Changes in diastolic function during development and correction of chronic LV volume overload produced by mitral regurgitation

Value of frontal QRS axis for risk stratification of individuals with prolonged PR interval

BACKGROUND

There is ongoing controversy regarding the prognostic value of PR prolongation among individuals free of cardiovascular diseases. It is necessary to risk-stratify this population according to other electrocardiographic parameters.

METHODS

This study is based on the Third National Health and Nutrition Examination Survey. Cox proportional hazard models were constructed and Kaplan-Meier method was used.

RESULTS

A total of 6188 participants (58.1 ± 13.1 years; 55% women) were included. The median frontal QRS axis of the entire study population was 37° (IQR: 11-60°). PR prolongation was present in 7.6% of the participants, of whom 61.2% had QRS axis ≤37°. In a multivariable-adjusted model, mortality risk was highest in the group with concomitant prolonged PR interval and QRS axis ≤37° (hazard ratio [HR]: 1.20; 95% confidence interval [CI]: 1.04-1.39). In models with similar adjustment where population were reclassified depending on PR prolongation and QRS axis, prolonged PR interval and QRS axis ≤37° was still associated with increased risk of mortality (HR: 1.18; 95% CI: 1.03-1.36) compared with normal PR interval.

CONCLUSIONS

QRS axis is an important factor for risk stratification in population with PR prolongation. The extent to which this population with PR prolongation and QRS axis ≤37° is at higher risk of death compared with the population without PR prolongation.

Left atrial myocardial intrinsic function remodeling response to repair of primary mitral regurgitation

Severe mitral regurgitation (MR) is a common valve disease which is associated with high mortality, if only managed medically. MR produces chronic and progressive volume overload with left atrial (LA) and left ventricular (LV) dilatation and dysfunction, atrial fibrillation (AF) and eventually myocardial fibrosis, irrespective of ejection fraction (EF). Surgical correction (mitral valve repair) of MR removes the volume overload, hence unmasks pre-operative LV structure and function disturbances, including reduced EF and global longitudinal and circumferential strain, as well as LA volume and strain. This review aims at describing LA remodeling before and after surgical repair.

Intrinsic cardiac elastography in patients with primary mitral regurgitation: predictive role after mitral valve repair

AIMS

Chronic volume-overload can impair systolic and diastolic myocardial properties. We tested the hypothesis that Intrinsic Cardiac Elastography may detect alterations in passive myocardial elasticity in patients with chronic severe mitral regurgitation (MR) and predict worsening left ventricular (LV) function after mitral valve repair (MVr).

METHODS AND RESULTS

Comprehensive transthoracic echocardiography and cardiac elastography were performed in 80 patients with primary MR (prolapse and/or flail leaflets) of varying severity and compared with 40 normal subjects. In patients who underwent MVr (n = 51), elastography measurements were related to changes in left ventricular ejection fraction (LVEF) at short-term (3-4 days post-op) and mid-term (1 year) follow-up. Most patients were asymptomatic or mildly symptomatic and had preserved LVEF (>60%). Intrinsic velocity propagation (iVP) of myocardial stretch, a direct measure of myocardial stiffness, was higher in patients with severe MR {median 2.0 [interquartile range (IQR) 1.5-2.2] m/s, range 1.1-3.4 m/s; n = 56} compared to normal subjects [median 1.7 (IQR 1.5-1.8) m/s; n = 40; P = 0.0005], but not in those with mild or moderate MR [median 1.7 (IQR 1.4-1.9) m/s; n = 24]. A higher iVP was associated with more severe LV volume-overload and LV and left atrial enlargement (P < 0.05 for all). In patients undergoing MVr, a higher iVP independently predicted a larger drop in LVEF post-intervention (short-term, P = 0.001; 1 year, P = 0.007), incrementally to pre-operative LVEF (P < 0.05).

CONCLUSION

Non-invasive measurements of myocardial stiffness were able to predict functional deterioration after MVr for chronic primary MR. Further studies should investigate the mechanisms and practical utility of this novel measurement.

Pivotal Role of Heart for Orthostasis: Left Ventricular Untwisting Mechanics and Physical Fitness

Augmentation of left ventricular (LV) untwisting due to central hypovolemia is likely to be a compensatory mechanism for maintaining stroke volume, which is reduced by a decrease in cardiac filling during orthostatic stress. Orthostatic intolerance observed in both high and low fitness levels may be explained by the impaired response of LV untwisting due to central hypovolemia.

