Depression of systolic and diastolic myocardial reserve during atrial pacing tachycardia in patients with dilated cardiomyopathy

Optimizing the Direction and Order of the Motion Unveiled the Ability of Conventional Monolayers of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes to Show Frequency-Dependent Enhancement of Contraction and Relaxation Motion

Contractility of the human heart increases as its beating rate is elevated, so-called positive force-frequency relationship; however, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been reported to exert a negative force-frequency relationship. We tested the hypothesis that the regulation of motion directions by electrical pacing and/or oxygen supply may improve the electro-mechanical properties of hiPSC-CMs monolayers. To better evaluate the spatial and temporal relationship between electrical excitation and contractile motion, we simultaneously observed the field potential and motion vector of hiPSC-CMs sheets. Under spontaneous contraction, although an electrical excitation originating from a region propagated unidirectionally over the cell sheet, contraction wave started from multiple sites, and relaxation wave was initiated from a geometric center of hiPSC-CMs sheet. During electrical pacing, contraction and relaxation waves were propagated from the stimulated site. Interestingly, the maximum contraction speed was more increased when the hiPSC-CMs sheet was stimulated at an area relaxation initiated under spontaneous condition. Furthermore, motion vector analysis demonstrated that "positive contraction velocity-frequency relationship" in contraction and "frequency-dependent enhancement of relaxation" were produced in the cell sheet by optimizing the direction and order of the contractile motion with pacing at the relaxation-initiating area. A close analysis of motion vectors along with field potential recording demonstrated that relaxation process consists of fast and slow phases, and suggest that intracellular Ca²⁺ dynamics may be closely related to functions of Ca²⁺-ATPase pump and Na⁺-Ca²⁺ exchangers. Namely, the slow relaxation phase occurred after the second peak of field potential, suggesting that the slow phase may be associated with extrusion of Ca²⁺ by Na⁺-Ca²⁺ exchangers during repolarization. Increase of oxygen concentration from 20 to 95% as well as β-adrenergic stimulation with isoproterenol accelerated the fast relaxation, suggesting that it could depend on Ca²⁺ uptake via Ca²⁺-ATPase during the depolarization phase. The ratio of maximum contraction speed to field potential duration was increased by the β-adrenergic stimulation, indicating the elevated contraction efficiency per Ca²⁺-influx. Thus, these findings revealed potential ability of conventional monolayers of hiPSC-CMs, which will help apply them to translational study filling the gap between physiological as well as pharmacological studies and clinical practice.

An Augmented Negative Force-Frequency Relationship and Slowed Mechanical Restitution Are Associated With Increased Susceptibility to Drug-Induced Torsade de Pointes Arrhythmias in the Chronic Atrioventricular Block Dog

Introduction: In the chronic AV-block (CAVB) dog model, structural, contractile, and electrical remodeling occur, which predispose the heart to dofetilide-induced Torsade de Pointes (TdP) arrhythmias. Previous studies found a relation between electrical remodeling and inducibility of TdP, while structural remodeling is not a prerequisite for arrhythmogenesis. In this study, we prospectively assessed the relation between in vivo markers of contractile remodeling and TdP inducibility.

Methods: In 18 anesthetized dogs, the maximal first derivative of left ventricular pressure (LV dP/dt_max) was assessed at acute AV-block (AAVB) and after 2 weeks of chronic AV-block (CAVB2). Using pacing protocols, three markers of contractile remodeling, i.e., force-frequency relationship (FFR), mechanical restitution (MR), and post-extrasystolic potentiation (PESP) were determined. Infusion of dofetilide (0.025 mg/kg in 5 min) was used to test for TdP inducibility.

Results: After infusion of dofetilide, 1/18 dogs and 12/18 were susceptible to TdP-arrhythmias at AAVB and CAVB2, respectively (p = 0.001). The inducible dogs at CAVB2 showed augmented contractility at a CL of 1200 ms (2354 ± 168 mmHg/s in inducible dogs versus 1091 ± 59 mmHg/s in non-inducible dogs, p < 0.001) with a negative FFR, while the non-inducible dogs retained their positive FFR. The time constant (TC) of the MR curve was significantly higher in the inducible dogs (158 ± 7 ms versus 97 ± 8 ms, p < 0.0001). Furthermore, a linear correlation was found between a weighted score of the number and severity of arrhythmias and contractile parameters, i.e., contractility at CL of 1200 ms (r = 0.73, p = 0.002), the slope of the FFR (r = -0.58, p = 0.01) and the TC of MR (r = 0.66, p = 0.003). Thus, more severe arrhythmias were seen in dogs with the most pronounced contractile remodeling.

Conclusion: Contractile remodeling is concomitantly observed with susceptibility to dofetilide-induced TdP-arrhythmias. The inducible dogs show augmented contractile remodeling compared to non-inducible dogs, as seen by a negative FFR, higher maximal response of MR and PESP and slowed MR kinetics. These altered contractility parameters could reflect disrupted Ca²⁺ handling and Ca²⁺-overload, which predispose the heart to delayed- and early afterdepolarizations that could trigger TdP-arrhythmias.

Left ventricular long axis tissue Doppler systolic velocity is independently related to heart rate and body size

Background

The physiological factors which affect left ventricular (LV) long-axis function are not fully defined. We investigated the relationships of resting heart rate and body size with the peak velocities and amplitudes of LV systolic and early diastolic long axis motion, and also with long-axis contraction duration.

Methods

Two groups of adults free of cardiac disease underwent pulsed-wave tissue Doppler imaging at the septal and lateral mitral annular borders. Group 1 (n = 77) were healthy subjects <50 years of age and Group 2 (n = 65) were subjects between 40–80 years of age referred for stress echocardiography. Systolic excursion (SExc), duration (SDur) and peak velocity (s') and early diastolic excursion (EDExc) and peak velocity (e') were measured.

Results

SExc was not correlated with heart rate, height or body surface area (BSA) for either LV wall in either group, but SDur was inversely correlated with heart rate for both walls and both groups, and after adjustment for heart rate, males in both groups had a shorter septal SDur. Septal and lateral s` were independently and positively correlated with SExc, heart rate and height in both groups, independent of sex and age. There were no correlations of heart rate, height or BSA with either e` or EDExc for either wall in either group.

Conclusion

Heart rate and height independently modify the relationship between s` and SExc, but neither are related to EDExc or e`. These findings suggest that s` and SExc cannot be used interchangeably for the assessment of LV long-axis contraction.

New and Emerging Therapies and Targets: Beta-3 Agonists

While crucial for the acute physiologic response to stress, the adrenergic system may become maladaptive upon prolonged stimulation in the course of development of heart failure. This has been the basis for the development of beta-blocking therapies, targeting mainly beta1-2 adrenoreceptors (B1-2AR). The third isotype, B3AR, was more recently identified in cardiac myocytes and endothelial cells from human (and many other animal species), where its distinctive coupling to nitric oxide and antioxidant pathways suggested potential protective properties that were unexploited so far. The observation of beneficial effects of B3AR expression/activation on myocardial remodeling and the availability of specific agonists for clinical use now open the way for directly testing the hypothesis in heart failure patients. We will briefly review the specificities of B3AR signaling in the context of the cardiovascular adrenergic system, the evidence supporting its beneficial effects and outline an ongoing clinical trial using the B3AR agonist, mirabegron in patients with/at risk of developing heart failure with preserved ejection fraction (HFpEF).

Does P-Wave Dispersion Predict the Atrial Fibrillation Occurrence After Direct-Current Shock Therapy?

