Effect of cardiac resynchronization on myocardial efficiency and regional oxidative metabolism

Association between obesity paradox in the all-cause mortality among patients with cardiac resynchronization therapy device

BACKGROUND

Recent studies have demonstrated an obesity paradox, where obese patients with cardiovascular disease have a better outcome compared to those with normal weight. However, the effect of obesity and body mass index (BMI) on the outcome of patients with cardiac resynchronization therapy (CRT) devices remains unclear. The current study aims to investigate this relationship using all available published data.

METHODS

We systematically reviewed studies from Medline and EMBASE databases from inception to January 2024. Eligible studies must investigate the association between BMI status and all-cause mortality in individuals with CRT devices. Relative risk (RR) or hazard ratio (HR) and 95% CIs were retrieved from each study and combined using the generic inverse variance method.

RESULTS

A total of 12 cohort studies were included in the meta-analysis. Pooled analysis showed that overweight and obesity patients had lower all-cause mortality compared to those with normal body weight with the pooled risk ratios (RR) for overweight of 0.77 (95% CI 0.69-0.87, I2 47%) and for obesity of 0.81 (95% CI 0.67-0.97, I2 59%). Conversely, the underweight exhibited higher all-cause mortality than the group with normal weight, with a pooled RR of 1.37 (95% CI 1.14-1.64, I2 0%). Additionally, higher BMI as continuous data was associated with decreased all-cause mortality, with a pooled HR of 0.94 (95% CI 0.89-0.98, I2 72%).

CONCLUSIONS

The pooled analyses observed an obesity paradox in patients with CRT, where overweight and obesity were associated with reduced all-cause mortality, while underweight individuals exhibited higher all-cause mortality. Further research is necessary to investigate the underlying mechanisms and their implications for clinical practice.

[History of cardiac resynchronization therapy : 30 years of electrotherapeutic management for heart failure]

The first permanent biventricular pacing system was implanted more than 30 years ago. In this article, the historical development of cardiac resynchronization therapy (CRT), starting with the pathophysiological concept, followed by the initial "proof of concept" studies and finally the large prospective-randomized studies that led to the implementation of CRT in heart failure guidelines, is outlined. Since the establishment of CRT, both an expansion of indications, e.g., for patients with mild heart failure and atrial fibrillation, but also the return to patients with broad QRS complex and left bundle branch block who benefit most of CRT has evolved. New techniques such as conduction system pacing will have major influence on pacemaker therapy in heart failure, both as an alternative or adjunct to CRT.

Long-Term Outcomes of Resynchronization-Defibrillation for Heart Failure

BACKGROUND

The Resynchronization-Defibrillation for Ambulatory Heart Failure Trial (RAFT) showed a greater benefit with respect to mortality at 5 years among patients who received cardiac-resynchronization therapy (CRT) than among those who received implantable cardioverter-defibrillators (ICDs). However, the effect of CRT on long-term survival is not known.

METHODS

We randomly assigned patients with New York Heart Association (NYHA) class II or III heart failure, a left ventricular ejection fraction of 30% or less, and an intrinsic QRS duration of 120 msec or more (or a paced QRS duration of 200 msec or more) to receive either an ICD alone or a CRT defibrillator (CRT-D). We assessed long-term outcomes among patients at the eight highest-enrolling participating sites. The primary outcome was death from any cause; the secondary outcome was a composite of death from any cause, heart transplantation, or implantation of a ventricular assist device.

RESULTS

The trial enrolled 1798 patients, of whom 1050 were included in the long-term survival trial; the median duration of follow-up for the 1050 patients was 7.7 years (interquartile range, 3.9 to 12.8), and the median duration of follow-up for those who survived was 13.9 years (interquartile range, 12.8 to 15.7). Death occurred in 405 of 530 patients (76.4%) assigned to the ICD group and in 370 of 520 patients (71.2%) assigned to the CRT-D group. The time until death appeared to be longer for those assigned to receive a CRT-D than for those assigned to receive an ICD (acceleration factor, 0.80; 95% confidence interval, 0.69 to 0.92; P = 0.002). A secondary-outcome event occurred in 412 patients (77.7%) in the ICD group and in 392 (75.4%) in the CRT-D group.

CONCLUSIONS

Among patients with a reduced ejection fraction, a widened QRS complex, and NYHA class II or III heart failure, the survival benefit associated with receipt of a CRT-D as compared with ICD appeared to be sustained during a median of nearly 14 years of follow-up. (RAFT ClinicalTrials.gov number, NCT00251251.).

Short-term effects of sacubitril/valsartan therapy on myocardial oxygen consumption and energetic efficiency of cardiac work in heart failure with reduced ejection fraction: A randomized controlled study

AIMS

We sought to evaluate the mechanism of angiotensin receptor-neprilysin inhibitor (ARNI) sacubitril/valsartan therapy and compare it with a valsartan-only control group in patients with heart failure with reduced ejection fraction (HFrEF).

METHODS AND RESULTS

The study was a phase IV, prospective, randomized, double-blind, parallel-group study in patients with New York Heart Association class II-III heart failure and left ventricular ejection fraction (LVEF) ≤35%. During a 6-week run-in period, all patients received valsartan therapy, which was up-titrated to the highest tolerated dose level (80 mg bid or 160 mg bid) and then randomized to either valsartan or sacubitril/valsartan. Myocardial oxygen consumption, energetic efficiency of cardiac work, cardiac and systemic haemodynamics were quantified using echocardiography and 11 C-acetate positron emission tomography before and after 6 weeks of therapy (on stable dose) in 55 patients (ARNI group: n = 27, mean age 63 ± 10 years, LVEF 29.2 ± 10.4%; and valsartan-only control group: n = 28, mean age 64 ± 8 years, LVEF 29.0 ± 7.3%; all p = NS). The energetic efficiency of cardiac work remained unchanged in both treatment arms. However, both diastolic (-4.5 mmHg; p = 0.026) and systolic blood pressure (-9.8 mmHg; p = 0.0007), myocardial perfusion (-0.054 ml/g/min; p = 0.045), and left ventricular mechanical work (-296; p = 0.038) decreased significantly in the ARNI group compared to the control group. Although myocardial oxygen consumption decreased in the ARNI group (-5.4%) compared with the run-in period and remained unchanged in the control group (+0.5%), the between-treatment group difference was not significant (p = 0.088).