Nutritional interventions during bed rest and spaceflight: prevention of muscle mass and strength loss, bone resorption, glucose intolerance, and cardiovascular problems

Bed rest is necessary for many medical conditions but also used as a ground-based model for space flight (along with head-down tilt to simulate fluid shifts in microgravity). The purpose of this review is to examine nutritional interventions during bed rest and spaceflight for prevention of muscle and strength loss, glucose intolerance, bone resorption, and cardiovascular problems. Increased dietary protein intake and supplementation with amino acids, β-hydroxy-β-methylbutyrate, or cofactors with antioxidant properties are effective for ameliorating bed rest-induced loss of muscle mass and strength. Previous literature involving bed rest with dietary protein/amino acid supplementation had mixed findings, likely due to differences in dosage. Although high protein intake in some studies prevents bed rest-induced muscle loss, it also increases bone resorption. High calcium intake and vitamin D supplementation are not beneficial for preventing bone degradation during bed rest or spaceflight. Very few studies investigated countermeasures to prevent glucose intolerance and cardiovascular risks during bed rest/spaceflight. Low-glycemic index diets might be beneficial for the prevention of bed rest-induced glucose intolerance and cardiovascular problems. The present evidence warrants additional studies on the exact threshold of protein/amino acid intake to prevent the loss of muscle mass and strength during bed rest/spaceflight specifically to maintain the beneficial effects of proteins on muscle mass and function without increasing bone resorption. Furthermore, it is suggested to study the effects of vitamin K supplementation on bone health during bed rest/spaceflight and determine the role of long-term low-glycemic index diets on glucose regulation and cardiovascular health during extended bed rest.

A Comparison of Phenomenologic Growth Laws for Myocardial Hypertrophy

The heart grows in response to changes in hemodynamic loading during normal development and in response to valve disease, hypertension, and other pathologies. In general, a left ventricle subjected to increased afterload (pressure overloading) exhibits concentric growth characterized by thickening of individual myocytes and the heart wall, while one experiencing increased preload (volume overloading) exhibits eccentric growth characterized by lengthening of myocytes and dilation of the cavity. Predictive models of cardiac growth could be important tools in evaluating treatments, guiding clinical decision making, and designing novel therapies for a range of diseases. Thus, in the past 20 years there has been considerable effort to simulate growth within the left ventricle. While a number of published equations or systems of equations (often termed "growth laws") can capture some aspects of experimentally observed growth patterns, no direct comparisons of the various published models have been performed. Here we examine eight of these laws and compare them in a simple test-bed in which we imposed stretches measured during in vivo pressure and volume overload. Laws were compared based on their ability to predict experimentally measured patterns of growth in the myocardial fiber and radial directions as well as the ratio of fiber-to-radial growth. Three of the eight laws were able to reproduce most key aspects of growth following both pressure and volume overload. Although these three growth laws utilized different approaches to predict hypertrophy, they all employed multiple inputs that were weakly correlated during in vivo overload and therefore provided independent information about mechanics.

Simulated Microgravity and Recovery-Induced Remodeling of the Left and Right Ventricle

Physiological adaptations to microgravity involve alterations in cardiovascular systems. These adaptations result in cardiac remodeling and orthostatic hypotension. However, the response of the left ventricle (LV) and right ventricle (RV) following hindlimb unloading (HU) and hindlimb reloading (HR) is not clear and the underlying mechanism remains to be understood. In this study, three groups of mice were subjected to HU by tail suspension for 28 days. Following this, two groups were allowed to recover for 7 or 14 days. The control group was treated equally, with the exception of tail suspension. Echocardiography was performed to detect the structure and function changes of heart. Compared with the control, the HU group of mice showed reduced LV-EF (ejection fraction), and LV-FS (fractional shortening). However, mice that were allowed to recover for 7 days after HU (HR-7d) showed increased LVIDs (systolic LV internal diameter) and LV Vols (systolic LV volume). Mice that recovered for 14 days (HR-14d) returned to the normal state. In comparison, RV-EF and RV-FS didn't recover to the normal conditions till being reloaded for 14 days. Compared with the control, RVIDd (diastolic RV internal diameter), and RV Vold (diastolic RV volume) were reduced in HU group and recovered to the normal conditions in HR-7d and HR-14d groups, in which groups RVIDs (systolic RV internal diameter) and RV Vols (systolic RV volume) were increased. Histological analysis and cardiac remodeling gene expression results indicated that HU induces left and right ventricular remodeling. Western blot demonstrated that the phosphorylation of HDAC4 and ERK1/2 and the ratio of LC3-II / LC3-I, were increased following HU and recovered following HR in both LV and RV, and the phosphorylation of AMPK was inhibited in both LV and RV following HU, but only restored in LV following HR for 14 days. These results indicate that simulated microgravity leads to cardiac remodeling, and the remodeling changes can be reversed. Furthermore, in the early stages of recovery, cardiac remodeling may be intensified. Finally, compared with the LV, the RV is not as easily reversed. Cardiac remodeling pathways, such as, HDAC4, ERK1/2, LC3-II, and AMPK were involved in the process.

