Transcatheter microwave ablation can deliver deep and circumferential perivascular nerve injury without significant arterial injury to provide effective renal denervation

Abolition of Aorticorenal Ganglia Pacing Responses Improves Denervation Efficacy

BACKGROUND

Transcatheter renal denervation (RDN) remains inconsistent despite developments in ablation technologies, due to the lack of an intraprocedural physiological end point. The aim of this study was to identify if aorticorenal ganglion (ARG) guided RDN using microwave (MW) catheter leads to more consistent denervation outcomes compared with empirical MW ablation.

METHODS

Pigs underwent sham procedure (n=8) or bilateral RDN using an in-house built open-irrigated MW catheter. Before denervation, ipsilateral ARG pacing was performed leading to renal artery vasoconstriction. MW ablation group (MW-group; n=7) received 1 ablation (100-120 W for 360 seconds) in the mid-main renal artery based on artery caliber. ARG-guided-MW ablation group (ARG-MW-group; n=7) was permitted an additional ablation more distally or at higher power until a vasoconstrictive response was abolished. Animals were euthanized at 4 to 5 weeks post-procedure.

RESULTS

ARG pacing caused an ipsilateral reduction in renal artery caliber from 4.67 to 4 mm; P=0.0006 in MW-group and 4.8 to 3.9 mm; P=0.001 in ARG-MW-group. Repeat ARG pacing at euthanasia led to a reduction in renal artery caliber in MW-group from 5.1 to 4.8 mm; P=0.006, but not in ARG-MW-group from 4.88 to 4.55 mm; P=0.08. There were no differences in ablation injury volumes between the groups. Compared with undenervated sham controls, ARG-MW-RDN versus MW-RDN caused median reductions in viable nerve area (antityrosine hydroxylase staining) at 4 to 5 weeks by 92.6% (interquartile range, 0.94-19.59%; P<0.0001) versus 55.02% (interquartile range, 15.87-75.11%; P=0.006) and median renal cortical norepinephrine content by 68.06% (interquartile range, 27.16-38.39%; P<0.0001) versus 25.25% (interquartile range, 56.97-157.7%; P=NS).

CONCLUSIONS

ARG pacing serves as a physiological procedural end point to guide MW denervation to improve denervation outcomes.

Long-Term Safety and Efficacy of Transcatheter Microwave and Radiofrequency Denervation in a Chronic Ovine Model

BACKGROUND

Transcatheter renal denervation (RDN) has had inconsistent efficacy and concerns for durability of denervation. We aimed to investigate long-term safety and efficacy of transcatheter microwave RDN in vivo in normotensive sheep in comparison to conventional radiofrequency ablation.

METHODS AND RESULTS

Sheep underwent bilateral RDN, receiving 1 to 2 microwave ablations (maximum power of 80-120 W for 240 s-480 s) and 12 to 16 radiofrequency ablations (180 s-240 s) in the main renal artery in a paired fashion, alternating the side of treatment, euthanized at 2 weeks (acute N=15) or 5.5 months (chronic N=15), and compared with undenervated controls (N=4). Microwave RDN produced substantial circumferential perivascular injury compared with radiofrequency at both 2 weeks [area 239.8 (interquartile range [IQR] 152.0-343.4) mm2 versus 50.1 (IQR, 32.0-74.6) mm2, P <0.001; depth 16.4 (IQR, 13.9-18.9) mm versus 7.5 (IQR, 6.0-8.9) mm P <0.001] and 5.5 months [area 20.0 (IQR, 3.4-31.8) mm2 versus 5.0 (IQR, 1.4-7.3) mm2, P=0.025; depth 5.9 (IQR, 1.9-8.8) mm versus 3.1 (IQR, 1.2-4.1) mm, P=0.005] using mixed models. Renal denervation resulted in significant long-term reductions in viability of renal sympathetic nerves [58.9% reduction with microwave (P=0.01) and 45% reduction with radiofrequency (P=0.017)] and median cortical norepinephrine levels [71% reduction with microwave (P <0.001) and 72.9% reduction with radiofrequency (P <0.001)] at 5.5 months compared with undenervated controls.

CONCLUSIONS

Transcatheter microwave RDN produces deep circumferential perivascular ablations without significant arterial injury to provide effective and durable RDN at 5.5 months compared with radiofrequency RDN.

Review of the Capacity to Accurately Detect the Temperature of Human Skin Tissue Using the Microwave Radiation Method

Microwave radiometry (MWR) is instrumental in detecting thermal variations in skin tissue before anatomical changes occur, proving particularly beneficial in the early diagnosis of cancer and inflammation. This study concisely traces the evolution of microwave radiometers within the medical sector. By analyzing a plethora of pertinent studies and contrasting their strengths, weaknesses, and performance metrics, this research identifies the primary factors limiting temperature measurement accuracy. The review establishes the critical technologies necessary to overcome these limitations, examines the current state and prospective advancements of each technology, and proposes comprehensive implementation strategies. The discussion elucidates that the precise measurement of human surface and subcutaneous tissue temperatures using an MWR system is a complex challenge, necessitating an integration of antenna directionality for temperature measurement, radiometer error correction, hardware configuration, and the calibration and precision of a multilayer tissue forward and inversion method. This study delves into the pivotal technologies for non-invasive human tissue temperature monitoring in the microwave frequency range, offering an effective approach for the precise assessment of human epidermal and subcutaneous temperatures, and develops a non-contact microwave protocol for gauging subcutaneous tissue temperature distribution. It is anticipated that mass-produced measurement systems will deliver substantial economic and societal benefits.

Irrigated Microwave Catheter Ablation Can Create Deep Ventricular Lesions Through Epicardial Fat With Relative Sparing of Adjacent Coronary Arteries

BACKGROUND

Radiofrequency ablation depth can be inadequate to reach intramural or epicardial substrate, and energy delivery in the pericardium is limited by penetration through epicardial fat and coronary anatomy. We hypothesized that open irrigated microwave catheter ablation can create deep myocardial lesions endocardially and epicardially though fat while acutely sparing nearby the coronary arteries.

METHODS

In-house designed and constructed irrigated microwave catheters were tested in in vitro phantom models and in 15 sheep. Endocardial ablations were performed at 140 to 180 W for 4 minutes; epicardial ablations via subxiphoid access were performed at 90 to 100 W for 4 minutes at sites near coronary arteries.

RESULTS

Epicardial ablations at 90 to 100 W produced mean lesion depth of 10±4 mm, width 18±10 mm, and length 29±8 mm through median epicardial fat thickness of 1.2 mm. Endocardial ablations at 180 W reached depths of 10.7±3.3 mm, width of 16.6±5 mm, and length of 20±5 mm. Acute coronary occlusion or spasm was not observed at a median separation distance of 2.7 mm (IQR, 1.2-3.4 mm). Saline electrodes recorded unipolar and bipolar electrograms; microwave ablation caused reductions in voltage and changes in electrogram morphology with loss of pace-capture. In vitro models demonstrated the heat sink effect of coronary flow, as well as preferential microwave coupling to myocardium and blood as opposed to lung and epicardial fat phantoms.

CONCLUSIONS

Irrigated microwave catheter ablation may be an effective ablation modality for deep ventricular lesion creation with capacity for fat penetration and sparing of nearby coronary arteries because of cooling endoluminal flow. Clinical translation could improve the treatment of ventricular tachycardia arising from mid myocardial or epicardial substrates.