CONCLUSIONS

We found no differences in the energetic efficiency of cardiac work between ARNI and valsartan-only groups in HFrEF patients. However, ARNI appears to have haemodynamic and cardiac mechanical effects over valsartan in heart failure patients.

Myocardial perfusion and flow reserve in the asynchronous heart: mechanistic insight from a computational model

The tight coupling between myocardial oxygen demand and supply has been recognized for decades, but it remains controversial whether this coupling persists under asynchronous activation, such as during left bundle branch block (LBBB). Furthermore, it is unclear whether the amount of local cardiac wall growth, following longer-lasting asynchronous activation, can explain differences in myocardial perfusion distribution between subjects. For a better understanding of these matters, we built upon our existing modeling framework for cardiac mechanics-to-perfusion coupling by incorporating coronary autoregulation. Regional coronary flow was regulated with a vasodilator signal based on regional demand, as estimated from regional fiber stress-strain area. Volume of left ventricular wall segments was adapted with chronic asynchronous activation toward a homogeneous distribution of myocardial oxygen demand per tissue weight. Modeling results show that 1) both myocardial oxygen demand and supply are decreased in early activated regions and increased in late-activated regions; 2) but that regional hyperemic flow remains unaffected; while 3) regional myocardial flow reserve (the ratio of hyperemic to resting myocardial flow) decreases with increases in absolute regional myocardial oxygen demand as well as with decreases in wall thickness. These findings suggest that septal hypoperfusion in LBBB represents an autoregulatory response to reduced myocardial oxygen demand. Furthermore, oxygen demand-driven remodeling of wall mass can explain asymmetric hypertrophy and the related homogenization of myocardial perfusion and flow reserve. Finally, the inconsistent observations of myocardial perfusion distribution can primarily be explained by the degree of dyssynchrony, the degree of asymmetric hypertrophy, and the imaging modality used.NEW & NOTEWORTHY This versatile modeling framework couples myocardial oxygen demand to oxygen supply and myocardial growth, enabling simulation of resting and hyperemic myocardial flow during acute and chronic asynchronous ventricular activation. Model-based findings suggest that reported inconsistencies in myocardial perfusion and flow reserve responses with asynchronous ventricular activation between patients can primarily be explained by the degree of dyssynchrony and wall mass remodeling, which together determine the heterogeneity in regional oxygen demand and, hence, supply with autoregulation.

Ventricular conduction abnormality in patients with mild to moderate cardiomyopathy

BACKGROUND

In mild-to-moderate cardiomyopathy, cardiac resynchronization therapy (CRT) is indicated in patients with high burden of right ventricular pacing but not in those with intrinsic ventricular conduction abnormalities.

HYPOTHESIS

We hypothesized that CRT positively impacts outcomes of patients with intrinsic ventricular conduction delay and left ventricular ejection fraction (LVEF) of 36%-50%.

METHODS

Of 18 003 patients with LVEF ≤ 50%, 5966 (33%) patients had mild-to-moderate cardiomyopathy, of whom 1741 (29%) have a QRS duration ≥120 ms. Patients were followed to the endpoints of death and heart failure (HF) hospitalization. Outcomes were compared between patients with narrow versus wide QRS.

RESULTS

Of the 1741 patients with mild-to-moderate cardiomyopathy and wide QRS duration, only 68 (4%) were implanted with a CRT device. Over a median follow-up of 3.35 years, 849 (51%) died and 1004 (58%) had a HF hospitalization. The adjusted risk of death (hazard ratio (HR) = 1.11, p = 0.046) and of death or HF hospitalization (HR = 1.10, p = 0.037) were significantly higher in patients with wide versus narrow QRS duration. In patients with wide QRS complex, CRT was associated with reduction in the adjusted risk of death (HR = 0.47, p = 0.020) and of death or HF hospitalization (HR = 0.58, p = 0.008).

CONCLUSIONS

Patients with mild-to-moderate cardiomyopathy and wide QRS duration are rarely implanted with CRT devices and have worse outcomes compared to those with narrow QRS. Randomized trials are needed to examine if CRT has salutary effects in this population.

Dyssynchronous Heart Failure: A Clinical Review

PURPOSE OF THE REVIEW

Dyssynchrony occurs when portions of the cardiac chambers contract in an uncoordinated fashion. Ventricular dyssynchrony primarily impacts the left ventricle and may result in heart failure. This entity is recognized as a major contributor to the development and progression of heart failure. A hallmark of dyssynchronous heart failure (HF_d) is left ventricular recovery after dyssynchrony is corrected. This review discusses the current understanding of pathophysiology of HF_d and provides clinical examples and current techniques for treatment.

RECENT FINDINGS

Data show that HF_d responds poorly to medical therapy. Cardiac resynchronization therapy (CRT) in the form of conventional biventricular pacing (BVP) is of proven benefit in HF_d, but is limited by a significant non-responder rate. Recently, conduction system pacing (His bundle or left bundle branch area pacing) has also shown promise in correcting HF_d. HF_d should be recognized as a distinct etiology of heart failure; HF_d responds best to CRT.