Effects of sex and gender on adaptation to space: cardiovascular alterations

Sex and gender differences in the cardiovascular adaptation to spaceflight were examined with the goal of optimizing the health and safety of male and female astronauts at the forefront of space exploration. Female astronauts are more susceptible to orthostatic intolerance after space flight; the visual impairment intracranial pressure syndrome predominates slightly in males. Since spaceflight simulates vascular aging, sex-specific effects on vascular endothelium and thrombotic risk warrant examination as predisposing factors to atherosclerosis, important as the current cohort of astronauts ages. Currently, 20% of astronauts are women, and the recently selected astronaut recruits are 50% women. Thus there should be expectation that future research will reflect the composition of the overall population to determine potential benefits or risks. This should apply both to clinical studies and to basic science research.

Evaluation of right and left ventricular diastolic filling

A conceptual fluid-dynamics framework for diastolic filling is developed. The convective deceleration load (CDL) is identified as an important determinant of ventricular inflow during the E wave (A wave) upstroke. Convective deceleration occurs as blood moves from the inflow anulus through larger-area cross-sections toward the expanding walls. Chamber dilatation underlies previously unrecognized alterations in intraventricular flow dynamics. The larger the chamber, the larger becomes the endocardial surface and the CDL. CDL magnitude affects strongly the attainable E wave (A wave) peak. This underlies the concept of diastolic ventriculoannular disproportion. Large vortices, whose strength decreases with chamber dilatation, ensue after the E wave peak and impound inflow kinetic energy, averting an inflow-impeding, convective Bernoulli pressure rise. This reduces the CDL by a variable extent depending on vortical intensity. Accordingly, the filling vortex facilitates filling to varying degrees, depending on chamber volume. The new framework provides stimulus for functional genomics research, aimed at new insights into ventricular remodeling.

Volume overload

Structural cardiac volume overload comprises a group of heterogeneous diseases, each creating a nearly unique set of loading conditions on the left ventricle and/or right ventricle. In turn, the heart responds to each with unique patterns of remodeling, leading to both adaptive and maladaptive consequences. An understanding of these different patterns of hypertrophy and/or remodeling should be useful in developing strategies for the timing and correction of cardiac volume overload.

Left ventricular filling and diastolic myocardial deformation in chronic primary mitral regurgitation

AIMS

Chronic primary mitral regurgitation (MR) results in enhanced filling of the left ventricle (LV) during early diastole. Filling is impaired with the onset of LV systolic dysfunction, due to increased myocardial stiffness and reduced restoring forces. We investigated echocardiographic parameters of early diastolic function in relation to LV systolic function.

METHODS AND RESULTS

Early diastolic transmitral flow and tissue Doppler velocities, propagation velocity of early filling (V(p)), and early diastolic strain rates (SR-E) were measured in 30 patients with chronic degenerative MR and 30 age-matched controls. MR subjects were further subdivided into group 1 (14 subjects) if they had well compensated LV, and group 2 (16 subjects) if they had one or more of the following: functional limitation (> NYHA class I), LV end-systolic diameter >or=4.0 cm, and LV ejection fraction <or=60%. Group 1 had increased early diastolic transmitral flow and tissue velocities, V(p) and SR-E, compared with controls. V(p) and SR-E in group 2 (46.5 +/- 9.92 cm/s and 1.44 +/- 0.36 s(-1), respectively) decreased significantly compared with group 1 (74.4 +/- 19.9 cm/s and 1.96 +/- 0.53 s(-1), P <or= 0.002). Onset and peak of early long-axis expansion and myocardial lengthening were significantly delayed in MR, and this delay was directly correlated with preload parameters.

CONCLUSION

In chronic MR, novel echocardiographic measurements of early diastolic function exhibit a biphasic pattern depending on the state of LV systolic function, and may prove useful in the timing of surgery.

