Structural Heart Interventions – The new frontier in Interventional Cardiology
Over the past few decades, major strides have been made in Interventional Cardiology. Coronary angiography, Balloon angioplasty and drug eluting stents were treatments offered for patients who would otherwise be treated with either medications or open-heart surgery. These therapies for patients with critical coronary artery disease and acute myocardial infarction were able to improve not just mortality but also led to improvement in the quality of life for the patients.
Over the past few years strides have been made in the field of structural heart intervention not just in the refinement of techniques but also novel devices. An example is transcatheter aortic valve replacement that has evolved from an innovative experimental approach for valve disease to a valuable therapeutical option patients with all risk profiles of patients with severe aortic stenosis.
Structural heart interventions can be broadly divided into valve replacements and valve repairs.
Transcatheter Aortic valve replacements/implantation (TAVR/TAVI)
Transcatheter Aortic valve replacements/implantation (TAVR/TAVI) has been the poster child of percutaneous structural heart interventions. Alan Cribier in France did the first balloon expandable valve for severe Aortic stenosis. In 2006, the first in man Self Expanding CoreValve was performed in our institution, Metro Hospital & Heart Institute. Since then this therapy has been used to treat thousands of patients across the world and is now considered to be the standard of care. The pivotal Partners B trial compared TAVR to medical therapy in inoperable extremely high-risk patients with Aortic Stenosis. TAVR demonstrated a 20% absolute risk reduction in those who received the transcatheter valve compared to medical therapy. This magnitude of mortality benefit rivals those of primary angioplasty in acute myocardial infarction.
Since then multiple trials have demonstrated benefit of the therapy across risk profiles including high risk, moderate risk and most recently low risk patients who would otherwise receive open surgical valve replacement. There has been considerable improvement in the device and procedure technique as well and now it is performed with a 14-16F sheath in the femoral artery that has resulted in significant reduction in procedural complications. Heart block requiring permanent pacemakers is another known complication, but with improvement in device design and implantation techniques this risk has also reduced significantly.
Most centers now do the procedure under conscious sedation and uncommonly use general anesthesia. A 14-16F sheath is placed in the right femoral artery. After predilation of the aortic valve, the prosthetic valve is advanced via this access site and deployed across the aortic valve(Fig 1a). The patient is observed in the CCU and discharged home in a few days.
Transcatheter Aortic valves can broadly be divided into Balloon expandable (picture 1b) and Self Expandable valves (Pic 1c). Both these valves are equally efficacious, and most procedures can be done with either types of valves. This therapy is also coming as a savior for patients with prosthetic valve stenosis, the treatment for which was a second open heart surgery. These subsets of patients are also being treated with TAVR with good outcome.
Another landmark treatment has been in the space of mitral valve. Severe mitral regurgitation(MR) even in asymptomatic patients typically progresses to left ventricular dilatation, left ventricular failure, worsening MR, and eventual symptom onset and surgical therapy has traditionally been advocated to break this cycle. Surgical mitral valve repair has primarily been reserved for patients with suitable anatomy and performed in very few institutions. This is where catheter-based therapies have evolved.
Different transcatheter mitral valve repair techniques have been developed over the past few years addressing the leaflets, the mitral annulus, or the left ventricle. These techniques usually mimic well-known surgical techniques. The MitraClip (Picture 2) is the most commonly used catheter-based mitral valve repair technique. It mimics the surgical edge-to edge technique first described by Alfieri (pic 2b) and coworkers and creates a double orifice mitral valve.
EVEREST II trial, demonstrated in extremely high-risk patients, although MV surgery is superior to transcatheter MV repair using Mitraclip in reducing severity of MR, the clip reduces symptoms, produces durable reduction in MR, and promotes favorable reverse remodeling of the LV. Patient admissions were heart failure were also reduced because of this therapy. These clips are also used to treat tricuspid regurgitation. Newer and more novel devices including specialized mitral valves are being developed to treat mitral regurgitation.
In some cases of mitral stenosis specially with mitral annular calcification (MAC) who are ineligible for balloon valvuloplasty are not being treated with TAVR valve implanted. Small studies have shown encouraging results in these subsets of patients.
Left Atrial Appendage Occlusion
Atrial fibrillation is one of the most common arrythmia’s with its incidence increasing with age. This abnormal heart rhythm increases the risk of thromboembolism and strokes. To reduce this risk, patients require lifelong anticoagulation with warfarin or any of the newer anticoagulants. However, many patients either do not want to take anticoagulation or are unable to tolerate the same secondary to side effects like bleeding.
There are now devices that are used to plug the left atrial appendage (the most common site for thrombus formation in atrial fibrillation) and absolve the patient from taking lifelong anticoagulation. This has been widely accepted as an alternative for anticoagulation in patient who either do not wish or are unable to take the medication. One of the commonly used is “the watchman device”. This is a parachute-shaped, self-expanding device that closes the LAA (Fig 3a). A similar device is the “Amplatzer Plug device” that has a similar mechanism of action. These have been tested in several studies that showed the devices are a good alternative treatment for patients who cannot tolerate treatment with blood thinners.The procedure is done via the right femoral vein and after a trans-septal puncture into the left atrium, the device is deployed into the left atrial appendage.
Percutaneous interventions in structural heart diseases are emerging rapidly. There has been considerable innovation in this space and now able to offer treatment for diseases that otherwise had only medications. With advancement structural heart disease interventions it has emerged as an independent specialty catering to patients with various valvular and other structural conditions.
Dr. Sameer Gupta , FACC, FSCAI
Consultant, Interventional Cardiology & Peripheral Intervention
Director, Cardiac Cath Lab, Metro Group of Hospitals,
(Limb Disease Specialist)