Size and function of the atria

Takotsubo syndrome: left atrial and ventricular myocardial strain impairment in the subacute and convalescent phases assessed by CMR

BACKGROUND

We investigated the differences in impairment of left ventricle (LV) and left atrium (LA) contractile dysfunction between subacute and convalescent takotsubo syndrome (TTS), using myocardial strain analysis by cardiac magnetic resonance (CMR) feature-tracking technique.

METHODS

We retrospectively selected 50 patients with TTS clinical-radiological diagnosis who underwent CMR within 30 days since symptoms onset: 19 studied during the early subacute phase (sTTS, ≤ 7 days) and 31 during the convalescence (cTTS, 8-30 days). We measured the following: LV global longitudinal, circumferential, and radial strain (lvGLS, lvGCS, lvGRS) and strain rate (SR) and LA reservoir (laS_r), conduit (laS_cd), and booster pump strain (laS_bp) and strain rate (laSR_r, laSR_cd, laSR_bp). Patients were compared with 30 age- and sex-matched controls.

RESULTS

All patients were women (mean age 63 years). TTS patients showed altered LV- and LA-strain features, compared to controls. sTTS was associated with increased laS_bp (12.7% versus 9.8%) and reduced lvEF (47.4% versus 54.8%), lvGLS (-12.2% versus 14.6%), and laS_cd (7.0% versus 9.5%) compared to cTTS (p ≤ 0.029). The interval between symptoms onset and CMR was correlated with laS_bp (r = -0.49) and lvGLS (r = 0.47) (p = 0.001 for both). At receiver operating characteristics analysis, laS_bp was the best discriminator between sTTS and cTTS (area under the curve [AUC] 0.815), followed by lvGLS (AUC 0.670).

CONCLUSIONS

LA dysfunction persists during the subacute and convalescence of TTS. laS_bp increases in subacute phase with progressive decrease during convalescence, representing a compensatory mechanism of LV dysfunction and thus a useful index of functional recovery.

RELEVANCE STATEMENT

Atrial strain has the potential to enhance the delineation of cardiac injury and functional impairment in TTS patients, assisting in the identification of individuals at higher risk and facilitating the implementation of more targeted and personalized medical therapies.

KEY POINTS

• In TTS, after ventricular recovery, atrial dysfunction persists assessable with CMR feature tracking. • Quantitative assessment of atrial strain discriminates atrial functions: reservoir, conduit, and booster pump. • Atrial booster pump changes after acute TTS, regardless of ventricular function. • Atrial strain may serve as a temporal marker in TTS.

Tbx5 maintains atrial identity in post-natal cardiomyocytes by regulating an atrial-specific enhancer network

Understanding how the atrial and ventricular heart chambers maintain distinct identities is a prerequisite for treating chamber-specific diseases. Here, we selectively knocked out (KO) the transcription factor Tbx5 in the atrial working myocardium to evaluate its requirement for atrial identity. Atrial Tbx5 inactivation downregulated atrial cardiomyocyte (aCM) selective gene expression. Using concurrent single nucleus transcriptome and open chromatin profiling, genomic accessibility differences were identified between control and Tbx5 KO aCMs, revealing that 69% of the control-enriched ATAC regions were bound by TBX5. Genes associated with these regions were downregulated in KO aCMs, suggesting they function as TBX5-dependent enhancers. Comparing enhancer chromatin looping using H3K27ac HiChIP identified 510 chromatin loops sensitive to TBX5 dosage, and 74.8% of control-enriched loops contained anchors in control-enriched ATAC regions. Together, these data demonstrate TBX5 maintains the atrial gene expression program by binding to and preserving the tissue-specific chromatin architecture of atrial enhancers.

An expert review of the inverse problem in electrocardiographic imaging for the non-invasive identification of atrial fibrillation drivers

BACKGROUND AND OBJECTIVE

Electrocardiographic imaging (ECGI) has emerged as a non-invasive approach to identify atrial fibrillation (AF) driver sources. This paper aims to collect and review the current research literature on the ECGI inverse problem, summarize the research progress, and propose potential research directions for the future.

