Assessment of right ventricular oxidative metabolism by PET in patients with idiopathic dilated cardiomyopathy undergoing cardiac resynchronisation therapy

Positron Emission Tomography in Heart Failure: From Pathophysiology to Clinical Application

Imaging modalities are increasingly being used to evaluate the underlying pathophysiology of heart failure. Positron emission tomography (PET) is a non-invasive imaging technique that uses radioactive tracers to visualize and measure biological processes in vivo. PET imaging of the heart uses different radiopharmaceuticals to provide information on myocardial metabolism, perfusion, inflammation, fibrosis, and sympathetic nervous system activity, which are all important contributors to the development and progression of heart failure. This narrative review provides an overview of the use of PET imaging in heart failure, highlighting the different PET tracers and modalities, and discussing fields of present and future clinical application.

Characterization of myocardial oxidative metabolism and myocardial external efficiency in high-risk alcohol cardiotoxicity and alcoholic cardiomyopathy via dynamic 11C-Acetate positron emission tomography

INTRODUCTION

The purpose of this study was to evaluate subjects with high-risk alcohol cardiotoxicity and patients with alcoholic cardiomyopathy (ACM) via dynamic 11C-Acetate positron emission tomography (PET) imaging as a myocardial oxidative metabolic probe.

METHODS AND RESULTS

We recruited 37 subjects with chronic alcohol consumption [18 with moderate consumption (MC), 19 with heavy consumption (HC)], 5 ACM patients, and 12 healthy controls to receive dynamic 11C-Acetate PET scans. PET imaging data were analyzed to calculate kinetic parameters (e.g., Kmono, K1 and k2) based on the mono-exponential and one-tissue compartmental models. Myocardial oxygen consumption (MVO2) and myocardial external efficiency (MEE) were then derived from these kinetic parameters. MVO2 was significantly lowered in the HC group and in ACM patients (0.121± 0.018 and 0.111 ± 0.017 mL·g-1·min-1, respectively) compared with those in healthy controls and MC subjects (0.144 ± 0.023 and 0.146 ± 0.027 mL·g-1·min-1, respectively; P < .01). MEE was significantly reduced in ACM patients (13.0% ± 4.3%) compared with those of healthy controls (22.4% ± 4.6%, P < .01), MC subjects (20.1% ± 4.5%, P < .05), and HC subjects (22.3% ± 4.5%, P < .001).

CONCLUSION

Functional assessment via dynamic 11C-Acetate PET imaging may represent a clinically feasible probe for identifying cohorts with high-risk cardiotoxicity due to addictive alcohol consumption and ACM.

Electrical remodelling post cardiac resynchronization therapy in patients with ischemic and non-ischemic heart failure

BACKGROUND

The beneficial effects of cardiac resynchronization therapy (CRT) in heart failure are largely considered to be due to improved mechanical contractility. The contributory role of electrical remodelling is less clear. We sought to evaluate the impact of electrical remodelling in these patients.

METHODS

33 patients with conventional indications for CRT and with ischemic (ICM) (n = 17) and non-ischemic (NICM) (n = 16) aetiologies for heart failure were prospectively recruited. Functional parameters of peak exercise oxygen consumption (VO₂max) and Minnesota quality of life (QOL) score, echocardiographic measures of LV functions and parameters of electrical remodelling, e.g. intrinsic QRS duration (iQRSD), intracardiac conduction times of LV pacing to RV electrocardiogram (LVp-RVegm), were measured at CRT implant and after 6 months.

RESULTS

Only two electrical parameters predicted functional or symptomatic improvement. LVp-RVegm reduction significantly correlated with improvement in VO₂max (r = -0.42, p = 0.03 while reduction in iQRSD significantly correlated with improvement in QOL score (r = 0.39, p = 0.04). The extent of changes in LVp-RVegm and iQRSD was significantly greater in NICM than in ICM patients (p = 0.017 and p = 0.042 for heterogeneity). There was also significant differential impact on QOL score in the NICM relative to the ICM group (p = 0.003) but none with VO₂max. On multivariate analysis, only non-ischemic aetiology was a significant determinant of reduction in iQRSD.

CONCLUSION

CRT induces potentially beneficial reduction in LVp-RVegm and iQRSD, which are seen selectively in NICM rather than ICM patients. The extent of improvement in these markers is associated with some functional and symptomatic measures of CRT efficacy.