Supraventricular tachycardia attacks, including atrial fibrillation (AF), occur after both external and internal cardioversions. These attacks of atrial fibrillation after direct-current (DC) shock may be related to hemodynamic impairment, thromboembolic events, or enhanced electrical instability of the ventricular and atrial myocardium, especially in predisposed patients. In this study, the authors aimed to show the importance of P-wave dispersion (PWD), which lead the atrium to fibrillate, in predicting post-DC shock AF after external cardioversion. Thus physicians may be able to choose the patients with high risk for AF occurrence and apply some other therapeutic modalities to those patients. The authors identified 18 patients in whom an AF attack was induced by urgent or elective cardioversion for a ventricular tachycardia attack and compared these patients with a control group composed of 40 patients without AF in regard to some clinical, echocardiographic, and electrocardiographic parameters. Left atrial diameters were greater (4.3 ±0.3 vs 3.5 ±0.5 cm, p=0.001), left ventricular ejection fractions (LVEF) were lower (45.2 ±8.2 vs 54.9 ±7.5, p=0.001), the energy needed for successful cardioversion was higher (166.6 ±59.4 vs 80.8 ±51.6 J, p=0.001), and P max (135.2 ±7.4 vs 118.7 ±10.5 ms, p=0.001) and PWD (53.8 ±12.2 vs 23.8 ±9.5 ms, p=0.001) values were higher in patients with AF when compared to those without AF. Thus, the patients with higher PWD values had a greater risk for development of AF after a DC shock.

The relationship between biventricular myocardial performance and metabolic parameters during incremental exercise and recovery in healthy adolescents

Background left ventricular (LV) and right ventricular (RV) myocardial reserve during exercise in adolescents has not been directly characterized. The aim of this study was to quantify myocardial performance response to exercise by using two-dimensional (2-D) speckle tracking echocardiography and describe the relationship between myocardial reserve, respiratory, and metabolic exercise parameters. A total of 23 healthy boys and girls (mean age 13.2 ± 2.7 yr; stature 159.1 ± 16.4 cm; body mass 49.5 ± 16.6 kg; BSA 1.47 ± 0.33 m(2)) completed an incremental cardiopulmonary exercise test (25 W · 3 min increments) with simultaneous acquisition of 2-D transthoracic echocardiography at rest, each exercise stage up to 100 W, and in recovery at 2 min and 10 min. Two-dimensional LV (LV Sl) and RV (RV Sl) longitudinal strain and LV circumferential strain (LV Sc) were analyzed to define the relationship between myocardial performance reserve and metabolic exercise parameters. Participants achieved a peak oxygen uptake (V̇o 2peak) of 40.6 ± 8.9 ml · kg(-1) · min(-1) and a work rate of 154 ± 42 W. LV Sl and LV Sc and RV Sl increased significantly across work rates (P < 0.05). LV Sl during exercise was significantly correlated to resting strain, V̇o 2peak, oxygen pulse, and work rate (0.530 ≤ r ≤ 0.784, P < 0.05). This study identifies a positive and moderate relationship between LV and RV myocardial performance and metabolic parameters during exercise by using a novel methodology. Relationships detected present novel data directly describing myocardial adaptation at different stages of exercise and recovery that in the future can help directly assess cardiac reserve in patients with cardiac pathology.

Resting heart rate and risk of adverse cardiovascular outcomes in asymptomatic aortic stenosis: the SEAS study

BACKGROUND

An elevated resting heart rate (RHR) may be an early sign of cardiac failure, but its prognostic value during watchful waiting in asymptomatic aortic stenosis (AS) is largely unknown.

METHODS

RHR was determined by annual ECGs in the Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) study of asymptomatic mild-to-moderate AS patients. Primary endpoint in this substudy was major cardiovascular events (MCEs) and secondary outcomes its individual components. Multivariable Cox-models using serially-measured RHR were used to examine the prognostic impact of RHR per se.

RESULTS

1563 patients were followed for a mean of 4.3years (6751 patient-years of follow-up), 553 (35%) MCEs occurred, 10% (n=151) died, including 75 cardiovascular deaths. In multivariable analysis, baseline RHR was independently associated with MCEs (HR 1.1 per 10min(-1) faster, 95% CI: 1.0-1.3) and cardiovascular mortality (HR 1.3 per 10min(-1) faster, 95% CI: 1.0-1.7, both p≤0.03). Updating RHR with annual in-study reexaminations, time-varying RHR was highly associated with excess MCEs (HR 1.1 per 10min(-1) faster, 95% CI: 1.1-1.3) and cardiovascular mortality (HR 1.4 per 10min(-1) faster, 95% CI: 1.2-1.7, both p≤0.006). The association of RHR with MCEs and cardiovascular mortality was not dependent on atrial fibrillation status (both p≥0.06 for interaction).

CONCLUSIONS

RHR is independently associated with MCEs and cardiovascular death in asymptomatic AS (Clinicaltrials.gov; unique identifier NCT00092677).

Heart rate-dependent left ventricular diastolic function in patients with and without heart failure

BACKGROUND

Chronic heart rate (HR) reduction in the treatment of heart failure (HF) with systolic dysfunction is beneficial, but the immediate mechanical advantages or disadvantages of altering HR are incompletely understood. We examined the effects of increasing HR on early and late diastole in humans with and without HF.

METHODS AND RESULTS

We studied force-interval relationships of the left ventricle (LV) in 11 HF patients and 14 control subjects. HR was controlled by right atrial pacing, and LV pressure was recorded by a micromanometer-tipped catheter. The time constant of isovolumic relaxation (tau) was calculated, and simultaneous sonographic images were analyzed for LV volumes. The end-diastolic pressure-volume relationship (EDPVR) was analyzed with the use of a single-beat method. Tau was shortened in response to increasing HR in both groups; the slope of this relationship was steeper in HF than in control subjects. The predicted volume at a theoretic pressure of 0 mm Hg (V30) increased at higher HRs compared with baseline, shifting the predicted EDPVR compliance curve to the right in HF patients but not in control subjects.

CONCLUSIONS

In HF, changes in HR affect early relaxation and diastolic compliance to a greater extent than in control subjects. Our study reinforces current recommendations for HR-lowering drug treatment in HF.

Preliminary observations of prognostic value of left atrial functional reserve during dobutamine infusion in patients with dilated cardiomyopathy

BACKGROUND

The importance of left atrial (LA) functional reserve in patients with depressed left ventricular function remains unclear. Thus, the aim of this study was to test the hypothesis that diminished augmentation of LA function during dobutamine stress might be associated with cardiovascular events in patients with dilated cardiomyopathy.

METHODS

Eighty-four patients with dilated cardiomyopathy with a mean ejection fraction of 34 ± 9% were retrospectively recruited, and LA strain was determined as the averaged global speckle-tracking longitudinal strain from apical four-chamber and two-chamber views during dobutamine stress (20 μg/kg/min). The systolic component of LA strain was considered to reflect reservoir function, whereas the passive and active emptying components were considered to reflect passive and active emptying function, respectively. Event-free survival was tracked for 17 months.

RESULTS

Multivariate Cox proportional-hazards analysis identified LA volume index (hazard ratio [HR], 1.060; P < .001) and β-blocker use (HR, 0.048; P < .05) as the independent variables associated with cardiovascular events among the baseline parameters and changes in systolic LA strain (HR, 0.971; P = .02), in passive emptying LA strain (HR, 0.942; P < .001), and in left ventricular early diastolic strain rate (HR, 0.986; P = .03) under dobutamine as the variables among the functional reserve parameters. In sequential Cox models, a model based on clinical variables (χ(2) = 9.3) was improved by conventional echocardiographic parameters (χ(2) = 19.2, P = .012) and LA strain parameters at rest (χ(2) = 40.1, P = .005) and further improved by the addition of changes in LA strain parameters under dobutamine (χ(2) = 61.6, P < .001).

