphy in association with improved LV diastolic filling in patients with stable CAD.

Noninvasive indexes of left atrial diastolic function in hypertrophic cardiomyopathy

OBJECTIVES

Our goal was to noninvasively assess left atrial diastolic function and its relation to the impaired left ventricular filling in patients with hypertrophic cardiomyopathy.

METHODS AND RESULTS

We studied 34 patients with hypertrophic cardiomyopathy, 26 patients with secondary forms of left ventricular hypertrophy (aortic stenosis, fixed subaortic stenosis, hypertension), and 21 control subjects. Left atrial diastolic function was assessed by measuring acceleration time (SAT), deceleration time (SDT), and the EF (mean deceleration rate) slope of the pulmonary venous flow systolic wave (SW). Left ventricular diastolic function assessed by transmitral Doppler included peak early left ventricular and peak atrial filling velocities, the ratio of early-to-late peak velocities, isovolumic relaxation time, deceleration time, and EF slope. In patients with hypertrophic cardiomyopathy, acceleration time was significantly reduced (P<.05), deceleration time was significantly prolonged (P<.0001), and EF slope was significantly reduced (P<.01). These indexes were similar among the other two groups. No statistically significant difference existed between the subgroups of hypertrophic cardiomyopathy in the above indexes. Patients with hypertrophic cardiomyopathy and secondary forms of left ventricular hypertrophy had evidence of left ventricular diastolic dysfunction. In patients with hypertrophic cardiomyopathy, no correlation existed between left atrial and left ventricular diastolic function indexes (r = -0.26 to 0.33).

CONCLUSIONS

Echocardiographic indexes of left atrial relaxation and filling are abnormal in patients with hypertrophic cardiomyopathy but not in secondary forms of left ventricular hypertrophy. These indexes are abnormal in all forms of hypertrophic cardiomyopathy irrespective of left ventricular outflow tract obstruction and distribution of hypertrophy; they are not solely attributable to left ventricular diastolic dysfunction. The above may imply that hypertrophic cardiomyopathy is a cardiac myopathic disease that involves the heart muscle as a whole, irrespective of distribution of hypertrophy and obstruction.

Role of myofilaments and calcium handling in left ventricular relaxation

Myocardial relaxation is governed by the interplay of two macromolecular systems: (1) myofilaments and (2) calcium extruding pumps/exchangers. In myocardium from failing hearts, both systems act more slowly than normal, and cause relaxation to decelerate, which may impede early rapid filling and can often limit cardiac pumping ability--especially during exercise. Gene-based therapy to augment sluggish SERCA pumps is a possibility being currently investigated in research laboratories. In normal myocardium, the rate of dissociation of myosin crossbridges sets the rate of relaxation. In this case, relaxation is characterized by two features: (1) load-dependence and (2) displacement-dependence. Load-dependence derives from cooperative mechanisms acting among ensembles of crossbridges and myofilament regulatory proteins (troponin, tropomyosin); it allows contraction to be prolonged when more crossbridges are attached and mutually support each other. The rate of relaxation can still be rapid, however, as this cooperative system begins to collapse. Displacement-dependence is more important later in contraction, because tenuous crossbridge attachments cannot easily re-form after being disrupted when myofilaments slide along each other. Myofilaments control normal relaxation because the calcium extruding systems reduce calcium to near diastolic levels relatively early; however, when the relative timing of crossbridge dissociation versus calcium sequestration is altered, and calcium uptake is slowed (relative to crossbridges), then removal of calcium can become rate limiting instead. In this case, load- and displacement-dependence are less marked. Both the timing of calcium removal and the sensitivity of the myofilaments to calcium affect relaxation timing.