Progressive nature of chronic mitral regurgitation and the role of tissue Doppler-derived indexes

The aim of this study was to determine whether severe mitral regurgitation (MR) is progressive and whether tissue-Doppler (TD)-derived indexes can detect early left ventricular (LV) dysfunction in chronic severe MR. Percutaneous rupture of mitral valve chordae was performed in pigs ( n = 8). Before MR (baseline), immediately after MR (post-MR), and at 1 and 3 mo after MR, cardiac function was assessed using conventional and TD-derived indexes. The severity of MR was quantified using regurgitant fraction and effective regurgitant orifice area (EROA). In all animals, MR was severe. On follow-up, the LV dilated progressively over time, but LV ejection fraction did not decrease. With the increase in LV dimensions, the forward stroke volume remained unchanged, but the mitral annular dimensions, EROA, and regurgitant fraction increased (EROA = 41 ± 2 and 51 ± 2 mm2 post-MR and at 3 mo, respectively, P < 0.01). Peak systolic myocardial velocities, strain, and strain rate increased acutely post-MR and remained elevated at 1 mo but declined by 3 mo (anterior strain rate = 2.9 ± 0.1 and 2.4 ± 0.2 s−1 post-MR and at 3 mo, respectively, P < 0.001). Therefore, in a chronic model of MR, serial echocardiography demonstrated that MR begets MR and that those TD-derived indexes that initially increased post-MR decreased to baseline before any changes in LV ejection fraction.

Diastolic suction is impaired by bed rest: MRI tagging studies of diastolic untwisting

Bed rest deconditioning leads to physiological cardiac atrophy, which may compromise left ventricular (LV) filling during orthostatic stress by reducing diastolic untwisting and suction. To test this hypothesis, myocardial-tagged magnetic resonance imaging (MRI) was performed, and maximal untwisting rates of the endocardium, midwall, and epicardium were calculated by Harmonic Phase Analysis (HARP) before and after -6 degrees head-down tilt bed rest for 18 days with (n = 14) and without exercise training (n = 10). LV mass and LV end-diastolic volume were measured using cine MRI. Exercise subjects cycled on a supine ergometer for 30 min, three times per day at 75% maximal heart rate (HR). After sedentary bed rest, there was a significant reduction in maximal untwisting rates of the midwall (-46.8 +/- 14.3 to -35.4 +/- 12.4 degrees /s; P = 0.04) where untwisting is most reliably measured, and to a lesser degree of certainty in the endocardium (-50.3 +/- 13.8 to -40.1 +/- 18.5 degrees /s; P = 0.09); the epicardium was unchanged. In contrast, when exercise was performed in bed, untwisting rates were enhanced at the endocardium (-48.4 +/- 20.8 to -72.3 +/- 22.3 degrees /ms; P = 0.05) and midwall (-39.2 +/- 12.2 to -59.0 +/- 19.6 degrees /s; P = 0.03). The differential response was significant between groups at the endocardium (interaction P = 0.02) and the midwall (interaction P = 0.004). LV mass decreased in the sedentary group (156.4 +/- 30.3 to 149.5 +/- 27.9 g; P = 0.07), but it increased slightly in the exercise-trained subjects (156.4 +/- 34.3 to 162.3 +/- 40.5 g; P = 0.16); (interaction P = 0.03). We conclude that diastolic untwisting is impaired following sedentary bed rest. However, exercise training in bed can prevent the physiological cardiac remodeling associated with bed rest and preserve or even enhance diastolic suction.

Left ventricular diastolic function

Cardiovascular morbidity and mortality resulting from congestive heart failure are major concerns for the critical care physician. Although heart failure is commonly associated with impaired systolic function, in up to one half of cases, heart failure occurs exclusively on the basis of an impairment of diastolic function. Diastole is the summation of processes by which the heart loses its ability to generate force and shorten and returns to its precontractile state. The two principal processes responsible for diastole are relaxation and passive pressure-volume properties of the ventricle. Echocardiography provides a comprehensive, noninvasive evaluation of diastolic filling of the ventricle, myocardial relaxation, and ventricular stiffness; the information obtained by echocardiography has prognostic value and is a guide to proper therapy. This article reviews the physiology of diastole, the pathogenesis of diastolic heart failure, and the diagnosis of diastolic dysfunction, with a focus on the diagnostic utility of echocardiography and an emphasis on those areas of greatest interest to the critical care physician.

