Cardiovascular structure and function assessed by MRI in healthy South Asians compared to White Europeans: a UK Biobank study

Background

There is limited data on ethnic specific comparisons for measures of cardiovascular structure and function in healthy cohorts. Echocardiographic data indicate South Asian's (SAs) have smaller mass and evidence of more concentric remodelling compared to White Europeans (WEs). Furthermore, there is no data published for strain or strain rates.

Purpose

To compare Cardiac Magnetic Resonance (CMR) derived measures of structure and function between age and sex matched healthy SAs and WEs from the UK biobank cohort.

Methods

South Asian and WE participants from the UK Biobank who underwent CMR imaging were included. Individuals with a history of cardiovascular disease, hypertension, obesity (BMI ≥30 kg/m2 in WEs and ≥27 kg/m2 in SAs) and diabetes were excluded. Ethnic groups were matched according to age and sex at recruitment. Cine images (bSSFP) were analysed blinded to participant details using commercially available software. Left ventricular (LV) mass, LV volumes, global longitudinal and circumferential systolic strain (GLS and GCS), together with peak early diastolic strain rates (PEDSR), were obtained. Data distributions were assessed and T-Test or Man Whitney U conducted as appropriate.

Results

Datasets from the UK biobank were screened (n=45000). After applying exclusion criteria, 111 pairs of matched SAs and WEs were available for analysis (n=69 male and n=42 female matched pairs). Mean age of the entire cohort was 58±8 years. Data has been corrected according to body surface area (BSA),(males: WE 2.0±0.1 vs SA 1.8±0.1 m2, p≤0.001; females: WE 1.7±0.2 vs SA 1.6±0.1 m2, p≤0.001). There was no difference in heart rate (males: WE 64.5±9.3 vs SA 65.8±9.6 bpm, p=0.113; females: WE 66.2±7.8 vs SA 69.5±10.3 bpm, p=0.125). Results by sex and ethnicity are displayed in table 1. In males there was no difference in ejection fraction (EF) or indexed LV end diastolic volume (LVEDV). However indexed mass and mass/volume ratio were significantly lower in SAs, and GLS but not GCS was significantly higher than in SAs. Longitudinal PEDSR were significantly higher in SAs than in WE. By contrast, SA females had significantly lower EF with no difference in indexed LVEDV compared to WE females. However, as seen with the males SA females had significantly lower indexed LV mass and mass/volume ratio compared to WE females. Finally, both GLS and GCS were significantly higher in SAs compared to WE females, whereas there was no difference in longitudinal PEDSR.

Conclusion

Substantial differences in cardiovascular structure and function exist between SA and WE ethnic groups, in both men and women. Contrary to previous echocardiographic studies, LV volumes were similar between ethnicities and SA have less, not increased, concentric remodelling than WE. These findings highlight the need for ethnicity and sex-specific healthy reference ranges derived from CMR.

Funding Acknowledgement

Type of funding sources: None.

Magnetic resonance imaging in the evaluation of idiopathic frequent premature ventricular complexes with normal ventricular function

Background

The role of cardiac magnetic resonance (CMR) imaging in the diagnostic evaluation of patients with frequent premature ventricular complexes (PVCs) and normal left ventricular ejection fraction (LVEF) remains unclear. Existing data has been predominantly derived from highly selected populations, that may overestimate the true prevalence of abnormal findings on CMR in this patient population.

Purpose

The aim of this study was 2-fold: 1) to establish the prevalence of CMR imaging abnormalities in a cohort with normal LVEF and high PVC burden; 2) to identify predictors of CMR imaging abnormalities in patients with frequent PVCs and normal LVEF.

Methods

In this cohort study, 211 patients (age 53.2±19 years; 41% male) with frequent PVCs (≥5%/24 h), of normal LVEF (≥50% by echocardiography) and no known underlying structural heart disease were prospectively enrolled from 2016–2020. Of these, 166 (79%) patients were symptomatic from their PVCs in the form of palpitations, fatigue, chest pain, dizziness, and/or dyspnea. Patients underwent CMR imaging (1.5 Tesla) with a late gadolinium enhancement (LGE) protocol at the time of enrollment for the detection of scarring and/or fibrosis.

