Derivation of in vivo pressure-volume loops for post-heart transplant patients using real-time 3D echocardiography and left ventricular catheterisation

Background

Image-based methods that combine catheterisation with non-concurrent cardiac magnetic resonance (CMR) imaging data and echocardiography (echo) is gaining more interest than the conductance catheter method to derive pressure-volume loops (PVLs) due to improved accuracy and accessibility of LV volume quantification [1–3]. However, accurate temporal registration between LV pressure and volume is not well developed.

Purpose

We propose a framework for temporally registering invasive LV and aortic pressures (LVP and AOP) acquired during left heart catheterisation with real time 3D echocardiography (RT3DE) to generate in vivo PVLs in a group of heart transplant (HTx) recipients.

Methods

25 orthotopic HTx recipients (mean age: 54±8 years and 7 female) indicated for routine coronary assessment were recruited for invasive hemodynamic measurement and RT3DE imaging. A fluid-filled pigtail catheter was used to measure LVP and AOP with simultaneous electrocardiogram (ECG) over several (9–15) heartbeats. Within an hour of catheterisation, single-beat transthoracic RT3DE of the LV was performed from the apical window in a left lateral decubitus position. Imaging parameters were optimized for each patient to maximize the temporal resolution (between 15–41 imaging frames per cycle). We developed a piecewise linear temporal scaling method based on cardiac events (end-diastole (ED), end of isovolumic contraction (eIVC), end-systole (ES), end of isovolumic relaxation (eIVR), and diastasis (DS)) of RT3DE and haemodynamic measurement to resample the LVP at the RT3DE imaging frames between the cardiac events to construct PVLs (Fig. 1a). Geometric LV models were manually fitted at ED and ES, followed by automatic tracking across intermediary frames to estimate LV volume over the entire cardiac cycle (Fig. 1b). The temporally aligned pressure values were further averaged to find the beat-averaged LV PVL (Fig. 1c).

Results

Based on the number of cardiac cycles selected for haemodynamic analysis, multiple in vivo PVLs were constructed for each patient. A beat-averaged PVL was also computed for each patient (Fig.1d). With the exception of one case, the beat-averaged PVLs exhibited classically representative shape with distinct isovolumic contraction and isovolumic relaxation phases. The individual diastolic PVRs for all patients are shown in Fig.1e, with beat-to-beat variation observed in most patients. For some cases, the variation manifested as an offset in LVP, whereas changes in the diastolic PVR slope were observed in other cases.

Conclusion

Temporal alignment scheme based on cardiac events allowed accurate derivation of patient-specific in vivo PVLs from catheterization and RT3DE measurements. Application to heart transplant recipients revealed beat-to-beat variation of haemodynamic state. Further analysis of the diastolic PVRs will allow quantification of chamber stiffness for HTx recipients.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Health Research Council of New Zealand Patient-specific PVLs

Age-related differences in ventricular remodeling and long-term heart failure outcomes following acute coronary syndrome

Background

Older patients are at increased risk of heart failure hospitalization following acute coronary syndrome (ACS).

Purpose

We sought to determine whether this increased hazard was related to differing patterns in left ventricular (LV) remodeling over the first 12 months after ACS.

Methods

In a prospective multi-centre observational cohort study, 2,140 patients with ACS underwent echocardiography at 1, 4, and 12 months following the index event. Long-term heart failure hospitalisation events were captured for a median 4.8 (IQR 3.4–6.5) years and the relative risk compared between individuals ≤65 years and those >65 years using a multivariable Cox model adjusted for baseline clinical (sex, blood pressure, coronary revascularisation) and echocardiographic (LV end diastolic and end systolic volumes, LV ejection fraction, interventricular septal wall thickness, and E/e') variables recorded at baseline and 12 months.

Results

The 1177 (55%) participants who were >65 years were more likely to be women (34% versus 22%), had higher blood pressure, were more likely to present with non-ST elevation ACS, demonstrated smaller increases in peak myocardial biomarkers and were less likely to undergo coronary revascularization during the index admission (43.2% versus 72.3%; p<0.001 for all comparisons). At the 1 month visit, after indexing for body surface area, older patients had similar LV end diastolic but larger end systolic volumes (p=0.029), lower LV ejection fractions, and greater left ventricular mass and diastolic filling pressure estimates (E/e' 14 versus 10; p<0.001 for all) compared with the young. Systolic volumes appeared to further diverge at 12 months (p=0.064) however LV mass did not change in either group. In unadjusted analysis older patients were at increased risk of future heart failure hospitalization (HR 4.1, 95% CI 3.2–5.3). This increased risk persisted after adjustment for differences in baseline clinical and echocardiography data, and LV remodeling (adjusted HR 2.4, 95% CI 1.5–3.9).