Cardiac atrophy in women following bed rest

Both chronic microgravity exposure and long-duration bed rest induce cardiac atrophy, which leads to reduced standing stroke volume and orthostatic intolerance. However, despite the fact that women appear to be more susceptible to postspaceflight presyncope and orthostatic hypotension than male astronauts, most previous high-resolution studies of cardiac morphology following microgravity have been performed only in men. Because female athletes have less physiological hypertrophy than male athletes, we reasoned that they also might have altered physiological cardiac atrophy after bed rest. Magnetic resonance imaging was performed in 24 healthy young women (32.1 +/- 4 yr) to measure left ventricular (LV) and right ventricular (RV) mass, volumes, and morphology accurately before and after 60 days of 6 degrees head-down tilt (HDT) bed rest. Subjects were matched and then randomly assigned to sedentary bed rest (controls, n = 8) or two treatment groups consisting of 1) exercise training using supine treadmill running within lower body negative pressure plus resistive training (n = 8), or 2) protein (0.45 g x kg(-1) x day(-1) increase) plus branched-chain amino acid (BCAA) (7.2 g/day) supplementation (n = 8). After sedentary bed rest without nutritional supplementation, there were significant reductions in LV (96 +/- 26 to 77 +/- 25 ml; P = 0.03) and RV volumes (104 +/- 33 to 86 +/- 25 ml; P = 0.02), LV (2.2 +/- 0.2 to 2.0 +/- 0.2 g/kg; P = 0.003) and RV masses (0.8 +/- 0.1 to 0.6 +/- 0.1 g/kg; P < 0.001), and the length of the major axis of the LV (90 +/- 6 to 84 +/- 7 mm. P < 0.001), similar to what has been observed previously in men (8.0%; Perhonen MA, Franco F, Lane LD, Buckey JC, Blomqvist Zerwekh JE, Peshock RM, Weatherall PT, Levine BD. J Appl Physiol 91: 645-653, 2001). In contrast, there were no significant reductions in LV or RV volumes in the exercise-trained group, and the length of the major axis was preserved. Moreover, there were significant increases in LV (1.9 +/- 0.4 to 2.3 +/- 0.3 g/kg; P < 0.001) and RV masses (0.7 +/- 0.1 to 0.8 +/- 0.2 g/kg; P = 0.002), as well as mean wall thickness (9 +/- 2 to 11 +/- 1 mm; P = 0.02). The interaction between sedentary and exercise LV and RV masses was highly significant (P < 0.0001). Protein and BCAA supplementation led to an intermediate phenotype with no change in LV or RV mass after bed rest, but there remained a significant reduction in LV volume (103 +/- 14 to 80 +/- 16 ml; P = 0.02) and major-axis length (91 +/- 5 to 88 +/- 7 mm; P = 0.003). All subjects lost an equivalent amount of body mass (3.4 +/- 0.2 kg control; 3.1 +/- 0.04 kg exercise; 2.8 +/- 0.1 kg protein). Cardiac atrophy occurs in women similar to men following sedentary 60 days HDT bed rest. However, exercise training and, to a lesser extent, protein supplementation may be potential countermeasures to the cardiac atrophy associated with chronic unloading conditions such as in spaceflight and prolonged bed rest.

Adaptive mechanisms of left ventricular diastolic function to the physiologic load of pregnancy

BACKGROUND

Pregnancy is associated with marked alteration in cardiovascular hemodynamics. Recent reports have characterized the effects on cardiac systolic function. Little has been written on the influences of loading conditions on Doppler measures of diastolic function during pregnancy.

HYPOTHESIS

Stage of pregnancy has an impact on Doppler indices of diastolic function independent of loading conditions, systolic function, and heart rate.

METHOD

Thirty healthy women were prospectively evaluated by serial echocardiography and Doppler examinations at six time periods: 10-12, 18-20, 28-30, 36-38 weeks gestation, 2-4 and 12-14 weeks postpartum. The related effects on indices of diastolic function and its interaction with load, heart rate, mass, and systolic function were determined.

RESULTS

Compared with the nonpregnant state, early (E) velocity increased (0.7+/-0.1-0.9+/-0.1 m/s, p = 0.0001), peaking at 18 weeks and returning to normal levels during late pregnancy. Atrial phase (A) velocity peaked at 18 weeks (0.48+/-0.12-0.60+/-0.13 m/s, p = 0.0001), remaining high throughout the rest of pregnancy. Consequently, the EWA ratio fell significantly during late pregnancy, from 1.9+/-0.4 to 1.4+/-0.3 (p = 0.02). In addition, mean acceleration was significantly increased in early pregnancy with a peak at 18 weeks (7.4+/-1.3 m/s2), returning to nonpregnant level at term (5.7+/-1.4 m/s2, p = 0.0001). Generalized estimating equation using multivariate regression analysis demonstrated that rising heart rate and stroke volume index had an independent effect on A velocity, and that contractility and preload had an independent effect on E velocity. Pregnancy itself had an independent influence on early filling, not explained by the other parameters.

CONCLUSIONS

During normal pregnancy, there is a reversible shift in transmitral flow velocities from early to late filling with a decrease in acceleration, consistent with an increase in ventricular compliance. Changes in heart rate, preload, and contractility, as well as stage of pregnancy influence this alteration.

Lower body negative pressure vs. lower body positive pressure to prevent cardiac atrophy after bed rest and spaceflight. What caused the controversy?

Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 ( n = 5) and 12 ( n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 ± 2.2% ( P = 0.005) after 6 wk with an additional atrophy of 7.6 ± 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 ± 12.2 vs. 153.4 ± 12.1 g, P = 0.81). Mean wall thickness decreased (4 ± 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 ± 1.7% ( P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 ± 2.7% ( P = 0.06) and RV end-diastolic volume by 16 ± 7.9% ( P = 0.06). After spaceflight, LV mass decreased by 12 ± 6.9% ( P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.

Functional mitral regurgitation predicts 1-year mortality in elderly patients with systolic chronic heart failure

BACKGROUND AND AIM

Mitral regurgitation (MR) has been demonstrated to be a powerful predictor of adverse outcome in middle-aged patients with chronic heart failure (CHF). In this study, we sought to define the prognostic impact of functional mitral regurgitation in a population of elderly patients with systolic CHF.

METHODS

One hundred seventy-five outpatients aged >70 years with validated CHF and left ventricular ejection fraction <40% underwent clinical and echocardiographic evaluations at baseline. Mitral regurgitation was diagnosed by Color Doppler and quantified in 5 categorical values using a 0-4+ grading system. Outcome measures included 1-year mortality and hospitalization for worsening CHF.

RESULTS

The distribution of patients according to the 5 different degrees of MR detected at baseline was: absent=11%, 1+=31%, 2+=38%, 3+=16%, 4+=4%. The relationship between MR and mortality was direct and approximately linear (r=0.39, p=0.00001). The prevalence of death in the 5 subgroups was 0%, 7%, 15%, 45%, 57%, respectively. Multivariate logistic regression analysis showed that MR was the strongest predictor of death (OR 4.47, 95% CI 1.50-13.0), independently of the presence of diabetes mellitus, older age and larger left ventricular end-diastolic volume. No association was found between MR and hospitalization for worsening CHF (r=0.08, p=0.41).

CONCLUSIONS

This study establishes the direct and independent relationship between MR severity and one-year mortality among elders with systolic CHF. Conversely, MR does not provide useful information regarding the risk of subsequent hospitalization for worsening CHF.

Thin Filament Remodeling in Failing Myocardium

While the remodeling process in myocardial failure involves changes in ventricular structure and performance, it is now appreciated that it is also associated with changes in thin filament composition and function. As is discussed, changes at the level thick filament may affect thin filament activation in heart failure. Alterations in actin, troponin and tropomyosin isoform composition do not appear to be significant factors in human heart failure. In contrast, proteolytic degradation of troponin subunits are likely to be playing a functional role in some forms of cardiomyopathy (e.g. ischemic). Finally, phosphorylation of troponin I and troponin T by kinases (most notably protein kinase C) substantially affect thin filament function in failing human myocardium. These findings indicate that functional deficits in thin filament function in failing myocardium are largely reversible and create the potential for future targeted therapies in the treatment of this deadly disease.

Development of a new animal model of chronic mitral regurgitation in rats under transesophageal echocardiographic guidance

Large animal models (dog and sheep) are often used for the investigation of the pathophysiology of chronic mitral regurgitation (MR). A major limitation of large animal models is cost. The aim of this study was to develop a new animal model of chronic MR. Left thoracotomy was performed in 34 rats. Under the guidance of transesophageal echocardiography, a fine needle was inserted into the left ventricle (LV) to damage the mitral leaflets and produce MR. Serial transthoracic echocardiography was performed to assess LV remodeling and function. Left atrial and LV diameters were significantly larger, and LV fractional shortening was lower in the MR group than in the sham group. The 150-day survival was 59% in the MR group and 100% in the sham group (P < .01). This new animal model of chronic MR may be used in the study of the pathophysiology of chronic MR and pharmacologic therapies.

Myocardial velocity gradient reflects the severity of myocardial damage regardless of the presence or absence of mitral regurgitation