Results

Patients had a median baseline echocardiographic LVEF of 60% (± 5%) with 195 (92%) of patients having a normal native QRS morphology. Median PVC burden of the study cohort was 16% (± 14%). CMR LGE abnormalities were found in 19 (9%) patients including 17 scans with non-ischemic LGE and 2 with ischemic LGE. Age >60 (odds ratio [OR]: 3.20, 95% confidence interval [CI]: 1.20–8.51, p=0.020), male sex (OR: 4.67, 95% CI: 1.61–13.50, p=0.004), history of hypertension (OR: 3.43, 95% CI: 1.31–8.97, p=0.012), native QRS duration (OR: 1.03, 95% CI: 1.00–1.05, p=0.031), and history of non-sustained ventricular tachycardia (OR: 2.81, 95% CI: 1.03–7.68, p=0.044) were significantly associated with the presence of imaging abnormalities on CMR. Dominant PVC origin from the left ventricle had a positive trend (OR: 2.60, 95% CI: 0.99–7.66, p=0.083) to association with CMR imaging abnormalities. On multivariate analysis, male sex (OR: 4.10, 95% CI: 1.40–12.04, p=0.010) and history of hypertension (OR: 2.89, 95% CI: 1.08–7.75, p=0.035) remained significantly associated with the presence of CMR abnormalities. There was no association between CMR imaging abnormalities and the burden of PVCs or the number of PVC morphologies.

Conclusion

In this cohort, only 9% of patients with apparently idiopathic frequent PVCs and normal LVEF had concealed myocardial abnormalities on CMR imaging. Male sex and history of hypertension were associated with a higher rate of CMR abnormalities.

Funding Acknowledgement

Type of funding sources: None.

Cardiac magnetic resonance strain and mechanical dispersion assessment in patients with chronic total coronary artery occlusion

Background

Chronic total occlusions (CTO) are a frequent angiographic finding. Viability of CTO-subtended myocardium is dependent on the presence of an adequate collateral circulation. At rest, collateral supply may be sufficient to avert ischaemia and maintain normal systolic function. However, it remains unclear whether CTO-subtended myocardium may be considered truly normal, or whether subtle functional abnormalities may be present at rest.

Purpose

To determine whether, in the absence of infarction and hibernation, CTO-subtended myocardium remains functionally normal or whether abnormalities of strain and/or mechanical dispersion may be present at rest.

Methods

In a retrospective, single centre, observational study, we studied patients with ≥1 angiographically-diagnosed CTO referred for clinical stress perfusion cardiovascular magnetic resonance (CMR), and compared healthy volunteers (HVs) with a normal stress CMR scan. CMR imaging comprised functional and scar assessment with qualitative [visual] evaluation of infarction and segmental wall motion. Patients with infarction and/or wall motion score index (WMSI) ≥1 were excluded from further analysis. In remaining CTO subjects and HVs, segmental peak systolic longitudinal strain and circumferential strain were analysed (in 3 long-axis planes and 3 short-axis planes, respectively) and mechanical dispersion for both orientations was computed. Image analysis was performed using Medis (QStrain) software blinded to all clinical information.

Results

From a total of 389 patients with ≥1 angiographically-diagnosed CTO, 68 had normal WMSI and no infarction (63.0±11.7 years, 79.4% male, LVEF 62.6±4.5%). Fifty HVs (61.1±7.0 years, 74.0% males, LVEF 61.1±5.3%) were also studied. The majority of CTO patients had concomitant coronary artery disease in at least one non-CTO vessel (n=37, 54.4%). GLS was lower in CTO patients than HVs (−21.8%±1.5% versus −24.0±1.1%; p<0.0001; Figure 1). By contrast, GCS was greater in CTO patients (−32.7±2.5% versus −28.8±2.1%; p<0.0001). Mechanical dispersion was increased in CTO patients (Figure 2), both longitudinally (90.3±14.6 ms in CTO patients versus 68.6±11.1 ms in HVs; p<0.0001) and circumferentially (66.7±9.1 ms versus 55.3±6.6 ms, respectively; p=0.02).

