• Aortic valve replacement is an open, intracardiac surgery procedure in which the stenotic or regurgitant aortic valve is replaced with a healthy valve. The 2 basic artificial heart valves are mechanical and tissues valves.
• Following sternotomy, opening of the pericardium, and routine venous and arterial cannulation, the patient is taken onto full cardiopulmonary bypass (CPB). After the heart is arrested, the aorta is opened to expose the aortic valve. The valve leaflets are excised and the annulus is debrided. The annulus is then measured to properly match the prosthetic valve. Interrupted sutures are placed through the annulus for its entire circumference and then passed through the sewing ring. The prosthesis is tied securely in place.
• Systemic rewarming is initiated during the final stages of the valve implantation, and the left ventricle is allowed to fill during aortic closure. With the patient in the head-down position, all remaining air is vented from the left heart and aorta. The cross-clamp is removed.
• Pacing wires and chest tubes are placed and the patient is weaned from bypass. Once the patient is stable, decannulation and heparin reversal are accomplished in routine manner.
• Concomitant root replacement may be necessary in patients with aortic stenosis secondary to bicuspid valve pathology and concurrent aortic root dilations.
• Pulmonary autograft (Ross procedure) involves replacing the aortic valve with a pulmonary valve autograft and right-sided reconstruction with a homograft; it is used in children and adolescents.
• Minimally invasive aortic valve surgery through smaller incisions with specialized instruments is being explored; for the surgery on the valve itself conventional instruments and techniques are used.
  • Only selected patients are eligible for these approaches.
  • Initial results are favorable in regard to clinical outcome, perioperative complications and cost.
  • No randomized controlled trials are available comparing minimally invasive and open surgery.
• Transcatheter aortic valve replacement is a new catheter-approach that obviates the need for open heart surgery. It is being used in Europe and parts of the world, but only tested in clinical trials in the US. The results for high-risk patients with severe aortic stenosis who are not surgical candidates are promising (1) [B].

• Supine, arms tucked
• Temporary Trendelenburg at the time of left ventricle de-airing, prior to coming off bypass

• Standard: Median sternotomy
• Alternative incision sites (e.g., right second intercostal anterior thoracotomy) are used as part of "minimally invasive aortic valve surgery."

4–8 hours, depending on the experience of the team and technical difficulties

• CPB machine leads to dilution.
• Blood loss typically ranges from 1,000 to 2,000 mL.

Typical length of stay in the surgical ICU is 1–3 days and 3–7 days in the hospital overall.

• Valve (mechanical or tissue)
• CPB machine (operated by perfusionist)
• Minimally invasive approaches require special equipment.
• Transesophageal echocardiography probe (intraoperative examination performed by echo trained anesthesiologists or cardiologist)

Prevalence

In 2009 approximately 70,000 patients underwent aortic valve replacement in the US.

• The 2008 ACC/AHA Valvular Disease guidelines refer to risk stratification models to estimate the risk of in-hospital mortality and morbidity of valve surgery with or without coronary artery bypass (2). All models have drawbacks such as estimating risk for only one specific procedure or not including patient's variable like nutritional status. There are 3 major models:
  • The US-based registry by the Society of Thoracic Surgeons (STS) (3) [B]. It includes data from nearly 90% of cardiac surgery providers in the US and may provide the most accurate risk stratification for aortic valve replacement.
  • The European System for Cardiac Operative Risk Evaluation ("EuroScore")
  • The scoring system developed from Great Britain's and Ireland's national database

• Varies significantly with age, comorbidities, type of valvular lesion, ventricular function, other concomitant valvular surgery, and/or bypass surgery
• Risk stratification models are useful to predict mortality risk for the individual patient. Example: Mortality <1% in a 65-year-old patient with symptomatic severe aortic stenosis, normal left ventricular function and otherwise healthy; however, mortality increases >1% for the same patient with hypertension and diabetes.

History

Determine if there is a history of esophageal strictures or other abnormality that would prohibit placement of transesophageal echocardiography during the procedure.

Signs/Physical Exam

See "Aortic Stenosis" and "Aortic Regurgitation" chapters

Labs/Studies

• Preoperative transthoracic echocardiography and sometimes a transesophageal echocardiography are performed.
• Coronary angiography is routinely performed since significant coronary artery disease is a common comorbidity and may require concurrent coronary bypass grafting.

Consider gentle anxiolysis with benzodiazepines

Morbidity and mortality risks vary with the extent of surgery (e.g., coronary bypass surgery in addition to valve replacement) and pre-existing comorbidities.

Skin flora poses the greatest concern; cefazolin is utilized if the patient is not a carrier of multi-resistant bacteria and there is no allergy. It is administered intravenously within 60 minutes prior to incision and repeated q3–4h until chest closure.

• General anesthesia in the US
• There are case reports of open heart surgery performed under epidural with sedation in other parts of the world.

• ASA standard monitoring; core and shell temperatures are measured.
• Arterial line placement most often prior to induction; the absence of pulsatile blood flow during bypass precludes noninvasive blood pressure measurement.
• Central venous access is usually obtained after induction; pulmonary artery catheter placement may be considered.
• Transesophageal echocardiography is frequently used intraoperatively to guide and assess aortic valve replacement.

• Goal is to provide hemodynamic stability throughout the induction period. Gentle propofol administration (with vasopressors and inotropes as needed) or etomidate in combination with fentanyl.
• In the event of hemodynamic instability CPB may be instituted immediately.

• Patients are usually maintained with oxygen/volatile agents and intermittent doses of opioids and non-depolarizing muscle relaxants.
• During bypass, volatile agent is added to the blood by the perfusionist through the bypass machine.
• The management of patients during bypass varies substantially by institution and practitioner.
• On bypass the target mean arterial blood pressure is typically between 50 and 80 mmHg.
• On bypass the patient's body temperature is cooled at the beginning and warmed to normal body temperature before termination of bypass.

• Patients remain intubated and are transferred to the ICU.
• Sedation is typically provided with propofol or dexmedetomidine infusion. The latter appears to have a lower risk for the development of postoperative delirium.