Supine-exercise-induced oxygen supply to the right myocardium is attenuated in patients with severe idiopathic pulmonary arterial hypertension

[Invasive Cardiopulmonary Exercise Testing: A Review]

Right heart catheterization (RHC) is the internationally standardized reference method for measuring pulmonary hemodynamics under resting conditions. In recent years, increasing efforts have been made to establish the reliable assessment of exercise hemodynamics as well, in order to obtain additional diagnostic and prognostic data. Furthermore, cardiopulmonary exercise testing (CPET), as the most comprehensive non-invasive exercise test, is increasingly performed in combination with RHC providing detailed pathophysiological insights into the exercise response, so-called invasive cardiopulmonary exercise testing (iCPET).In this review, the accumulated experience with iCPET is presented and methodological details are discussed. This complex examination is especially helpful in differentiating the underlying causes of unexplained dyspnea. In particular, early forms of cardiac or pulmonary vascular dysfunction can be detected by integrated analysis of hemodynamic as well as ventilatory and gas exchange data. It is expected that with increasing validation of iCPET parameters, a more reliable differentiation of normal from pathological stress reactions will be possible.

Myocardial Blood Flow and Metabolic Rate of Oxygen Measurement in the Right and Left Ventricles at Rest and During Exercise Using 15O-Labeled Compounds and PET

Aims: Simultaneous measurement of right (RV) and left ventricle (LV) myocardial blood flow (MBF), oxygen extraction fraction (OEF), and oxygen consumption (MVO₂) non-invasively in humans would provide new possibilities to understand cardiac physiology and different patho-physiological states. Methods: We developed and tested an optimized novel method to measure MBF, OEF, and MVO₂ simultaneously both in the RV and LV free wall (FW) using positron emission tomography in healthy young men at rest and during supine bicycle exercise. Results: Resting MBF was not significantly different between the three myocardial regions. Exercise increased MBF in the LVFW and septum, but MBF was lower in the RV compared to septum and LVFW during exercise. Resting OEF was similar between the three different myocardial regions (~70%) and increased in response to exercise similarly in all regions. MVO₂ increased approximately two to three times from rest to exercise in all myocardial regions, but was significantly lower in the RV during exercise as compared to septum LVFW. Conclusion: MBF, OEF, and MVO₂ can be assessed simultaneously in the RV and LV myocardia at rest and during exercise. Although there are no major differences in the MBF and OEF between LV and RV myocardial regions in the resting myocardium, MVO₂ per gram of myocardium appears to be lower the RV in the exercising healthy human heart due to lower mean blood flow. The presented method may provide valuable insights for the assessment of MBF, OEF and MVO₂ in hearts in different pathophysiological states.

The right ventricle and pulmonary hypertension

In patients with pulmonary hypertension (PH), the primary cause of death is right ventricular (RV) failure. Improvement in RV function is therefore one of the most important treatment goals. In order to be able to reverse RV dysfunction and also prevent RV failure, a detailed understanding of the pathobiology of RV failure and the underlying mechanisms concerning the transition from a pressure-overloaded adapted right ventricle to a dilated and failing right ventricle is required. Here, we propose that insufficient RV contractility, myocardial fibrosis, capillary rarefaction, and a disturbed metabolism are important features of a failing right ventricle. Furthermore, an overview is provided about the potential direct RV effects of PH-targeted therapies and the effects of RV-directed medical treatments.

Novel technologies and devices for monitoring and treating pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature associated with significant morbidity and mortality. Despite significant advances in the past 2 decades with the development of pharmacological therapies to target key molecular pathways of PAH, there remains an ongoing need for novel technologies and devices for diagnosis, monitoring, and treatment to improve PAH outcomes. The advent of sophisticated imaging tools, including cardiac magnetic resonance imaging, positron emission tomography, and speckle tracking echocardiography, offer novel opportunities for advanced, noninvasive assessment of right ventricular function, the most powerful predictor of death in patients with PAH. Noninvasive cardiac output monitors and implantable hemodynamic sensors are among the additional promising novel technologies that might offer daily access to hemodynamic data to influence clinical decision-making and potentially improve outcomes. Percutaneous interventional therapeutics might offer a nonpharmacological treatment option in select patients with PAH, ranging from the percutaneous creation of right to left shunts, pulmonary artery denervation, and right ventricular pacing. Finally, mechanical circulatory support with durable ventricular assist devices offers hope to one day provide a realistic strategy to treat life-threatening right ventricular failure in PAH. Future clinical trials and carefully designed prospective observational studies will be needed to evaluate the full potential of many of these novel devices and technologies for monitoring and treating PAH.

