Histologic Assessment of Thromboemboli Due to Plaque Rupture, Plaque Erosion, or COVID-19 Microthrombi.

Plaque rupture, plaque erosion, and COVID-19 infection can cause acute coronary syndromes (ACS). We illustrate case examples demonstrating the distinctive and characteristic pathologic findings underlying each of these various causes of acute myocardial infarction. A deeper understanding of the pathophysiology of ACS is necessary for the development of newer agents and techniques to improve outcomes after ACS. (Level of Difficulty: Advanced.).

Comprehensive Assessment of Human Accessory Renal Artery Periarterial Renal Sympathetic Nerve Distribution.

OBJECTIVES: The aim of this study was to understand the anatomy of periarterial nerve distribution in human accessory renal arteries (ARAs). BACKGROUND: Renal denervation is a promising technique for blood pressure control. Despite the high prevalence of ARAs, the anatomic distribution of periarterial nerves around ARAs remains unknown. METHODS: Kidneys with surrounding tissues were collected from human autopsy subjects, and histological evaluation was performed using morphometric software. An ARA was defined as an artery arising from the aorta above or below the dominant renal artery (DRA) or an artery that bifurcated within 20 mm of the takeoff of the DRA from the aorta. The DRA was defined as an artery that perfused >50% of the kidney. RESULTS: A total of 7,287 nerves from 14 ARAs and 9 DRAs were evaluated. The number of nerves was smaller in the ARA than DRA (median: 30 [interquartile range: 17.5 to 48.5] vs. 49 [interquartile range: 36 to 76]; p < 0.0001). In both ARAs and DRAs, the distance from the arterial lumen to nerve was shortest in the distal, followed by the middle and proximal segments. On the basis of the post-mortem angiography, ARAs were divided into large (≥3 mm diameter) and small (<3 mm) groups. The number of nerves was greatest in the DRA, followed by the large and small ARA groups (53 [41 to 97], 38 [25 to 53], and 24.5 [10.5 to 36.3], respectively; p = 0.001). CONCLUSIONS: ARAs showed a smaller number of nerves than DRAs, but these results were dependent on the size of the ARA. Ablation, especially in large ARAs, may allow more complete denervation with the potential to further reduce blood pressure.

Ex vivo assessment of vascular response to coronary stents by optical frequency domain imaging.

OBJECTIVES: This study sought to examine the capability of optical frequency domain imaging (OFDI) to characterize various morphological and histological responses to stents implanted in human coronary arteries. BACKGROUND: A precise assessment of vascular responses to stents may help stratify the risk of future adverse events in patients who have been treated with coronary stents. METHODS: Fourteen human stented coronary segments with implant duration ≥ 1 month from 10 hearts acquired at autopsy were interrogated ex vivo by OFDI and intravascular ultrasound (IVUS). Comparison with histology was assessed in 134 pairs of images where the endpoints were to investigate: 1) accuracy of morphological measurements; 2) detection of uncovered struts; and 3) characterization of neointima. RESULTS: Although both OFDI and IVUS provided a good correlation of neointimal area with histology, the correlation of minimum neointimal thickness was inferior in IVUS (R(2) = 0.39) as compared with OFDI (R(2) = 0.67). Similarly, IVUS showed a weak correlation of the ratio of uncovered to total stent struts per section (RUTSS) (R(2) = 0.24), whereas OFDI maintained superiority (R(2) = 0.66). In a more detailed analysis by OFDI, identification of individual uncovered struts demonstrated a sensitivity of 77.9% and specificity of 96.4%. Other important morphological features such as fibrin accumulation, excessive inflammation (hypersensitivity), and in-stent atherosclerosis were characterized by OFDI; however, the similarly dark appearance of these tissues did not allow for direct visual discrimination. The quantitative analysis of OFDI signal reflections from various in-stent tissues demonstrated distinct features of organized thrombus and accumulation of foamy macrophages. CONCLUSIONS: The results of the present study reinforce the potential of OFDI to detect vascular responses that may be important for the understanding of long-term stent performance, and indicate the capability of this technology to serve as a diagnostic indicator of clinical success.