Left ventricular chamber stiffness at rest as a determinant of exercise capacity in heart failure subjects with decreased ejection fraction

Differences in cardiac adaptation to exercise in male and female athletes assessed by noninvasive techniques: a state-of-the-art review

Athlete's heart is generally regarded as a physiological adaptation to regular training, with specific morphological and functional alterations in the cardiovascular system. Development of the noninvasive imaging techniques over the past several years enabled better assessment of cardiac remodeling in athletes, which may eventually mimic certain pathological conditions with the potential for sudden cardiac death, or disease progression. The current literature provides a compelling overview of the available methods that target the interrelation of prolonged exercise with cardiac structure and function. However, this data stems from scientific studies that included mostly male athletes. Despite the growing participation of females in competitive sport meetings, little is known about the long-term cardiac effects of repetitive training in this population. There are several factors-biochemical, physiological and psychological, that determine sex-dependent cardiac response. Herein, the aim of this review was to compare cardiac adaptation to endurance exercise in male and female athletes with the use of electrocardiographic, echocardiographic, and biochemical examination, to determine the sex-specific phenotypes, and to improve the healthcare providers' awareness of cardiac remodeling in athletes. Finally, we discuss the possible exercise-induced alternations that should arouse suspicion of pathology and be further evaluated.

Compliant Titin Isoform Content Is Reduced in Left Ventricles of Sedentary Versus Active Rats

A sedentary lifestyle is associated with increased cardiovascular risk factors and reduced cardiac compliance when compared to a lifestyle that includes exercise training. Exercise training increases cardiac compliance in humans, but the mechanisms underlying this improvement are unknown. A major determinant of cardiac compliance is the compliance of the giant elastic protein titin. Experimentally reducing titin compliance in animal models reduces exercise tolerance, but it is not known whether sedentary versus chronic exercise conditions cause differences in titin isoform content. We hypothesized that sedentary conditions would be associated with a reduction in the content of the longer, more compliant N2BA isoform relative to the stiffer N2B isoform (yielding a reduced N2BA:N2B ratio) compared to age-matched exercising controls. We obtained left ventricles from 16-week old rats housed for 12 weeks in standard (sedentary) or voluntary running wheel (exercised) housing. The N2BA:N2B ratio was decreased in the hearts of sedentary versus active rats (p = 0.041). Gene expression of a titin mRNA splicing factor, RNA Binding Motif 20 protein (RBM20), correlated negatively with N2BA:N2B ratios (p = 0.006, r = -0.449), but was not different between groups, suggesting that RBM20 may be regulated post-transcriptionally. Total phosphorylation of cardiac titin was not different between the active and sedentary groups. This study is the first to demonstrate that sedentary rats exhibit reduced cardiac titin N2BA:N2B isoform ratios, which implies reduced cardiac compliance. These data suggest that a lack of exercise (running wheel) reduces cardiac compliance and that exercise itself increases cardiac compliance.

The link between exercise and titin passive stiffness

NEW FINDINGS

What is the topic of this review? This review focuses on how in vivo and molecular measurements of cardiac passive stiffness can predict exercise tolerance and how exercise training can reduce cardiac passive stiffness. What advances does it highlight? This review highlights advances in understanding the relationship between molecular (titin-based) and in vivo (left ventricular) passive stiffness, how passive stiffness modifies exercise tolerance, and how exercise training may be therapeutic for cardiac diseases with increased passive stiffness. Exercise can help alleviate the negative effects of cardiovascular disease and cardiovascular co-morbidities associated with sedentary behaviour; this may be especially true in diseases that are associated with increased left ventricular passive stiffness. In this review, we discuss the inverse relationship between exercise tolerance and cardiac passive stiffness. Passive stiffness is the physical property of cardiac muscle to produce a resistive force when stretched, which, in vivo, is measured using the left ventricular end diastolic pressure-volume relationship or is estimated using echocardiography. The giant elastic protein titin is the major contributor to passive stiffness at physiological muscle (sarcomere) lengths. Passive stiffness can be modified by altering titin isoform size or by post-translational modifications. In both human and animal models, increased left ventricular passive stiffness is associated with reduced exercise tolerance due to impaired diastolic filling, suggesting that increased passive stiffness predicts reduced exercise tolerance. At the same time, exercise training itself may induce both short- and long-term changes in titin-based passive stiffness, suggesting that exercise may be a treatment for diseases associated with increased passive stiffness. Direct modification of passive stiffness to improve exercise tolerance is a potential therapeutic approach. Titin passive stiffness itself may be a treatment target based on the recent discovery of RNA binding motif 20, which modifies titin isoform size and passive stiffness. Translating these discoveries that link exercise and left ventricular passive stiffness may provide new methods to enhance exercise tolerance and treat patients with cardiovascular disease.