Conclusions

Older patients experience a more eccentric remodeling pattern over the 12 months following ACS. Older individuals remain at increased risk of long-term heart failure hospitalization after accounting for clinical and echocardiographic characteristics.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): New Zealand Heart Foundation, New Zealand Health Research Council

Sex differences in ventricular remodeling and long-term heart failure outcomes following acute coronary syndrome

Background

Compared with men, women are at increased risk of heart failure hospitalization following acute coronary syndrome (ACS).

Purpose

We sought to determine whether this increased hazard was associated with differing patterns in left ventricular (LV) remodeling over the first 12 months after ACS.

Methods

In a prospective multi-centre observational cohort study, 2,140 patients with ACS underwent echocardiography at 1, 4, and 12 months following the index event. Heart failure hospitalisation events were captured over a median 4.8 (IQR 3.4–6.5) years and relative risk compared between women and men using a multivariable Cox model adjusted for baseline demographics (age and systolic blood pressure) and echocardiographic variables (LV end diastolic and end systolic volumes, LV ejection fraction, interventricular septal wall thickness, and E/e') captured at baseline and 12 months.

Results

The 609 (28.5%) women were older (mean [SD] age 70 [12] versus 65 [12] years), had higher systolic blood pressure, demonstrated smaller increases in peak myocardial biomarkers, and were less likely to undergo coronary revascularization during the index admission (41.9% versus 62.0%; p<0.001 for all). After indexing for body surface area, women had smaller LV end diastolic and end systolic volumes, greater LV ejection fractions, and greater septal wall thickness and diastolic filling pressure estimates (E/e' 14 versus 11; p<0.001 for all). Diastolic volumes further diverged at 12 months (p=0.05) and septal wall thickness increased compared with men (p=0.016). In unadjusted and adjusted analyses women were at increased risk of future heart failure hospitalization (unadjusted HR 1.5, 95% CI 1.2–1.9, adjusted HR 1.6, 95% CI 1.1–2.4).

Conclusions

Women experience a more concentric remodeling pattern over the 12 months following ACS. Women remain at increased risk of long-term heart failure hospitalization after accounting for clinical and echocardiographic characteristics.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): National Heart Foundation of New Zealand, New Zealand Health Research Council

The relationship between glycosylation of proBNP at threonine 71, BNP, BNP1–32 and obesity in patients with heart failure

Background

Heart failure (HF) is a leading cause of morbidity and mortality worldwide. Measurement of BNP and NTproBNP are used in HF for diagnosis and prognosis but levels of these peptides are inappropriately low in obesity, a condition which is associated with increased HF. Cleavage of proBNP to produce BNP and NT-proBNP requires proBNP to be unglycosylated at threonine 71 (T71). Gycosylation at T71 is affected by obesity, resulting in lower plasma NT-proBNP concentrations in patients with higher BMI. However the relationships between BMI, proBNP glycosylation and BNP (particularly the bioactive cardio-protective peptide BNP1-32) have not previously been described.

Methods

Validated in-house assays for BNP, BNP1-32, proBNP, proBNP unglycosylated at T71 (NG-T71) and the commercial Roche assay for NT-proBNP were applied to plasma samples obtained from patients with HF (n=321, PEOPLE study: Prospective Evaluation of Outcome in Patients with Left Ventricular Ejection Fraction).

Results

Median (IQR) concentrations of BNP, BNP1-32, proBNP, NG-T71 and NTproBNP were 10.7 (5–21), 5 (2–9), 27.8 (9–62), 6.2 (3–22) and 217 (104–425) pmol/L respectively. BMI was inversely related to NG-T71, NT-proBNP, BNP and BNP1-32 (r=−0.19, −0.40, −0.36 and −0.34 respectively, all p<0.01) but not proBNP (r=0.11, ns). ProBNP levels in patients with BMI above or below 30 kg/m2 were similar (29.8 (11.2–56.6) and 22.5 (3.9–65) pmol/L, p=0.51), whereas NG-T71, NT-proBNP, BNP and BNP1-32 levels were increased (p<0.001) in patients with BMI <30 (11.6 (3–25.6), 263 (153–486), 13.8 (6.5–25.5) and 6.3 (2.8–10.4)) compared to BMI >30 (3 (1–16), 127 (63–274), 7.8 (3–14) and 3.6 (1.1–7) respectively. The BMI >30 group had increased ProBNP:NT-proBNP, ProBNP:BNP and ProBNP:BNP1-32 ratios (all p<0.001) and proBNP:NG-T71 (p=0.037), whereas ratios of NG-T71 to BNP, BNP1-32 or NT-proBNP were not related to BMI. Patients with diabetes (n=90) also had lower BNP, BNP1-32 (both p<0.01), NG-T71 and NT-proBNP concentrations (both p<0.05), but not proBNP (p=0.46), and a trend towards a higher proBNP:BNP1-32 ratio (p=0.06).