CONCLUSIONS

The assessment of LA reservoir and passive emptying function during dobutamine stress provides important incremental prognostic value in patients with dilated cardiomyopathy.

Left ventricular contractile reserve after arterial switch operation for complete transposition of the great arteries: an exercise echocardiographic study

AIMS

This study tested the hypothesis that left ventricular (LV) contractile reserve is altered in patients after arterial switch operation (ASO) for complete transposition of the great arteries (TGA) by non-invasive determination of LV force-frequency relationship (FFR).

METHODS AND RESULTS

Thirty-two patients aged 16.2 ± 2.1 years and 22 healthy controls were studied. M-mode parameters, transmitral early (E) and late (A) diastolic velocities, and tissue Doppler-derived systolic (sm), early (em), and late (am) diastolic mitral annular velocities were determined at baseline and during submaximal exercise testing. The LV myocardial isovolumic acceleration (IVA) was measured at different heart rates during exercise for derivation of LV FFR and the average slope of IVA increment with heart rate. At baseline, patients had significantly greater E velocity, E/A and E/em ratios, shorter E deceleration time, and reduced mitral annular sm, em, and am velocities (all P < 0.05), but similar IVA (P = 0.29) compared with controls. During exercise, sm and em remained significantly reduced (P < 0.001), and LV IVA became lower (P < 0.001) in patients. The average FFR slope was significantly lower in patients (0.039 ± 0.019 vs. 0.070 ± 0.024 m/s(2) bpm, P < 0.001). The weighted average FFR curve of patients was flattened compared with the reported positive FFR reference curve based on a healthy paediatric cohort (P < 0.0001). Patients with variant compared with those with usual coronary arterial anatomy had significant flattening of FFR (P < 0.001) and a reduced FFR slope (P = 0.007).

CONCLUSION

In adolescents and young adults after ASO, exercise stress revealed reduced LV contractile reserve, which is worse in those having variant coronary arterial anatomy.

Development of dilated cardiomyopathy in Bmal1-deficient mice

Circadian rhythms are approximate 24-h oscillations in physiology and behavior. Circadian rhythm disruption has been associated with increased incidence of hypertension, coronary artery disease, dyslipidemia, and other cardiovascular pathologies in both humans and animal models. Mice lacking the core circadian clock gene, brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein (Bmal1), are behaviorally arrhythmic, die prematurely, and display a wide range of organ pathologies. However, data are lacking on the role of Bmal1 on the structural and functional integrity of cardiac muscle. In the present study, we demonstrate that Bmal1(-/-) mice develop dilated cardiomyopathy with age, characterized by thinning of the myocardial walls, dilation of the left ventricle, and decreased cardiac performance. Shortly after birth the Bmal1(-/-) mice exhibit a transient increase in myocardial weight, followed by regression and later onset of dilation and failure. Ex vivo working heart preparations revealed systolic ventricular dysfunction at the onset of dilation and failure, preceded by downregulation of both myosin heavy chain isoform mRNAs. We observed structural disorganization at the level of the sarcomere with a shift in titin isoform composition toward the stiffer N2B isoform. However, passive tension generation in single cardiomyocytes was not increased. Collectively, these findings suggest that the loss of the circadian clock gene, Bmal1, gives rise to the development of an age-associated dilated cardiomyopathy, which is associated with shifts in titin isoform composition, altered myosin heavy chain gene expression, and disruption of sarcomere structure.

Overdrive ventricular pacing in pacemaker recipients with permanent atrial fibrillation and sleep apnea

STUDY OBJECTIVES

Cardiac pacing is ineffective in obstructive sleep apnea (SA), but it can alleviate central SA/Cheyne-Stokes respiration (CSA) in patients with heart failure (HF). We examined whether overnight overdrive ventricular pacing (OVP) has an effect on SA in pacemaker recipients with permanent atrial fibrillation (AF).

METHODS

An apnea-hypopnea index (AHI) ≥ 15 was confirmed in 28/38 patients screened by finger pulse oximetry during overnight ventricular pacing at a backup rate of 40 bpm (BUV40). These patients (23 men, 77.9 ± 7.6 y, BMI 27.6 ± 5.1 kg/m(2)) were randomly assigned to 2 consecutive nocturnal ventilation polygraphies with BUV40 versus OVP at 20 bpm above the mean nocturnal heart rate observed during screening.

RESULTS

During BUV40 versus OVP, (1) mean heart rate was 49 ± 8 versus 71 ± 8 bpm (p < 0.0001) and percent ventricular pacing 36% ± 38% versus 96% ± 6% (p < 0.0001); (2) AHI was 35.4 ± 11.9 versus 32.5 ± 15.5 (p = ns), central AHI 23.9 ± 11.8 versus 19.1 ± 12.7 (p < 0.001), and obstructive AHI 11.6 ± 13.1 versus 13.5 ± 15.9 (p = ns). In 15/28 patients without HF, mean left ventricular ejection fraction (LVEF) was 51% ± 17%, AHI was 37.6 ± 11.0 during BUV40 and 39.0 ± 11.5 during OVP, versus 32.8 ± 12.9 and 24.9 ± 16.5 in 13/28 patients with HF (p = 0.02) and mean LVEF 35% ± 15% (p = 0.01). Between the 2 subgroups, (1) central AHI was 23.6 ± 12.4 during BUV40 and 21.5 ± 14.0 during OVP versus 24.1 ± 11.6 and 16.2 ± 10.7 (p = 0.05); (2) obstructive AHI was 14.0 ± 13.7 during BUV40 and 17.6 ± 16.5 during OVP versus 8.8 ± 12.3 and 8.7 ± 14.3 (p = ns).

CONCLUSIONS

The prevalence of SA, predominantly central, was high in our pacemaker recipients with permanent AF. In those with HF, a single overnight OVP resulted in modest improvement in central events.

Remodeling of calcium handling in human heart failure

Heart failure (HF) is an increasing public health problem accelerated by a rapidly aging global population. Despite considerable progress in managing the disease, the development of new therapies for effective treatment of HF remains a challenge. To identify targets for early diagnosis and therapeutic intervention, it is essential to understand the molecular and cellular basis of calcium handling and the signaling pathways governing the functional remodeling associated with HF in humans. Calcium (Ca(2+)) cycling is an essential mediator of cardiac contractile function, and remodeling of calcium handling is thought to be one of the major factors contributing to the mechanical and electrical dysfunction observed in HF. Active research in this field aims to bridge the gap between basic research and effective clinical treatments of HF. This chapter reviews the most relevant studies of calcium remodeling in failing human hearts and discusses their connections to current and emerging clinical therapies for HF patients.

Aortic wave dynamics and its influence on left ventricular workload

The pumping mechanism of the heart is pulsatile, so the heart generates pulsatile flow that enters into the compliant aorta in the form of pressure and flow waves. We hypothesized that there exists a specific heart rate at which the external left ventricular (LV) power is minimized. To test this hypothesis, we used a computational model to explore the effects of heart rate (HR) and aortic rigidity on left ventricular (LV) power requirement. While both mean and pulsatile parts of the pressure play an important role in LV power requirement elevation, at higher rigidities the effect of pulsatility becomes more dominant. For any given aortic rigidity, there exists an optimum HR that minimizes the LV power requirement at a given cardiac output. The optimum HR shifts to higher values as the aorta becomes more rigid. To conclude, there is an optimum condition for aortic waves that minimizes the LV pulsatile load and consequently the total LV workload.