METHODS AND RESULTS

The effectiveness and feasibility of using ECGI to map AF driver sources may be influenced by several factors, such as inaccuracies in the atrial model due to heart movement or deformation, noise interference in high-density body surface potential (BSP), inconvenient and time-consuming BSP acquisition, errors in solving the inverse problem, and incomplete interpretation of the AF driving source information derived from the reconstructed epicardial potential. We review the current research progress on these factors and discuss possible improvement directions. Additionally, we highlight the limitations of ECGI itself, including the lack of a gold standard to validate the accuracy of ECGI technology in locating AF drivers and the challenges associated with guiding AF ablation based on post-processed epicardial potentials due to the intrinsic difference between epicardial and endocardial potentials.

CONCLUSIONS

Before performing ablation, ECGI can provide operators with predictive information about the underlying locations of AF driver by non-invasively and globally mapping the biatrial electrical activity. In the future, endocardial catheter mapping technology may benefit from the use of ECGI to enhance the diagnosis and ablation of AF.

Tbx5 maintains atrial identity by regulating an atrial enhancer network

Understanding how the atrial and ventricular chambers of the heart maintain their distinct identity is a prerequisite for treating chamber-specific diseases. Here, we selectively inactivated the transcription factor Tbx5 in the atrial working myocardium of the neonatal mouse heart to show that it is required to maintain atrial identity. Atrial Tbx5 inactivation downregulated highly chamber specific genes such as Myl7 and Nppa , and conversely, increased the expression of ventricular identity genes including Myl2 . Using combined single nucleus transcriptome and open chromatin profiling, we assessed genomic accessibility changes underlying the altered atrial identity expression program, identifying 1846 genomic loci with greater accessibility in control atrial cardiomyocytes compared to KO aCMs. 69% of the control-enriched ATAC regions were bound by TBX5, demonstrating a role for TBX5 in maintaining atrial genomic accessibility. These regions were associated with genes that had higher expression in control aCMs compared to KO aCMs, suggesting they act as TBX5-dependent enhancers. We tested this hypothesis by analyzing enhancer chromatin looping using HiChIP and found 510 chromatin loops that were sensitive to TBX5 dosage. Of the loops enriched in control aCMs, 73.7% contained anchors in control-enriched ATAC regions. Together, these data demonstrate a genomic role for TBX5 in maintaining the atrial gene expression program by binding to atrial enhancers and preserving tissue-specific chromatin architecture of atrial enhancers.

The Indices of Cardiovascular Magnetic Resonance Derived Atrial Dynamics May Improve the Contemporary Risk Stratification Algorithms in Children with Hypertrophic Cardiomyopathy

Introduction: The most efficient risk stratification algorithms are expected to deliver robust and indefectible identification of high-risk children with hypertrophic cardiomyopathy (HCM). Here we compare algorithms for risk stratification in primary prevention in HCM children and investigate whether novel indices of biatrial performance improve these algorithms. Methods and Results: The endpoints were defined as sudden cardiac death, resuscitated cardiac arrest, or appropriate implantable cardioverter-defibrillator discharge. We examined the prognostic utility of classic American College of Cardiology/American Heart Association (ACC/AHA) risk factors, the novel HCM Risk-Kids score and the combination of these with indices of biatrial dynamics. The study consisted of 55 HCM children (mean age 12.5 ± 4.6 years, 69.1% males); seven had endpoints (four deaths, three appropriate ICD discharges). A strong trend (DeLong p = 0.08) was observed towards better endpoint identification performance of the HCM Risk-Kids Model compared to the ACC/AHA strategy. Adding the atrial conduit function component significantly improved the prediction capabilities of the AHA/ACC Model (DeLong p = 0.01) and HCM Risk-Kids algorithm (DeLong p = 0.04). Conclusions: The new HCM Risk-Kids individualised algorithm and score was capable of identifying high-risk children with very good accuracy. The inclusion of one of the atrial dynamic indices improved both risk stratification strategies.

