Minimally Invasive Techniques for the Treatment of Patients with Structural Heart Disease

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Patent foramen ovale (PFO) is a common anatomical finding in a quarter of the general population and under certain conditions may shunt clot, deoxygenated blood or gas bubbles right-to-left across the atrial septum to cause cryptogenic stroke, platypnoea orthodeoxia or decompression illness respectively. PFO has also been linked to migraine with aura. Treatment by percutaneous closure as a day case is technically feasible and has been aided by the recent development of intracardiac and 3D transoesophageal imaging, as well as improvements in device technology. The results from several large randomised controlled trials designed to assess superiority of PFO closure above medical therapy alone for cryptogenic stroke are eagerly awaited.

Percutaenous closure of atrial septal defects has become common place over the last 10 years. Patients with ASDs are at risk of atrial fibrillation and heart failure as the years progress and although little categorical evidence exists, expert consensus recommends closure of ASDs which are large enough to cause either symptoms or any change in right ventricular chamber size. The HELEX and in particular AMPLAZTER devices are well suited to device closure of ASDs, with high efficacy, low procedureal complication rates and very low long term complications rates. Patients with ASDS are now routinely considered for percutaneous rather than surgical closure of ASDs, though some requirement for surgery still exists amond patients with either very large ASDs or devicient inferior rims.

Transcatheter aortic valve implantation is an emerging technology which has brought promise for high risk patients with symptomatic severe aortic stenosis deemed unsuitable for surgery. Aortic stenosis is a common valvular problem representing 4.6% of population aged > 75 [1]. This presents a long term public problem as the prevalence of the disease increase with age so does other morbidities which deem some portion of this group inoperable due to increased surgical morbidity and mortality. First transcatheter aortic valve was implanted by Cribier in 2002 [2]. The initial results were promising but antegrade technique was challenging which led to innovation of a flexible retrograde delivery system with improved procedural outcome [3]. To avoid access problems and provide more stability, transapical approach was developed. They are two systems available, the Edwards SAPIEN valve is a bovine pericardium prosthesis mounted on a balloon-expandable stent that is placed in the subcoronary position and the CoreValve Revalving system compromises of self expanding bioprosthetic valve with a ninitol frame{2}[4]. The initial and median results have been promising whilst the long term results are awaited. With development of new delivery system and devices, the technology will promise a better procedural and clinical effective outcome.

Balloon valvuloplasty is a percutaneous technique that has transformed the lives of thousands of patients disabled by valvular stenosis. However, it is not a panacea for all stenoses and the key to success is in patient selection. Balloon valvuloplasty works best in valves with predominately commissural fusion and little in the way of leaflet thickening or calcification. Young patients with congenital bicuspid aortic or congenital pulmonary valvular stenosis, or any valve with early rheumatic stenosis often have mobile leaflets with commissural fusion. These patients enjoy excellent results from valvuloplasty with extended periods of freedom from re-intervention including surgery [1-5]. Once the valve becomes heavily thickened and calcified, regardless of the original aetiology, not only are the benefits of valvuloplasty reduced, but the risks are also higher. This chapter aims to explain the details behind valvuloplasty of the aortic, mitral and pulmonary valves.

Mitral Regurgitation presents a significant health burden to patients and the resources of the NHS. It is the most common form of cardiac valve disease affecting more than 150 million people worldwide [1]. Typically treatment has been symptom management until such time that there is evidence of adverse ventricular remodeling or a failing left ventricle. At this time surgery can be offered in the form of mitral valve repair or replacement.

The aetiology of mitral regurgitation may to some degree define it’s treatment. Currently there are a proportion of patients who would be refused conventional mitral valve surgery but would benefit from a less invasive therapy.

Newer technology is facilitating a percutaneous approach to the treatment of mitral regurgitation. These less invasive procedures replicate the tradition surgical approaches. The benefits of minimally invasive therapeutics include the avoidance of a sternotomy, cardio-pulmonary bypass and in some cases, life-long anticoagulation. Patients also require a shorter hospital stay.

These procedures have the advantage of being an option for ‘high-risk’ patient groups who would have previously been declined surgery.

Clinical expertise is growing in this field and thus far safety and efficacy data look promising.

The results of the first randomized head to head trial comparing surgery with percutaeous devices are due in 2010. The outcome of this trial will have exciting implications for the field of mitral valve therapies.

Functional Mitral Regurgitation (MR), due to incomplete mitral leaflet closure rather than an inherent abnormality in the valve apparatus, is a highly prevalent condition that is associated with an adverse prognosis in patients with heart failure. To date, traditional medical therapies have largely been ineffective, and enthusiasm for various surgical strategies has been limited by their lack of prognostic benefit and perceived high risk. In order to overcome some of these issues, a number of percutaneous approaches have recently emerged, and while these techniques are still in the research arena, there is already encouraging early data. This chapter will address the pathophysiologal mechanisms involved in functional MR, and summarise the current data available on percutaneous mitral valve therapies, with a particular emphasis on devices involving ‘indirect annuloplasty’ via the coronary sinus.

Atrial fibrillation is the commonest sustained arrhythmia and is the commonest cause of stroke due to embolization of thrombi from the left atrium. Risk of stroke increases with age and other co-morbidities and can be reduced by oral anticoagulation with warfarin. However warfarin has a narrow therapeutic window and can be affected by drugs and some foods, resulting in many patients being inadequately anti-coagulated. In addition other patients may have contra-indications to its use. Surgical and echocardiographic studies have demonstrated the source of thrombi to be the left atrial appendage in over 90% of cases. Therefore excluding the left atrial appendage from the systemic circulation may be a viable alternative to anti-coagulation in reducing the risk of stroke.

Three devices have been developed for percutaneous deployment to exclude the left atrial appendage. The Percutaneous Left Atrial Appendage Transcatheter Occlusion System - PLAATO (ev3), Watchman (Aritech) and Amplatzer Cardiac Plug (AGA Medical) are all delivered via the femoral vein with transpetal access to the left atrium. Each consists of a self-expanding nitinol mesh which is lodged in the left atrial appendage occluding the appendage and allowing endothelialisation of the atrial facing surface.

Early non-randomized studies demonstrated the technique to be simple and feasible with acceptable risks associated with implantation. A recent randomized controlled trial comparing device occlusion of the appendage to warfarin demonstrated that the device was at least non-inferior to warfarin in preventing stroke in non-valvular atrial fibrillation.

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