Shortening velocity of skeletal muscle from humans with malignant hyperthermia susceptibility: effects of halothane

The aim of this investigation was to assess the effect of halothane on the velocity of shortening and lengthening of muscle from normal subjects and from patients with malignant hyperthermia susceptibility. Strips were mounted horizontally at optimal length in normal Krebs-Ringer's solution and mechanical parameters were obtained before and after exposure to 3 vol.% halothane. The maximun shortening velocity at zero load (V(max)) was determined by using Hill's characteristic equation. The contraction and relaxation indices were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (maxV(c) and maxV(r), respectively); isometric peak twitch tension; peak of the positive (+dP/dt(max)) and negative (-dP/dt(max)) twitch tension derivative; ratio R1=maxV(c)/maxV(r) and ratio R2=(+dP/dt(max))/(-dP/dt(max)). In normal muscle, halothane markedly increased V(max), maxV(c) and peak twitch tension by 30+/-10%, 30+/-5% and 40+/-15%, respectively. The maxV(r) values increased concomitantly with the maxV(c) values, such that no change in the ratio R1 was observed. Both +dP/dt(max) and -dP/dt(max) increased such that the ratio R2 did not vary. In malignant hyperthermia susceptibility muscle, halothane induced a significant decrease in V(max) (-30+/-10%) and maxV(r) (-45+/-15%) without changing maxV(c). The decrease in maxV(r) was greater than that of maxV(c), such that the ratio R1 increased significantly. Peak twitch tension and +dP/dt(max) remained unchanged whereas -dP/dt(max) decreased significantly; the ratio R2 increased by 40+/-10%. These results suggest that halothane alters the contractile properties of malignant hyperthermia susceptibility muscle.

Assessment of right ventricular function by right ventricular systolic time intervals in acute respiratory failure

OBJECTIVE

Whether right ventricular systolic time intervals accurately reflect right ventricular function in patients with acute respiratory failure was determined by assessing the correlation between right ventricular systolic time intervals and the right ventricular end-systolic pressure-volume relationship.

DESIGN

A prospective study.

SETTING

A surgical intensive care unit in a university hospital.

PATIENTS

Twenty patients with acute respiratory failure.

MEASUREMENTS AND MAIN RESULTS

Right ventricular systolic time intervals were determined by the simultaneous graphic display of the electrocardiogram, the phonocardiogram, and the pulmonary artery pressure curve and were expressed as a ratio of the pre-ejection period/right ventricular ejection time. The total electromechanical systole was measured from the onset of the electrocardiographic wave complex to the pulmonic component of the second heart sound. Right ventricular ejection time was measured from the rapid upstroke of the pulmonary artery pressure curve to the dicrotic notch. Right ventricular ejection fraction, from which right ventricular end-systolic volume was derived, was measured by the thermodilution technique. Pulmonary artery dicrotic notch pressure was used as an estimate of right ventricular end-systolic pressure. Data were collected at the baseline and after one or two alterations in preload, to define the right ventricular end-systolic pressure-volume relationship line. There was an inverse correlation between the pre-ejection period/right ventricular ejection time ratio and the slope of the right ventricular end-systolic pressure-volume relationship line (r2 = .67; p < .0001). When patients were divided into two groups, based on the pre-ejection period/right ventricular ejection time ratio, the slope of the right ventricular end-systolic pressure-volume relationship line was lower in the group with a high pre-ejection period/right ventricular ejection time ratio (p < .0001). No difference in other hemodynamic data, between the two groups, was noted.

CONCLUSIONS

These data suggest that right ventricular systolic time intervals reflect right ventricular performance accurately in patients with acute respiratory failure.