What global diastolic function is, what it is not, and how to measure it

Despite Leonardo da Vinci's observation (circa 1511) that “the atria or filling chambers contract together while the pumping chambers or ventricles are relaxing and vice versa,” the dynamics of four-chamber heart function, and of diastolic function (DF) in particular, are not generally appreciated. We view DF from a global perspective, while characterizing it in terms of causality and clinical relevance. Our models derive from the insight that global DF is ultimately a result of forces generated by elastic recoil, modulated by cross-bridge relaxation, and load. The interaction between recoil and relaxation results in physical wall motion that generates pressure gradients that drive fluid flow, while epicardial wall motion is constrained by the pericardial sac. Traditional DF indexes (τ, E/E′, etc.) are not derived from causal mechanisms and are interpreted as approximating either stiffness or relaxation, but not both, thereby limiting the accuracy of DF quantification. Our derived kinematic models of isovolumic relaxation and suction-initiated filling are extensively validated, quantify the balance between stiffness and relaxation, and provide novel mechanistic physiological insight. For example, causality-based modeling provides load-independent indexes of DF and reveals that both stiffness and relaxation modify traditional DF indexes. The method has revealed that the in vivo left ventricular equilibrium volume occurs at diastasis, predicted novel relationships between filling and wall motion, and quantified causal relationships between ventricular and atrial function. In summary, by using governing physiological principles as a guide, we define what global DF is, what it is not, and how to measure it.

Shortening of the elastic tandem immunoglobulin segment of titin leads to diastolic dysfunction

BACKGROUND

Diastolic dysfunction is a poorly understood but clinically pervasive syndrome that is characterized by increased diastolic stiffness. Titin is the main determinant of cellular passive stiffness. However, the physiological role that the tandem immunoglobulin (Ig) segment of titin plays in stiffness generation and whether shortening this segment is sufficient to cause diastolic dysfunction need to be established.

METHODS AND RESULTS

We generated a mouse model in which 9 Ig-like domains (Ig3-Ig11) were deleted from the proximal tandem Ig segment of the spring region of titin (IG KO). Exon microarray analysis revealed no adaptations in titin splicing, whereas novel phospho-specific antibodies did not detect changes in titin phosphorylation. Passive myocyte stiffness was increased in the IG KO, and immunoelectron microscopy revealed increased extension of the remaining titin spring segments as the sole likely underlying mechanism. Diastolic stiffness was increased at the tissue and organ levels, with no consistent changes in extracellular matrix composition or extracellular matrix-based passive stiffness, supporting a titin-based mechanism for in vivo diastolic dysfunction. Additionally, IG KO mice have a reduced exercise tolerance, a phenotype often associated with diastolic dysfunction.

CONCLUSIONS

Increased titin-based passive stiffness is sufficient to cause diastolic dysfunction with exercise intolerance.

Left atrial enlargement and reduced physical function during aging

Diastolic dysfunction, often seen with increasing age, is associated with reduced exercise capacity and increased mortality. Mortality rates in older individuals are linked to the development of disability, which may be preceded by functional limitations. The goal of this study was to identify which echocardiographic measures of diastolic function correlate with physical function in older subjects. A total of 36 men and women from the Louisiana Healthy Aging Study, age 62-101 yr, received a complete echocardiographic exam and performed the 10-item continuous-scale physical-functional performance test (CS-PFP-10). After adjustment for age and gender, left atrial volume index (ρ = -0.59; p = .0005) correlated with the total CS-PFP-10 score. Increased left atrial volume index may be a marker of impaired performance of activities of daily living in older individuals.

Interrelation between myocardial oxidative metabolism and diastolic function in patients undergoing surgical ventricular reconstruction

PURPOSE

Diastolic function is impaired in patients with end-stage heart failure. Favorable structural changes by surgical ventricular reconstruction (SVR) are thought to improve diastolic function, however, previous studies reported the contradictory results. We hypothesized that cardiac oxidative metabolism and diastolic dysfunction might improve in parallel to the reduction of left ventricular chamber size after SVR.