11C-Acetate clearance as an index of oxygen consumption of the right myocardium in idiopathic pulmonary arterial hypertension: a validation study using 15O-labeled tracers and PET

Idiopathic pulmonary arterial hypertension (IPAH) results in increased right ventricular (RV) workload and oxygen demand. It has been shown that myocardial oxygen consumption (MVO2) of the hypertrophied right ventricle of IPAH patients can be measured using PET and (15)O-labeled tracers. This method is, however, not very suitable for routine clinical practice. The purpose of the present study was to assess whether MVO2 can also be determined in the right ventricle of IPAH patients from the clearance of (11)C-acetate, a simple method that is in use for MVO2 measurements of the left myocardium.

METHODS

Seventeen of 26 IPAH patients performed the total PET study. Nine other patients were scanned only for (11)C-acetate. (15)O-H2O, (15)O-O2, and (15)O-CO scans were used to derive RV flow, oxygen extraction fraction, and blood volume, respectively, from which RV MVO2 was calculated. The rate of clearance determined by monoexponential curve fitting (K(mono)) and the efflux rate constant k2 were derived from the (11)C-acetate scan. The RV rate-pressure product was also determined by means of right heart catheterization, as an index of the RV MVO2, and was calculated as the product of systolic pulmonary artery pressure and heart rate.

RESULTS

Both (11)C-acetate clearance rates, K(mono) (R(2) = 0.41, P = 0.006) and k2 (R(2) = 0.45, P = 0.003), correlated with RV MVO2. They also correlated with RV rate-pressure product (K(mono), R(2) = 0.41, P = 0.0005; k2, R(2) = 0.48, P < 0.0001).

CONCLUSION

(11)C-acetate clearance rates correlated moderately with quantitative RV MVO2 measurements in IPAH. Therefore, (11)C-acetate PET can be used only as an index of RV oxidative metabolism in IPAH patients.

[11C]Acetate rest-stress protocol to assess myocardial perfusion and oxygen consumption reserve in a model of congestive heart failure in rats

This study describes an [(11)C]acetate rest-stress method to obtain an indirect estimate of myocardial blood flow (MBF) and myocardial oxygen consumption (MVO(2)) in rats. Doxorubicin cardiotoxicity was used to test the usefulness of this approach for the assessment of congestive heart failure.

METHODS

[(11)C]Acetate rest-stress studies have been used in clinical research to assess the capacity of the coronary arteries to respond to stress. In this article, we used this approach to assess the cardiotoxicity of doxorubicin in a rat model. The method was first validated in a group of healthy rats and then used to follow the effect of doxorubicin chemotherapy on cardiac function. The effect of doxorubicin on myocardial perfusion and oxygen consumption reserve was measured at rest and under dobutamine stimulation.

RESULTS

Validation of the protocol showed a good correlation between the MBF and MVO(2) (r(2)=.68). The doxorubicin-treated group showed a significant (P=.04) decrease in cardiovascular perfusion reserve at 1.3±0.2 compared with the control animals at 1.6±0.2. Similar results were obtained for the MVO(2) reserve (treated 1.8±0.4 vs. controls 2.3±0.3; P=.02).

CONCLUSIONS

We describe an [(11)C]acetate PET rest-stress protocol for the assessment of congestive heart failure in rats and its application to the follow-up of cardiotoxicity under doxorubicin chemotherapy. This is a rapid and reliable approach to the measurement of cardiac perfusion and oxygen consumption reserve that could be applied to the development of new strategies to reduce the cardiotoxicity of anthracycline.

Simultaneous quantification of myocardial perfusion, oxidative metabolism, cardiac efficiency and pump function at rest and during supine bicycle exercise using 1-11C-acetate PET--a pilot study

BACKGROUND

PET using 1-(11)C-acetate (ACE-PET) applied at rest is used for measuring absolute myocardial blood flow (MBF) and oxidative metabolic rate (k(mono)). We evaluated the feasibility of quantitative ACE-PET during exercise.

METHODS

Five endurance athletes underwent dynamic PET scanning at rest and during supine bicycle stress. Exercise was maintained at a workload of 120 Watt for 17 min. The rate-pressure product (RPP) was recorded repeatedly. MBF, k(mono) in left (LV) and right (RV) ventricular wall, cardiac output (CO), cardiac efficiency and a lung uptake value reflecting left heart diastolic pressures were calculated from the PET data using previously validated models.

RESULTS

MBF increased from 0.71 +/- 0.17 to 2.48 +/- 0.25 ml min(-1) per ml, LV-k(mono) from 0.050 +/- 0.005 to 0.146 +/- 0.021 min(-1), RV-k(mono) from 0.023 + 0.006 to 0.087 + 0.014 min(-1), RPP from 4.7 +/- 0.8 to 13.2 +/- 1.4 mmHg x min(-1) x 10(3) and Cardiac Output from 5.2 +/- 1.1 to 12.3 +/- 1.2 l min (-1) (all P < 0.001). Cardiac efficiency was unchanged (P = 0.99). Lung uptake decreased from 1.1 +/- 0.2 to 0.6 +/- 0.1 ml g(-1) (P < 0.001).