Complicating mitral regurgitation (MR) apparently enhances left ventricular ejection fraction, thereby leading to the underestimation of myocardial damage by routine echocardiography. We sought to assess the significance of myocardial velocity gradient (MVG) derived from Doppler tissue imaging as an indicator of the severity of myocardial damage in the presence or absence of MR. Peak systolic and diastolic MVG was obtained from 39 participants: 12 healthy participants, 10 patients with dilated cardiomyopathy complicating moderate to severe MR [MR (+) group], and 17 patients with dilated cardiomyopathy without significant MR [MR (-) group]. MVG was compared with standard echocardiographic and Doppler transmitral flow velocity indices. Plasma brain natriuretic peptide levels were measured in all patients. Left ventricular dimension and fractional shortening was similar between MR (+) and MR (-) groups. Plasma brain natriuretic peptide levels were significantly increased in MR (+) group (440 +/- 417 pg/mL) as compared with MR (-) group (122 +/- 107 pg/mL, P <.05). Peak systolic MVG was significantly attenuated in dilated cardiomyopathy group with or without MR [MR (+) group = 1.3 +/- 0.5 seconds(-1), MR (-) group = 2.1 +/- 0.5 seconds(-1), where normal = 4.0 +/- 0.9 seconds(-1), P <.01, respectively]. Peak systolic MVG was further attenuated in MR (+) group than in MR (-) group (P <.01). Plasma brain natriuretic peptide levels were negatively correlated with peak systolic MVG (r = -0.66, P <.0005). Peak diastolic MVG was attenuated in MR (+) and also in MR (-) groups [MR (+) group = -4.5 +/- 2.0 seconds(-1), MR (-) group = -4.4 +/- 1.1 seconds(-1), where normal = -8.7 +/- 2.4 seconds(-1), P <.01, respectively], whereas transmitral flow indices failed to distinguish MR (+) group from normal as a result of pseudonormalization. MVG may reflect the severity of myocardial damage regardless of the presence or absence of complicating MR.

Viscoelastic properties of pressure overload hypertrophied myocardium: effect of serine protease treatment

To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in viscoelasticity, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial viscoelasticity in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.

Cardiac atrophy after bed rest and spaceflight

Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 (n = 5) and 12 (n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 +/- 2.2% (P = 0.005) after 6 wk with an additional atrophy of 7.6 +/- 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 +/- 12.2 vs. 153.4 +/- 12.1 g, P = 0.81). Mean wall thickness decreased (4 +/- 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 +/- 1.7% (P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 +/- 2.7% (P = 0.06) and RV end-diastolic volume by 16 +/- 7.9% (P = 0.06). After spaceflight, LV mass decreased by 12 +/- 6.9% (P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.

Surgical timing for mitral valve regurgitation

Advances in diagnostic and surgical techniques in the management of mitral regurgitation have resulted in improved survival rates and clinical outcomes. Echocardiography is a valuable noninvasive diagnostic tool in the determination of the timing of surgical correction of mitral regurgitation. Improved surgical techniques, the growing role of mitral valve repair, low operative mortality rates, and improved long-term survival rates are important considerations for earlier surgical intervention in symptomatic patients and in asymptomatic patients with echocardiographic criteria of left ventricular dilatation. Intraoperative transesophageal echocardiography is very useful in mitral valve repair and valve replacement with preservation of chordal structures.

Gel stretch method: a new method to measure constitutive properties of cardiac muscle cells

Diastolic dysfunction is an important cause of congestive heart failure; however, the basic mechanisms causing diastolic congestive heart failure are not fully understood, especially the role of the cardiac muscle cell, or cardiocyte, in this process. Before the role of the cardiocyte in this pathophysiology can be defined, methods for measuring cardiocyte constitutive properties must be developed and validated. Thus this study was designed to evaluate a new method to characterize cardiocyte constitutive properties, the gel stretch method. Cardiocytes were isolated enzymatically from normal feline hearts and embedded in a 2% agarose gel containing HEPES-Krebs buffer and laminin. This gel was cast in a shape that allowed it to be placed in a stretching device. The ends of the gel were held between a movable roller and fixed plates that acted as mandibles. Distance between the right and left mandibles was increased using a stepper motor system. The force applied to the gel was measured by a force transducer. The resultant cardiocyte strain was determined by imaging the cells with a microscope, capturing the images with a CCD camera, and measuring cardiocyte and sarcomere length changes. Cardiocyte stress was characterized with a finite-element method. These measurements of cardiocyte stress and strain were used to determine cardiocyte stiffness. Two variables affecting cardiocyte stiffness were measured, the passive elastic spring and viscous damping. The passive spring was assessed by increasing the force on the gel at 1 g/min, modeling the resultant stress vs. strain relationship as an exponential [sigma = A/k(ekepsilon - 1)]. In normal cardiocytes, A = 23.0 kN/m2 and k = 16. Viscous damping was assessed by examining the loop area between the stress vs. strain relationship during 1 g/min increases and decreases in force. Normal cardiocytes had a finite loop area = 1.39 kN/m2, indicating the presence of viscous damping. Thus the gel stretch method provided accurate measurements of cardiocyte constitutive properties. These measurements have allowed the first quantitative assessment of passive elastic spring properties and viscous damping in normal mammalian cardiocytes.

Short-term hemodynamic evaluation of circumferential mitral annuloplasty for correction of mitral valve regurgitation in dogs

OBJECTIVE

To determine the short-term hemodynamic effects associated with circumferential mitral annuloplasty (CMA) in dogs with mitral regurgitation.

