Noninvasive Assessment of Right Ventricular Function: Will There Be Resurgence in Radionuclide Imaging Techniques?

Right Heart Pulmonary Circulation Unit Involvement in Left-Sided Heart Failure: Diagnostic, Prognostic, and Therapeutic Implications

Although long neglected, the right heart (RH) is now widely accepted as a pivotal player in heart failure (HF) either with reduced or preserved ejection fraction. The chronic overload of the pulmonary microcirculation results in an initial phase characterized by right ventricular (RV) hypertrophy, right atrial dilation, and diastolic dysfunction. This progresses to overt RH failure when RV dilation and systolic dysfunction lead to RV-pulmonary arterial (RV-PA) uncoupling with low RV output. In the context of its established relevance to progression of HF, clinicians should consider assessment of the RH with information from clinical assessment, biomarkers, and imaging. Notably, no single parameter can predict prognosis alone in HF. Assessments simultaneously should encompass RV systolic function, pulmonary pressures, an estimation of RV-PA coupling, and RH morphologic features. Despite a large volume of evidence indicating the relevance of RH function to the clinical syndrome of HF, evidence-based management strategies are lacking. Targeting RH dysfunction in HF should be an objective of future investigations, being an unmet need in the current management of HF.

Noninvasive Assessment of Right Ventricular Function in Patients with Pulmonary Arterial Hypertension and Left Ventricular Assist Device

PURPOSE OF REVIEW

Right ventricular (RV) failure in patients with pulmonary arterial hypertension (PAH) and left ventricular assist device (LVAD) is associated with increased hospitalizations, worsening functional class, and poor survival. Accurate RV function assessment is essential in diagnosing RV failure, guiding therapies, and determining prognosis. Noninvasive imaging techniques provide fast and reliable quantification of RV morphology and function.

RECENT FINDINGS

We review echocardiography, nuclear medicine, and cardiac magnetic resonance imaging (MRI) uses for RV function assessment in patients with PAH and LVAD. We identify current knowledge gaps in utilizing noninvasive tests to assess RV function. Echocardiography is most widely used to quantify RV function in patients with PAH and LVAD, followed by cardiac MRI for RV morphology and function measurement in PAH patients. The first-pass radionuclide angiography with radiolabeled RBC is the gold standard for calculating RV function. Gated blood pool SPECT can be an alternative as it separates the cardiac chambers well and provides accurate assessment of the RV function with high reproducibility, which is particularly useful for monitoring treatment. More research is needed to compare and validate these modalities in evaluating RV function.

Early Diagnostic Features of Left-to-Right Shunt-Induced Pulmonary Arterial Hypertension in Piglets

BACKGROUND

We aimed to establish early diagnostic characteristics of left-to-right shunt-induced pulmonary arterial hypertension (PAH) in a piglet model.

METHODS

A shunt-induced PAH in piglets (n = 9) was successfully established by anastomosis of vascular prosthesis from aorta to pulmonary artery with follow-up for 6 months by a number of diagnostic procedures.

RESULTS

PAH developed with mean pulmonary arterial pressure [PAP] of 30.2 ± 6.0 mm Hg immediately after operation and 33.5 ± 8.7 mm Hg at 3 months after operation with pulmonary vascular resistance increased to 4.0 ± 0.9 Wood units. There was a weak correlation on systolic PAP between catheterization and echocardiography but the Tei index was significantly correlated to systolic PAP. Magnetic resonance imaging demonstrated that the end-diastolic volume index, systolic volume index, ejection fraction of the ventricle, and ventricular mass index were sensitive indices. Technetium-99m single-photon emission computed tomography indicated increased blood flow in the upper and middle zones of both lungs. Positron emission tomography-computed tomography (PET-CT) demonstrated a higher kilo count (kct) of ¹⁸F-fluorodeoxyglucose in the right ventricular wall and both chambers at 3 months postoperatively (right ventricular wall: 5,708.3 ± 428.4 versus 3,965.5 ± 138.6 preoperatively, p = 0.003; both chambers: 2,963.6 ± 219.4 versus 1,710.1 ± 35.4 preoperatively, p < 0.05) as well as at 6 months for both chambers (p < 0.05).

CONCLUSIONS

In this successful left-to-right shunt-induced PAH model in piglets, sensitive indices including the Tei index, systolic volume index, ejection fraction, ventricular mass index, lung perfusion, and glycometabolism by PET-CT in early PAH are determined. For the first time, we report that glycometabolism by PET-CT is useful in early diagnosis. These indices may be used for the early diagnosis in the left-to-right shunt-induced PAH.