METHODS

We studied 11 patients underwent SVR associated with mitral valve repair for end-stage heart failure due to dilated cardiomyopathy. Diastolic function was assessed by echocardiography and myocardial oxidative metabolism was measured by the monoexponential clearance (k-mono) of (11)C-acetate positron emission tomography at baseline and 1 month after SVR.

RESULTS

All patients had preoperative severe diastolic dysfunction [E/A 4.11 ± 1.18, deceleration time (DT) 134 ± 26 ms]. The study patients were divided into 2 groups according to the changes in diastolic function after SVR; unchanged or worsened diastolic function in 6 patients (55 %, Non-responder) and improved diastolic function in 5 (45 %, Responder). K-mono and wall stress decreased only in responder. The changes in k-mono before and after SVR correlated with those in deceleration time (r =  -0.63; p < 0.05) and wall stress (r = 0.75; p < 0.01).

CONCLUSIONS

Improvement of diastolic dysfunction in patients with end-stage heart failure by SVR was in parallel to that in oxidative metabolism. It suggests that SVR reduced excessive metabolism during the diastolic phase, in part, via the improvement in diastolic function and the reduction in LV wall stress.

Noninvasive methods for determining pulmonary vascular function in children with pulmonary arterial hypertension: application of a mechanical oscillator model

OBJECTIVE

Noninvasive diagnostics for pulmonary arterial hypertension (PAH) have traditionally sought to predict main pulmonary artery pressure from qualitative or direct quantitative measures of the flow velocity pattern obtained from spectral Doppler ultrasound examination of the main pulmonary artery. A more detailed quantification of flow velocity patterns in the systemic circuit has been obtained by parameterizing the flow trace with a simple dynamic system model. Here, we investigate such a model's utility as a noninvasive predictor of total right heart afterload and right heart function.

DESIGN

Flow velocity and pressure was measured within the main pulmonary artery during right heart catheterization of patients with normal hemodynamics (19 subjects, 20 conditions) and those with PAH undergoing reactivity evaluation (34 patients, 69 conditions). Our model parameters were obtained by least-squares fitting the model velocity to the measured flow velocity.

RESULTS

Five parameter means displayed significant (P < .05) differences between normotensive and hypertensive groups. The model stiffness parameter correlated to actual pulmonary vascular resistance (r = 0.4924), pulmonary vascular stiffness (r = 0.6811), pulmonary flow (r = 0.6963), and stroke work (r = 0.7017), while the model initial displacement parameter had good correlation to stiffness (r = 0.6943) and flow (r = 0.6958).

CONCLUSIONS

As predictors of total right heart afterload (resistance and stiffness) and right ventricle work, the model parameters of stiffness and initial displacement offer more comprehensive measures of the disease state than previous noninvasive methods and may be useful in routine diagnostic monitoring of patients with PAH.

The relationship between resting lung-to-lung circulation time and peak exercise capacity in chronic heart failure patients

BACKGROUND

Peak exercise capacity (VO2peak) is a measure of the severity of chronic heart failure (CHF); however, few indices of resting cardiopulmonary function have been shown to predict VO2peak. A prolonged circulation time has been suggested as an index of increased severity of CHF. The aim of this study was to investigate the relationship between resting lung-to-lung circulation time (LLCT) and VO2peak in CHF.

METHODS AND RESULTS

Thirty CHF patients (59 +/- 13 years, New York Heart Association: 1.9 +/- 1.0) undertook the study. Each subject completed resting pulmonary and echocardiography measures and an incremental exercise test. LLCT was measured using the reappearance of end-tidal acetylene (P(ET),C2H2) after a single inhalation. Univariate and multivariate stepwise linear regression was used to determine the predictors of VO2peak. Univariate correlates of VO2peak (group mean 1.53 +/- 0.44 L/min(-1)) included LLCT (r = -0.75), inspiratory capacity (r = 0.41), ejection fraction (r = 0.33), peak early flow velocity (r = -0.39), and the ratio of early to late flow velocity (r = -0.31). LLCT was the only independent predictor where VO(2peak) = 3.923-0.045 (LLCT); r2 = 54%.