Contraction-relaxation coupling: determination of the onset of diastole

Left ventricular relaxation is dependent on afterload conditions during systole. An abrupt increase in afterload while the ventricle is actively contracting prolongs the duration of systole. An increase in afterload during ventricular relaxation shortens the duration of systole. Therefore, we hypothesized that the point during systole when an abrupt increase in afterload had no effect on the duration of systole represented the onset of ventricular relaxation. To determine when this point occurs, we performed aortic occlusions progressively throughout the duration of systole in six dogs. We determined the change in systolic time (t(sys)) after an intervention normalized to t(sys) of a control beat (t(sys,i)/t(sys, c)) as a function of systolic occlusion time as a percentage of total systolic time (t(occ)/t(sys,c)), where t(sys) is the duration from time of left ventricular end-diastolic pressure to the time of minimum first derivative of left ventricular pressure. Our results show the onset of left ventricular relaxation during normal ejection occurs at 34 +/- 3% of systolic time and approximately 16% after the onset of ejection. Thus the beginning of relaxation occurs soon after the beginning of ejection, suggesting that relaxation is modulated by variable loading conditions during ejection, significantly before what has been conventionally been assumed to be the beginning of ventricular relaxation.

Color M-mode Doppler flow propagation velocity is a relatively preload-independent index of left ventricular filling

Standard Doppler indexes of transmitral filling vary in response to alterations in left ventricular (LV) relaxation or preload. To determine whether color M-mode Doppler flow propagation velocity (vp), a new index of LV relaxation, is affected by preload, we obtained LV volumes, standard Doppler filling indexes, and vp in 20 patients at baseline, during Trendelenburg's position, inverse Trendelenburg's position, and after inhalation of amyl nitrite. LV end-diastolic volume decreased from 111 +/- 41 mL at baseline and 116 +/- 43 mL during Trendelenburg's position, to 104 +/- 40 during inverse Trendelenburg's maneuver and 92 +/- 33 mL after inhalation of amyl nitrite (P <.0001). Peak early filling velocity decreased from 79 +/- 19 cm/s and 90 +/- 20 cm/s to 73 +/- 22 cm/s and 64 +/- 20 cm/s, respectively (P < 0.0001). In contrast, no significant changes were found in vp (48 +/- 24 and 50 +/- 26 cm/s vs 48 +/- 25 and 48 +/- 25 cm/s). We conclude that vp is not affected significantly by preload. Thus vp may provide a more reliable and independent assessment of LV relaxation.

Reappraisal of the multicellular preparation for the in vitro physiopharmacological evaluation of myocardial performance

In order to evaluate myocardial performance, single cardiomyocytes suffer from technical problems and from the fact that some basic functional properties vanish when one moves down the hierarchic scale from multicellularity to single cells. The isolated papillary muscle has at present proven to be superior to the isolated intact cardiomyocyte. A large number of major intra- and extracellular features required to describe myocardial performance can be derived from analyzing twitch contraction and relaxation in the multicellular isolated papillary muscle. In addition, the present paper illustrates the possibility to differentiate between effects of inotropic interventions on activating Ca2+ and Ca2+ sensitivity in multicellular preparations, from a grid analysis of isometric twitches in a coordinate system of peak rate of force development (+dF/dt; reflecting the time pattern of twitch contraction) versus time to half relaxation (tHR; reflecting the time pattern of twitch relaxation). The abundance of information about myocardial performance that can be derived from the easily accessible multicellular preparation reflects its physiological kinship with the intact ventricle.

[Left ventricular diastolic function: physiology, physiopathology, evaluation, therapy, consequences of anesthesia]

With the exception of cardiac surgery, the acute disturbance of the left ventricular diastole occurs mainly in the elderly. Today it represents 30 to 40% of congestive cardiac failures, however with a lower mortality than for acute systolic disturbances. Generally indicated are relaxation anomalies, proto-mesodiastolic mechanism and problems with compliance, an indicator of the pressure/volume diastolic relationship. Invasive techniques remain the standard method. Doppler echocardiography is becoming increasingly important for the assessment of diastolic function. In most cardiopathies, relaxation anomalies occur early, whereas compliance disturbances are mainly associated with advanced cardiac diseases. During anaesthesia, adverse events (auricular fibrillation, hypovolaemia) may worsen a fragile situation. Anaesthetic agents, in particular volatile agents, act on the ventricular diastole. Long-term therapy of diastolic anomalies includes agents amending left ventricular hypertrophy. Emergency therapy has not yet been systematised.