Combined assessment of left atrial volume parameters for predicting recurrence of atrial fibrillation following pulmonary vein isolation in patients with paroxysmal atrial fibrillation

OBJECTIVES

Our aim was to test the hypothesis that comprehensive simplified left atrial (LA) assessment derived from routine echocardiography may be more useful than assessment of LA volume alone for predicting atrial fibrillation (AF) recurrence after pulmonary vein isolation (PVI).

METHODS

We studied 156 patients with paroxysmal AF (PAF) who had undergone PVI. Echocardiography was performed within two days before PVI. Maximum (Max-LAVi) and minimum LA volume index (Min-LAVi) were calculated with the biplane modified Simpson's method, and then normalized to the body surface area. On the basis of previous findings, the predefined cutoff value of Max-LAVi for AF recurrence was set at Max-LAVi ≥ 34 mL/m² . ΔLA volume index (ΔLAVi) was also calculated as Max-LAVi minus Min-LAVi. The follow-up period after PVI was 24 months.

RESULTS

AF recurrence was observed in 35 patients. Multivariate logistic regression analysis showed that ΔLAVi (odds ratio [OR]: 1.131; 95% confidence interval [CI]: 1.057-1.221; P < 0.001) was an independent predictor of AF recurrence. Sequential logistic regression models for predicting AF recurrence revealed that a model based on clinical variables including age, gender and AF duration (χ²  = 1.65) was improved by the addition of Max-LAVi ≥ 34 mL/m² (χ²  = 13.8; P < 0.001), and further improved by the addition of ΔLAVi (χ²  = 18.2; P = 0.036). Of note is that only 1.02 ± 0.10 minutes per patient was needed to obtain a comprehensive LA assessment that included Max-LAVi, Min-LAVi, and ΔLAVi.

CONCLUSION

This easy-to-use comprehensive simplified LA approach from routine echocardiography may well have clinical implications for better management of PAF patients.

Biatrial performance in children with hypertrophic cardiomyopathy: CMR study

OBJECTIVES

To investigate biatrial mechanics and their relation with left ventricular outflow tract (LVOT) obstruction (LVOTO), the degree of hypertrophy, indices of ventricular diastolic function and fibrosis in children with hypertrophic cardiomyopathy (HCM).

METHODS

Fifty-five consecutive, prospectively recruited children with HCM (mean age 12.5 ± 4.6 years, 69.1% male), 19 (34.5%) of whom had LVOTO, underwent cardiac magnetic resonance and echocardiography with quantification of phasic components of biatrial function, biventricular diastolic function and fibrosis. Twenty healthy, sex-matched subjects served as controls.

RESULTS

We found a significant increase of left atrial (LA) and right atrial (RA) volumes and reduction in the majority of indices of contractile function, strains and strain rates (p < 0.05) in children with HCM compared with controls. Nearly all of the LA dynamics markers attained a significant association with the LVOT gradient (p < 0.05), the RA volumes and contractile functions were affected by LV fibrosis and mass (p < 0.05), and the RA mechanical components were related to the degree of LVOTO (p < 0.05). The minority of biatrial dynamics markers were associated with indices of ventricular diastolic function.

CONCLUSIONS

The majority of biatrial volumetric and functional indices were severely compromised in children with HCM compared with controls. The degree of LVOTO appears to trigger LA volumetric and LA and RA mechanical malfunction. On the other hand, the deterioration of RA volumetric components was linked to LV fibrosis and mass.

KEY POINTS

• Biatrial function was severely compromised in children with HCM. • Left atrial malfunction was associated with the degree of LVOTO. • Fibrosis and LV mass were related to RA volumetric and contractile dysfunction. • The degree of LVOTO was linked to right atrial mechanical abnormalities.