CONCLUSIONS

These results suggest that resting LLCT determined using the soluble inert gas technique represents a simple, noninvasive method that provides additional information regarding exercise capacity in CHF.

Exercise Capacity, Breathing Pattern, and Gas Exchange During Exercise for Patients with Isolated Diastolic Dysfunction

BACKGROUND

Left ventricular diastolic dysfunction (DiaD) is as common as left ventricular systolic dysfunction. Whether these causes of heart failure lead to similar breathing pattern and gas exchange responses to exercise remains unclear.

METHODS

Participants (control subjects [n = 47], systolic dysfunction [n = 46], and DiaD [n = 40]) underwent resting echocardiograms and cardiopulmonary exercise testing.

RESULTS

Patients demonstrated lower peak oxygen consumption and tidal volume than control subjects (P < .05). Ventilation tended to be highest in DiaD. The submaximal ventilatory equivalent for carbon dioxide was highest in DiaD. Left atrial volume (all groups) was correlated with peak oxygen consumption (r = -0.38) whereas the ratio of early mitral inflow velocity to early mitral annular velocity was related to peak oxygen consumption (r = -0.36) and treadmill time (r = -0.35).

CONCLUSION

Isolated DiaD is associated with altered breathing pattern and gas exchange similar to systolic dysfunction. Elevated left atrial volume, higher early mitral inflow velocity to early mitral annular velocity ratio, or both are predictive of exercise capacity and elevated ventilatory responses in patients with DiaD suggesting a role for dysfunctional ventricular relaxation.

E-wave deceleration time may not provide an accurate determination of LV chamber stiffness if LV relaxation/viscoelasticity is unknown

Average left ventricular (LV) chamber stiffness (ΔPavg/ΔVavg) is an important diastolic function index. An E-wave-based determination of ΔPavg/ΔVavg (Little WC, Ohno M, Kitzman DW, Thomas JD, Cheng CP. Circulation 92: 1933–1939, 1995) predicted that deceleration time (DT) determines stiffness as follows: ΔPavg/ΔVavg = N(π/DT)2 (where N is constant), which implies that if the DTs of two LVs are indistinguishable, their stiffness is indistinguishable as well. We observed that LVs with indistinguishable DTs may have markedly different ΔPavg/ΔVavg values determined by simultaneous echocardiography-catheterization. To elucidate the mechanism by which LVs with indistinguishable DTs manifest distinguishable chamber stiffness, we use a validated, kinematic E-wave model (Kovács SJ, Barzilai B, Perez JE. Am J Physiol Heart Circ Physiol 252: H178–H187, 1987) with stiffness ( k) and relaxation/viscoelasticity ( c) parameters. Because the predicted linear relation between k and ΔPavg/ΔVavg has been validated, we reexpress the DT-stiffness (ΔPavg/ΔVavg) relation of Little et al. as follows: DT k ≈ [Formula: see text]. Using the kinematic model, we derive the general DT-chamber stiffness/viscoelasticity relation as follows: DT k, c = [Formula: see text](where c and k are determined directly from the E-wave), which reduces to DT k when c ≪ k. Validation involved analysis of 400 E-waves by determination of five-beat averaged k and c from 80 subjects undergoing simultaneous echocardiography-catheterization. Clinical E-wave DTs were compared with model-predicted DT k and DT k, c. Clinical DT was better predicted by stiffness and relaxation/viscoelasticity ( r2 = 0.84, DT vs. DT k, c) jointly rather than by stiffness alone ( r2 = 0.60, DT vs. DT k). Thus LVs can have indistinguishable DTs but significantly different ΔPavg/ΔVavg if chamber relaxation/viscoelasticity differs. We conclude that DT is a function of both chamber stiffness and chamber relaxation viscoelasticity. Quantitative diastolic function assessment warrants consideration of simultaneous stiffness and relaxation/viscoelastic effects.