Worsening Heart Failure and Atrial Flutter in a Patient Secondary to Cardiac Resynchronization Therapy Dyssynchrony: A Case Report

Cardiac resynchronization therapy-defibrillator (CRT-D) and/or cardiac resynchronization therapy-pacemaker (CRT-P) play an important role in improving cardiac synchronization and reducing the risk of ventricular fibrillation arrest (VFA) in patients with severe left ventricular systolic dysfunction (LVSD). Patients with LVSD may notice worsening symptoms when CRT-D or CRT-P is in dyssynchrony. We present a case of 59-year-old patient who presented with worsening shortness of breath (SOB) and progressive exertional dyspnea for the past few weeks accompanied by pink, frothy sputum, occasional urinary incontinence and urge. He was known to have severe LVSD with an ejection fraction of 10% and had CRT-D in situ. Clinical examination revealed bilateral crepitation and normal heart sounds. A chest radiograph showed pulmonary oedema. An electrocardiogram (ECG) showed atrial fibrillation (AF)/flutter with wide QRS complexes. The patient was treated for acute pulmonary oedema and had CRT-D reprogrammed to achieve biventricular synchrony. He was treated with intravenous furosemide and alternate day metolazone initially. He showed significant subjective and objective improvement and was planned for outpatient synchronized intra-device cardioversion. This case is important because patients with severe LVSD with malfunctioning cardiac resynchronization therapy can result in worsening heart failure (HF) leading to higher morbidity and mortality.

What Have We Learned in the Last 20 Years About CRT Non-Responders?

Although cardiac resynchronization therapy (CRT) has become well established in the treatment of heart failure, the management of patients who do not respond after CRT remains a key challenge. This review will summarize what we have learned about non-responders over the last 20 years and discuss methods for optimizing response, including the introduction of novel therapies.

One step closer to myocardial physiology: From PV loop analysis to state-of-the-art myocardial imaging

Recent advances in cardiac imaging have revitalized the assessment of fundamental physiological concepts. In the field of cardiac physiology, invasive measurements with pressure-volume (PV) loops have served as the gold standard methodology for the characterization of left ventricular (LV) function. From PV loop data, fundamental aspects of LV chamber function are derived such as work, efficiency, stiffness and contractility. However, the parametrization of these aspects is limited because of the need for invasive procedures. Through the utilization of recent advances in echocardiography, magnetic resonance imaging and positron emission tomography, it has become increasingly feasible to quantify these fundamental aspects of LV function non-invasively. Importantly, state-of-the-art imaging technology enables direct assessment of myocardial performance, thereby extending functional assessment from the net function of the LV chamber, as is done with PV loops, to the myocardium itself. With a strong coupling to underlying myocardial physiology, imaging measurements of myocardial work, efficiency, stiffness and contractility could represent the next generation of functional parameters. The purpose of this review is to discuss how the new imaging parameters of myocardial work, efficiency, stiffness and contractility can bring cardiac physiologists, researchers and clinicians alike one step closer to underlying myocardial physiology.

Increased myocardial oxygen consumption rates are associated with maladaptive right ventricular remodeling and decreased event-free survival in heart failure patients

BACKGROUND

Reduced left ventricular (LV) function is associated with increased myocardial oxygen consumption rate (MVO2) and altered sympathetic activity, the role of which is not well described in right ventricular (RV) dysfunction.

METHODS AND RESULTS

33 patients with left heart failure were assessed for RV function/size using echocardiography. Positron emission tomography (PET) was used to measure 11C-acetate clearance rate (kmono), 11C-hydroxyephedrine (11C-HED) standardized uptake value (SUV), and retention rate. RV MVO2 was estimated from kmono. 11C-HED SUV and retention indicated sympathetic neuronal function. A composite clinical endpoint was defined as unplanned cardiac hospitalization within 5 years. Patients with (n = 10) or without (n = 23) RV dysfunction were comparable in terms of sex (male: 70.0 vs 69.5%), LV ejection fraction (39.6 ± 9.0 vs 38.6 ± 9.4%), and systemic hypertension (70.0 vs 78.3%). RV dysfunction patients were older (70.9 ± 13.5 vs 59.4 ± 11.5 years; P = .03) and had a higher prevalence of pulmonary hypertension (60.0% vs 13.0%; P = .01). RV dysfunction was associated with increased RV MVO2 (.106 ± .042 vs .068 ± .031 mL/min/g; P = .02) and decreased 11C-HED SUV and retention (6.05 ± .53 vs 7.40 ± 1.39 g/mL (P < .001) and .08 ± .02 vs .11 ± .03 mL/min/g (P < .001), respectively). Patients with an RV MVO2 above the median had a shorter event-free survival (hazard ratio = 5.47; P = .01). Patients who died within the 5-year follow-up period showed a trend (not statistically significant) for higher RV MVO2 (.120 ± .026 vs .074 ± .038 mL/min/g; P = .05).

CONCLUSIONS

RV dysfunction is associated with increased oxygen consumption (also characterized by a higher risk for cardiac events) and impaired RV sympathetic function.

Myocardial efficiency in patients with different aetiologies and stages of heart failure

AIMS

Myocardial external efficiency (MEE) is the ratio of cardiac work in relation with energy expenditure. We studied MEE in patients with different aetiologies and stages of heart failure (HF) to discover the role and causes of deranged MEE. In addition, we explored the impact of patient characteristics such as sex, body mass index (BMI), and age on myocardial energetics.

METHODS AND RESULTS

Cardiac energetic profiles were assessed with 11C-acetate positron emission tomography (PET) and left ventricular ejection fraction (LVEF) was acquired with echocardiography. MEE was studied in 121 participants: healthy controls (n = 20); HF patients with reduced (HFrEF; n = 25) and mildly reduced (HFmrEF; n = 23) LVEF; and patients with asymptomatic (AS-asymp; n = 38) and symptomatic (AS-symp; n = 15) aortic stenosis (AS). Reduced MEE coincided with symptoms of HF irrespective of aetiology and declined in tandem with deteriorating LVEF. Patients with AS-symp and HFmrEF had reduced MEE as compared with controls (22.2 ± 4.9%, P = 0.041 and 20.0 ± 4.2%, P < 0.001 vs. 26.1 ± 5.8% in controls) and a further decline was observed in patients with HFrEF (14.7 ± 6.3%, P < 0.001). Disproportionate left ventricular hypertrophy was a major cause of reduced MEE. Female sex (P < 0.001), a lower BMI (P = 0.001), and advanced age (P = 0.03) were associated with a lower MEE.