Discussion and conclusion

The negative association between BMI and plasma NT-proBNP and BNP is not well understood. We recently reported that obese patients with HF have reduced circulating levels of proBNP unglycosylated at T71. In this expanded sample we show that whilst proBNP remains unaffected by BMI, both immunoreactive BNP and more specifically bioactive BNP1–32 levels, and NT-proBNP, are decreased with obesity in conjunction with increased glycosylation at T71. Increased glycosylation at proBNP-T71 reduces the amount of proBNP cleaved to form NT-proBNP and BNP resulting in decreased production and lowered circulating concentrations of these clinically used marker peptides. Our results provide a robust mechanism to explain the reduction in NT-proBNP and BNP levels observed in obese patients and confirm this is associated with reduced bioactive BNP1–32.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Heart Foundation of New Zealand, nHealth Research Council of New Zealand

150 ProBNP glycosylation of threonine 71 is increased with obesity in patients with heart failure

Funding Acknowledgements

The National Heart Foundation of New Zealand

Background

Heart failure (HF) is a leading cause of morbidity and mortality worldwide. Plasma levels of B-type natriuretic peptide (BNP) or its amino terminal congener (NT-proBNP) are used for HF diagnosis and risk stratification.  Circulating levels of both BNP and NT-proBNP are reduced by obesity and this phenomenon is one of the key weaknesses of the diagnostic performance of the natriuretic peptides in HF.  Formation of BNP from enzymatic cleavage of proBNP1-108 between residues 76 and 77 by corin and/or furin is influenced by the degree of proBNP glycosylation, therefore we investigated the relationship between proBNP glycosylation, plasma NT-proBNP and body mass index (BMI) in HF patients.

Methods

Three assays were developed to distinguish between total proBNP (glycosylated plus non-glycosylated proBNP), proBNP not glycosylated at threonine 71 (NG-T71) and proBNP not glycosylated in the central region (NG-C). Intra and inter-assay CVs were <15%, limits of detection were <2 pmol/L and samples diluted in parallel.

Results

Applying these assays and an NT-proBNP assay to plasma samples from 106 healthy volunteers and 238 patients with HF determined that concentrations (median(IQR)) of proBNP, NG-T71 and NT-proBNP were greater in HF patients compared to controls (24.9 (3.6-55), 9.4 (1.5-21) and 212 (104-409) pmol/L vs 3.0 (1.5-19), 3.0 (1.5-14.5) and 4.7 (2-8) pmol/L respectively, all p < 0.012).  NG-C was undetectable in most samples. ProBNP levels in HF patients with BMI above and below 30 kg/m2 were not different (21.9 (2.6-70) pmol/L and 25.7 (3.9-53) pmol/L respectively, p = 0.85), whereas HF patients with BMI > 30 had lower NT-proBNP and NG-T71 levels (121 (64-248) and 3 (1.5-16) pmol/L verse 271 (178-486) and 13.5 (1.5-24.2) pmol/L respectively, p < 0.003) and higher proBNP:NT-proBNP and proBNP:NG-T71 ratios  (p = 0.001 and p = 0.02 respectively) than those with BMI < 30.

Discussion and Conclusion

Using three new assays specific for different glycosylated forms of proBNP we have shown that the processing of proBNP is dysregulated in heart failure compared to controls due to increased glycosylation at threonine 71 of proBNP.  Obese patients with HF have even greater dysregulation, demonstrated by decreased concentrations of proBNP that is not glycosylated at T71 (NG-T71), and concomitant decreases in NT-proBNP.  Thus, we have shown for the first time that increased BMI is associated with increased proBNP glycosylation at T71 in patients with heart failure.  Glycosylation-induced impairment of proBNP processing explains, at least in part, the reduction in plasma concentrations of B-type cardiac natriuretic peptides observed in obesity. Using these assays to evaluate the proBNP profile of larger patient cohorts will further develop understanding of the relationships between BNP production, BMI and heart failure pathogenesis, which would be expected to lead to increased diagnostic performance.