STUDY DESIGN

Prospective experimental study. Animals-Seven healthy adult mongrel dogs.

METHODS

Mitral regurgitation was surgically induced, and annular dilation occurred. Echocardiography and cardiac catheterization were used to determine forward ejection fraction (FEF), regurgitant fraction (RF), pulmonary capillary wedge pressure (PCWP), and annular diameter before and immediately after CMA in five dogs. FEF and RF were also evaluated 7 days after annuloplasty.

RESULTS

Mean annular diameter and PCWP were significantly reduced immediately after CMA. Significant increases in FEF of 19% and 22% were shown immediately and 7 days after CMA. Significant reductions in RF of 19% and 22% were also shown immediately and 7 days after annuloplasty.

CONCLUSIONS

Sustained hemodynamic benefits and a reduction in annular diameter were achieved by CMA in a canine model of mitral regurgitation.

CLINICAL IMPLICATIONS

CMA may be a suitable treatment for heart failure because of mitral regurgitation when early signs of cardiovascular decompensation persist despite appropriate medical management.

Effects of left ventricular systolic function on left ventricular diastolic filling patterns in severe mitral regurgitation

Significant mitral regurgitation (MR) may alter the normal pattern of Doppler detected left ventricular (LV) filling by causing a prominent early filling (E) wave velocity. The manner and extent to which the typical filling pattern of uncomplicated MR is affected by concomitant impaired LV systolic function has not been characterized. Twenty patients with severe LV systolic dysfunction (2-dimensional echocardiographic estimation of ejection fraction < or = 30%) and 21 age- and sex-matched case controls with normal systolic function (ejection fraction > or = 55%) were selected. In addition, 20 subjects with normal LV systolic function and no MR were analyzed as a reference group. Maximal E-wave velocity was increased and highest among MR patients with preserved LV systolic function (124 +/- 37 cm/s) than among those with LV systolic dysfunction (101 +/- 25 cm/s; p <0.05) and normal controls (74 +/- 18 cm/s; p <0.001). Concurrently, A-wave velocity was lowest in patients with systolic dysfunction and MR (47 +/- 23 cm/s; p <0.001) than in patients with normal systolic function and MR (79 +/- 33 cm/s) and normal controls (74 +/- 20 cm/s). Deceleration time of the E wave was longest among those with normal systolic function and MR (203 +/- 41 ms) than among those with systolic dysfunction and MR (152 +/- 35 ms; p <0.001) and normal controls (167 +/- 53 ms; p <0.05). Thus, systolic LV dysfunction in patients with severe MR, compared to patients with MR and normal LV systolic function, is associated with important changes in diastolic inflow velocities, including reduction of the maximal A-wave velocity to a greater extent than the E wave, resulting in an increased E/A ratio and shortening of deceleration time of the E wave.

Left ventricular function in chronic mitral regurgitation: preoperative and postoperative comparison

OBJECTIVES

The present study was designed to evaluate the effects of surgical procedure on left ventricular systolic and diastolic function in patients with mitral regurgitation.

BACKGROUND

Left ventricular systolic function has been shown to decline after operation in patients with chronic mitral regurgitation.

METHODS

Using simultaneous cineangiography and left ventricular micromanometry, we evaluated left ventricular systolic and diastolic function in 14 patients with chronic mitral regurgitation both preoperatively and at an average of 22 months after operation. Eight patients underwent mitral valve reconstruction, and six had a valve replacement with interruption of the chordae tendineae. We compared these patients with 10 control subjects.

RESULTS

Preoperatively, patients with mitral regurgitation demonstrated normal global and regional left ventricular systolic function. Peak rate of diastolic filling was increased (p < 0.01), and passive chamber stiffness was decreased, compared with that in control subjects (p < 0.01), and there was normal myocardial stiffness. Postoperatively, systolic and diastolic function returned to normal in patients undergoing mitral valve reconstruction. In contrast, global systolic function was depressed in patients after valve replacement (p < 0.05), with regional dysfunction in the area of papillary muscle attachment (p < 0.01). Diastolic function was depressed in this group, with a prolonged time constant of pressure decay (p < 0.01) and a depressed rate of early diastolic filling and strain rate (p < 0.05). Passive elastic stiffness was within the normal range in all postoperative patients.

CONCLUSIONS

The type of operation performed to correct chronic mitral regurgitation has an important effect on postoperative left ventricular function. Systolic and diastolic function are preserved after mitral valve reconstruction. Mitral valve replacement with chordal interruption is associated with global and regional systolic dysfunction and early diastolic filling and relaxation abnormalities.