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Background Experimental studies of radiofrequency renal denervation (RDN) have shown a strong relation of the depth of structural lesions and completeness of renal nerve injury to the relative drop in impedance during the treatment caused by the increased permeability of the cell membranes. Thus, the otherwise successful treatments but with low impedance drop may be, in fact, totally ineffective. Objective We assessed the relation between impedance drop during single radiofrequency treatments and local structural changes of vascular wall at the electrode positions using optical coherence tomography. Methods Optical coherence tomography of the treated segments was performed during radiofrequency RDN in 14 patients with resistant hypertension. The parameters of contrast injection depended on the position of the guiding catheter: for selective branch imaging 15 ml volume was injected at 8 ml/sec speed; otherwise 30 ml of contrast was injected at the speed 15 ml/sec to flush the whole renal artery. Automatic pullback of the sensor was done with the standard speed 20 mm/sec. In total, 423 mm of treated segments in 22 renal vessels (mostly distal branches) had sufficient quality of imaging and were studied for structural changes. Results There was almost no local structural changes of the arterial wall after the treatments with low impedance drop &amp;lt;10% reflecting a rather weak heating of even superficial tissue layers. No effect on the deeper tissue layers is expected in this case because these layers are heated almost exclusively by the heat transfer from superficial layer. In contrast, the treatments with the impedance drop 10% or greater were able to significantly affect the arterial structure causing local edema, small dissections, and local thrombi formation as a result of significant resistive heating of the superficial tissue, and, therefore, high potential for heating of the deep layers containing the renal nerves. Only approximately 40% of the point treatments had the impedance drop 10% or greater suggesting adequate lesion depth and sufficient completeness of renal nerve injury. This may indicate a rather low procedural efficacy of the current mode of radiofrequency RDN due to a large proportion of small-depth treatments marked by only a few percent decrease in impedance yet considered fully “successful”. Also, it means a potential for significant increase in the efficacy of radiofrequency RDN through controlling/guiding the treatment by the impedance drop. Conclusion Our study shows that variable efficacy of radiofrequency RDN may be explained by a significant proportion of the small-depth point treatments ineffective in terms of renal nerve injury, and, thereby, may be significantly improved if the procedure is guided by the impedance drop during the treatment. Funding Acknowledgement Type of funding source: None

Efficacy of radiofrequency RDN may be significantly improved if the procedure is guided by impedance drop during the treatment