Relation of left ventricular chamber stiffness at rest to exercise capacity in hypertrophic cardiomyopathy

The degree of exercise capacity is poorly predicted by conventional markers of disease severity in patients with hypertrophic cardiomyopathy (HC). The principal mechanism of exercise intolerance in patients with HC is the failure of stroke volume augmentation due to left ventricular (LV) diastolic dysfunction. The role of LV chamber stiffness, assessed noninvasively, as a determinant of exercise tolerance is unknown. Sixty-four patients with HC were studied with Doppler echocardiography, exercise testing, and gadolinium cardiac magnetic resonance. The LV chamber stiffness index was determined as the ratio of pulmonary capillary wedge pressure (derived from the E/Ea ratio) to LV end-diastolic volume (assessed by cardiac magnetic resonance). Maximal exercise tolerance was defined as achieved METs. There were inverse correlations between METs achieved and age (r = -0.38, p = 0.003), heart rate deficit (r = -0.39, p = 0.002), LV outflow tract gradient (r = -0.33, p = 0.009), the E/Ea ratio (r = -0.4, p = 0.001), mean LV wall thickness (r = -0.26, p = 0.04), and LV stiffness (r = -0.56, p <0.001) and a positive correlation between METs achieved and LV end-diastolic volume (r = 0.33, p = 0.01). On multivariate analysis, only LV chamber stiffness was associated with exercise capacity. A LV stiffness level of 0.18 mm Hg/ml had 100% sensitivity and 75% specificity (area under the curve 0.84) for predicting < or =7 METs achieved. In conclusion, LV diastolic dysfunction at rest, as manifested by increased LV chamber stiffness, is a major determinant of maximal exercise capacity in patients with HC.

Diastolic ventricular-vascular stiffness and relaxation relation: elucidation of coupling via pressure phase plane-derived indexes

Because systole and diastole are coupled and systolic ventricular-vascular coupling has been characterized, we hypothesize that diastolic ventricular-vascular coupling (DVVC) exists and can be characterized in terms of relaxation and stiffness. To characterize and elucidate DVVC mechanisms, we introduce time derivative of pressure (dP/d t) vs. time-varying pressure [P( t)] (pressure phase plane, PPP)-derived analogs of ventricular and vascular “stiffness” and relaxation parameters. Although volume change (dV) = 0 during isovolumic periods, and time-varying left ventricular (LV) stiffness, typically expressed as change in pressure per unit change in volume (dP/dV), is undefined, our formulation allows determination of a PPP-derived stiffness analog during isovolumic contraction and relaxation. Similarly, an aortic stiffness analog is also derivable from the PPP. LV relaxation was characterized via τ, the time constant of isovolumic relaxation, and vascular (aortic pressure decay) relaxation was characterized in terms of its equivalent (windkessel) exponential decay time constant κ. The results show that PPP-derived systolic and diastolic ventricular and vascular stiffness are strongly coupled [Formula: see text]. In support of the DVVC hypothesis, a strong linear correlation between relaxation (rate of pressure decay) indexes κ and τ (κ = 9.89τ − 90.3, r = 0.81) was also observed. The correlations observed underscore the role of long-term, steady-state DVVC as a diastolic function determinant. Awareness of the PPP-derived DVVC parameters provides insight into mechanisms and facilitates quantification of arterial stiffening and associated increase in diastolic chamber stiffness. The PPP method provides a tool for quantitative assessment and determination of the functional coupling of the vasculature to diastolic function.

Correlation of flow mediated dilation with inflammatory markers in patients with impaired cardiac function. Beneficial effects of inhibition of ACE

Impaired cardiac function is frequently accompanied by peripheral vascular dysfunction and a pro-inflammatory condition, which may be associated with elevated levels of angiotensin II. We hypothesized that the magnitude of flow mediated dilatation (FMD) of the brachial artery of post myocardial infarction patients will correlate with serum levels of tumor necrosis factor alpha (TNFalpha) and C-reactive protein (CRP), and that treatment with angiotensin converting enzyme inhibitors (ACEI) will increase FMD by reducing TNFalpha and CRP. Patients were treated with low dose (10 mg/day) quinapril (Q) or enalapril (E) and their effects on FMD and inflammatory markers were evaluated after 8 and 12 weeks. Before treatment, in both groups FMD showed a low value (Q: 2.95+0.42% and E: 3.3+/-0.33%), whereas TNF-alpha (Q: 31.65+/-8.23 pg/ml and E: 29.5+/-5.9 pg/ml) and CRP (Q: 7.28+/-2.96 mg/ml and E: 7.08+/-3.02 mg/ml) were elevated. In the Q group, but not in the E group FMD increased significantly, (to 5.96+1.10%), whereas TNF-alpha (19.0+/-12.21 pg/ml) and CRP (to 3.91+/-1.82 mg/L) significantly decreased after 8 and 12 weeks of Q treatment. Moreover, the magnitude of FMD showed a strong inverse correlation with serum levels of TNF-alpha and CRP after Q treatment. Thus, in post myocardial infarction patients endothelial dysfunction assessed by FMD correlates with elevated levels of plasma inflammatory markers, and low dose quinapril improves endothelial function, likely by reducing vascular inflammation.

