Anesthesiology

Aortic Valve Replacement

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What the Anesthesiologist Should Know before the Operative Procedure

It is essential for the anesthesiologist to know whether the patient is scheduled for aortic valve replacement (AVR) due to underlying aortic stenosis (AS) or aortic regurgitation (AR), as the hemodynamic goals for management of AS and AR are very different. Similarly, if the patient has AR, it is important to know whether the situation is acute or chronic in nature. Patients with chronic aortic valve disease often have had time to allow for ventricular compensation, whereas the patient with new-onset severe AR may display acute decompensation. AVR can be challenging cases as the hemodynamic management of the lesions is quite different and must be balanced to maintain the most stable hemodynamics. As with any surgical patient, it would also be important to understand all underlying comorbidities—in particular, whether there is coexisting coronary artery disease, congestive heart failure, pulmonary disease, renal disease, or history of cerebrovascular disease.

Aortic stenosis

AS may be the result of a congenitally bicuspid aortic valve, senile calcification of a tricuspid aortic valve, or rheumatic heart disease. The narrowing of the aortic valve opening leads to progressive left ventricular outflow obstruction and chronic pressure overload. The left ventricle compensates for the increased pressure by increasing muscle mass, resulting in left ventricular (LV) hypertrophy. This hypertrophy leads to decreased ventricular compliance, diastolic dysfunction, increased myocardial oxygen demand, and reduced myocardial oxygen delivery. If untreated, the initial concentric hypertrophy that occurs can progress to eccentric hypertrophy, which compromises contractility and further decreases cardiac function. The signs and symptoms of aortic stenosis include angina, dyspnea on exertion, and syncope. They typically occur when the aortic valve area is less than 1 cm2.

Aortic regurgitation (chronic)

AR may be the result of annular dilatation (aneurysms, dissection) or abnormal leaflet motion (calcification, rheumatic disease, bicuspid valves, endocarditis). The regurgitation of aortic blood into the left ventricle during diastole leads to chronic volume overload. If the regurgitation is chronic and slowly progressive in nature, the ventricle adjusts by dilating to accommodate the increased volume. In these chronic situations, LV end-diastolic volume can be significantly increased with relatively normal LV end-diastolic pressure. The dilation that occurs to accommodate the increased volume also leads to eccentric hypertrophy, resulting in decreasing coronary perfusion and the potential for irreversible myocardial ischemic damage. LV dysfunction leads to increased pulmonary pressures and congestive heart failure. Symptoms of chronic AR include dyspnea, palpitations, fatigue, and angina. Signs of AR include a wide pulse pressure and a bisferiens pulse.

Aortic regurgitation (acute)

Acute AR typically is due to endocarditis. In these cases the ventricle has not had time to dilate to accommodate the increase in LV end-diastolic volume and there is a significantly increased LV end-diastolic pressure. There is compensatory tachycardia and peripheral vasoconstriction, but severe congestive heart failure quickly follows.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

The urgency of the situation will depend on the acuity of the aortic valve disease and the ability of the patient’s left ventricle to tolerate the disorder. AS is typically a chronic condition that worsens over time. AVR for AS is typically an elective procedure. AR can be either chronic or acute in nature. The left ventricle poorly tolerates acute AR and AVR is typically done emergently or urgently, whereas AVR for chronic AR can often be done electively.

Emergent AVR for isolated AS is rare, and may be best seen in patients who have undergone previous AVR and have acute malfunction of the replaced valve (e.g., nonmobile mechanical valve leaflet). This would typically be associated with concomitant AR. Urgent AVR for AS may be required in the patient with AS who develops new-onset angina, congestive heart failure, or syncope. There is typically time to obtain a transthoracic echocardiogram, ECG, CBC, metabolic panel, and coagulation labs prior to surgery.

Elective AVR for AS is more common than urgent AVR as these patients are typically known to have AS and are followed over time. Once they develop symptoms of AS or the stenosis becomes severe by echocardiographic measurements, they are referred for surgical replacement. Stenosis in these patients is typically due to calcification of congenitally bicuspid valves, senile calcific degeneration of tricuspid aortic valves, or rheumatic heart disease. The patient should be thoroughly evaluated and optimized for surgery. In addition to full assessment of the patient’s valvular disease, the patient should undergo cardiac catheterization to assess for coronary artery disease that could be surgically revascularized at the time of AVR. The patient should also be assessed for carotid vascular disease, and surgery may be delayed for carotid endarterectomy prior to AVR if necessary. Any anemia or electrolyte abnormalities should be investigated and optimized prior to elective surgery.

Emergent AVR for AR is necessary in cases of acute AR. Although sympathetic tone is increased to maximize contractility and heart rate, the abrupt increase in LV end-diastolic volume can lead to rapid ventricular failure. These patients are often not able to generate enough forward cardiac output to maintain perfusion of vital organs. Acute AR is most likely to occur with acute aortic dissection involving the aortic valve, aortic valve endocarditis, or trauma. There is typically time to obtain a transthoracic echocardiogram, ECG, CBC, metabolic panel, and coagulation labs, but emergent surgery should not be delayed to wait for results.