P4360Personalised shape models of the left ventricle from 3D echocardiography: an initial comparison to cardiac magnetic resonance imaging

Background

The heart constantly adapts to maintain cardiac output. In the longer term, this process (remodeling) can manifest as changes in ventricular volume, sphericity, and/or wall thickness, amongst several other morphological indices. Previous studies have shown the significance of remodeling in evaluations of survival, and as a determinant of the clinical course of heart failure. Yet surprisingly, diagnostic measures, typically of left ventricular (LV) mass and ejection fraction, neglect much of the shape information that is available through imaging. A recent UK Biobank study revealed that morphometric atlases show more compelling associations with cardiovascular risk factors, than do LV mass and volumes. While it has been possible to construct shape models from cardiac magnetic resonance imaging (MRI), such a framework is still under development for echocardiography (echo).

Purpose

Despite MRI being long regarded as the gold standard, it is greatly limited by high costs, long scan times and incompatibility with ferromagnetic cardiac devices. In contrast, echo has presented as a convenient alternative, whilst also offering good temporal resolution. The advancements of 3D echo now provide adequate spatial resolution and thus elicit the possibility of conducting more complex analyses on this modality. With the ability to extract LV geometry directly from 3D echo acquisitions, we sought to create dynamic, 3D patient-specific models–and subsequently compare these results to those derived from MRI.

Methods

As part of an ongoing study, 8 volunteers with no known cardiovascular problems (nor family history thereof), were recruited for non-invasive imaging. Cine MRI and 3D echo of the LV were acquired within a 2 hour session. A Siemens Avanto Fit 1.5 T MRI scanner and Siemens ACUSON SC2000 Ultrasound System with a 4Z1c Transducer were used. 3D models of the LV were generated independently from echo (EchobuildR 2.7 prototype software, Siemens Ultrasound) and MRI acquisitions (Cardiac Image Modeller v8.1), and registered to fiducial landmarks (apex, base plane, right ventricular inserts) and myocardial contours.

Results

Euclidian distances between 1682 corresponding points sampled from the surface of echo/MRI models were calculated, and used as a discrepancy measure (Figure). Across the 8 cases, we found an average root mean square deviation (RMSD) of 5.71 mm at end-systole and 6.03 mm at end-diastole. The maximum RMSD for a single model was 9.47 mm (case 8, ES).

Conclusion

We demonstrate that it is possible to create shape models from 3D echo examinations for comparison with MRI. As more cases are collected, we will devise methods to objectively quantify the mismatch that may arise between models derived from the two modalities. The establishment of such a framework would not only provide previously unavailable measures of shape and function, but in turn leverage the significantly wider clinical reach of echocardiography.

Screening for Atrial Fibrillation

Approximately 10% of ischemic strokes are associated with atrial fibrillation (AF) first diagnosed at the time of stroke. Detecting asymptomatic AF would provide an opportunity to prevent these strokes by instituting appropriate anticoagulation. The AF-SCREEN international collaboration was formed in September 2015 to promote discussion and research about AF screening as a strategy to reduce stroke and death and to provide advocacy for implementation of country-specific AF screening programs. During 2016, 60 expert members of AF-SCREEN, including physicians, nurses, allied health professionals, health economists, and patient advocates, were invited to prepare sections of a draft document. In August 2016, 51 members met in Rome to discuss the draft document and consider the key points arising from it using a Delphi process. These key points emphasize that screen-detected AF found at a single timepoint or by intermittent ECG recordings over 2 weeks is not a benign condition and, with additional stroke factors, carries sufficient risk of stroke to justify consideration of anticoagulation. With regard to the methods of mass screening, handheld ECG devices have the advantage of providing a verifiable ECG trace that guidelines require for AF diagnosis and would therefore be preferred as screening tools. Certain patient groups, such as those with recent embolic stroke of uncertain source (ESUS), require more intensive monitoring for AF. Settings for screening include various venues in both the community and the clinic, but they must be linked to a pathway for appropriate diagnosis and management for screening to be effective. It is recognized that health resources vary widely between countries and health systems, so the setting for AF screening should be both country- and health system-specific. Based on current knowledge, this white paper provides a strong case for AF screening now while recognizing that large randomized outcomes studies would be helpful to strengthen the evidence base.