Aortic Stenosis (AS) refers to a clinical situation where Aortic Valve (AoV) that doesn't open well, causing impediment to blood flow. This leads to the heart working against resistance which adds undue stress to the heart. If this scenario is left unchecked for long period of time, the heart eventually fails leading to complications that often culminates in patient's demise. A nice depiction of AoV, AS and treatment options is laid out in this video (courtsey: Alliance for Aging Research)
Aortic valve (AoV) is one of the four valves present in a normal heart. It sits between Left Ventricle (LV, heart's main pumping chamber) and Aorta (main channel that carries blood from the heart to rest of the body). Role of AoV is to allow unidirectional blood flow from LV to Aorta offering minimal or no resistance while also preventing any blood leak back into LV from Aorta. Native AoV comprises of 'cusps' made up of extremely soft thin tissue which allows cusps to open and close without any significant fatigue (Figure 1A, 1B). Three symmetric cusps arranged in the shape of 'Mercedes Benz' logo constitutes a normal health AoV.
Few of us are born with cusps which are not perfectly symmetric, which causes flow turbulence across the valve. This leads to repetitive micro injury and healing of aortic cusps that over long time (years) adds scar tissue and calcium deposit causing structural deformity. Mechanical dynamics of degenerated/deformed cusps leads to restricted opening as well as imperfect seal during closure (Figure 2A, 2B). If cusps' opening is restricted significantly, blood flow may be restricted, leading to the clinical condition termed "Aortic Stenosis". Stenosis refers to restricted valve opening.
It is hypothesized that factors which puts as at risk for AS are similar to those for Coronary Artery Disease as well, namely Diabetes, High Cholesterol, Smoking etc. A healthy lifestyle and good control of risk factors can effect onset and progression of AS. On the other hand, few people are born with not three, but 2 or 1 Aortic Valve cusps. Such condition is called Bicuspid or Unicuspid valve respectively, and are at higher risk for developing AS early in their life (Figure 3A).
AS is typically graded as mild, moderate, and severe. While mild and moderate AS can be managed with medicines alone, patients with severe AS may need to undergo corrective measures.
Symptoms of severe AS may include: 1. Breathing difficulty 2. Exercise intolerance, getting tired easily
3. Chest discomfort
4. Dizziness, giddiness, or fainting
5. Leg swelling
6. Difficulty breathing when lying down
AS is a mechanical problem and need to be dealt with mechanical intervention. Once a patient is diagnosed with severe AS and has symptoms associated with it: these are the available options:
1. Medicines alone: In severe AS cases, medicines can alleviate the symptoms to some degree but don't modify the disease in any way, and don't prolong longevity. Overall, it is a fall back option when standard treatment options seem undesirable.
2. Surgery: This is the mainstay of therapy. Open heart surgery in which surgeon takes the degenerated valve out and replaces it with a man-made valve (mechanical or bio-prosthetic) that is immediately functional after implantation. Surgical Aortic Valve Replacement (SAVR) as it is called, is a well established technique for all patients with severe Aortic Stenosis. In routine cases, surgery related major complications are uncommon.
3. Minimally Invasive: Transcatheter Aortic Valve Replacement (TAVR) is a newer technique that crimps a bioprosthetic Aortic Valve on to a delivery system (Flexible tube called catheter). This catheter is now inserted inside the body via a small groin/leg incision similar to coronary angioplasty. Once in the body, the crimped valve is implanted at the site of diseased native AoV. All this is achieved via a simple 5-7 mm incision in the groin area. TAVR offers the advantage of less riskier surgical option, with early recovery. Because its a newer technique (first case done in 2002), clinical follow up is not as robust as with SAVR. Having said that, TAVR underwent rigorous clinical studies in the past 10 years and results are extraordinarily positive. TAVR is the standard therapy in western world in patients with severe AS who are considered intermediate or high risk for open heart surgery.
4. Balloon Valvuloplasty: This procedure involves inflating a balloon at the Aortic stenosis site, similar to angioplasty (Figure 4).
The procedure is simple, relatively safe, and offers temporary relief to patients who are too sick to undergo SAVR or TAVR. Major limitation with Balloon Valvuloplasty is that the positive benefits of intervention is temporary. Typically, stenosis recurs to severe level in about 6 months.
The Heart Team:
Landscape of AS treatment has seen a major overhaul in the past 10 years or so. TAVR is the most disruptive medical technology in recent times that the entire world is talking about. Multi-modality approach to individual patient case has shown to improve overall outcomes and due to this, the concept of "The Heart Team" has evolved lately. The Heart Team involves group of clinical and non-clinical staff coming together to discuss each patient case, use multi-disciplinary approach to handle the problem at hand, and come to a combined decision that is agreed upon by all the parties. It also provides holistic patient care targeting every aspect of patient well being rather than limiting to one particular problem. As someone seeks care for severe AS, its reasonable to approach to a healthcare institute which has an established Heart Team.
I am sure I haven't answered all of your questions. Please feel free to contact me for any queries and I will be happy to answer those.