Right ventricular functional analysis utilizing first pass radionuclide angiography for pre-operative ventricular assist device planning: a multi-modality comparison

BACKGROUND

Advanced heart failure treated with a left ventricular assist device is associated with a higher risk of right heart failure. Many advanced heart failures patients are treated with an ICD, a relative contraindication to MRI, prior to assist device placement. Given this limitation, left and right ventricular function for patients with an ICD is calculated using radionuclide angiography utilizing planar multigated acquisition (MUGA) and first pass radionuclide angiography (FPRNA), respectively. Given the availability of MRI protocols that can accommodate patients with ICDs, we have correlated the findings of ventricular functional analysis using radionuclide angiography to cardiac MRI, the reference standard for ventricle function calculation, to directly correlate calculated ejection fractions between these modalities, and to also assess agreement between available echocardiographic and hemodynamic parameters of right ventricular function.

METHODS

A retrospective review from January 2012 through May 2014 was performed to identify advanced heart failure patients who underwent both cardiac MRI and radionuclide angiography for ventricular functional analysis. Nine heart failure patients (8 men, 1 woman; mean age of 57.0 years) were identified. The average time between the cardiac MRI and radionuclide angiography exams was 38.9 days (range: 1 - 119 days). All patients undergoing cardiac MRI were scanned using an institutionally approved protocol for ICD with no device-related complications identified. A retrospective chart review of each patient for cardiomyopathy diagnosis, clinical follow-up, and echocardiogram and right heart catheterization performed during evaluation was also performed.

RESULTS

The 9 patients demonstrated a mean left ventricular ejection fraction (LVEF) using cardiac MRI of 20.7% (12 - 40%). Mean LVEF using MUGA was 22.6% (12 - 49%). The mean right ventricular ejection fraction (RVEF) utilizing cardiac MRI was 28.3% (16 - 43%), and the mean RVEF calculated by FPRNA was 32.6% (9 - 56%). The mean discrepancy for LVEF between cardiac MRI and MUGA was 4.1% (0 - 9%), and correlation of calculated LVEF using cardiac MRI and MUGA demonstrated an R of 0.9. The mean discrepancy for RVEF between cardiac MRI and FPRNA was 12.0% (range: 2 - 24%) with a moderate correlation (R = 0.5). The increased discrepancies for RV analysis were statistically significant using an unpaired t-test (t = 3.19, p = 0.0061). Echocardiogram parameters of RV function, including TAPSE and FAC, were for available for all 9 patients and agreement with cardiac MRI demonstrated a kappa statistic for TAPSE of 0.39 (95% CI of 0.06 - 0.72) and for FAC of 0.64 (95% of 0.21 - 1.00).

CONCLUSION

Heart failure patients are increasingly requiring left ventricular assist device placement; however, definitive evaluation of biventricular function is required due to the increased mortality rate associated with right heart failure after assist device placement. Our results suggest that FPRNA only has a moderate correlation with reference standard RVEFs calculated using cardiac MRI, which was similar to calculated agreements between cardiac MRI and echocardiographic parameters of right ventricular function. Given the need for identification of patients at risk for right heart failure, further studies are warranted to determine a more accurate estimate of RVEF for heart failure patients during pre-operative ventricular assist device planning.

Clinical significance of right ventricular activity on treadmill thallium-201 myocardial single-photon emission computerized tomography using cadmium-zinc-telluride cameras

OBJECTIVE

Identification of right ventricular (RV) abnormalities is important in patients with suspected coronary artery disease (CAD). RV activity can be better visualized on myocardial single-photon emission computerized tomography (SPECT) using a higher sensitivity cadmium-zinc-telluride (CZT) detector. The aim of this study was to investigate the clinical significance of RV/left ventricular (LV) uptake ratios during exercise thallium-201 SPECT using CZT detectors.

PATIENTS AND METHODS

A total of 102 patients underwent treadmill ECG-gated SPECT, coronary angiography, and echocardiography. SPECT myocardial perfusion was interpreted using a 17-segment model and a 0-4-point scale. RV/LV uptake ratios were calculated on the basis of maximum counts per pixel within the entire RV and LV walls. The relationships between RV/LV uptake ratio and gated SPECT, presence of CAD (≥50% stenosis in the left main or ≥70% in the main branches), demographics, and echocardiographic parameters were analyzed.

