TAVI -part1

Transcatheter aortic valve replacement

Aortic valve replacement is the mainstay of treatment of symptomatic aortic stenosis (AS). In properly selected patients, this surgical procedure offers substantial improvements in symptoms and life expectancy.

However, aortic valve surgery entails substantial risks for some patients with severe comorbidities, and for some considered at “extreme” risk, surgery is not appropriate. In others, technical limitations, eg, porcelain aorta, may mean that surgery is not feasible. Percutaneous aortic valvotomy was developed as a less invasive means to treat AS but has important limitations. Subsequently developed catheter-based techniques for aortic valve implantation may provide an alternative method for treating AS in patients with unacceptably high estimated surgical risks. A multidisciplinary team approach is recommended in approaching patients with symptomatic AS.

This topic will review transcatheter aortic valve implantation, which has been termed transcatheter aortic valve replacement (TAVR). Indications for aortic valve replacement, surgical aortic valve replacement, estimating the risk of aortic valve surgery, medical therapy of symptomatic AS, and percutaneous aortic valvuloplasty are discussed separately.

Transcatheter aortic valve replacement has been developed for the treatment of patients with severe symptomatic AS who have an unacceptably high estimated surgical risk, or in whom TAVR is preferred due to technical issues with surgery, eg, a porcelain aorta or prior significant mediastinal radiation, prior pericardiectomy with dense adhesions or prior sternal infection with complex reconstruction, or a patent left internal mammary graft lying beneath the sternum (as identified by computed tomography angiography).

Thus, accurate estimation of the risk of surgical aortic valve replacement performed by an experienced cardiothoracic surgeon and multidisciplinary valve team is vital to appropriate evaluation of potential candidates for this emerging experimental procedure. Risk calculators are available to estimate the risk of valvular surgery. However, risk estimates are subject to inaccuracies (eg, the logistic EuroSCORE appears to overestimate mortality risk in patients undergoing high-risk aortic valve replacement) and the models do not account for some clinical characteristics (eg, porcelain aorta, severe pulmonary hypertension, or RV dysfunction) that may impact surgical mortality. In patients undergoing aortic valve replacement, the Society of Thoracic Surgeons (STS) model may provide more accurate risk stratification than the logistic EuroSCORE or the Ambler risk score. The logistic EuroSCORE has been replaced by the EuroSCORE II.

Of note, these scoring systems are only applicable to patients undergoing surgery and are not validated nor considered accurate in a TAVR eligible cohort of patients. More appropriate scoring systems are not currently available, although they are being developed.

PATIENT SELECTION — Patient selection criteria for TAVR are evolving. Selected patients who have indications for aortic valve replacement for calcific aortic stenosis are candidates for TAVR. 

 The 2012 American College of Cardiology Foundation/American Association for Thoracic Surgery/Society for Cardiovascular Angiography and Interventions/Society of Thoracic Surgeons (ACCF/AATS/SCAI/STS) expert consensus document on
TAVR lists the following criteria based upon those used in randomized trials [1]:

• Calcific aortic valve stenosis with the following echocardiographic criteria:

• Severely calcified valve leaflets with reduced systolic motion AND 

Mean gradient >40 mm Hg or jet velocity >4.0 m/s

OR

Aortic valve area of <1.0 cm² or indexed effective orifice area <0.5 cm²/m² 

• In the setting of LV systolic dysfunction, severe AS is present when the leaflets are calcified, with reduced systolic motion, and dobutamine stress echocardiography shows an aortic velocity of >4.0 m/s OR mean gradient >40 mm Hg with a valve area <1.0 cm² OR AV index <0.6 cm²/m² at any flow rate.

• Patients are symptomatic (NYHA functional class II or greater) from aortic valve stenosis, rather than from symptoms related to comorbid conditions.
• A cardiac interventionalist and two experienced cardiothoracic surgeons agree that surgical aortic valve replacement is either precluded or high risk, based on a conclusion that the probability of death or serious irreversible morbidity exceeds the probability of meaningful improvement. At least one of the cardiac surgeon assessors must have physically evaluated the patient. The surgeon’s consult notes should specify the medical or anatomic factors leading to this conclusion and should include a printout of the calculation of the STS score.