CONCLUSION

MEE was reduced in patients with HFrEF, HFmrEF, and HF due to pressure overload and MEE may therefore constitute a treatment target in HF. Patients with LVH, advanced age, female sex, and low BMI had more pronounced reduction in MEE and personalized treatment within these patient subgroups could be relevant.

Novel Methodology for Measuring Regional Myocardial Efficiency

Our approach differs from the usual global measure of cardiac efficiency by using PET/MRI to measure efficiency of small pieces of cardiac tissue whose limiting size is equal to the spatial resolution of the PET scanner. We initiated a dynamic cardiac PET study immediately prior to the injection of 15.1 mCi of 11C-acetate acquiring data for 25 minutes while simultaneously acquiring MRI cine data. 1) A 3D finite element (FE) biomechanical model of the imaged heart was constructed by utilizing nonrigid deformable image registration to alter the Dassault Systèmes FE Living Heart Model (LHM) to fit the geometry in the cardiac MRI cine data. The patient specific FE cardiac model with estimates of stress, strain, and work was transformed into PET/MRI format. 2) A 1-tissue compartment model was used to calculate wash-in (K1) and the linear portion of the decay in the PET 11C-acetate time activity curve (TAC) was used to calculate the wash-out k2(mono) rate constant. K1 was used to calculate blood flow and k2(mono) was used to calculate myocardial volume oxygen consumption ( MVO2 ). 3) Estimates of stress and strain were used to calculate Myocardial Equivalent Minute Work ( MEMW ) and Cardiac Efficiency = MEMW/MVO2 was then calculated for 17 tissue segments of the left ventricle. The global MBF was 0.96 ± 0.15 ml/min/gm and MVO2 ranged from 8 to 17 ml/100gm/min. Six central slices of the MRI cine data provided a range of MEMW of 0.1 to 0.4 joules/gm/min and a range of Cardiac Efficiency of 6 to 18%.

Myocardial Efficiency: A Fundamental Physiological Concept on the Verge of Clinical Impact

Myocardial external efficiency is the relation of mechanical energy generated by the left (or right) ventricle to the consumed chemical energy from aerobic metabolism. Efficiency can be calculated invasively, and, more importantly, noninvasively by using positron emission tomography, providing a single parameter by which to judge the adequacy of myocardial metabolism to generated mechanical output. This parameter has been found to be impaired in heart failure of myocardial or valvular etiology, and it changes in a characteristic manner with medical or interventional cardiac therapy. The authors discuss the concept, strengths, and limitations, known applications, and future perspectives of the use of myocardial efficiency.

Body mass index and outcomes of cardiac resynchronization with implantable cardioverter-defibrillator therapy in older patients with heart failure

AIMS

To assess the association of body mass index (BMI) with heart failure (HF) outcomes after cardiac resynchronization therapy with defibrillator (CRT-D) implantation.

METHODS AND RESULTS

Medicare beneficiaries with HF aged ≥ 65 years (n = 18 922) undergoing first-time CRT-D from the National Cardiovascular Data Registry (NCDR) Implantable Cardioverter-Defibrillator Registry between 2010 and 2013, were followed for 3 years post-implantation. Survival curves and covariate adjusted hazard ratio (aHR) or odds ratio were used to assess the risks for death, readmission, and device-related complications by BMI status. Of 18 922 HF patients receiving CRT-D, 5265 (27.8%) were normal weight, 6896 (37%) were overweight, 6318 (33.4%) were obese, and 353 (1.8%) were underweight. Compared to those of normal weight (BMI 18.5-24.9 kg/m² ), underweight patients had a higher 3-year post-device implantation risk of death [aHR: 1.34 (95% confidence interval 1.09-1.65); P < 0.001] and of readmission [sub-aHR: 1.25 (1.09-1.42); P < 0.001]. The corresponding 3-year aHRs for death were 0.83 (0.77-0.89) for overweight, 0.74 (0.67-0.82) for obesity class I (BMI 30-34.9 kg/m² ), 0.78 (0.68-0.90) for obesity class II (BMI 35-39.9 kg/m² ), and 0.75 (0.60-0.93) for obesity class III (BMI ≥ 40 kg/m² , P for all categories < 0.001). Individuals with class III obesity had a higher risk of readmission [sub-aHR: 1.17 (1.06-1.30)]. There were no differences in rates of device-related complications within 90 days across BMI categories.

CONCLUSION

Most elderly patients with HF receiving CRT-D were overweight or obese. While being underweight was associated with greater risks of death and hospitalization, overweight and obese patients were at lower risk of death after CRT-D.

Cardiac Resynchronisation Therapy and Cellular Bioenergetics: Effects Beyond Chamber Mechanics

Cardiac resynchronisation therapy is a cornerstone in the treatment of advanced dyssynchronous heart failure. However, despite its widespread clinical application, precise mechanisms through which it exerts its beneficial effects remain elusive. Several studies have pointed to a metabolic component suggesting that, both in concert with alterations in chamber mechanics and independently of them, resynchronisation reverses detrimental changes to cellular metabolism, increasing energy efficiency and metabolic reserve. These actions could partially account for the existence of responders that improve functionally but not echocardiographically. This article will attempt to summarise key components of cardiomyocyte metabolism in health and heart failure, with a focus on the dyssynchronous variant. Both chamber mechanics-related and -unrelated pathways of resynchronisation effects on bioenergetics – stemming from the ultramicroscopic level – and a possible common underlying mechanism relating mechanosensing to metabolism through the cytoskeleton will be presented. Improved insights regarding the cellular and molecular effects of resynchronisation on bioenergetics will promote our understanding of non-response, optimal device programming and lead to better patient care.