RESULTS

Stress RV/LV ratios correlated positively with the presence of left main or multivessel disease, and tricuspid regurgitation maximum pressure gradient. After multivariate regression, stress/rest RV/LV ratios correlated positively with mitral flow deceleration time, age, female sex, and use of β-blockers.

CONCLUSION

RV/LV uptake ratios on the basis of exercise myocardial perfusion SPECT imaging using CZT cameras are useful for the detection of severe CAD and could serve as an indicator of pulmonary hypertension and LV diastolic dysfunction.

Right ventricular adaptation and failure in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an obstructive pulmonary vasculopathy, characterized by excess proliferation, apoptosis resistance, inflammation, fibrosis, and vasoconstriction. Although PAH therapies target some of these vascular abnormalities (primarily vasoconstriction), most do not directly benefit the right ventricle (RV). This is suboptimal because a patient's functional state and prognosis are largely determined by the success of the adaptation of the RV to the increased afterload. The RV initially hypertrophies but might ultimately decompensate, becoming dilated, hypokinetic, and fibrotic. A number of pathophysiologic abnormalities have been identified in the PAH RV, including: ischemia and hibernation (partially reflecting RV capillary rarefaction), autonomic activation (due to G protein receptor kinase 2-mediated downregulation and desensitization of β-adrenergic receptors), mitochondrial-metabolic abnormalities (notably increased uncoupled glycolysis and glutaminolysis), and fibrosis. Many RV abnormalities are detectable using molecular imaging and might serve as biomarkers. Some molecular pathways, such as those regulating angiogenesis, metabolism, and mitochondrial dynamics, are similarly deranged in the RV and pulmonary vasculature, offering the possibility of therapies that treat the RV and pulmonary circulation. An important paradigm in PAH is that the RV and pulmonary circulation constitute a unified cardiopulmonary unit. Clinical trials of PAH pharmacotherapies should assess both components of the cardiopulmonary unit.

Effects of filtration on right ventricular function by the gated blood pool SPECT

OBJECTIVE

Gated blood po ol single photon emission computed tomography (GBPS) offers the possibility of obtaining additional functional information from blood pool studies, including evaluation of left and right ventricular function simultaneously. The calculation of ventricular volumes based on the identification of the endocardial surface would be influenced by the spatial resolution in the reconstructed images. This study was performed to evaluate the effect of different filters on the right ventricular function.

METHODS

The normal four-dimensional (4-D) NURBS-based cardiac-torso (NCAT) phantom with known right ventricular volume and ejection fraction was generated. The SIMIND Monte Carlo program was used to create projections. The studies were reconstructed by FBP and post-processing filtration such as Butterworth, Hanning, Shepp-Logan, Metz and Wiener in different statuses (cutoff and order). Using the Cedars-Sinai QBS (quantitative blood pool SPECT) package, the ventricular functional parameters were computed. The calculated values were analyzed and compared with the normal NCAT results.

RESULTS

The results implied that the calculated right ventricular end diastolic volume (RVEDV) by Butterworth filtration (cutoff frequency = 0.3) agreed more with the NCAT Phantom characteristics [relative difference percentage (RDP) = 1.2 %], while the maximum accordance in the calculation of the RV ejection fraction (EF) (RDP = 3 %) was observed by Metz filter (FWHM 20 pixel). Also, the results of this study demonstrate that the Butterworth filter provided the most stable values (cutoff frequency = 0.4-0.5) in the estimation of RVEDV (RDP = 7.5 %). The Hanning and Shepp-Logan filters produced a much larger RDP, particularly in low frequency (41.1 and 21.5 %, respectively) compared to other filters.

CONCLUSIONS

This study demonstrated that the operation of different filters has a severe effect in computing right ventricular volume. The resolution recovery and Butterworth filters tend to give more comparable ventricular volumes with the actual normal NCAT value. Further evaluation using a large clinical database is underway to evaluate the optimum protocol in a clinical setting.

Evaluation of right ventricular volume and ejection fraction by gated (18)F-FDG PET in patients with pulmonary hypertension: comparison with cardiac MRI and CT

BACKGROUND

Right ventricular (RV) function is a powerful predictor of survival in patients with pulmonary hypertension (PH), but noninvasively assessing RV function remains a challenge. The aim of this study was to prospectively compare gated (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) myocardial imaging (gated PET), cardiac magnetic resonance (CMR), and cardiac computed tomography (CCT) for the assessment of RV volume and ejection fraction in patients with PH.

