BackgroundAtrial fibrillation (AF) is associated with myocardial infarction, and patients with AF and no obstructive coronary artery disease can present with symptoms and evidence of cardiac ischemia. We hypothesized that microvascular coronary dysfunction underlies these observations.Methods and ResultsMyocardial blood flow (MBF) at baseline and during adenosine stress and left ventricular and left atrial function were evaluated by magnetic resonance in 49 patients with AF (25 paroxysmal, 24 persistent) with no history of epicardial coronary artery disease or diabetes mellitus, before and 6 to 9 months after ablation. Findings were compared with those obtained in matched controls in sinus rhythm (n=25). Before ablation, patients with AF had impaired left atrial function and left ventricular ejection fraction and strain indices (all P<0.05 versus controls). MBF was impaired in patients both under baseline conditions (1.21±0.24 mL/min per g·[mm Hg·bpm/104]−1 versus 1.34±0.28 mL/min per g·[mm Hg·bpm/104]−1 in controls, P=0.044) and during adenosine stress (2.29±0.48 mL/min per g versus 2.73±0.37 mL/min per g in controls, P<0.001). Under baseline conditions, MBF correlated with left ventricular strain and left atrial function (all P≤0.001), so that cardiac function was most impaired in patients with the lowest MBF. Baseline and stress MBF remained unchanged postablation (both P=ns), and baseline MBF showed similar correlations with functional indices to those present preablation (all P≤0.001).ConclusionsBaseline and stress MBF are significantly impaired in patients with AF but no epicardial coronary artery disease. Reduction in MBF is proportional to severity of left ventricular and left atrial dysfunction, even after successful ablation. Coronary microvascular dysfunction may be a relevant pathophysiological mechanism in patients with a history of AF.
BackgroundThe Index of Microcirculatory Resistance (IMR) can identify Coronary Microcirculatory Dysfunction (CMD), but its pathophysiological effects are uncertain. We characterised relations between IMR and downstream myocardial perfusion and LV function.Methods60 patients with stable coronary disease (67±8 years, 72% male) had adenosine stress Cardiac MRI to assess myocardial perfusion reserve (MPR), systolic and diastolic function (LV strain). All patients had invasive angiography and Fractional Flow Reserve (FFR) and IMR assessment in all possible vessels (135/180).ResultsIn 96 vessels FFR>0.8, IMR was inversely related to MPR (rho −0.65), systolic (rho −0.57) and diastolic strain (rho −0.50), all p<0.001. An IMR cut-off of 25 detected ischaemia (AUC 0.93, p<0.001) (figure 1). In patients with all vessels FFR>0.80, as the number of high IMR (≥25) vessels increased, global myocardial perfusion, systolic and diastolic strain reduced in a step-wise fashion, reflecting increasing severity of CMD (all p<0.01). In vessels FFR≤0.8, IMR was not related to MPR (rho −0.23; p=0.15), systolic (rho −0.14; p=0.45) or diastolic strain (rho −0.12; p=0.49).Abstract 10 Figure 1 Relations of IMR with myocardial perfusion, systolic and diastolic strain on CMRConclusionsAn IMR of ≥25 is associated with impaired myocardial perfusion, systolic and diastolic dysfunction. The implications of these novel findings deserve further study.
We investigated how local and global stressors affect coral reefs in situ by taking advantage of a latitudinal gradient in the central equatorial Pacific driven by El Niño-Southern Oscillation, where the past frequency of heat stress decreases away from the equator. We compared benthic communities at 40 sites across 4 atolls in the Gilbert Islands, namely in Kiribati (Tarawa and Abaiang) and the Republic of the Marshall Islands (Majuro and Arno), representing gradients in local chronic human disturbance and past frequency of bleaching-level heat stress. A hierarchical clustering analysis found 3 groupings of benthic communities, corresponding to sites with (1) low human influence and frequency of heat stress, (2) low human influence and high frequency of heat stress, and (3) high human influence, suggesting that the effects of intense, ongoing local disturbance may mask the influence of heat stress on coral reef communities. The frequency of heat stress explained 8.0% of the differences in community compositions across all sites (PERMANOVA), while local anthropogenic stressors explained 16.2%, and the combined effects explained 7.0%. Interactions between stressors were multiplicative and acted synergistically to increase the percent cover of macroalgae and the stress-resistant coral Porites rus. The prevalence of P. rus at locally disturbed sites drives the positive relationship between local stress metrics and live coral cover. At the taxon level, half of the multiplicative interactions were antagonistic, suggesting that actions that reduce local stressors may help some coral taxa respond to climate stress, but possibly at the expense of other taxa.
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