Conclusion

Subclinical changes in left ventricular dynamics are present at rest in CTO patients with fully viable myocardium and no evidence of resting regional wall abnormality. Further study is warranted to evaluate the potential association between mechanical dispersion and arrhythmic events in CTO.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): NIHR Clinician Scientist Award (CS-2018-18-ST2-007 to J.R.A.) and Research Professorship award (RP-2017-08-ST2-007 to G.P.M.). Figure 1. Strain analysis. CTO vs HVFigure 2. Mechanical dispersion. CTO vs HV

Cardiovascular determinants of exercise capacity in people with type 2 diabetes

Background

The determinants of exercise capacity in people with type 2 diabetes (T2D), a group at high risk of heart failure, are unknown.

Purpose

To assess the relationship between subclinical cardiovascular dysfunction and peak VO2 in adults with T2D.

Methods

We enrolled asymptomatic adults with T2D and no prevalent cardiovascular disease. Matched controls were recruited for comparison. Subjects underwent echocardiography, cardiopulmonary exercise testing and adenosine stress cardiac MRI. Multivariable linear regression analysis was undertaken to identify independent associations between measures of cardiovascular structure and function and peak VO2 (Figure 1).

Results

247 adults with T2D (age 52±12y, 55% males, A1c 7.4±1.1%) and 78 controls were included. Subjects with T2D had increased concentric LV remodelling (LV mass/volume 0.84±0.14 vs. 0.76±0.11g/mL, p<0.001), reduced global longitudinal strain (−16.4±2.4 vs. −17.4±1.9%, p<0.001), lower aortic distensibility (2.75 (1.74–4.03) vs. 4.92 (2.65–7.13) mmHg-1x10–3, p<0.001), reduced myocardial perfusion reserve (2.60±1.24 vs. 3.54±1.15, p<0.001), and lower peak VO2 (19.0±5.6 vs. 28.0±9.1mL/kg/min, p<0.001) than controls. In a model containing age, sex, ethnicity, smoking status and systolic blood pressure, aortic distensibility (β=−0.466, p=0.033), E/e' (β=−0.344, p=0.001) and myocardial perfusion reserve (β=0.903, p=0.005) were independently associated with peak VO2 in subjects with T2D (Table 1).

Conclusions

In asymptomatic people with T2D, aortic stiffening, diastolic filling, and myocardial perfusion reserve are key determinants of peak VO2, independent of age, sex, ethnicity, smoking status, or blood pressure.

Figure 1

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): National Institute for Health Research - Career Development Fellowship (G P McCann, CDF-2014-07-045). British Heart Foundation - Clinical Research Training Fellowship (G S Gulsin)

Reproducibility of left atrial assessment in cardiac magnetic resonance imaging

Background

Left atrial (LA) volume and strain are recognised as predictors of adverse outcomes in cardiovascular disease. We aimed to determine the test-retest reproducibility of LA assessment derived from cardiac MRI in subjects with and without cardiovascular disease.

Methods

38 participants had two MRI scans a week apart: aortic stenosis (n=16); type 2 diabetes (n=16) and healthy volunteers (n=6). Images were analysed by a single trained observer using Medis v3.1, medical imaging system, Leiden, Netherlands. LA strain and strain rate were assessed with Feature Tracking (QStrain v2.0), corresponding to LA reservoir, conduit, and contractile function. LA ejection fraction (LAEF) was calculated using biplane area-length method (QMass v8.1). Both were assessed on 4- and 2-chamber long-axis standard steady-state free precession cine images, and average values calculated.

Results

As shown in the table, the test-retest reproducibility for strain and strain rate was moderate for reservoir phase (CoV 25–28%, ICC ∼0.70) and poor for conduit and contraction phases (CoV>40%). The test-retest repeatability for LA volumes and LAEF was good (CoV 16–29%, ICC≥0.70).

Conclusion

LA strain assessment using feature tracking is a poorly reproducible technique on CMR. However, good test-retest reproducibility for LA volumes and EF.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): King Saud bin Abdulaziz University for Health Sciences, Riyadh, Kingdom of Saudi Arabia.