Role of CaMKIIdelta phosphorylation of the cardiac ryanodine receptor in the force frequency relationship and heart failure

The force frequency relationship (FFR), first described by Bowditch 139 years ago as the observation that myocardial contractility increases proportionally with increasing heart rate, is an important mediator of enhanced cardiac output during exercise. Individuals with heart failure have defective positive FFR that impairs their cardiac function in response to stress, and the degree of positive FFR deficiency correlates with heart failure progression. We have identified a mechanism for FFR involving heart rate dependent phosphorylation of the major cardiac sarcoplasmic reticulum calcium release channel/ryanodine receptor (RyR2), at Ser2814, by calcium/calmodulin-dependent serine/threonine kinase-delta (CaMKIIdelta). Mice engineered with an RyR2-S2814A mutation have RyR2 channels that cannot be phosphorylated by CaMKIIdelta, and exhibit a blunted positive FFR. Ex vivo hearts from RyR2-S2814A mice also have blunted positive FFR, and cardiomyocytes isolated from the RyR2-S2814A mice exhibit impaired rate-dependent enhancement of cytosolic calcium levels and fractional shortening. The cardiac RyR2 macromolecular complexes isolated from murine and human failing hearts have reduced CaMKIIdelta levels. These data indicate that CaMKIIdelta phosphorylation of RyR2 plays an important role in mediating positive FFR in the heart, and that defective regulation of RyR2 by CaMKIIdelta-mediated phosphorylation is associated with the loss of positive FFR in failing hearts.

The restoration of chronotropic competence in heart failure patients with normal ejection fraction (RESET) study: rationale and design

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is the predominant form of heart failure among the elderly and in women. However, there are few if any evidence-based therapeutic options for HFpEF. The chief complaint of HFpEF is reduced tolerance to physical exertion. Recent data revealed that 1 potential mechanism of exertional intolerance in HFpEF patients is inadequate chronotropic response. Although there is considerable evidence demonstrating the benefits of rate-adaptive pacing (RAP) provided from implantable cardiac devices in patients with an impaired chronotropic response, the effect of RAP in HFpEF is unknown.

METHODS AND RESULTS

The Restoration of Chronotropic CompEtence in Heart Failure PatientS with Normal Ejection FracTion (RESET) study is a prospective, multicenter, double-blind, randomized with stratification, study assessing the effect of RAP on peak oxygen consumption and quality of life. RAP therapy will be evaluated in a crossover paired fashion for each patient within each study stratum. Study strata are based on patient beta-blocker usage at time of enrollment. The study is powered to assess the impact of pacing independently in both strata.

CONCLUSIONS

The RESET study seeks to evaluate the potential benefit of RAP in patients with symptomatic mild to moderate HFpEF and chronotropic impairment. Study enrollment began in July 2008.

Spontaneous calcium release in tissue from the failing canine heart

Abnormalities in calcium handling have been implicated as a significant source of electrical instability in heart failure (HF). While these abnormalities have been investigated extensively in isolated myocytes, how they manifest at the tissue level and trigger arrhythmias is not clear. We hypothesize that in HF, triggered activity (TA) is due to spontaneous calcium release from the sarcoplasmic reticulum that occurs in an aggregate of myocardial cells (an SRC) and that peak SCR amplitude is what determines whether TA will occur. Calcium and voltage optical mapping was performed in ventricular wedge preparations from canines with and without tachycardia-induced HF. In HF, steady-state calcium transients have reduced amplitude [135 vs. 170 ratiometric units (RU), P < 0.05] and increased duration (252 vs. 229 s, P < 0.05) compared with those of normal. Under control conditions and during beta-adrenergic stimulation, TA was more frequent in HF (53% and 93%, respectively) compared with normal (0% and 55%, respectively, P < 0.025). The mechanism of arrhythmias was SCRs, leading to delayed afterdepolarization-mediated triggered beats. Interestingly, the rate of SCR rise was greater for events that triggered a beat (0.41 RU/ms) compared with those that did not (0.18 RU/ms, P < 0.001). In contrast, there was no difference in SCR amplitude between the two groups. In conclusion, TA in HF tissue is associated with abnormal calcium regulation and mediated by the spontaneous release of calcium from the sarcoplasmic reticulum in aggregates of myocardial cells (i.e., an SCR), but importantly, it is the rate of SCR rise rather than amplitude that was associated with TA.

Cardiac resynchronization therapy and atrial overdrive pacing for the treatment of central sleep apnoea

AIMS

The combined therapeutic impact of atrial overdrive pacing (AOP) and cardiac resynchronization therapy (CRT) on central sleep apnoea (CSA) in chronic heart failure (CHF) so far has not been investigated. We aimed to evaluate the effect of CRT alone and CRT + AOP on CSA in CHF patients and to compare the influence of CRT on CHF between CSA positive and CSA negative patients.

METHODS AND RESULTS

Thirty patients with CRT indication underwent full night polysomnography, echocardiography, exercise testing, and neurohumoral evaluation before and 3 months after CRT implantation. In CSA positive patients (60%), two additional sleep studies were conducted after 3 months of CRT, with CRT alone or CRT + AOP, in random order. Cardiac resynchronization therapy resulted in significant improvements of NYHA class, left ventricular ejection fraction, N-terminal pro-brain natriuretic peptide, VO(2)max, and quality of life irrespective of the presence of CSA. Cardiac resynchronization therapy also reduced the central apnoea-hypopnoea index (AHI) (33.6 +/- 14.3 vs. 23.8 +/- 16.9 h(-1); P < 0.01) and central apnoea index (17.3 +/- 14.1 vs. 10.9 +/- 13.9 h(-1); P < 0.01) without altering sleep stages. Cardiac resynchronization therapy with atrial overdrive pacing resulted in a small but significant additional decrease of the central AHI (23.8 +/- 16.9 vs. 21.5 +/- 16.9 h(-1); P < 0.01).

CONCLUSION

In this study, CRT significantly improved CSA without altering sleep stages. Cardiac resynchronization therapy with atrial overdrive pacing resulted in a significant but minor additional improvement of CSA. Positive effects of CRT were irrespective of the presence of CSA.

From Bowditch to beta-blockers: evolution of the understanding of the importance of heart rate and myocardial energetics in cardiomyopathy - with reference to : a comparison of stimulation frequency and electro-augmentation on myocardial function, extensibility, coronary flow rate, oxygen consumption and glucose metabolism

During the past three decades, every aspect of cardiomyopathy has undergone dramatic change. When examining the literature on the physiological aspects of the failing heart, one immediately recognises that South Africa has made a contribution: Brink, Bester and Lochner evaluated the possible therapeutic aspects of the Bowditch phenomenon and myocardial energetics in cardiomyopathy almost four decades ago, at a time when the condition even had another name, myocardiopathy.

Negative stress echo: Further prognostic stratification with assessment of pressure–volume relation

BACKGROUND

A maximal negative stress echo identifies a low risk for subsequent hard events subset. However, the potentially prognostically relevant information on global contractile reserve on the left ventricle is missed by standard regional wall motion assessment, and can be obtained by end-systolic pressure-volume relationship (PVR) evaluation.