Clinical Utility of Left Atrial Strain in Children in the Acute Phase of Kawasaki Disease

BACKGROUND

We aimed to evaluate the diagnostic utility of peak left atrial longitudinal strain (PALS) during left ventricular (LV) systole to differentiate children in the acute phase of Kawasaki disease (aKD) from controls. We also aimed to compare the diagnostic utility of PALS with those of conventional echocardiographic indices of diastolic function.

METHODS

Retrospectively measured PALS, LV longitudinal peak systolic strain, and strain rate obtained via velocity vector imaging were compared in a derivation cohort comprising 95 aKD and 67 controls. The utility of PALS in differentiating aKD from controls was compared with those of E/E', E/A, and maximum left atrial volume index (LAVImax). Derived cutoffs from receiver operating characteristic curves were validated in a separate validation cohort comprising 37 aKD and 19 controls.

RESULTS

In the derivation cohort, PALS was significantly decreased in aKD as compared with in controls. For differentiating aKD from controls, PALS outperformed E/E', E/A, and LAVImax. However, cutoffs of PALS (≤40% and ≤39%, before and after adjusting for the presence of significant mitral regurgitation and LV systolic dysfunction, respectively), like those of E/E', E/A, and LAVImax, showed low sensitivity and poor discriminative ability for differentiating aKD from controls. In the validation cohort, for differentiating aKD from controls, both cutoffs of PALS showed low sensitivity, like those of E/E', E/A, and LAVImax.

CONCLUSION

In aKD, impaired left atrial reservoir function could be detected as decreased PALS. For differentiating aKD from controls, PALS outperforms E/E', E/A, and LAVImax. However, like E/E', E/A, and LAVImax, PALS as a single parameter is limited in its clinical utility to differentiate aKD from controls because of its low sensitivity and poor discriminative ability.

Left ventricular filling patterns in patients with previous myocardial infarction measured by conventional cine cardiac magnetic resonance

To explore left ventricular filling patterns in patients with a history of previous myocardial infarction (MI) using time-volume curves obtained from conventional cine-cardiac magnetic resonance (CMR) examinations. Consecutive patients with a history of previous MI who were referred for CMR evaluation constituted the study population, and a consecutive cohort of sex and age-matched patients with a normal CMR constituted the control group. The following CMR diastolic parameters were evaluated: peak filling rate (PFR), time to PFR (tPFR), normalised PFR adjusted for diastolic volume at PFR (nPFR), and percent RR interval between end systole and PFR. Fifty patients were included, 25 with a history of previous MI and 25 control. The mean age was 59.6 ± 13.9 years and 27 (54%) were male. Within the control group, age was significantly related to PFR (r = -0.53, p = 0.007), whereas among patients with previous MI age was not related to PFR (r = -0.16, p = 0.44). PFR (252.4 ± 96.7 ml/s vs. 316.0 ± 126.4 ml/s, p = 0.05) and nPFR (1.6 ± 1.2 vs. 3.3 ± 1.5, p < 0.001) were significantly lower in patients with previous MI, whereas no significant differences were detected regarding tPFR (143.0 ± 67.5 ms vs. 176.2 ± 83.9 ms, p = 0.13) and % RR to PFR (18.1 ± 9.7% vs. 20.6 ± 12.2%, p = 0.44). MI size was related to LV ejection fraction (r = -0.76, p < 0.001), PFR (r = -0.40, p = 0.004), nPFR (r = -0.52, p < 0.001) and left atrium area (r = 0.40, p = 0.004). Patients at the lowest PFR quartile (<200 ml/s) showed a larger MI size (Q1 26.5 ± 25.5%, Q2 15.5 ± 20.9%, Q3 6.3 ± 12.4%, Q4 8.8 ± 14.1%, p = 0.04). At multivariate analysis, MI size was the only independent predictor of the lowest PFR (p = 0.017). Infarct size has an impact on LV filling profiles, as assessed by conventional cine CMR without additional specific pulse sequences.