Nistri, Stefano

BACKGROUND: Bicuspid aortic valve (BAV) is a frequent congenital heart defect with a high heritability. Despite this, only a limited number of genes have been associated with the disease, and the molecular mechanisms remain unexplained in most cases. This study aimed to further understand the genetic architecture of BAV. METHODS: A genome-wide association study meta-analysis including 9631 cases among 65 677 participants was performed. Genes were prioritized using transcriptomic analyses based on RNA sequencing in relevant tissues, including human fetal and adult aortic valves. The impact of the knockdown or knockout of 4 candidate genes on cardiac development was verified in zebrafish. A polygenic risk score was developed, its association with BAV was evaluated in an independent cohort, and its association with a wide range of phenotypes (n=976) was evaluated in UK Biobank (n=355 618 individuals). RESULTS: Thirty-six genomic loci were identified, including 32 that were not described previously. Among the prioritized genes, KANK2 and ERBB4 were identified as potentially causal through transcriptomic analyses, colocalization, and Mendelian randomization based on gene expression in human aortic valves (n=484), whereas PRDM6 and STRN were prioritized using similar analyses from aortic (n=326) and left ventricular tissues (n=326), respectively. Targeting 4 candidate genes ( WNT4 , LEF1 , STRN , and KANK2 ) in zebrafish led to disruption in cardiac development. A polygenic risk score was associated with an odds ratio of 2.07 (95% CI, 1.90–2.25; P =5.43×10 -62 ) per SD for BAV and significantly associated with thoracic aortic aneurysm and atrial fibrillation in UK Biobank. CONCLUSIONS: This study supports a significant polygenic contribution to BAV, where the combination of multiple common variants in genes involved in heart morphogenesis disrupts aortic valve development.

Background: Left atrial assessment is complex, particularly in heart failure with reduced ejection fraction due to interactions with functional mitral regurgitation (FMR). Pilot data suggest that left atrial volumetric/mechanical coupling index (LACI) may be useful, but large outcome data are lacking. Methods: We enrolled a comprehensively characterized cohort of patients in sinus rhythm with heart failure with reduced ejection fraction diagnosis at Mayo Clinic from 2007 to 2011. Routinely measured left atrial volume index and tissue-doppler-imaging a’ allowed LACI calculation as (left atrial volume index)/(tissue-doppler-imaging a’). Survival was the outcome measured. Results: The cohort’s 4196 patients (69 [58–77] years, ejection fraction 40 [31–45]%) had mild FMR in 1505 and moderate-severe FMR in 1068. LACI was overall 5.06 (3.50–8.10) and increased with each FMR grade (3.86 [2.94–5.29] without FMR, 5.38 [3.80–8.02] with mild, 5.45 [1.49–8.07] with moderate/severe FMR; P <0.0001). At diagnosis, higher LACI was independently determined by more severe FMR and by higher left ventricular mass index, lower ejection fraction, higher E/e’, and lower glomerular filtration rate (all P <0.0001). During follow-up 1588 (38%) patients died. In spline modeling, excess mortality appeared around LACI=6 and steeply increased thereafter (5-year survival 72±1% with LACI<6 and 49±2% with LACI ≥6, P <0.0001). Multivariable comprehensive adjustment showed LACI strong association with excess mortality (adjusted hazard ratio, 1.41 [1.23–1.61], P <0.0001 for LACI ≥6). Independent link to mortality persistent across FMR grades (adjusted hazard ratio, 1.45 [1.13–1.86], P =0.004 without FMR, 1.42 [1.16–1.77], P =0.0008 with mild FMR, and 1.38 [1.01–1.66], P =0.04 with moderate/severe FMR) without interaction ( P =0.3). LACI independent impact on outcome was incremental to that of left atrial volume index, tissue-doppler-imaging a’, or any other characteristic including the Meta-Analysis Global Group in Chronic-score (least significant P =0.02). Conclusions: In this large cohort, left atrial volumetric/mechanical coupling measured by LACI in routine practice integrates the influence of several morphological/hemodynamic determinants but displays progressive deterioration with increasing FMR severity in heart failure with reduced ejection fraction. About outcome, higher LACI is strongly, independently, and incrementally associated with excess mortality, irrespective of FMR grade and in all subsets. Hence, LACI is a novel and critical measure in heart failure with reduced ejection fraction, quantifiable in routine practice, which should be integrated in prognostication and decision-making.

Coronary microvascular dysfunction (CMD) is an important primary feature of hypertrophic cardiomyopathy (HCM), contributing to myocardial ischemia and ventricular remodelling, and is predictive of adverse outcome. Whether there is any association between presence/severity of CMD and HCM’s pathogenic substrate remains to be determined. To address this issue, we used positron emission tomography (PET) to assess CMD in an HCM cohort that received comprehensive genetic testing for sarcomeric/myofilament-HCM. We measured maximum (intravenous dipyridamole, 0.56 mg/kg) myocardial blood flow (Dip-MBF), using 13 N-labeled ammonia and PET in 46 HCM patients (age 38±14 years, 32 male). Genetic testing was performed by denaturing high performance liquid chromatography and automatic DNA sequencing of nine myofilament-encoding genes including both thick filament proteins (myosin binding protein C, beta-myosin heavy chain, regulatory and essential light chains); and thin filament proteins (troponin-T, troponin-I, troponin-C, alpha-tropomyosin and alpha-actin). Results . Thirty-four mutations were identified in 30/46 patients (myofilament-HCM; 65%), including 29 with thick filament and 6 with thin filament mutations, as well as 4 with complex genotype. Despite similar age and clinical features, patients with myofilament-HCM showed lower Dip-MBF values than the patients with a negative genetic test (1.6±0.7 versus 2.2±0.9 ml/min/g, respectively; p=0.03). Specifically, 13/30 (43%) patients with myofilament-HCM had a Dip-MBF below the lower tertile for the study group (≤1.38 ml/min/g), compared to 2/16 (12%) patients with a negative genetic test (p=0.034). No difference in Dip-MBF was evident with respect to the particular sarcomeric gene involved (ANOVA p=0.63). HCM due to sarcomere gene mutations is characterized by more severe impairment in microvascular function compared to myofilament negative disease, irrespective of the involved contractile protein. These findings suggest that sarcomeric mutations might be implicated in adverse remodelling of the microcirculation in patients with HCM, and account for the greater prevalence of ventricular dysfunction and failure in this subset.

The need for multiple transducer positions, especially from right parasternal windows, is consistently mentioned in the recommendations for the accurate measurement of peak velocities across a stenotic aortic valve, but yet poorly adopted. We performed a subanalysis of the largest prospective series on the right parasternal acoustic windows in patients with aortic stenosis (330 consecutive) to calculate the degree of misalignment and estimate the potential outcome implication of this often-forgotten approach. The right parasternal view was highly feasible with an average estimated misalignment from the apical view of 14 ± 16 degree; in 10 cases, an estimated misalignment >40 degree. Right parasternal assessment (vs. apical alone) provided a significant reclassification from moderate to severe or even very-severe aortic valve stenosis. Considering a wellestablished survival benefit provided by either percutaneous or surgical valve replacement in patients with severe aortic stenosis the reclassification would result in approximately 1 life-year saved for every 30–35 patients in whom parasternal view were effectively utilized.