Cardiac Resynchronization Therapy Optimization: A Comprehensive Approach

Since the first report on biventricular pacing in 1994, cardiac resynchronization therapy (CRT) has become standard for patients with advanced heart failure (HF) and ventricular conduction delay. CRT improves myocardial function by resynchronizing myocardial contraction, which results in reverse left ventricular remodeling and improves symptoms and clinical outcomes. Despite the accelerated development of CRT device technology and its increased application in treating HF patients, almost one-third of these patients do not respond to the therapy or gain any clinical benefit from device implantation. Over the last decade, multiple cardiac imaging modalities have provided a deeper understanding of myocardial pathophysiology, thereby improving HF treatment management. However, the optimal strategy for improving the CRT response remains debatable. This article provides an updated overview of the electropathophysiology of myocardial dysfunction in ventricular conduction delay and the diagnostic approaches involving the use of multiple modalities.

Repeatable and reproducible measurements of myocardial oxidative metabolism, blood flow and external efficiency using 11C-acetate PET

BACKGROUND

Non-invasive approaches to investigate myocardial efficiency can help track the progression of heart failure (HF). This study evaluates the repeatability and reproducibility of 11C-acetate positron emission tomography (PET) imaging of oxidative metabolism.

METHODS AND RESULTS

Dynamic 11C-acetate PET scans were performed at baseline and followup (47 ± 22 days apart) in 20 patients with stable HF with reduced ejection fraction. Two observers blinded to patients' clinical data used FlowQuant® to evaluate test-retest repeatability, as well as intra- and inter-observer reproducibility of 11C-acetate tracer uptake and clearance rates, for the measurement of myocardial oxygen consumption (MVO2), myocardial external efficiency (MEE), work metabolic index (WMI), and myocardial blood flow. Reproducibility and repeatability were evaluated using intra-class-correlation (ICC) and Bland-Altman coefficient-of-repeatability (CR). Test-retest correlations and repeatability were better for MEE and WMI compared to MVO2. All intra- and inter-observer correlations were excellent (ICC = 0.95-0.99) and the reproducibility values (CR = 3%-6%) were significantly lower than the test-retest repeatability values (22%-54%, P < 0.001). Repeatability was improved for all parameters using a newer PET-computed tomography (CT) scanner compared to older PET-only instrumentation.

CONCLUSION

11C-acetate PET measurements of WMI and MEE exhibited excellent test-retest repeatability and operator reproducibility. Newer PET-CT scanners may be preferred for longitudinal tracking of cardiac efficiency.

Heart failure with recovered ejection fraction

Substantial or complete myocardial recovery occurs in many patients with heart failure (HF). HF patients with myocardial recovery or recovered left ventricular (LV) ejection fraction (EF; HFrecEF) are a distinct population of HF patients with different underlying etiologies, comorbidities, response to therapies, and outcomes compared with HF patients with persistent reduced or preserved EF. Improvement in LVEF has been systematically linked to improved quality of life, and lower rehospitalization rates and mortality. However, the mortality and morbidity in HFrecEF patients remain higher than those in the normal population. Currently, data to guide the management of HFrecEF patients are lacking. This review discusses specific characteristics, pathophysiology, and clinical implications for HFrecEF.

Assessment of dyssynchrony by gated myocardial perfusion imaging does not improve patient management

Clinical trials have demonstrated improved outcomes with cardiac resynchronization therapy in patients with heart failure and electrical evidence of dyssynchrony. There has been intense effort at developing imaging markers of dyssynchrony with the aim of improved risk stratification. However, these efforts have not been fruitful to date. This article discusses mechanisms of cardiac dyssynchrony, reviews clinical data supporting resynchronization therapy, and addresses the lack of convincing evidence to support the use of noninvasive imaging measures of dyssynchrony in improving patient management.

Cardiac Resynchronization Therapy for Heart Failure

Cardiac resynchronization therapy (CRT) has emerged as a valued nonpharmacologic therapy in patients with heart failure, reduced ejection fraction (EF), and ventricular dyssynchrony manifest as left bundle branch block. The mechanisms of benefit include remodeling of the left ventricle leading to decreased dimensions and increased EF, as well as a decrease in the severity of mitral regurgitation. This article reviews the rationale, effects, and indications for CRT, and discusses the patient characteristics that predict response and considerations for nonresponders.

Heart Failure with Myocardial Recovery - The Patient Whose Heart Failure Has Improved: What Next?

In an important number of heart failure (HF) patients substantial or complete myocardial recovery occurs. In the strictest sense, myocardial recovery is a return to both normal structure and function of the heart. HF patients with myocardial recovery or recovered ejection fraction (EF; HFrecEF) are a distinct population of HF patients with different underlying etiologies, demographics, comorbidities, response to therapies and outcomes compared to HF patients with persistent reduced (HFrEF) or preserved ejection fraction (HFpEF). Improvement of left ventricular EF has been systematically linked to improved quality of life, lower rehospitalization rates and mortality. However, mortality and morbidity in HFrecEF patients remain higher than in the normal population. Also, persistent abnormalities in biomarker and gene expression profiles in these patients lends weight to the hypothesis that pathological processes are ongoing. Currently, there remains a lack of data to guide the management of HFrecEF patients. This review will discuss specific characteristics, pathophysiology, clinical implications and future needs for HFrecEF.

Cellular and Molecular Aspects of Dyssynchrony and Resynchronization

Dyssynchronous contraction of the ventricle significantly worsens morbidity and mortality in patients with heart failure (HF). Approximately one-third of patients with HF have cardiac dyssynchrony and are candidates for cardiac resynchronization therapy (CRT). The initial understanding of dyssynchrony and CRT was in terms of global mechanics and hemodynamics, but lack of clinical benefit in a sizable subgroup of recipients who appear otherwise appropriate has challenged this paradigm. This article reviews current understanding of these cellular and subcellular mechanisms, arguing that these aspects are key to improving CRT use, as well as translating its benefits to a wider HF population.

