Gadolinium Augmentation of Myocardial Tissue Heating During Radiofrequency Ablation

Ambient circulation surrounding an ablation catheter tip affects ablation lesion characteristics

INTRODUCTION

The association between ambient circulating environments (CEs) and ablation lesions has been largely underexplored.

METHODS

Viable bovine myocardium was placed in a saline bath in an ex vivo endocardial model. Radiofrequency (RF) ablation was performed using three different ablation catheters: 3.5 mm open irrigated (OI), 4, and 8 mm. Variable flow rates of surrounding bath fluids were applied to simulate standard flow, high flow, and no flow. For in vivo epicardial ablation, 24 rats underwent a single OI ablation and performed with circulating saline (30 ml/min; n = 12), versus those immersed in saline without circulation (n = 12).

RESULTS

High flow reduced ablation lesion volumes for all three catheters. In no-flow endocardial CE, both 4 mm and OI catheters produced smaller lesions compared with standard flow. However, the 8 mm catheter produced the largest lesions in a no-flow CE. Ablation performed in an in vivo model with CE resulted in smaller lesions compared with ablation performed in a no-flow environment. No statistically significant differences in steam pops were found among the groups.

CONCLUSION

A higher endocardial CE flow can decrease RF effectiveness. Cardiac tissue subjected to no endocardial CE flow may also limit RF for 4 mm catheters, but not for OI catheters; these findings may have implications for RF ablation safety and efficacy, especially in the epicardial space without circulating fluid or in the endocardium under varying flow conditions.

Microbubble-Facilitated Ultrasound Catheter Ablation Causes Microvascular Damage and Fibrosis

High-intensity ultrasound (US) ablation produces deeper myocardial lesions than radiofrequency ablation. The presence of intravascular microbubble (MB) contrast agents enhances pulsed-wave US ablation via cavitation-related histotripsy, potentially facilitating ablation in persistently perfused/conducting myocardium. US ablation catheters were developed and tested in the presence of MBs using ex vivo and in vivo models. High-frame-rate videomicroscopy and US imaging of gel phantom models confirmed MB destruction by inertial cavitation. MB-facilitated US ablation in an ex vivo perfused myocardium model generated shallow (2 mm) lesions and, in an in vivo murine hindlimb model, reduced perfusion by 42% with perivascular hemorrhage and inflammation, but no myonecrosis.

Impact of epicardial adipose tissue and catheter ablation strategy on biophysical parameters and ablation lesion characteristics

BACKGROUND

Epicardial adipose (EA) tissue may limit effective radiofrequency ablation (RFA).

OBJECTIVES

We sought to evaluate the lesion formation of different ablation strategies on ventricular myocardium with overlying EA.

METHODS

Bovine myocardium with EA was placed in a circulating saline bath in an ex vivo model. Open-irrigated (OI) RFA was performed, parallel to the myocardium, over fat at 50 W for variable RF durations, variable contact force, catheter configurations (unipolar RF vs bipolar RF), and catheter irrigants (normal saline vs half-normal saline). Ablation was also performed with a needle-tipped ablation catheter (NTAC), perpendicular to the myocardium.

RESULTS

Increasingly thick EA attenuated lesion size regardless of ablation strategy. RF applied with longer durations and increasing CF produced larger lesion volumes and deeper lesions with ablation over EA more than 3 mm but was unable to produce measurable lesions when EA less than 3 mm. Similarly, ablation with half normal saline irrigant created slightly deeper lesions than bipolar RF and unipolar RF with normal saline as EA thickness increased, but was unable to produce measurable lesions when EA more than 3 mm. Of all ablation strategies, only NTAC produced effective lesion volumes when ablating over thick (>3 mm) EA.

CONCLUSIONS

While EA attenuates lesion depth and size, relatively larger, and deeper lesions can be achieved with longer RFA duration, higher CF, half normal saline irrigant, and, to a greater extent, by utilizing bipolar RF or NTAC, but only over thin adipose (<3 mm). Of those catheters/strategies tested, only NTAC was able to effectively deliver RF over thick (>3 mm) EA with this model.

Cardiac Electrophysiology Under MRI Guidance: an Emerging Technology

MR-guidance of electrophysiological (EP) procedures offers the potential for enhanced arrhythmia substrate assessment, improved procedural guidance and real-time assessment of ablation lesion formation. Accurate device tracking techniques, using both active and passive methods, have been developed to offer an interface similar to electroanatomic mapping platforms, and MR-compatible EP equipment continues to be developed. Progress to clinical implementation of these technically complex fields has been relatively slow over the last 10 years, but recent developments have led to successful clinical experience. However, further advances, particularly in harnessing the full imaging potential of CMR, are required to realise the mainstream adoption of this powerful guidance modality.