The expert consensus document lists numerous exclusion criteria, including the following criteria related to the aortic valve:

• Bicuspid or unicuspid or noncalcified aortic valve
• Severe aortic regurgitation (>3+)
• Native aortic annulus size as measured by echocardiography <18 mm or >the largest annulus size for which a TAVR device is available (eg, 29 mm for the largest Medtronic CoreValve). Of note, this criterion is subject to change as the range of available device sizes changes.

Other exclusion criteria may include the following:

• Evidence (CK plus CK-MB elevation and/or troponin elevation) of an acute myocardial infarction within one month before the intended treatment.
• Hemodynamic or respiratory instability requiring inotropic support, mechanical ventilation, or mechanical heart assistance within 30 days of screening evaluation.
• Need for emergency surgery.
• Hypertrophic cardiomyopathy with or without obstruction.
• Left ventricular ejection fraction <20 percent.
• Severe pulmonary hypertension and right ventricular dysfunction.
• A known contraindication or hypersensitivity to all anticoagulation regimens or inability to be anticoagulated for the study procedure.
• Renal insufficiency (eg, creatinine >3.0 mg/dL) and/or end-stage renal disease requiring chronic dialysis.
• Echocardiographic evidence of intracardiac mass, thrombus, or vegetation.
• MRI confirmed CVA or TIA within six months (180 days) of the procedure.
• Severe incapacitating dementia.
• Estimated life expectancy <12 months due to noncardiac comorbid conditions.
• Severe mitral regurgitation.
• Significant aortic disease including the following abnormalities may preclude a transfemoral approach:

• Thoracic or abdominal aortic aneurysm (luminal diameter ≥5 cm), marked tortuosity (hyperacute bend)
• Aortic arch atheroma (especially if >5 mm thick, protruding, or ulcerated)
• Narrowing (especially with calcification and surface irregularities) of the abdominal or thoracic aorta
• Marked tortuosity (hyperacute bend) of the aorta or severe “unfolding” of the thoracic aorta

Two major catheter-based techniques for replacing the aortic valve have been investigated: retrograde percutaneous implantation and direct apical puncture. In addition, there is rapidly growing use of direct aortic access via either ministernotomy or right anterior thoracotomy.

An antegrade transseptal approach has also been studied but adoption has been limited due to procedural complexity and associated risks (eg, development of acute mitral regurgitation) .

A retrograde femoral arterial approach via the aortic arch and through the stenotic valve is an alternative to the antegrade approach, and devices were designed to overcome some of the limitations seen with transseptal antegrade delivery. Two stent-valve devices with different designs have been successfully implanted in humans using the retrograde femoral approach: a balloon-expandable valve (Edwards SAPIEN, which has replaced the Cribier-Edwards valve) and a self-expanding valve (Medtronic CoreValve) . The Medtronic CoreValve had also been delivered in a retrograde fashion from the subclavian/axillary artery and via direct aortic access via either ministernotomy or right anterior thoracotomy.

An alternate catheter-based approach consists of direct left ventricular apical puncture and antegrade aortic valve implantation via a small anterolateral thoracotomy without cardiopulmonary bypass or sternotomy. This approach is particularly suited to patients with severe peripheral artery disease and heavily calcified ascending aorta and arch (porcelain aorta) who have an increased risk of stroke and other embolic events using other approaches.

PERIPROCEDURAL MANAGEMENT

Candidates for TAVR should be evaluated for potential risk factors such as depressed left ventricular ejection fraction, coronary artery disease, and kidney disease . For patients at risk of hemodynamic decompensation, preparations should include availability of rapid institution of cardiopulmonary bypass (and rarely elective bypass may be instituted).