Relationships between left ventricular asynchrony and myocardial blood flow

OBJECTIVE

82Rb PET protocols enable determination of left ventricular asynchrony (LVAS) at rest and stress, along with myocardial blood flow (MBF). We hypothesized that in patients with resting LVAS, MBF differs between those with stress-induced LVAS improvement and those with stress-induced LVAS deterioration.

METHODS

We retrospectively analyzed 82Rb rest/regadenoson stress PET studies of 195 patients evaluated for known or suspected coronary artery disease. MBF was computed from first-pass data; function and relative perfusion were computed from myocardial equilibrium data. LVAS was defined as phase contraction bandwidth (BW) above 82Rb gender-specific normal limits, with changes defined as BW moving into or out of normal ranges.

RESULTS

Among the 195 patients, 64 had LVAS at rest, of whom 13 reverted to normal and 51 continued to have LVAS with stress. Patients who did not improve had lower stress MBF (1.04 ± 0.69 vs 1.58 ± 0.67, p = .02) and coronary flow reserve (1.94 ± 1.16 vs 3.04 ± 1.22, p = .01) than those who did improve. ROC analysis indicated that the parameter most strongly associated with improvement in asynchrony for patients with resting LVAS was reduction in MBF heterogeneity (ROC area (accuracy) = 84%, sensitivity = 92%, and specificity = 67%).

CONCLUSION

LVAS is highly correlated with MBF and CVR, with stress-induced improvement in synchronicity most strongly associated with improved MBF homogeneity.

Relation of Body Mass Index to Long-Term Survival After Cardiac Resynchronization Therapy

Obesity confers a paradoxical survival benefit in patients with heart failure, but this obesity paradox has not been well established in those who have undergone cardiac resynchronization therapy with a defibrillator (CRT-D). We sought to determine the impact of body mass index (BMI) on long-term survival in patients with heart failure after CRT-D. We identified 113 patients implanted with CRT-D at our institution from May 2002 to November 2003. Patients were divided into 3 categories by pre-implant BMI (kg/m²): normal weight (BMI <25), overweight (BMI 25-29), and obese (BMI ≥30). Ten-year survival free from orthotopic heart transplant or ventricular assist device implantation was analyzed with Kaplan-Meier plots, the log-rank test, and Cox proportional hazards modeling. Thirty-three patients (29%) were normal weight, 47 (42%) were overweight, and 33 were obese (29%). Median follow-up time was 4.5 years (interquartile range 1.9 to 8.7 years). Obese patients were younger and had a higher proportion of women (both p <0.05). Ten-year survival free of orthotopic heart transplant or ventricular assist device was highest in obese patients (36.3%) followed by overweight (19.2%) and then normal-weight patients (12.1%), log-rank p trend = 0.004. After adjustment for clinical risk factors, every 1 kg/m² increase in BMI was associated with a 8% reduction in the risk of the primary end point (adjusted hazard ratio 0.92, 95% confidence interval 0.88 to 0.97, p = 0.002). In conclusion, higher BMI is associated with improved long-term survival after CRT-D.

Current Treatment Strategies for Heart Failure: Role of Device Therapy and LV Reconstruction

OPINION STATEMENT

Medical care of heart failure (HF) begins with the determination of the cause of the heart failure and diagnosing potential reversible causes (i.e., coronary heart disease, hyperthyroidism, etc.). Medical therapy includes pharmacological and nonpharmacological strategies that limit and/or reverse the signs and symptoms of HF. Initial behavior modification includes dietary sodium and fluid restriction to avoid weight gain; and encouraging physical activity when appropriate. Optimization of medical therapy is the first line of treatment that includes the use of diuretics, vasodilators (i.e., ACE inhibitors or ARBs), beta blockers, and potentially inotropic agents and anticoagulation depending on the patient's severity of heart failure and LV dysfunction. As heart failure advances despite optimized medical management, cardiac resynchronization therapy (CRT), and implantable cardioverter defibrillators (ICDs) are appropriate device therapies. The development of progressive end-stage HF, despite maximal medical therapy, necessitates the consideration of mechanical circulatory devices such as ventricular assist devices (VADs) either as a bridge to heart transplantation or as destination therapy. Despite the advances in the treatment of heart failure, there is still a large morbidity and mortality associated with HF, thus the need to develop newer strategies for the treatment of HF.

Accelerated (99m)Tc-sestamibi clearance associated with mitochondrial dysfunction and regional left ventricular dysfunction in reperfused myocardium in patients with acute coronary syndrome

Background

Accelerated clearance of ^99mtechnetium-sestamibi (MIBI) has been observed after reperfusion therapy in patients with acute coronary syndrome (ACS), but the mechanisms have not been fully investigated. MIBI retention may depend on mitochondrial function. The clearance rate of ¹¹carbon-acetate reflects such mitochondrial functions as oxidative metabolism. The purpose of this study was to examine the mechanisms of accelerated MIBI clearance in ACS. We therefore compared it to oxidative metabolism estimated using ¹¹C-acetate positron emission tomography (PET).

Methods

Eighteen patients [mean age 69.2 ± 8.7 years, 10 males (56 %)] with reperfused ACS underwent MIBI single-photon emission computed tomography (SPECT), echocardiography, and ¹¹C-acetate PET within 3 weeks of the onset of ACS. MIBI images were obtained 30 min and 3 h after MIBI administration. Regional left ventricular (LV) function was evaluated by echocardiography. The measurement of oxidative metabolism was obtained through the mono-exponential fitting of the ¹¹C-acetate time-activity curve (k_mono).

Results

Among 95 segments of reperfused myocardium, MIBI SPECT showed 64 normal segments (group N), 14 segments with accelerated MIBI clearance (group AC), and 17 segments with fixed defect (group F). Group AC showed lower k_mono than group N (0.041 ± 0.009 vs 0.049 ± 0.010, p = 0.02). Group F showed lower k_mono than group N (0.039 ± 0.012 vs 0.049 ± 0.010, p = 0.01). However, k_mono was similar in group AC and group F (p = 0.99).