The Incremental Benefit of Rate-Adaptive Pacing on Exercise Performance During Cardiac Resynchronization Therapy

OBJECTIVES

The purpose of this research was to investigate the effect of using rate-adaptive pacing and atrioventricular interval (AVI) adaptation on exercise performance during cardiac resynchronization therapy (CRT).

BACKGROUND

The potential incremental benefits of using rate-adaptive pacing and AVI adaptation with CRT during exercise have not been studied.

METHODS

We studied 20 patients with heart failure, chronotropic incompetence (<85% age-predicted heart rate [AP-HR] and <80% HR reserve), and implanted with CRT. All patients underwent a cardiopulmonary exercise treadmill test using DDD mode with fixed AVI (DDD-OFF), DDD mode with adaptive AVI on (DDD-ON), and DDDR mode with adaptive AVI on (DDDR-ON) to measure metabolic equivalents (METs) and peak oxygen consumption (VO2max).

RESULTS

During DDD-OFF mode, not all patients reached 85% AP-HR during exercise, and 55% of patients had <70% AP-HR. Compared to patients with >70% AP-HR, patients with <70% AP-HR had significantly lower baseline HR (66 +/- 3 beats/min vs. 80 +/- 5 beats/min, p = 0.015) and percentage HR reserve (27 +/- 5% vs. 48 +/- 6%, p = 0.006). In patients with <70% AP-HR, DDDR-ON mode increased peak exercise HR, exercise time, METs, and VO2max compared with DDD-OFF and DDD-ON modes (p < 0.05), without a significant difference between DDD-OFF and DDD-ON modes. In contrast, there were no significant differences in peak exercise HR, exercise time, METs, and VO2max among the three pacing modes in patients with >70% AP-HR. The percentage HR changes during exercise positively correlated with exercise time (r = 0.67, p < 0.001), METs (r = 0.56, p < 0.001), and VO2max (r = 0.55, p < 0.001).

CONCLUSIONS

In heart failure patients with severe chronotropic incompetence as defined by failure to achieve >70% AP-HR, appropriate use of rate-adaptive pacing with CRT provides incremental benefit on exercise capacity during exercise.

Diabetes and diastolic function: stiffness and relaxation from transmitral flow

To characterize the mechanism by which diabetes affects the heart in diabetic (n = 15) and age-matched control subjects (n = 15), we quantified and compared diastolic function (DF) in terms of chamber stiffness and viscosity/relaxation by analyzing Doppler E- and E'-waves and simultaneous (high-fidelity) hemodynamic data. We compared tau, standard Doppler indexes and indexes of stiffness and viscosity/relaxation computed via the parameterized diastolic filling (PDF) formalism. Three PDF parameters uniquely characterize each E-wave in terms of load (x(o)), viscoelasticity or viscosity/relaxation (c) and stiffness (k). Significant differences for c (p = 0.00004), the peak atrioventricular pressure gradient (kx(o)) (p = 0.02) and the stored elastic energy available for early filling (1/2kx(o)2) (p = 0.04) were found. The only conventional index attaining significance was E-wave acceleration time (p = 0.007). Neither time constant of isovolumic relaxation (tau) nor E-wave deceleration time, E', k or x(o) differentiated between groups. We conclude that PDF based DF assessment differentiates between diabetic and nondiabetic controls better than conventional echo- or cath-based indexes. Our results in humans agree with published results from animal studies. We conclude that diabetes affects the heart via a quantifiable increase in chamber viscoelasticity (c) rather than an increase in chamber stiffness (k) and that phenotypic characterization of diabetic cardiomyopathy is facilitated by DF assessment via the PDF formalism.

Left Atrial Index Is a Predictor of Exercise Capacity in Patients with Hypertrophic Cardiomyopathy

BACKGROUND

Left atrial (LA) enlargement is related to diastolic dysfunction and mitral regurgitation (MR), both of which are common in patients with hypertrophic cardiomyopathy (HCM). This study investigates the association between LA size and exercise capacity in patients with HCM.