DISCUSSION

A number of important parameters related to cardiac function can be quantified non-invasively and simultaneously with a short scanning protocol during steady state supine bicycling. This might open up new opportunities for studies of the integrated cardiac physiology in health and early asymptomatic disease.

Cardiac resynchronization therapy: assessment of dyssynchrony and effects on metabolism

In recent years cardiac resynchronization therapy has emerged as a promising new treatment strategy in a subgroup of patients with congestive heart failure and an asynchronous contraction pattern. By simultaneously pacing both right ventricular apex and lateral side of the left ventricle, ventricular synchrony can be partially restored and beneficial effects on cardiac performance can be observed. This review discusses the principles of ventricular dyssynchrony, and the acute and chronic effects of cardiac resynchronization therapy on systolic function, cardiac metabolism, and clinical parameters. Furthermore, the issue of identifying patients who do not respond to this therapy is addressed.

Role of cardiac MRI and nuclear imaging in cardiac resynchronization therapy

Cardiac resynchronization has emerged as a highly effective therapy for heart failure. However, up to 40% of patients do not benefit from this treatment. In this Review, we discuss the potential role of MRI and nuclear molecular imaging in providing additional insights into the response to cardiac resynchronization therapy. Variables with potential prognostic and therapeutic values include the evaluation of cardiac dyssynchrony, scar, cardiac sympathetic function, myocardial blood flow, myocardial glucose and oxidative metabolism. Other molecular targets to characterize apoptosis, fatty acid metabolism, angiogenesis and angiotensin-converting enzyme activity will also be described. The potential use of these techniques in identifying and measuring responses to cardiac resynchronization therapy and future areas of research will be explored.

Myocardial Doppler velocities as a marker of prognosis in the ICU

Relatively simple measures of echocardiography and Doppler, as left ventricular end-systolic area and volume, should be taken in consideration when performing a Doppler echocardiographic examination, as they could have both clinical and prognostic value.

Stem Cells Improve Right Ventricular Functional Recovery After Acute Pressure Overload and Ischemia Reperfusion Injury

BACKGROUND

In many clinical scenarios, a relatively untrained right ventricle may be subjected to acute elevations in pulmonary artery and right ventricular pressures. The right and left heart are distinctly different in this regard and there is currently no in vivo model to study right ventricular ischemia in the setting of acute pressure overload. In acute injury, cardiomyocytes produce tumor necrosis factor, which mediates a proinflammatory pathway, eventually leading to myocardial dysfunction. Stem cells have been shown to reduce the production of proinflammatory mediators by the ischemic myocardium and protect the myocardium. Pretreatment with stem cells has been shown to protect the left ventricle. The effect of acute pressure overload to the untrained right ventricle is still not well understood. Furthermore, it is unclear whether pretreatment with stem cells would protect the right ventricle when it is subjected to acute pressure overload and concomitant ischemia reperfusion injury. The purpose of this study was (1) to create a simple model of acute pressure overload for the study of concomitant right ventricular ischemia and reperfusion, and (2) to evaluate the effect of pretreatment with stem cells prior to ischemia reperfusion injury.

MATERIALS AND METHODS

Isolated rat hearts were perfused with the modified Langendorff technique with the latex balloon in the right ventricle instead of the left, with a pressure-transduced balloon being used to create an acute elevation in right ventricular pressure before ischemia. In the first of a two-series experiment, there were two experimental groups (N = 8 per group): one with right ventricular balloon end-diastolic pressure (EDP) of 5 mmHg (physiological), and the other with an EDP of 40 mmHg (pathologic). In the second series, the hearts with the higher balloon pressure (EDP 40 mmHg) were divided into two experimental groups (N = 5 per group). The control group was not pretreated. One group was pretreated with human mesenchymal stem cells 5 min immediately prior to ischemia reperfusion injury. Right ventricular developed pressure (RVDP), contractility (+dP/dt), and compliance (-dP/dt) were continuously assessed. Additionally, mesenchymal stem cells (MSCs) in culture were stressed by hypoxia and activation was determined by measuring vascular endothelial growth factor-A (VEGF) and hepatocyte growth factor (HGF) production by enzyme-linked immunosorbent assay.

