Left ventricular volume reduction by radiofrequency heating of chronic myocardial infarction in patients with congestive heart failure

Quantitative Imaging Assessment of an Alternative Approach to Surgical Mitral Valve Leaflet Resection: An Acute Porcine Study

This study reports the initial in vivo use of a combined radiofrequency ablation and cryo-anchoring (RFC) catheter as an alternative to surgical mitral valve (MV) leaflet resection. Radiofrequency ablation thermally shrinks enlarged collagenous tissues, providing an alternative to leaflet resection, and cryo-anchoring provides reversible attachment of a catheter to freely mobile MV leaflets. Excised porcine MVs (n = 9) were tested in a left heart flow simulator to establish treatment efficacy criteria. Resected leaflet area was quantified by tracking markers on the leaflet surface, and leaflet length reductions were directly measured on echocardiography. Leaflet area decreased by 38 ± 2.7%, and leaflet length decreased by 9.2 ± 1.8% following RFC catheter treatment. The RFC catheter was then tested acutely in healthy pigs (n = 5) under epicardial echocardiographic guidance, open-chest without cardiopulmonary bypass, using mid-ventricular free wall access. Leaflet length was quantified using echocardiography. Quantitative assessment of MV leaflet length revealed that leaflet resection was successful in 4 of 5 pigs, with a leaflet length reduction of 13.3 ± 4.6%. Histological, mechanical, and gross pathological findings also confirmed that RFC catheter treatment was efficacious. The RFC catheter significantly reduces MV leaflet size in an acute animal model, providing a possible percutaneous alternative to surgical leaflet resection.

Development of a simultaneous cryo-anchoring and radiofrequency ablation catheter for percutaneous treatment of mitral valve prolapse

Mitral valve prolapse (MVP) is one subtype of mitral valve (MV) disease and is often characterized by enlarged leaflets that are thickened and have disrupted collagen architecture. The increased surface area of myxomatous leaflets with MVP leads to mitral regurgitation, and there is need for percutaneous treatment options that avoid open-chest surgery. Radiofrequency (RF) ablation is one potential therapy in which resistive heating can be used to reduce leaflet size via collagen contracture. One challenge of using RF ablation to percutaneously treat MVP is maintaining contact between the RF ablation catheter tip and a functioning MV leaflet. To meet this challenge, we have developed a RF ablation catheter with a cryogenic anchor for attachment to leaflets in order to apply RF ablation. We demonstrate the effectiveness of the dual-energy catheter in vitro by examining changes in leaflet biaxial compliance, thermal distribution with infrared (IR) imaging, and cryogenic anchor strength. We report that 1250 J of RF energy with cryo-anchoring reduced the determinant of the deformation gradient tensor at systolic loading by 23%. IR imaging revealed distinct regions of cryo-anchoring and tissue ablation, demonstrating that the two modalities do not counteract one another. Finally, cryogenic anchor strength to the leaflet was reduced but still robust during the application of RF energy. These results indicate that a catheter having combined RF ablation and cryo-anchoring provides a novel percutaneous treatment strategy for MVP and may also be useful for other percutaneous procedures where anchored ablation would provide more precise spatial control.

Feasibility of myxomatous mitral valve repair using direct leaflet and chordal radiofrequency ablation

OBJECTIVE

Minimally invasive repair of mitral valve prolapse (MVP) causing severe mitral regurgitation (MR) should reduce MR and have chronic durability. Our ex vivo, acute in vivo, and chronic in vivo studies suggest that direct application of radiofrequency ablation (RFA) to mitral leaflets and chordae can effect these repair goals to decrease MR.

METHODS

A total of seven canines were studied to assess the effects of RFA on mitral valve structure and function. RFA was applied ex vivo (n = 1), acutely in vivo using a right lateral thoracotomy and cardiopulmonary bypass (n = 3), and chronically in vivo using percutaneous access to the heart (n = 3). RFA was applied to the mitral valve and its associated chordae. Mitral valve structure and function (in vivo preparations) were then assessed.

RESULTS

Ex vivo application of RFA resulted in qualitative reduction in mitral leaflet surface area and chordal length. Acute in vivo application of RFA to canines found to have MVP causing severe MR demonstrated a 43.7-60.7% statistically significant (P = 0.039) reduction in postablation MR. Chronic, in vivo, percutaneous application of RFA was found to be feasible and the engendered alterations durable.

CONCLUSION

These data suggest that myxomatous mitral valve repair using radiofrequency energy delivered via catheter is feasible.

Left atrial contractility is preserved after successful circumferential pulmonary vein ablation in patients with atrial fibrillation

INTRODUCTION

Circumferential pulmonary vein ablation (CPVA) for atrial fibrillation (AF) consists of creating extensive lesions in the left atrium (LA). The aim of the study was to evaluate changes in LA contractility after ablation and their relationship with procedure outcome.

METHODS AND RESULTS

A series of 90 consecutive patients underwent cardiac magnetic resonance imaging (MRI) before and 4-6 months after CPVA. Only patients in sinus rhythm during both imaging acquisitions were included in the study to measure LA end-diastolic (LAmax) and LA end-systolic (LAmin) volumes. Fifty-five patients were finally analyzed (41 men, 52 +/- 11 years, 74% paroxysmal AF). During a mean follow-up of 12 +/- 7 months and after 1.2 +/- 0.3 ablation procedures, 38 patients (69%) were arrhythmia-free (group I), and the remaining 17 patients had recurrences (group II). There was a significant decrease in mean LAmax volume in both groups, whereas mean LAmin volume only decreased in group I. Mean LA ejection fraction (EF) was preserved after CPVA in group I (40 +/- 11% vs 38 +/- 10%; P = 0.27) but decreased in patients with arrhythmia recurrences (37 +/- 10% vs 27 +/- 10%; P < 0.001). In fact, LA EF remained stable or increased in 68% of patients without arrhythmia recurrences.

CONCLUSIONS

LAmax volume reduction following CPVA occurs regardless of the clinical efficacy of the procedure, whereas mean LAmin volume only decreased in patients without recurrences. LA EF was preserved or even increased in most patients with successful CPVA.

Reading tarot cards

In some patients acute myocardial infarction and/or infarct expansion induces progressive left ventricular dilatation that eventually leads to heart failure and death. The five year mortality after onset of heart failure is 50%. Chronically stretched viable myocardium adjacent to or remote from an expanding infarction initiates a myopathic process that leads to progressive myocyte apoptosis and adverse postinfarction remodeling. Revascularization of stunned or hibernating myocardium restores contractility and benefits patients in heart failure; however, revascularization does not restore contractility to myopathic, remodeling myocardium. Contemporary operations for heart failure temporarily reduce ventricular wall stress, but fail to reverse stretch induced myocyte apoptosis, which may not be reversible. Logically, prevention of this myopathic process after acute infarction seems required to extend survival. It follows that surgeons should operate before adverse postinfarction left ventricular remodeling occurs, using new operations, rather than afterwards.

Surgical management of heart failure

This article introduces the mechanisms and theories behind the surgical treatments for heart failure; however, heart failure is a complex problem and requires multiple solutions. Surgery offers treatment strategies that target underlying physiologic changes and may provide both quality of life and survival benefit to patients who have specific clinical characteristics consistent with the aims of the procedure. Nurses must include surgical treatment early in their hierarchy of treatment plans, especially when coronary artery occlusion, hibernating myocardium, or mitral valve regurgitation is the cause of heart failure. In addition, newer investigational surgical therapies must also be considered for patients with advanced heart failure who have already been optimized on medical and cardiac resynchronization therapies and who require a novel approach to potentially improve individual outcomes.