The expert consensus document recommends routine antibiotic prophylaxis for all patients undergoing TAVR prior to surgical incision or vascular access to prophylax against wound infection and endocarditis .

Patients undergoing TAVR generally receive general anesthesia, a temporary pacing lead, at least one large bore intravenous line, warming to avoid hypothermia, and monitoring by arterial line, pulmonary artery catheter, and transesophageal echocardiography.

Some transfemoral procedures are performed with local anesthesia and conscious sedation. Heparin is administered after placement of standard sheaths and prior to placement of the large sheath.

Management includes early identification and treatment of volume depletion, positive inotropic agents in patients with low cardiac output or greater than moderate pulmonary hypertension, and treatment of severe pulmonary hypertension and right ventricular failure with inhaled nitric oxide or epoprostenol.
Measures to avoid prolonged hypotension include maintenance of mean arterial pressure of >75 mmHg prior to initiation of rapid ventricular pacing (required during valve placement of prostheses other than the CoreValve) with cautious use of intravenous vasopressor (norepinephrine, epinephrine, or phenylephrine) therapy as needed while avoiding hypertension.

expert consensus document on transcatheter aortic valve replacement
http://www.sciencedirect.com/science/article/pii/S0735109712000022

Comparison of three methods of assessing cardiovascular disability

Class	New York Heart Association functional classification[1]	Canadian Cardiovascular Society functional classification[2]	Specific activity scale[3]
I	Patients with cardiac disease but without resulting limitations of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain.	Ordinary physical activity, such as walking and climbing stairs, does not cause angina. Angina with strenuous or rapid prolonged exertion at work or recreation.	Patients can perform to completion any activity requiring ≥7 metabolic equivalents, eg, can carry 24 lb up eight steps; do outdoor work (shovel snow, spade soil); do recreational activities (skiing, basketball, squash, handball, jog/walk 5 mph).
II	Patients with cardiac disease resulting in slight limitation of physical activity. They are comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain.	Slight limitation of ordinary activity. Walking or climbing stairs rapidly, walking uphill, walking or stair climbing after meals, in cold, in wind, or when under emotional stress, or only during the few hours after awakening. Walking more than two blocks on the level and climbing more than one flight of ordinary stairs at a normal pace and in normal conditions.	Patients can perform to completion any activity requiring ≤5 metabolic equivalents, eg, have sexual intercourse without stopping, garden, rake, weed, roller skate, dance fox trot, walk at 4 mph on level ground, but cannot and do not perform to completion activities requiring ≥7 metabolic equivalents.
III	Patients with cardiac disease resulting in marked limitation of physical activity. They are comfortable at rest. Less than ordinary physical activity causes fatigue, palpitation, dyspnea, or anginal pain.	Marked limitation of ordinary physical activity. Walking one to two blocks on the level and climbing one flight in normal conditions.	Patients can perform to completion any activity requiring ≤2 metabolic equivalents, eg, shower without stopping, strip and make bed, clean windows, walk 2.5 mph, bowl, play golf, dress without stopping, but cannot and do not perform to completion any activities requiring >5 metabolic equivalents.
IV	Patient with cardiac disease resulting in inability to carry on any physical activity without discomfort. Symptoms of cardiac insufficiency or of the anginal syndrome may be present even at rest. If any physical activity is undertaken, discomfort is increased.	Inability to carry on any physical activity without discomfort - anginal syndrome may be present at rest.	Patients cannot or do not perform to completion activities requiring >2 metabolic equivalents. Cannot carry out activities listed above (Specific activity scale III).

References:

1. The Criteria Committee of the New York Heart Association. Nomenclature and Criteria for Diagnosis of Diseases of the Heart and Great Vessels, 9th ed, Little, Brown & Co, Boston, 1994. p.253.
2. Lucien C. Grading of angina pectoris. Circulation 1976; 54:5223.
3. Goldman L, Hashimoto B, et al. Comparative reproducibility and validity of systems for assessing cardiovascular functional class: Advantages of a new specific activity scale. Circulation 1981; 64:1227