CLINICAL IMAGE Microvascular impairment after COVID‑19 561 a positive result. However, besides general mus‑ cle weakness, the patient did not manifest any serious symptoms of infection. On admission, the levels of D‑dimer, B‑type natriuretic peptide, and cardiac troponin were within reference rang‑ es. On 2‑dimensional echocardiography, normal left ventricular ejection fraction (65%) was not‑ ed, without regional dysfunction. Additionally, speckle tracking echocardiography showed nor‑ mal (–22.4%) left ventricular global longitudinal strain (FIGurE 1A). We subsequently performed microcirculation measurements on the forearm during and fol‑ lowing brachial artery occlusion simultaneously by LSCI (PeriCam PSI System, Perimed, Järfäl‑ la, Sweden) and FMSF (Angionica Ltd, Łódź, Po‑ land). Speckle contrast analysis with colors rang‑ ing from blue (no perfusion) to red (high per‑ fusion) showed basal microvascular perfusion (FIGurE 1B). A relatively weak postocclusive reac‑ tive hyperemic response was revealed by LSCI, suggesting a reduced endothelium‑dependent vasodilatation potential (FIGurE 1C). Likewise, us‑ ing FMSF, we observed modest oscillations as well as slightly reduced ischemic and hyperemic responses. While hyperemic response refects COVID‑19, caused by SARS‑CoV‑2 infection, may induce signifcant cardiovascular conditions, in‑ cluding myocarditis, heart failure, severe arrhyth‑ mias, and thromboembolic complications. Impor‑ tantly, increasing number of scientifc reports in‑ dicate that SARS‑CoV‑2 afects microcirculation, causing serious dysfunction and infammation of endothelial cells (endotheliitis) and, frequent‑ ly, massive thrombosis in microvessels. Indeed, SARS‑CoV‑2 enters target cells via angiotensin‑ ‑converting enzyme 2 receptors, which are spe‑ cifcally extensively expressed on the surface of the lung epithelial and vascular endothelial cells in various tissues and organs. 1 Due to accessibil‑ ity of its assessment, peripheral microcirculation has been considered an indicator of systemic mi‑ crovascular function. 2 Laser speckle contrast imaging (LSCI) is a new‑ ly developed method based on speckle contrast analysis which allows for a noninvasive and real‑ ‑time microcirculation imaging over a wide area of tissue in response to a given stimulus. 3 It shows an excellent reproducibility as well as very good spatial and temporal resolutions. 4 Nowadays, we are also able to assess the changes in tissue biochemistry in vivo. A brand new technique, known as fow mediated skin fuorescence (FMSF) is based on monitoring the intensity of nicotin‑ amide adenine dinucleotide (NADH) fuorescence on the forearm in response to blocking and restor‑ ing the blood fow. 5 Terefore, FMSF enables non‑ invasive evaluation of the microvascular and met‑ abolic regulation. Importantly, NADH is a major mitochondrial component, and plays a key role in cellular energy metabolism. 5 A 36‑year‑old man, with unremarkable med‑ ical history, was referred to our cardiology out‑ patient clinic because of reduced exercise tol‑ erance, shortness of breath, and fatigue, which had been continuing for about 2 months after COVID‑19. Te molecular test performed in De‑ cember 2020 using the real‑time reverse tran‑ scriptase–polymerase chain reaction yielded CLINICAL IMAGE Subtle microvascular endothelial impairment in a young patient recovered from mild COVID‑19 Marcin Hellmann, Marzena Romanowska‑Kocejko, Marta Żarczyńska‑Buchowiecka, Maria Dudziak Department of Cardiac Diagnostics, Medical University of Gdansk, Gdańsk, Poland Correspondence to: Prof. Marcin Hellmann, MD, PhD, Department of Cardiac Diagnostics, Medical University of Gdańsk, ul. Smoluchowskiego 17, 80-214 Gdańsk, Poland, phone: +48 58 349 33 80, email: marcin.hellmann@gmail.com Received: March 22, 2021. Revision accepted: April 11, 2021. Published online: April 14, 2021. Pol Arch Intern Med. 2021; 131 (6): 561-562 doi:10.20452/pamw.15938 Copyright by the Author(s), 2021 FIGurE 1 A – bull’s‑eye plot obtained by speckle tracking echocardiography showing left ventricular global longitudinal strain (GS) range of –22.4% A