Conclusions

Segments with accelerated MIBI clearance showed reduced oxidative metabolism in ACS. Loss of MIBI retention may be associated with mitochondrial dysfunction.

Cellular and Molecular Aspects of Dyssynchrony and Resynchronization

Dyssynchronous contraction of the ventricle significantly worsens morbidity and mortality in patients with heart failure (HF). Approximately one-third of patients with HF have cardiac dyssynchrony and are candidates for cardiac resynchronization therapy (CRT). The initial understanding of dyssynchrony and CRT was in terms of global mechanics and hemodynamics, but lack of clinical benefit in a sizable subgroup of recipients who appear otherwise appropriate has challenged this paradigm. This article reviews current understanding of these cellular and subcellular mechanisms, arguing that these aspects are key to improving CRT use, as well as translating its benefits to a wider HF population.

Radionuclide Assessment of Left Ventricular Dyssynchrony

Phase analysis of gated myocardial perfusion single-photon emission computed tomography is a widely available and reproducible measure of left ventricular (LV) dyssynchrony, which also provides comprehensive assessment of LV function, global and regional scar burden, and patterns of LV mechanical activation. Preliminary studies indicate potential use in predicting cardiac resynchronization therapy response and elucidation of mechanisms. Because advances in technology may expand capabilities for precise LV lead placement in the future, identification of specific patterns of dyssynchrony may have a critical role in guiding cardiac resynchronization therapy.

Cardiac resynchronization therapy induces adaptive metabolic transitions in the metabolomic profile of heart failure

BACKGROUND

Heart failure (HF) is associated with ventricular dyssynchrony and energetic inefficiency, which can be alleviated by cardiac resynchronization therapy (CRT). The aim of this study was to determine the metabolomic signature in HF and its prognostic value regarding the response to CRT.

METHODS AND RESULTS

This prospective study consisted of 24 patients undergoing CRT for advanced HF and 10 control patients who underwent catheter ablation for supraventricular arrhythmia but not CRT. Blood samples were collected before and 3 months after CRT. Metabolomic profiling of plasma samples was performed with the use of gas chromatography-mass spectrometry and nuclear magnetic resonance. The plasma metabolomic profile was altered in the HF patients, with a distinct panel of metabolites, including Krebs cycle and lipid, amino acid, and nucleotide metabolism. CRT improved the metabolomic profile. The succinate-glutamate ratio, an index of Krebs cycle activity, improved from 0.58 ± 0.13 to 2.84 ± 0.60 (P < .05). The glucose-palmitate ratio, an indicator of the balance between glycolytic and fatty acid metabolism, increased from 0.96 ± 0.05 to 1.54 ± 0.09 (P < .01). Compared with nonresponders to CRT, responders had a distinct baseline plasma metabolomic profile, including higher isoleucine, phenylalanine, leucine, glucose, and valine levels and lower glutamate levels at baseline (P < .05).

CONCLUSIONS

CRT improves the plasma metabolomic profile of HF patients, indicating harmonization of myocardial energy substrate metabolism. CRT responders may have a favorable metabolomic profile as a potential biomarker for predicting CRT outcome.

Current concepts relating coronary flow, myocardial perfusion and metabolism in left bundle branch block and cardiac resynchronisation therapy

Cardiac resynchronisation therapy (CRT) improves mortality and symptoms in heart failure patients with electromechanically dyssynchronous ventricles. There is a 50% non-response rate and reproducible biomarkers to predict non-response have not been forthcoming. Therefore, there has been increasing interest in the pathophysiological effects of dyssynchrony particularly focusing on coronary flow, myocardial perfusion and metabolism. Studies suggest that dyssynchronous electrical activation effects coronary flow throughout the coronary vasculature from the epicardial arteries to the microvascular bed and that these changes can be corrected by CRT. The effect of both electrical and mechanical dyssynchrony on myocardial perfusion is unclear with some studies suggesting there is a reduction in septal perfusion whilst others propose that there is an increase in lateral perfusion. Better understanding of these effects offers the possibility for better prediction of non-response. CRT appears to improve homogeneity in myocardial perfusion where heterogeneity is described in the initial substrate. Novel approaches to the identification of non-responders via metabolic phenotyping both invasively and non-invasively have been encouraging. There remains a need for further research to clarify the interaction of coronary flow with perfusion and metabolism in patients who undergo CRT.

Effects of short-term continuous positive airway pressure on myocardial sympathetic nerve function and energetics in patients with heart failure and obstructive sleep apnea: a randomized study

BACKGROUND

Heart failure with reduced ejection fraction and obstructive sleep apnea (OSA), 2 states of increased metabolic demand and sympathetic nervous system activation, often coexist. Continuous positive airway pressure (CPAP), which alleviates OSA, can improve ventricular function. It is unknown whether this is due to altered oxidative metabolism or presynaptic sympathetic nerve function. We hypothesized that short-term (6-8 weeks) CPAP in patients with OSA and heart failure with reduced ejection fraction would improve myocardial sympathetic nerve function and energetics.

METHODS AND RESULTS

Forty-five patients with OSA and heart failure with reduced ejection fraction (left ventricular ejection fraction 35.8±9.7% [mean±SD]) were evaluated with the use of echocardiography and 11C-acetate and 11C-hydroxyephedrine positron emission tomography before and ≈6 to 8 weeks after randomization to receive short-term CPAP (n=22) or no CPAP (n=23). Work metabolic index, an estimate of myocardial efficiency, was calculated as follows: (stroke volume index×heart rate×systolic blood pressure÷Kmono), where Kmono is the monoexponential function fit to the myocardial 11C-acetate time-activity data, reflecting oxidative metabolism. Presynaptic sympathetic nerve function was measured with the use of the 11C-hydroxyephedrine retention index. CPAP significantly increased hydroxyephedrine retention versus no CPAP (Δretention: +0.012 [0.002, 0.021] versus -0.006 [-0.013, 0.005] min(-1); P=0.003). There was no significant change in work metabolic index between groups. However, in those with more severe OSA (apnea-hypopnea index>20 events per hour), CPAP significantly increased both work metabolic index and systolic blood pressure (P<0.05).