State of the art: advanced imaging of the right ventricle and pulmonary circulation in humans (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by remodeling and vasoconstriction of the pulmonary vasculature, ultimately leading to right ventricular (RV) failure and death. Recent developments in echocardiography, cardiovascular magnetic resonance imaging, computed tomography, and positron emission tomography allow advanced, noninvasive, in vivo assessment of the RV and have contributed to the identification of risk factors, prognostic factors, and monitoring of therapeutic responses in patients with PAH. Although far from reaching its future potential, these techniques have not only provided global RV assessment but also allowed evaluation of changes in cellular and molecular tissue processes, such as metabolism, oxygen balance and ischemia, angiogenesis, and apoptosis. Integrated application of these techniques could provide full insights into the different pathophysiological aspects of a failing RV in the setting of PAH. Recent advances in hybrid imaging have implemented simultaneous measurements of myocardial and vascular interactions and will be one of the most important potential future developments.

Impairment of pulmonary vascular reserve and right ventricular systolic reserve in pulmonary arterial hypertension

Background

Exercise capacity is impaired in pulmonary arterial hypertension (PAH). We hypothesized that cardiovascular reserve abnormalities would be associated with impaired hemodynamic response to pharmacological stress and worse outcome in PAH.

Methods

Eighteen PAH patients (p) group 1 NYHA class II/III and ten controls underwent simultaneous right cardiac catheterization and intravascular ultrasound at rest and during low dose-dobutamine (10 mcg/kg/min) with trendelenburg (DST). We estimated cardiac output (CO), pulmonary vascular resistance (PVR) and capacitance (PC), and PA elastic modulus (EM). We concomitantly measured tricuspid annular plane systolic excursion (TAPSE), RV myocardial peak systolic velocity (Sm) and isovolumic myocardial acceleration (IVA) in PAH patients. Based on the rounded mean + 2 SD of the increase in mPAP in our healthy control group during DST (2.8 + 1.8 mm Hg), PAH p were divided into two groups according to mean PA pressure (mPAP) response during DST, 1: ΔmPAP > 5 mm Hg and 2: ΔmPAP ≤ 5 mm Hg. Cardiovascular reserve was estimated as the change (delta, Δ) during DST compared with rest, including ΔmPAP with respect to ΔCO (ΔmPAP/ΔCO). All patients were prospectively followed up for 2 years.

Results

PAH p showed significant lower heart rate and CO increase than controls during DST, with a significant mPAP and pulse PAP increase and higher ΔmPAP/ΔCO (p < 0.05). Neither hemodynamic, IVUS and echocardiographic data were different between both PAH groups at rest. In group 1, DST caused a higher ΔEM, ΔmPAP/ΔCO, ΔPVR, and ΔTAPSE than group 2, with a lower IVA increase and a negative ΔSV (p < 0.05). TAPSE correlated with mPAP and RVP (p < 0.05) and, IVA and Sm correlated with CO (p < 0.05). ΔEM correlated with ΔmPAP and ΔIVA with ΔCO (p < 0.05). There were two deaths/pulmonary transplantations in group 1 and one death in group 2 during the follow-up (p > 0.05).

Conclusions

Pulmonary vascular reserve and RV systolic reserve are significantly impaired in patients with PAH. The lower recruitable cardiovascular reserve is significantly related to a worse hemodynamic response to DST and it could be associated with a poor clinical outcome.

Pulmonary vascular remodeling and right heart failure in pulmonary hypertension: future role of positron emission tomography in decoding the enigma

Whereas the insights into the cellular and molecular mechanisms of pulmonary arterial hypertension (PAH) and associated right heart failure have increased in recent years, there is a lack of clinical tools to assess the pathobiological mechanisms in patients. Positron emission tomography (PET) provides an array of new possibilities to image and quantify relevant disease processes, including proliferation, angiogenesis, matrix remodeling, shifts in metabolism and neurohormonal signaling. Here we describe the first studies which were conducted to image pulmonary vascular remodeling and right heart failure in vivo and discuss additional targets for imaging which hold great promise for future use in PAH patients.

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.

Today's and tomorrow's imaging and circulating biomarkers for pulmonary arterial hypertension

The pathobiology of pulmonary arterial hypertension (PAH) involves a remodeling process in distal pulmonary arteries, as well as vasoconstriction and in situ thrombosis, leading to an increase in pulmonary vascular resistance, right heart failure and death. Its etiology may be idiopathic, but PAH is also frequently associated with underlying conditions such as connective tissue diseases. During the past decade, more than welcome novel therapies have been developed and are in development, including those increasingly targeting the remodeling process. These therapeutic options modestly increase the patients' long-term survival, now approaching 60% at 5 years. However, non-invasive tools for confirming PAH diagnosis, and assessing disease severity and response to therapy, are tragically lacking and would help to select the best treatment. After exclusion of other causes of pulmonary hypertension, a final diagnosis still relies on right heart catheterization, an invasive technique which cannot be repeated as often as an optimal follow-up might require. Similarly, other techniques and biomarkers used for assessing disease severity and response to treatment generally lack specificity and have significant limitations. In this review, imaging as well as current and future circulating biomarkers for diagnosis, prognosis, and follow-up are discussed.