AIM

To assess the relative prognostic value of PVR in patients with negative stress echo.

METHODS

We enrolled 99 consecutive patients (age=61+/-14 years; 81 males, LVEF 47+/-14%, WMSI=1.42+/-0.50) with negative exercise stress echo for standard wall motion criteria. To build the PVR, the force was determined at rest and peak stress as the ratio of the systolic pressure/end-systolic volume index. All patients were followed-up on medical therapy.

RESULTS

Median follow-up was 21 months (interquartile range 12-26). Twenty-nine events have been observed: 6 deaths, 10 heart failure related hospitalization and 13 worsening NYHA class of >or=1 grade. Using Cox's proportional hazard model the best independent predictor of total events was SP/ESV index change (rest-stress) <1.5 mm Hg/ml/m(2) as determined by ROC analysis cut-off (RR=29, p=0.001, sensitivity=80%, specificity=93%). The overall survival and event-free survival was 34% in patients with change (rest-stress) SP/ESV index<1.5 mm Hg/ml/m(2) and 97% in whose with >1.5 mm Hg/ml/m(2).

CONCLUSIONS

In patients with negative stress echo, a preserved global contractility response can be easily identified through stress-induced variation in SP/ESV index, with powerful further risk stratification.

Prognostic value of left-ventricular and peripheral vascular performance in patients with dilated cardiomyopathy

BACKGROUND

The goal of the heart during exercise is to increase cardiac output to metabolizing tissues. Our aim was to assess the relative role of systolic versus diastolic dysfunction in modulating cardiac output in patients with idiopathic left-ventricular (LV) dysfunction.

METHODS

We enrolled 51 patients (LV ejection fraction, mean +/- SD, = 36% +/- 9%) and 24 controls with a normal LV ejection fraction. All were scheduled for exercise radionuclide angiography for the evaluation of LV functional reserve, and were followed for a median of 129 months.

RESULTS

Stroke volume increased in control subjects mainly through a decrease in end-systolic volume, while it increased in patients through an increase in end-diastolic volume (EDV), albeit heterogeneously. Patients were divided into group I, with stroke volume increase, versus group II, without stroke volume increase, during stress. Despite similar blunted inotropic reserves, group I showed a decrease in arterial elastance during stress: a better ventricular-arterial coupling occurred, leading to increased cardiac efficiency. At long-term follow-up, the overall event-free survival was 88% in group I, compared with 61% for group II (log rank = 4.7, P = .03).

CONCLUSIONS

In the presence of idiopathic LV dysfunction, a preserved LV pumping reserve can be identified easily through stress-induced variations in the EDV and stroke volume, with a powerful, long-term death-risk stratification.

Impact of heart rate on mechanical dyssynchrony and left ventricular contractility in patients with heart failure and normal QRS duration

AIMS

The quantification of mechanical dyssynchrony has important diagnostic value and may help to determine optimal therapy in heart failure (HF). We hypothesized that mechanical dyssynchrony may be augmented at increased heart rates in patients with HF and normal QRS duration.

METHODS AND RESULTS

From online segmental conductance catheter signals, we derived indices to quantify temporal and spatial aspects of mechanical dyssynchrony during systole in 20 control subjects, 20 HF patients with normal QRS duration, and 12 HF patients with complete left bundle branch block (CLBBB). Data were collected at baseline, and then following a 40 bpm increase in heart rate induced by right atrial pacing. Mechanical dyssynchrony in HF patients with normal QRS duration or CLBBB was higher than that found in control subjects. In HF patients with normal QRS duration, mechanical dyssynchrony increased from 37.4+/-4.8% at baseline to 43.2+/-4.4% with increased heart rate (p<0.01), the resultant degree of mechanical dyssynchrony was similar to that at baseline in the HF patients with CLBBB. Increased heart rate did not affect dyssynchrony in the control patients.

CONCLUSION

Mechanical dyssynchrony was augmented as heart rate increased by right atrial pacing in patients with HF and normal QRS duration.

Direct myocardial effects of levosimendan in humans with left ventricular dysfunction: alteration of force-frequency and relaxation-frequency relationships

BACKGROUND

Enthusiasm for the development of Ca2+ sensitizers as inotropic agents for heart failure has been tempered by reports of impaired relaxation. Levosimendan, which increases myofilament Ca2+ sensitivity via Ca2+-dependent binding to troponin C, exerts positive inotropic and lusitropic effects in failing human myocardium in vitro. We sought to determine the direct effects of levosimendan on failing human myocardium in vivo, and in particular whether levosimendan exerts heart rate-dependent effects on systolic or diastolic function.

METHODS AND RESULTS

Ten patients with left ventricular dysfunction caused by nonischemic dilated cardiomyopathy (mean left ventricular ejection fraction, 27+/-2%) were instrumented with an infusion catheter in the left main coronary artery, a high-fidelity micromanometer-tipped catheter in the left ventricle, and a bipolar pacing wire in the right atrium. Inotropic (peak +dP/dt) and lusitropic (Tau) responses were assessed during continuous intracoronary drug infusion in sinus rhythm followed by atrial pacing at 20, 40, and 60 beats per minute above the sinus rate. Under control conditions (intracoronary 5% dextrose in water), atrial-pacing tachycardia decreased Tau by 13% (P<0.05), but did not increase +dP/dt. Intracoronary levosimendan (3.75 and 12.5 microg/min for 15 minutes each) increased +dP/dt dose-dependently and decreased Tau over a range of heart rates, but did not alter the slope of the force-frequency or relaxation-frequency relationship.

CONCLUSIONS

Myocardial calcium sensitization with levosimendan exerts mild inotropic and lusitropic effects in humans with left ventricular dysfunction, but does not alter the force-frequency or relaxation-frequency relationship.

Novel means to monitor cardiac performance: the impact of the force-frequency and force-interval relationships on recirculation fraction and potentiation ratio

Insights into intracellular calcium regulation and contractile state can be accomplished by changing pacing rate. Steady-state increases in heart rate (HR) (force-frequency relationship, FFR), and introduction of extrasystoles (ES) (force-interval relationship, FIR) have been used to investigate this relationship. This study focused on the recirculation fraction (RF) and potentiation ratio (PR), obtained from the recovery of the FFR and FIR. These parameters may provide insight on intracellular Ca(2+) regulation. Left ventricular (LV) pressures and HR were assessed in anesthetized canines (n = 7). Intrinsic data were collected prior to and following HR increases to 150, 180, and 200 bpm, as well as following delivery of an ES at 280 ms. The RF was calculated as the slope of dP/dt(max(n + 1)) vs. dP/dt(max(n)), where n = beat number. The PR was calculated by normalizing dP/dt(max) from the first beat following the ES (or the last paced beat) to the steady-state dP/dt(max). The RF due to an ES was not significantly different than that from a HR of 200 bpm. The PR from an ES was not significantly different than from a HR of 150 bpm. The impact of an ES delivered at an interval of 280 ms produces a PR similar to that from a HR of 150 bpm; yet, it recovers similarly to the termination of pacing at 200 bpm, eliciting a similar RF value. The method of measuring RF by an ES versus an increased HR may provide a safer and more feasible approach to collecting diagnostic information.

Force- and relaxation-frequency relations in patients with diastolic heart failure

BACKGROUND

Chronotropic effects on myocardial contractility (the positive force-frequency relation) and relaxation (the positive relaxation-frequency relation) are impaired in patients with congestive heart failure and depressed left ventricular (LV) ejection fraction (systolic heart failure [SHF]). However, the force- and relaxation-frequency relation and LV-arterial coupling in patients with diastolic heart failure (DHF) has not been fully investigated.

