Histological Justification for the Need of Radiofrequency Ablation of Pulmonary Arteries in Patients with High-Grade Secondary Pulmonary Hypertension

The aim of the study was to perform a histological assessment of the effectiveness of radiofrequency exposure for circular denervation of the pulmonary artery in patients with secondary high pulmonary hypertension. MATERIALS AND METHODS: The study was carried out on the autopsy material derived from non-operated patients. Three groups were formed. The experimental group included the material (207 histological samples) from the patients with chronic high pulmonary hypertension arising on the background of mitral heart disease. The samples of this group were exposed to circular radiofrequency ablation. In the comparison group, we used autopsy material (24 samples) obtained from the patients with high pulmonary hypertension. The control group included material (35 samples) from the patients without pulmonary hypertension who died from causes not associated with cardiovascular diseases. The samples of the comparison and control groups were not exposed to radiofrequency. Visual evaluation of the damage to the vascular wall was performed after hematoxylin and eosin staining, according to Van Gieson. Damage to the nerve plexuses was evaluated after their impregnation by silver salts. To assess the degree of damage to the vascular wall on the stained sections, a scoring method of semi-quantitative analysis of the observed pathological processes (fibrinoid necrosis, metachromasia, karyorrhexis, karyolysis, fibrinoid and mucoid swelling, lipid presence) was used. Silver salt impregnation allowed visualizing damage to the reticular fibers, trunks and endings of peripheral nerve fibers. RESULTS: The mean optical density of the ablation group was statistically significantly lower than in the comparison and control groups (p<0.001). The mean specific area of tissue dissociation was higher in the “marginal zones” of the ablated sections, under pronounced mechanical compression in these areas. The difference in the mean areas of the argentophilic samples of the ablation and comparison and control groups was expressed in a lower percentage of argentophilic fibrous structures (p<0.05). At the same time, the highest concentration of argentophilic structures was observed in the comparison group, which points to a bigger content of nerve fiber structures in the patients with high pulmonary hypertension. CONCLUSION: The results of the histological study demonstrated the feasibility of radiofrequency ablation of the pulmonary arteries in patients with high-grade secondary pulmonary hypertension. Radiofrequency denervation leads to the destruction of the sympathetic ganglia in the adventitial layer of the pulmonary arteries, which are responsible for the spasm of the precapillary bed of the pulmonary circulation, which promotes vasodilation, an increase in the vascular bed, and, as a result, a reduction in pulmonary hypertension.