METHODS

All HCM patients who underwent a treadmill test with direct measurement of oxygen consumption (VO2) and a standard transthoracic echocardiography within 30 days in the years 2001-2003 were identified. Patients with significant comorbidities were excluded. Exercise capacity was defined as percentage of predicted peak VO2. Clinical and echocardiographic parameters were compared with those of a group of normal subjects.

RESULTS

Compared with normal subjects, HCM patients had increased left atrial (LA) volume index (36 vs 21 mL/m2; P < .0001) and mitral E/e' ratio (14 vs 9; P < .0001); 27% of the patients had at least moderate MR. LA volume index demonstrated borderline correlation with exercise capacity (r = -.20; P = .06) but was an independent predictor of exercise capacity in a multivariate linear analysis, together with body mass index, heart rate at rest, and left ventricular end-systolic diameter. Including the parameters E/e' ratio or moderate or severe MR did not add incremental value to the model.

CONCLUSION

LA volume index, reflecting the combined influences of MR and diastolic dysfunction, was independently associated with objective measures of exercise capacity in patients with isolated HCM.

Relationship of diastolic intraventricular pressure gradients and aerobic capacity in patients with diastolic heart failure

We sought to elucidate the relationship between diastolic intraventricular pressure gradients (IVPG) and exercise tolerance in patients with heart failure using color M-mode Doppler. Diastolic dysfunction has been implicated as a cause of low aerobic potential in patients with heart failure. We previously validated a novel method to evaluate diastolic function that involves noninvasive measurement of IVPG using color M-mode Doppler data. Thirty-one patients with heart failure and 15 normal subjects were recruited. Echocardiograms were performed before and after metabolic treadmill stress testing. Color M-mode Doppler was used to determine the diastolic propagation velocity ( Vp) and IVPG off-line. Resting diastolic function indexes including myocardial relaxation velocity, Vp, and E/ Vp correlated well with V̇o2 max ( r = 0.8, 0.5, and −0.5, respectively, P < 0.001 for all). There was a statistically significant increase in Vp and IVPG in both groups after exercise, but the change in IVPG was higher in normal subjects compared with patients with heart failure (2.6 ± 0.8 vs. 1.1 ± 0.8 mmHg, P < 0.05). Increase in IVPG correlated with peak V̇o2 max ( r = 0.8, P < 0.001) and was the strongest predictor of exercise capacity. Myocardial relaxation is an important determinant of exercise aerobic capacity. In heart failure patients, impaired myocardial relaxation is associated with reduced diastolic suction force during exercise.

Quantitation of mitral annular oscillations and longitudinal "ringing" of the left ventricle: a new window into longitudinal diastolic function

For diastolic function (DF) quantification, transmitral flow velocity has been characterized in terms of the geometric features of a triangle (heights, widths, areas, durations) approximating the E-wave contour, whereas mitral annular velocity has only been characterized by E'-wave peak amplitude. The fact that E-waves convey global DF information, whereas annular E'-waves provide longitudinal DF information, has not been fully characterized, nor has the physiological legitimacy of combining fluid motion (E)- and tissue motion (E')-derived measurements into routinely used indexes (E/E') been fully elucidated. To place these Doppler echo measurements on a firmer causal, physiological, and clinical basis, we examined features of the E'-wave (and annular motion in general), including timing, amplitude, duration, and contour (shape), in kinematic terms. We derive longitudinal rather than global indexes of stiffness and relaxation of the left ventricle and explain the observed difference between E- and E'-wave durations. On the basis of the close agreement between model prediction and E'-wave contour for subjects having normal physiology, we propose damped harmonic oscillation as the proper paradigm in which to view and analyze the motion of the mitral annulus during early filling. Novel, longitudinal indexes of left ventricular stiffness, relaxation, viscosity, and stored (end-systolic) elastic strain can be determined from the E'-wave (and any subsequent waves) by modeling annular motion during early filling as damped harmonic oscillation. A subgroup exploratory analysis conducted in diabetic subjects (n = 9) and nondiabetic controls (n = 12) indicates that longitudinal DF indexes differentiate between these groups on the basis of longitudinal damping (P < 0.025) and longitudinal stored elastic strain (P < 0.005).