METHODS AND RESULTS

To examine inotropic and lusitropic responsiveness to atrial pacing, LV pressure-volume relations were measured using a conductance catheter and microtip manometer in patients with DHF (n = 18) and SHF (n = 11). In patients with SHF, an increase in heart rate by 40 beat/min did not affect LV end-systolic elastance (Ees), which reflects LV contractility, or the time constant of LV relaxation. By contrast, in patients with DHF, an increase in heart rate by 40 beat/min significantly enhanced Ees (2.1 vs 2.9 mm Hg/mL, P < .05) but not the time constant. Furthermore, LV-arterial coupling, quantified as Ees/arterial elastance, was impaired during pacing in patients with DHF (1.1 vs 0.8, P < .05) as well as SHF.

CONCLUSIONS

In patients with DHF, the force-frequency relation was preserved, but the relaxation-frequency relation was impaired. Furthermore, LV-arterial coupling was impaired as heart rate increased, which may be related to the impaired LV function. These results suggest that the impaired relaxation-frequency relation and exacerbated LV-arterial coupling during tachycardia may be an important therapeutic target in patients with DHF.

Cardiac Rest and Reserve Function in Patients With Fontan Circulation

OBJECTIVES

In the present study, we systematically tested cardiac rest and reserve function in patients with Fontan physiology to check for inherent limitations of this circulation.

BACKGROUND

Details of the mechanisms of cardiac performance that could account for adverse outcome after Fontan surgery are not well understood.

METHODS

The subjects were 17 Fontan patients with good functional status (Fontan group) and 20 patients with normal two-ventricle circulation (control group). We examined baseline ventricular contractility, diastolic function, and loading factors, and examined changes in those parameters in response to increased heart rate (HR) due to atrial pacing and in response to beta-adrenergic stimulation, using ventricular pressure-area relationships during preload reduction.

RESULTS

At baseline, the Fontan patients exhibited minimal abnormality of cardiac properties, but the significant increase in afterload resulted in decreased cardiac index. In addition, Fontan circulation was associated with limited inotropic response and worsening of diastolic filling with increased HR, leading to decreased systolic pressure and elevation of central venous pressure at higher HRs (p < 0.05 vs. control). Furthermore, beta-adrenergic reserve was markedly decreased in the Fontan group, compared with controls, owing to limited preload reserve rather than limited contractile reserve.

CONCLUSIONS

Because normal ventricular-vascular interaction and augmentation of cardiac performance during increased HR and adrenergic stimulation are important for maintaining cardiac output and exercise capacity, the present results may have important implications for the mechanisms underlying adverse outcome after Fontan surgery. Thus, improvement of long-term prognosis of patients after Fontan surgery requires the development of medical interventions that can overcome such limitations inherent in Fontan circulation.

Biventricular Pacing Improves the Blunted Force–Frequency Relation Present During Univentricular Pacing in Patients With Heart Failure and Conduction Delay

Background— In patients with chronic heart failure (CHF) and conduction delay, biventricular (BiV) and left ventricular (LV) pacing similarly improve systolic function at resting heart rates. We hypothesized that BiV and univentricular pacing differentially affect contractile function at increasing heart rates.

Methods and Results— Twenty-two patients (aged 66±2 years, QRS 179±8 ms, LV ejection fraction 23±1%) underwent cardiac catheterization before device implantation to measure LV hemodynamics at baseline (rate 68±2 bpm; sinus rhythm n=18; atrial fibrillation n=4) and during BiV, LV, and right ventricular (RV) stimulation at 80, 100, 120, and 140 bpm. BiV and LV pacing at 80 bpm equally augmented dP/dt max as compared with baseline and RV pacing ( P <0.001). Stimulation rate significantly interacted with the effect of BiV, LV, and RV pacing on LV end-diastolic pressure (LVEDP), systolic pressure (LVSP), and dP/dt max . Increasing the rate from 80 to 140 bpm enhanced dP/dt max from 913±28 to 1119±50 mm Hg/s during BiV stimulation ( P <0.001) but had no significant effect on contractility during single-site LV (951±47 versus 1002±54 mm Hg/s) or RV (800±46 versus 881±49 mm Hg/s) pacing. At 140 bpm, LVEDP was lower and LVSP higher during BiV pacing than during RV and LV pacing (LVEDP 12±1 versus 17±1 and 16±1 mm Hg, P <0.001; LVSP 112±5 versus 106±5 and 108±6 mm Hg, P <0.01 and P =0.09; BiV versus RV and LV pacing, respectively).

Conclusions— Different modes of ventricular stimulation alter the in vivo force–frequency relation of CHF patients. In contrast to single-site LV and RV pacing, contractile function improves with increasing heart rates during BiV stimulation. This effect may contribute to the enhanced exercise capacity during BiV pacing and could provide a functional benefit over LV-only pacing in patients for whom resynchronization therapy is indicated.

CaMKII tethers to L-type Ca2+ channels, establishing a local and dedicated integrator of Ca2+ signals for facilitation

Ca²⁺-dependent facilitation (CDF) of voltage-gated calcium current is a powerful mechanism for up-regulation of Ca²⁺ influx during repeated membrane depolarization. CDF of L-type Ca²⁺ channels (Ca_v1.2) contributes to the positive force–frequency effect in the heart and is believed to involve the activation of Ca²⁺/calmodulin-dependent kinase II (CaMKII). How CaMKII is activated and what its substrates are have not yet been determined. We show that the pore-forming subunit α_1C (Ca_vα1.2) is a CaMKII substrate and that CaMKII interaction with the COOH terminus of α_1C is essential for CDF of L-type channels. Ca²⁺ influx triggers distinct features of CaMKII targeting and activity. After Ca²⁺-induced targeting to α_1C, CaMKII becomes tightly tethered to the channel, even after calcium returns to normal levels. In contrast, activity of the tethered CaMKII remains fully Ca²⁺/CaM dependent, explaining its ability to operate as a calcium spike frequency detector. These findings clarify the molecular basis of CDF and demonstrate a novel enzymatic mechanism by which ion channel gating can be modulated by activity.

Cardiac sympathetic dysfunction correlates with abnormal myocardial contractile reserve in dilated cardiomyopathy patients

OBJECTIVES

We investigated the relationship between iodine-123-metaiodobenzylguanidine (123I-MIBG) findings and myocardial contractile reserve in patients with mild to moderate dilated cardiomyopathy (DCM).

BACKGROUND

Little is known regarding the relationship between cardiac sympathetic nervous function and myocardial contractile reserve in DCM.

METHODS

Twenty-four DCM patients who showed sinus rhythm underwent echocardiography, biventricular catheterization, and myocardial 123I-MIBG scintigraphy. Left ventricular (LV) pressures were measured using a micromanometer-tipped catheter. The myocardial contractile function (LV dP/dt(max)) was determined at rest and during atrial pacing. The messenger ribonucleic acid (mRNA) expressions of intracellular Ca2+-regulatory proteins were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. Myocardial 123I-MIBG accumulation was quantified as a heart-mediastinum ratio (HMR).

RESULTS

A significant correlation was observed between the delayed 123I-MIBG HMR and the percentage change in LV dP/dt(max) from the baseline to the peak or critical heart rate (r = 0.64; p < 0.001). The delayed 123I-MIBG HMR was significantly lower in patients showing a worsening change in LV dP/dt(max) than in those showing a favorable change (p < 0.005). The maximum LV dP/dt(max) during pacing and the sarcoplasmic reticulum Ca2+-ATPase (SERCA2) mRNA levels were significantly more reduced in patients with a delayed HMR < or =1.8 than in those with a delayed HMR >1.8 (p < 0.05, respectively).

