Nicotinamide adenine dinucleotide fluorescence to assess microvascular disturbances in post-COVID-19 patients

Coronavirus disease 2019 (COVID-19) revealed many different faces, from severe to completely asymptomatic course.An increasing number of patients are starting to emerge with significant cardiovascular problems, including myocarditis, heart failure, severe arrhythmias, and thromboembolic complications.Accumulating data suggest that COVID-19 is a systemic vascular endothelial dysfunction with different and unpredictable clinical manifestations, including pulmonary, neurological, cardiac, or thromboembolic problems.Of note, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters target cells via angiotensin--converting enzyme 2 (ACE2) receptors, which are widely expressed on the endothelial cells in several organs, including the heart and lungs [1].Indeed, an increasing amount of evidence indicates that SARS-CoV-2 affects endothelial function via inflammation of endothelial cells (endotheliitis), causing microvascular disturbances and microthrombosis in different vascular beds, leading to COVID-19--related acute and long-term complications [2].More precisely, SARS-CoV-2 affects vascular endothelium by multiple mechanisms, including a cytokine storm.Interestingly, exocytosis of granules from endothelial cells induces platelet aggregation and leukocyte influx into the vessel wall, which causes inflammation, microthrombosis, and capillary obstruction [3].The blood flow disturbances in capillaries due to endotheliitis or accumulation of leukocytes shortens the time of blood flow resulting in reduced oxygen exchange between blood and tissue.Hypoxia of endothelial