METHODS

Twenty-three consecutive patients aged more than 16 years diagnosed with PH were included. All patients underwent gated PET, CMR, and CCT within 7 days. Right ventricular end-diastolic volume (RVEDV), right ventricular end-systolic volume (RVESV), and right ventricular ejection fraction (RVEF) were calculated by three imaging modalities. RV (18)F-FDG uptake was determined as RV-corrected standardized uptake value (SUV), and the ratio of RV to left ventricular (LV)-corrected SUV (Corrected SUV R/L).

RESULTS

Gated PET showed a moderate correlation (r = 0.680, P < .001) for RVEDV, good correlation for RVESV (r = 0.757, P < .001) and RVEF (r = 0.788, P < .001) with CMR, and good correlation for RVEDV (r = 0.767, P < .001), RVESV (r = 0.837, P < .001), and RVEF (r = 0.730, P < .001) with CCT. Bland-Altman analysis revealed systematic underestimation of RVEDV and RVESV and overestimation of RVEF with gated PET compared with CMR and CCT. The correlation between RVESV (r = 0.863, P < .001), RVESV (r = 0.903, P < .001), and RVEF (r = 0.853, P < .001) of CMR and those of CCT was excellent; Bland-Altman analysis showed only a slight systematic variation between CMR and CCT. There were statistically significant negative correlations between RV-corrected SUV and RVEF-CMR (r = -0.543, P < .01), Corrected SUV R/L and RVEF-CMR (r = -0.521, P < .05), RV-corrected SUV and RVEF-CCT (r = -0.429, P < .05), Corrected SUV R/L and RVEF-CCT (r = -0.580, P < .01), respectively.

CONCLUSION

Gated PET had moderate-to-high correlation with CMR and CCT in the assessments of RV volume and ejection fraction. It is an available method for simultaneous assessing of RV function and myocardial glucose metabolism in patients with PH.

Comparison of 18F-FDG uptake by right ventricular myocardium in idiopathic pulmonary arterial hypertension and pulmonary arterial hypertension associated with congenital heart disease

This study measured glucose uptake in the right ventricle (RV) of patients with pulmonary hypertension and investigated the relationship to hemodynamics and survival. Myocardial 18F-fluorodeoxy-glucose (FDG) uptake was measured using single-photon positron emission tomography (SPECT) in 24 patients with idiopathic pulmonary arterial hypertension (IPAH) and 43 patients with congenital heart disease (CHD). In both IPAH and CHD-PAH, RV FDG uptake (RV/LV ratio) was associated with pulmonary vascular resistance (PVR). A second SPECT scan was performed in nine patients after 6 months treatment with sildenafil. PVR decreased from 1683±426 to 1207±383 dyn s(-1) cm(-5) (P < 0.05) and cardiac index improved from 2.2±0.2 to 2.8±0.5 L/min/m(2) (P < 0.01). RV/LV FDG uptake decreased from 1.28±0.32 before treatment to 0.99±0.23 (P < 0.05). Survival in the IPAH group with a baseline RV/LV FDG uptake greater than the median value of 1.20 was significantly lower than that of the group with RV/LV FDG uptake below 1.20 (log-rank test, P < 0.05). In contrast, baseline RV/LV FDG was of little informative value in CHD. FDG uptake by the RV reflects the severity of PVR in PAH. Increased RV FDG uptake is a marker of poor prognosis in IPAH and is reduced in patients receiving effective therapy. It could prove useful in the early clinical assessment of novel therapies for PAH.

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.

Imaging the right heart: the use of integrated multimodality imaging

During recent years, right ventricular (RV) structure and function have been found to be an important determinant of outcome in different cardiovascular and also pulmonary diseases. Currently, echocardiography and cardiac magnetic resonance (CMR) imaging are the two imaging modalities most commonly used to visualize the RV. Most structural abnormalities of the RV can be reliably described by echocardiography but due its complex geometrical shape, echocardiographic assessment of RV function is more challenging. Newer promising echocardiographic techniques are emerging but lack of validation and limited normal reference data influence their routine clinical application. Cardiac magnetic resonance is generally considered the clinical reference technique due to its unlimited imaging planes, superior image resolution, and three-dimensional volumetric rendering. The accuracy and reliability of CMR measurements make it the ideal tool for serial examinations of RV function. Multidetector computed tomography (MDCT) plays an important role in the diagnosis of pulmonary emboli but can also be used for assessing RV ischaemic disease or as an alternative for CMR if contra-indicated. Radionuclide techniques have become more obsolete in the current era. The different imaging modalities should be considered complimentary and each plays a role for different indications.