CONCLUSIONS

Abnormal myocardial 123I-MIBG accumulation is related to an impaired myocardial contractile reserve and down-regulation of SERCA2 mRNA in DCM. Myocardial 123I-MIBG scintigraphy can be useful in noninvasively evaluating myocardial contractile reserve in patients with mild to moderate DCM.

Myocardial contractility in the echo lab: molecular, cellular and pathophysiological basis

In the standard accepted concept, contractility is the intrinsic ability of heart muscle to generate force and to shorten, independently of changes in the preload or afterload with fixed heart rates. At molecular level the crux of the contractile process lies in the changing concentrations of Ca²⁺ ions in the myocardial cytosol. Ca²⁺ ions enter through the calcium channel that opens in response to the wave of depolarization that travels along the sarcolemma. These Ca²⁺ ions "trigger" the release of more calcium from the sarcoplasmic reticulum (SR) and thereby initiate a contraction-relaxation cycle.

In the past, several attempts were made to transfer the pure physiological concept of contractility, expressed in the isolated myocardial fiber by the maximal velocity of contraction of unloaded muscle fiber (Vmax), to the in vivo beating heart. Suga and Sagawa achieved this aim by measuring pressure/volume loops in the intact heart: during a positive inotropic intervention, the pressure volume loop reflects a smaller end-systolic volume and a higher end-systolic pressure, so that the slope of the pressure volume relationship moves upward and to the left. The pressure volume relationship is the most reliable index for assessing myocardial contractility in the intact circulation and is almost insensitive to changes in preload and after load. This is widely used in animal studies and occasionally clinically. The limit of the pressure volume relationship is that it fails to take into account the frequency-dependent regulation of contractility: the frequency-dependent control of transmembrane Ca²⁺ entry via voltage-gated Ca2⁺ channels provides cardiac cells with a highly sophisticated short-term system for the regulation of intracellular Ca²⁺ homeostasis. An increased stimulation rate increases the force of contraction: the explanation is repetitive Ca²⁺ entry with each depolarization and, hence, an accumulation of cytosolic calcium. As the heart fails, there is a change in the gene expression from the normal adult pattern to that of fetal life with an inversion of the normal positive slope of the force-frequency relation: systolic calcium release and diastolic calcium reuptake process is lowered at the basal state and, instead of accelerating for increasing heart rates, slows down. Since the force-frequency relation uncovers initial alteration of contractility, as an intermediate step between normal and abnormal contractility at rest, a practical index to measure it is mandatory.

Measuring end-systolic elastance for increasing heart rates is impractical: increasing heart rates with atrial pacing has to be adjunct to the left ventricular conductance catheter, to the left ventricular pressure catheter, to the vena cava balloon, and to afterload changes. Furthermore, a noninvasive index is needed. Noninvasive measurement of the pressure/volume ratio for increasing heart rates during stress in the echo lab could be the practical answer to this new clinical demand in the current years of a dramatic increase in the number of heart failure patients.

Atrial overdrive pacing compared to CPAP in patients with obstructive sleep apnoea syndrome

AIMS

Obstructive sleep apnoea (OSA) is associated with oxygen desaturation, blood pressure increase, and neurohumoral activation, resulting in possible detrimental effects on the cardiovascular system. Continuous positive airway pressure (CPAP) is the therapy of choice for OSA. In a recent study, nocturnal atrial overdrive pacing (pacing) reduced the severity of sleep apnoea in pacemaker patients. We compared the effects of CPAP with those of pacing in patients with OSA but without pacemaker indication or clinical signs of heart failure.

METHODS AND RESULTS

Ten patients with OSA on CPAP therapy were studied for three nights by polysomnography. During the nights that followed a night without any treatment (baseline), the patients were treated with CPAP or pacing in a random order. Pacing was performed with a temporary pacing lead. The pacing frequency was 15 b.p.m. higher than the baseline heart rate. The apnoea-hypopnoea index was 41.0 h(-1) (12.0-66.6) at baseline and was significantly lower during CPAP [2.2 h(-1) (0.3-12.4)] compared with pacing [39.1 h(-1) (8.2-78.5)]. Furthermore, duration and quality of sleep were significantly improved during CPAP when compared with pacing.

CONCLUSION

Nocturnal atrial overdrive pacing is no alternative therapeutic strategy to CPAP for the treatment of OSA in patients without clinical signs of heart failure and without conventional indication for anti-bradycardia pacing.

End-systolic pressure/volume relationship during dobutamine stress echo: a prognostically useful non-invasive index of left ventricular contractility

AIMS

Left ventricular end-systolic pressure-volume relationship (PVR) provides a robust, relatively load-insensitive evaluation of contractility and can be assessed non-invasively during exercise echo. Dobutamine might provide an exercise-independent alternative approach to assess inotropic reserve. The feasibility of a non-invasive estimation of PVR during dobutamine stress in the echo lab and its relationship with subsequent clinical events was assessed.

METHODS AND RESULTS

We enrolled 137 consecutive patients referred for dobutamine stress echo. To build the PVR, the force was determined at different heart rate increments during stepwise dobutamine infusion as the ratio of the systolic pressure/end-systolic volume index. The PVR at increasing heart rate was flat-biphasic in 65 and up-sloping in 72 patients: 42 patients underwent surgery and 95 patients were treated medically (median follow-up, 18 months; interquartile range, 12-24). Events occurred in 18 patients (death in eight, acute heart failure in 10); a flat-biphasic PVR was independent predictor of events (RR=10.16, P<0.01).

CONCLUSION

PVR is feasible during dobutamine stress. This index of global contractility is reasonably simple, does not affect the imaging time, and only minimally prolongs the off-line analysis time. It allows unmasking quite different, and heterogeneous, contractility reserve patterns underlying a given ejection fraction at rest. The best survival is observed in patients with up-sloping PVR, whereas flat-biphasic pattern is a strong predictor of cardiac events.

Atrial Overdrive Pacing in Patients with Sleep Apnea with Implanted Pacemaker

RATIONALE

Atrial overdrive pacing markedly improved sleep-disordered breathing in a recent study.

OBJECTIVES

Using a single-blind, randomized, crossover design, we aimed to reproduce these findings and investigate the possible underlying mechanisms.

METHODS

Twenty ambulatory patients with an implanted pacemaker or cardioverter defibrillator were studied by polysomnography on 3 consecutive nights in a randomized, single-blind, crossover study in which devices were programmed for nonpacing or for overdrive pacing at 7 or 15 beats/minute faster than the mean nocturnal heart rate. Ventilation and biomarkers (urinary norepinephrine excretion, amino-terminal portion of the precursor of brain natriuretic peptide, or NT-proBNP, were also evaluated.

MEASUREMENTS AND MAIN RESULTS

Neither the primary endpoint apnea-hypopnea index, nor the apnea index, oxygen desaturation, ventilation, or biomarkers were affected by the nocturnal atrial overdrive pacing. A small, clinically insignificant, rate-dependent reduction in the hypopnea index was evoked by pacing (nonpacing, 13.4 +/- 1.4; pacing 7, 12.9 +/- 1.4; pacing 15, 10.9 +/- 1.0; p < 0.01, analysis of variance).

CONCLUSIONS

The lack of effect on the apnea-hypopnea index means that atrial overdrive pacing is inappropriate for treating sleep-disordered breathing.