RESULTS

Recovery of RVDP, +dP/dt, and -dP/dt was significantly higher (P < 0.001) in the group with lower EDP compared to the group with the higher EDP [RVDP: 79.53 +/- 6.34 versus 54.28 +/- 10.76%; +dP/dt: 76.54 +/- 8.79 versus 38.75 +/- 19.74%; -dP/dt: 72.29 +/- 7.02 versus 30.54 +/- 12.44%]. In the higher EDP groups, pretreatment with human mesenchymal stem cells significantly improved myocardial function recovery (P < 0.01) when compared to controls [RVDP: 75.76 +/- 7.97 versus 59.10 +/- 11.18%; +dP/dt: 71.78 +/- 10.36 versus 54.93 +/- 12.64%; -dP/dt: 77.38 +/- 11.09 versus 59.30 +/- 15.20%]. Further, hypoxic MSCs demonstrated significantly greater VEGF and HGF release than controls.

CONCLUSION

This compounded injury model allowed the study of right ventricular dysfunction in the setting of acute pressure overload and ischemia. Additionally, we have also demonstrated that pretreatment with stem cells of an acutely pressure overloaded right ventricle prior to ischemia reperfusion injury improves functional recovery. This is the first report of a modified Langendorff technique to study right ventricular function in the setting of acute pressure overload and ischemia and the effect of pretreatment with stem cells.

Metabolic imaging using PET

INTRODUCTION

There is growing evidence that myocardial metabolism plays a key role not only in ischaemic heart disease but also in a variety of diseases which involve myocardium globally, such as heart failure and diabetes mellitus. Understanding myocardial metabolism in such diseases helps to elucidate the pathophysiology and assists in making therapeutic decisions.

MEASUREMENT

As well as providing information on regional changes, PET can deliver quantitative information about both regional and global changes in metabolism. This capability of quantitative measurement is one of the major advantages of PET along with physiological positron tracers, especially relevant in evaluating diseases which involve the whole myocardium.

DISCUSSION

This review discusses major PET tracers for metabolic imaging and their clinical applications and contributions to research regarding ischaemic heart disease and other diseases such as heart failure and diabetic heart disease. Future applications of positron metabolic tracers for the detection of vulnerable plaque are also highlighted briefly.

Elevated Estimated Pulmonary Artery Systolic Pressure is Associated with an Adverse Clinical Outcome in Patients Receiving Cardiac Resynchronization Therapy

BACKGROUND

A substantial percentage of patients with heart failure remain nonresponsive to cardiac resynchronization therapy (CRT). There is a paucity of information on the impact of baseline elevated pulmonary artery pressure on clinical outcome and on left ventricular reverse remodeling (LV-RR) after CRT. We sought to investigate the impact of elevated estimated pulmonary artery systolic pressure (ePASP) on clinical outcome and LV-RR after CRT.

METHODS

This study retrospectively analyzed data from 68 subjects with standard indications for CRT over a 12-month period. Subjects were stratified into two groups based on the echocardiographic estimation of pulmonary artery pressure i.e., ePASP > or = 50 mmHg (n = 27) and ePASP < 50 mmHg (n = 41). Long-term response was measured as a combined endpoint of heart failure hospitalizations and all cause mortality at 12 months, and compared within the two groups using the Kaplan-Meier method. Follow up echocardiograms to assess for LV-RR were available in 51 subjects (mean duration 7.1 months). LV-RR was defined as any improvement in global systolic function with reduction in left ventricular internal diameter.

RESULTS

The study population was composed of 24 women and 44 men (age, mean +/- SD; 70 +/- 11 years), with a decreased left ventricular ejection fraction ([25 +/- 9]%) and a wide QRS (171 +/- 54 ms). There were no significant differences in the clinical features between the high and low ePASP group. Subjects with ePASP > or = 50 mmHg had a significantly worse clinical outcome (Hazard ratio (95% CI), 2.0 (1.2-5.5), P = 0.02). Baseline ePASP was not predictive of LV-RR (P = 0.32).

CONCLUSION

In patients receiving CRT, although elevated estimated pulmonary artery systolic pressure (ePASP > or = 50 mmHg) does not significantly impact LV reverse remodeling, it is associated with an adverse long-term outcome.

Cardiac Resynchronization Therapy

Encouraged by the clinical success of cardiac resynchronization therapy (CRT), the implantation rate has increased exponentially, although several limitations and unresolved issues of CRT have been identified. This review concerns issues that are encountered during implantation of CRT devices, including the role of electroanatomical mapping, whether CRT implantation should be accompanied by simultaneous atrioventricular nodal ablation in patients with atrial fibrillation, procedural complications, and when to consider surgical left ventricular lead positioning. Furthermore, (echocardiographic) CRT optimization and assessment of CRT benefits after implantation are highlighted. Also, controversial issues such as the potential value of CRT in patients with mild heart failure or narrow QRS complex are addressed. Finally, open questions concerning when to combine CRT with implantable cardioverter-defibrillator therapy and the cost-effectiveness of CRT are discussed.