Pathology after combined epicardial and endocardial ablation for ventricular tachycardia in a postmortem heart with hypertrophic cardiomyopathy

Malignant Ventricular Tachycardia, Ventricular Wall Ablation, and Orthotopic Heart Transplantation

Described herein are three patients with refractory ventricular tachycardia and one or more unsuccessful ablation procedures finally leading to orthotropic heart transplantation (OHT). The latter procedure allowed examination of the ventricular ablation sites, an unusual opportunity reported previously in few patients (all case reports). The acute ablation lesions are unique, with necrosis of the myocardial fibers adjacent to the endocardium and encircled by layers of extravasated erythrocytes in the deeper myocardial wall. All 3 patients returned to normal activities following the OHT.

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.

Radiofrequency Ablation Using an Open Irrigated Electrode Cooled With Half-Normal Saline

OBJECTIVES

This study evaluated the use of half-normal saline (HNS) as the radiofrequency ablation (RFA) cooling irrigant.

BACKGROUND

Some instances of ventricular arrhythmia may originate deep within myocardium and can be refractory to standard ablation using open irrigated RFA. Recent data suggest that deeper ablation lesions can be created by decreasing the irrigant ionic concentration delivered through open irrigated RFA than by using normal saline (NS).

METHODS

Bovine myocardium was placed in a circulating saline bath. Two RFA catheters were oriented across from each other, with myocardium in between. Sequential unipolar HNS-irrigated RFA was performed and compared to bipolar ablation by using NS or HNS. Unipolar HNS ablation of the ventricles in a porcine model was performed and compared to ablation using NS.

RESULTS

Sequential ex vivo unipolar RFA with HNS produced larger lesions than sequential unipolar RFA with NS and produced lesions of similar size to those created with bipolar RFA using NS. Ex vivo bipolar RFA using HNS created the largest lesions. In vivo unipolar HNS ablation in porcine endocardium created larger lesion volumes, 152.9 ± 29.2 μl, compared to 94.7 ± 33.4 μl for unipolar ablation using NS.

CONCLUSIONS

By decreasing ionic concentration and charge density in RFA using HNS instead of NS irrigant, larger ablation lesions can be created and are similar in size to lesions created using bipolar ablation. This may be a useful ablation strategy for deep myocardial circuits refractory to standard ablation. Further studies are needed to evaluate this novel RFA strategy.