CONCLUSIONS

In patients with heart failure with reduced ejection fraction and OSA, short-term CPAP increased hydroxyephedrine retention, indicating improved myocardial sympathetic nerve function, but overall did not affect energetics. In those with more severe OSA, CPAP may improve cardiac efficiency. Further outcome-based investigation of the consequences of CPAP is warranted.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT00756366.

Efficacy of cardiac resynchronization in acutely infarcted canine hearts with electromechanical dyssynchrony

BACKGROUND

Patients with acute myocardial infarction (MI), left bundle branch block (LBBB), and marked left ventricular (LV) decompensation suffer from nearly 50% early mortality. Whether cardiac resynchronization therapy (CRT) improves hemodynamic status in this condition is unknown. We tested CRT in this setting by using a canine model of delayed lateral wall (LW) activation combined with 2 hours of coronary artery occlusion-reperfusion.

OBJECTIVE

This study aimed to evaluate the acute hemodynamic effects of CRT during and immediately after MI.

METHODS

Adult dogs (n = 8) underwent open-chest 2-hour mid-left anterior descending artery occlusion followed by 1-hour reperfusion. Four pacing modes were compared: right atrial pacing, pseudo-left bundle block (right ventricular pacing), and CRT with the LV lead positioned at either the LW (LW-CRT) or the peri-infarct zone (peri-infarct zone-CRT). Continuous LV pressure-volume data, regional segment length, and proximal left anterior descending flow rates were recorded.

RESULTS

At baseline, both right ventricular pacing and peri-infarct zone CRT reduced anterior wall regional work by ~50% (vs right atrial pacing). During coronary occlusion, this territory became dyskinetic, and dyskinesis rose further with both CRT modes as compared to pseudo-LBBB. Global cardiac output, stroke work, and ejection fraction all still improved by 11%-23%. After reperfusion, both CRT modes elevated infarct zone regional work and blood flow by ~10% as compared to pseudo-LBBB, as well as improved global function.

CONCLUSION

CRT improves global chamber systolic function in left ventricles with delayed LW activation during and after sustained coronary occlusion. It does so while modestly augmenting infarct zone dyskinesis during occlusion and improving regional function and blood flow after reperfusion. These findings support CRT in the setting of early post-MI dyssynchronous heart failure.

Attenuated right ventricular energetics evaluated using ¹¹C-acetate PET in patients with pulmonary hypertension

PURPOSE

The right ventricle (RV) has a high capacity to adapt to pressure or volume overload before failing. However, the mechanisms of RV adaptation, in particular RV energetics, in patients with pulmonary hypertension (PH) are still not well understood. We aimed to evaluate RV energetics including RV oxidative metabolism, power and efficiency to adapt to increasing pressure overload in patients with PH using (11)C-acetate PET.

METHODS

In this prospective study, 27 patients with WHO functional class II/III PH (mean pulmonary arterial pressure 39.8 ± 13.5 mmHg) and 9 healthy individuals underwent (11)C-acetate PET. (11)C-acetate PET was used to simultaneously measure oxidative metabolism (k mono) for the left ventricle (LV) and RV. LV and RV efficiency were also calculated.

RESULTS

The RV ejection fraction in PH patients was lower than in controls (p = 0.0054). There was no statistically significant difference in LV k mono (p = 0.09). In contrast, PH patients showed higher RV k mono than did controls (0.050 ± 0.009 min(-1) vs. 0.030 ± 0.006 min(-1), p < 0.0001). PH patients exhibited significantly increased RV power (p < 0.001) and hence increased RV efficiency compared to controls (0.40 ± 0.14 vs. 0.017 ± 0.12 mmHg·mL·min/g, p = 0.001).

CONCLUSION

The RV oxidative metabolic rate was increased in patients with PH. Patients with WHO functional class II/III PH also had increased RV power and efficiency. These findings may indicate a myocardial energetics adaptation response to increasing pulmonary arterial pressure.

Cardiac resynchronization sensitizes the sarcomere to calcium by reactivating GSK-3β

Cardiac resynchronization therapy (CRT), the application of biventricular stimulation to correct discoordinate contraction, is the only heart failure treatment that enhances acute and chronic systolic function, increases cardiac work, and reduces mortality. Resting myocyte function also increases after CRT despite only modest improvement in calcium transients, suggesting that CRT may enhance myofilament calcium responsiveness. To test this hypothesis, we examined adult dogs subjected to tachypacing-induced heart failure for 6 weeks, concurrent with ventricular dyssynchrony (HF(dys)) or CRT. Myofilament force-calcium relationships were measured in skinned trabeculae and/or myocytes. Compared with control, maximal calcium-activated force and calcium sensitivity declined globally in HF(dys); however, CRT restored both. Phosphatase PP1 induced calcium desensitization in control and CRT-treated cells, while HF(dys) cells were unaffected, implying that CRT enhances myofilament phosphorylation. Proteomics revealed phosphorylation sites on Z-disk and M-band proteins, which were predicted to be targets of glycogen synthase kinase-3β (GSK-3β). We found that GSK-3β was deactivated in HF(dys) and reactivated by CRT. Mass spectrometry of myofilament proteins from HF(dys) animals incubated with GSK-3β confirmed GSK-3β–dependent phosphorylation at many of the same sites observed with CRT. GSK-3β restored calcium sensitivity in HF(dys), but did not affect control or CRT cells. These data indicate that CRT improves calcium responsiveness of myofilaments following HF(dys) through GSK-3β reactivation, identifying a therapeutic approach to enhancing contractile function