Background: Vitamin D has been implicated in several biological pathways involved in atrial remodeling, yet its association with incident atrial fibrillation (AF) remains uncertain across epidemiological studies. Objectives: The objective was to evaluate the association between circulating vitamin D levels and the risk of incident AF through a systematic review and meta-analysis of prospective studies using a harmonized continuous analytical framework. Methods: A systematic review and meta-analysis of prospective cohort studies was performed. Hazard ratios (HRs) and 95% confidence intervals (CIs) were pooled using the generic inverse variance method. To improve comparability across studies, effect estimates were harmonized to a common continuous contrast corresponding to a 1-standard-deviation (1-SD) difference in circulating vitamin D levels. Estimates were then oriented such that higher values reflected lower vitamin D status and higher AF risk. Random-effects models were used as the primary analytical approach. Sensitivity analyses included leave-one-out testing and an additional pooled analysis incorporating a threshold-based study after approximate rescaling to the continuous 1-SD framework. Results: Five prospective studies were eligible for quantitative assessment. In the primary continuous harmonized analysis, including the four studies with directly reported or more reliably rescaled continuous estimates, lower vitamin D status was associated with a higher risk of incident AF (HR 1.08, 95% CI 1.05–1.11), with no statistical heterogeneity (I² = 0%). In a sensitivity analysis including the HUNT study after approximation of its threshold-based estimate to the continuous 1-SD framework, the pooled association remained statistically significant (HR 1.08, 95% CI 1.05–1.11), with low heterogeneity (I² = 7%). The direction of effect remained stable across sensitivity analyses. Conclusions: Lower circulating vitamin D levels were associated with a modestly higher risk of incident AF in prospective studies. The most internally consistent quantitative signal emerged from analyses conducted within a common continuous 1-SD framework. Inclusion of a threshold-based study through approximate rescaling did not materially alter the pooled estimate, although this step relied on additional assumptions. These findings support an observational association but do not establish causality or justify vitamin D supplementation specifically for AF prevention.

Heart rate variability (HRV) is a non-invasive marker of cardiac autonomic regulation that reflects the dynamic interaction between sympathetic and parasympathetic influences on the sinoatrial node. Reduced HRV is a hallmark of autonomic dysfunction and has been consistently associated with adverse outcomes across a wide range of cardiovascular conditions, particularly heart failure (HF). HRV is markedly reduced in HF, reflecting profound autonomic imbalance characterized by vagal withdrawal, impaired baroreflex sensitivity, and altered cardiorespiratory coupling. In heart failure with reduced ejection fraction (HFrEF), lower global HRV, particularly reduced SDNN, is consistently associated with mortality, sudden cardiac death, and disease progression. In heart failure with preserved ejection fraction (HFpEF), emerging observational evidence suggests that HRV alterations may accompany early autonomic dysregulation and may be associated with sex-specific patterns, although their mechanistic and prognostic significance remains incompletely defined. In acute HF, HRV assessed during hospitalization may provide additional prognostic information, although current evidence remains limited and heterogeneous. Pharmacological therapies, cardiac resynchronization therapy, exercise training, and lifestyle interventions have variably modulated HRV across studies, but the evidence is heterogeneous and changes in HRV should not be assumed to translate directly into improved clinical outcomes. Despite persistent challenges related to methodological standardization and clinical implementation, emerging technologies and multimodal approaches may refine the feasibility of integrating HRV into risk assessment frameworks. This narrative review aims to summarize the physiological basis of HRV, critically evaluate its alterations across different HF phenotypes, and discuss its prognostic associations, therapeutic modulation, and current practical limitations in clinical application.

Q fever endocarditis remains a diagnostic challenge today. Although it is a rare condition, it is crucial to recognize, as it represents the most common cause of endocarditis with persistently negative blood cultures. Here, we present the case of a 73-year-old woman with a history of coronary artery disease and systemic sclerosis who was admitted to the hospital complaining of asthenia and dyspnea. An echocardiographic examination revealed a highly mobile pedunculated mass on the mitral valve, suggestive of endocarditis. During the diagnostic workup, blood cultures were repeatedly negative, but serological testing confirmed positivity for Coxiella burnetii (IgG phase I 1:128). After diagnosing Q fever endocarditis, antibiotic therapy with doxycycline and hydroxychloroquine was initiated but was soon discontinued due to the development of renal impairment and thrombocytopenia. The clinical course was further complicated by cardiac arrest, leading to the patient's death. Given the rarity of this condition, this case highlights the importance of considering Q fever endocarditis in the differential diagnosis of blood culture-negative endocarditis and underscores the need for rapid diagnosis using advanced diagnostic techniques to improve patient outcomes.