Noninvasive assessment of left ventricular contractility by pacemaker stress echocardiography

BACKGROUND

Estimating contractility of the left ventricle with noninvasive techniques is an important yet elusive goal. Positive inotropic interventions are mirrored by smaller end-systolic volumes and higher end-systolic pressures. An increased heart rate progressively increases the force of ventricular contraction (Bowditch treppe or staircase phenomenon).

AIM

To assess the feasibility of a noninvasive estimation of force-frequency relation (FFR) during pacing stress in the echo lab in patients with permanent pacemaker (PM).

METHODS

Transthoracic stress pacing echocardiography was performed in 26 patients with a permanent pacemaker (age 69+/-11 years; 21 men, 5 women). Seven patients had normal function at baseline and during stress ("normals"); eight had angiographically assessed coronary artery disease (three with and five without induced ischemia with stress echo); eleven patients had dilated cardiomyopathy (DC). To build the FFR, the force was determined at different steps as the ratio of the systolic pressure (SP, cuff sphygmomanometer)/end-systolic volume index (ESV, biplane Simpson rule/body surface area). Heart rate was determined from ECG.

RESULTS

The absolute value of the FFR slope was highest in controls and lowest in DC patients. A flat-downsloping FFR was found in 12/19 patients but not for normals (p<0.01).

CONCLUSIONS

Noninvasive pacemaker stress echocardiography (PASE) is a simple and efficient option to assess left ventricular (LV) contractility in patients with permanent pacemaker.

Regional differences in the force-frequency relation of human left ventricular myocardium in mitral regurgitation: implications for ventricular shape

Sphericalization of the left ventricular (LV) chamber shape in patients with mitral regurgitation (MR) contributes to increased LV wall stress and energy consumption. On the basis of previous observations, we hypothesized the existence of regional differences in the force-frequency relation (FFR) within the LV that may contribute to its shape. Accordingly, in the present study, we assessed regional variation in the FFR in patients undergoing surgery for chronic, nonischemic MR with class II–III heart failure symptoms and related our findings to the in vivo LV shape. FFRs (steady-state isometric twitches, 0.2–3.4 Hz, 37°C) were evaluated in MR myocardium from the LV subepicardial free wall (MR-FW) and papillary muscle (MR-PM) and from the subepicardial free wall in coronary artery bypass graft patients with normal LV contraction patterns [nonfailing (NF)]. Ascending slope, optimal stimulation frequency, and maximal twitch tension of the FFR were depressed in MR-FW and MR-PM compared with NF ( P < 0.05). FFR depression was greater in MR-PM than in MR-FW. Between 107 and 134 beats/min, twitch tension became weaker in MR-PM, whereas it increased in MR-FW. Elevation of intracellular cAMP with forskolin eliminated FFR depression in MR-FW but not in MR-PM. MR-PM also had a 35% lower myosin heavy chain content and slowed twitch kinetics. In MR patients, the echocardiographic end-diastolic LV shape (end-diastolic eccentricity index = long axis/short axis) correlated with the ratio of ascending FFR slopes such that the end-diastolic eccentricity index increased 10% per 15% increase in slope ratio ( r = 0.88, P = 0.01). These regional differences in the frequency dependence of contractility between the free wall and papillary myocardium may contribute to changes in LV shape in MR as well as during exercise.

Physiology of the abnormal response of heart failure patients to exercise

Chronic heart failure is associated with reduced exercise capacity. Altered diastolic function and reduced chronotropic response play an important role. However, there is no clear correlation between any hemodynamic parameter and exercise capacity. Peripheral factors, long overlooked, seem to play a major role. Altered peripheral vasodilatation, involving endothelial abnormalities, alters the optimal distribution of blood flow. Muscular abnormalities are constant: aside from muscle atrophy, altered muscle metabolism results in an altered utilization of oxygen. A comprehensive understanding of all these determinants of exercise response is important to optimize the care of the patient. Sole improvement of cardiac function may be insufficient to correct their exercise intolerance; regular training may well have beneficial effects on exercise capacity, functional impairment, and quality of life.

Force-frequency relationship in the echocardiography laboratory: a noninvasive assessment of Bowditch treppe?

BACKGROUND

Estimation of contractility of the left ventricle is an important, and as yet elusive, goal with noninvasive techniques.

OBJECTIVE

We sought to assess the feasibility of a totally noninvasive estimation of force-frequency relation (FFR) during exercise stress in the echocardiography laboratory.

METHODS

We enrolled 13 healthy control patients (12 men, age 38 +/- 15 years) as group I, and 50 patients (38 men, age 64 +/- 11 years) referred for exercise echocardiography as group II. To build the FFR, the force was determined at each step as the ratio of the systolic pressure (cuff sphygmomanometer)/end-systolic volume index (biplane Simpson's rule/body surface area). The slope of the relationship was calculated with the linear best fit of the FFR.

RESULTS

Noninvasive systolic pressure/end-systolic volume ratio was obtained in all patients. The slope of the linear best fit of the force-frequency curve was lower in group II compared with group I (group II = 10.1 +/- 9.3 x 10(-2) vs group I = 14.9 +/- 9.9 x 10(-2) group I, P =.04). By regional wall-motion analysis, 2 subgroups were identified in group II: group IIA (n = 8) had a positive echocardiogram; and group IIB (n = 42) had a negative echocardiogram. The slope of the force-frequency curve was lower in patients with ischemia compared with those without (group IIA = 3.5 +/- 4.2 x 10(-2) vs group IIB = 11.4 +/- 9.5 x 10(-2); P =.012). Heart rate-systolic pressure/end-systolic volume index relation was biphasic, with an initial positive slope and a subsequent negative slope in 1 patient of group I, 4 patients of group IIA, and 15 patients of group IIB (P <.05 vs group I).

CONCLUSION

A noninvasive estimation of FFR can be easily determined during exercise echocardiography. This index of global contractility is theoretically appealing for identification of limited contractile reserve and latent global left ventricular dysfunction.

Cellular basis of abnormal calcium transients of failing human ventricular myocytes

Depressed contractility is a central feature of the failing human heart and has been attributed to altered [Ca2+]i. This study examined the respective roles of the L-type Ca2+ current (ICa), SR Ca2+ uptake, storage and release, Ca2+ transport via the Na+-Ca2+ exchanger (NCX), and Ca2+ buffering in the altered Ca2+ transients of failing human ventricular myocytes. Electrophysiological techniques were used to measure and control V(m) and measure I(m), respectively, and Fluo-3 was used to measure [Ca2+]i in myocytes from nonfailing (NF) and failing (F) human hearts. Ca2+ transients from F myocytes were significantly smaller and decayed more slowly than those from NF hearts. Ca2+ uptake rates by the SR and the amount of Ca2+ stored in the SR were significantly reduced in F myocytes. There were no significant changes in the rate of Ca2+ removal from F myocytes by the NCX, in the density of NCX current as a function of [Ca2+]i, ICa density, or cellular Ca2+ buffering. However, Ca2+ influx during the late portions of the action potential seems able to elevate [Ca2+]i in F but not in NF myocytes. A reduction in the rate of net Ca2+ uptake by the SR slows the decay of the Ca2+ transient and reduces SR Ca2+ stores. This leads to reduced SR Ca2+ release, which induces additional Ca2+ influx during the plateau phase of the action potential, further slowing the decay of the Ca2+ transient. These changes can explain the defective Ca2+ transients of the failing human ventricular myocyte.