Elective AVR for isolated AR is often the result of aortic root dilation. This may result from connective tissue disorders such as Marfan syndrome, chronic aortic dissection, or degenerative aortic dilatation. Elective AVR for AR may also be due to intrinsic aortic valve disease (bicuspid aortic valve, calcific degeneration, rheumatic valve disease) and is often combined with AS in these cases. These patients are often well known to cardiologists and their diseases are followed over time until they become severe enough to be referred to surgery. Therefore, there is ample time to thoroughly assess the patient for comorbidities. At a minimum, the patient should have a full cardiac workup to assess for other valvular lesions and coronary disease that can be corrected at the time of AVR. The patient should also have evaluation of carotid stenosis as, if present, they may benefit from carotid endarterectomy prior to AVR. Any anemia or electrolyte abnormalities should be investigated and optimized prior to elective surgery.

2. Preoperative evaluation

Preoperative evaluation of the patient coming to the operating room for AVR should include a thorough history and physical. In addition to determining whether the patient has underlying AS or AR, a complete cardiac evaluation is of paramount importance as it may impact both the procedure and the anesthetic plan. It is necessary to assess for LV hypertrophy (concentric or eccentric), congestive heart failure, concomitant coronary artery disease, and other potential valvular lesions. The patient should also be assessed for carotid artery disease, as it is advisable to treat significant carotid disease prior to proceeding with elective cardiac surgery. As with any patient presenting to surgery, all organ systems should be thoroughly reviewed.

Delaying surgery is only indicated if the patient has stable aortic valve disease and preserved cardiac function. If the patient is in cardiac failure or unable to compensate for either the increase in LV volume or pressure, then surgery should proceed.

Medically unstable conditions that warrant further evaluation include significant carotid artery disease, pulmonary disease, and renal disease. Patients with severe carotid artery stenosis can benefit from carotid endarterectomy prior to AVR. Underlying pulmonary and renal pathology should be evaluated and optimized prior to surgery. Other reasons for surgical delay in the stable patient include optimization of hematocrit preoperatively to reduce the risk of requiring blood transfusion, evaluation and treatment of electrolyte abnormalities, and treatment of any current infection that would increase the risk of postoperative infection.

3. What are the implications of co-existing disease on perioperative care?

b. Cardiovascular system

As the patient is presenting for cardiac surgery, a complete cardiac evaluation is essential. At a minimum, the etiology and severity of the patient’s aortic valve disease should be known. The patient should be evaluated for coexisting coronary artery disease and have preoperative coronary catheterization to define the lesions if it is suspected as coronary artery bypass grafting could occur at the same time as the aortic valve surgery. Similarly, the patient should be evaluated for other valvular or structural cardiac lesions that could also be treated at the time of aortic valve surgery. Obviously, it would be important to know whether the patient had any history of previous cardiac surgery as this may impact the surgical approach and risk of bleeding.

Aortic stenosis

The patient should have a preoperative echocardiogram to evaluate the aortic valve and determine whether the degree of stenosis is mild (aortic valve area >1.5 cm2), moderate (aortic valve area 1.0 to 1.5 cm2), or severe (aortic valve area <1.0 cm2) and whether there is concomitant AR. The echocardiogram should also reveal information about ventricular hypertrophy, ventricular function, and wall motion abnormalities. A thorough history should be obtained to assess for symptoms of AS including angina, syncope, and CHF. The patient with ASs does not tolerate dysrhythmias well as the stiffened ventricle depends heavily on the atrial kick for ventricular filling and should be assessed for history of atrial fibrillation.

Acute AR is characterized by sudden LV volume overload, increased sympathetic tone leading to tachycardia and increased contractility, and compensatory increased preload and fluid retention leading to sudden, severe dyspnea, and ensuing cardiovascular collapse. Beyond an echocardiogram, there is typically not time for additional preoperative cardiac evaluation as the patient can be quite unstable, requiring urgent repair.

Goals of management include increasing heart rate to minimize regurgitation and maximize forward cardiac output while taking care not to cause ischemia, decreasing systemic vascular resistance to minimize stroke work, and augmentation of preload to maintain cardiac output.

c. Pulmonary

Chronic obstructive pulmonary disease (COPD)

COPD is a risk factor for postoperative pulmonary complications such as pneumonia and respiratory failure. Perioperative treatment with inhaled steroids, leukotriene antagonists, and beta-agonists should be optimized to improve pulmonary function.

Reactive airway disease (asthma)

Similar to the patient with COPD, the patient with asthma should have their medications and pulmonary function optimized prior to elective surgery. It may be prudent to postpone elective surgery if the patient has an active respiratory infection to minimize the risk of postoperative pulmonary complications.

Obstructive sleep apnea

The severity of the patient’s OSA should be assessed as significant disease can lead to pulmonary hypertension and right heart failure. The patient may benefit from preoperative assessment and treatment with CPAP to minimize postoperative hypercapnia and hypoxia.

d. Renal-GI:

Renal insufficiency

Preoperative renal function should be evaluated and creatinine level obtained. Patients with decreased renal function are at an elevated risk for postoperative hemodialysis, and any elective surgery should be delayed until acute renal insufficiency has resolved. Similarly, abnormal renal labs in the elective patient should prompt evaluation by a nephrologist in an attempt to treat the underlying disorder and minimize the risk for postoperative hemodialysis. The patient with chronic renal failure already undergoing hemodialysis should be dialyzed within the 24 hours prior to surgery to optimize fluid status and electrolytes.

Hepatic insufficiency

These patients should have their liver function assessed preoperatively. Any elective surgery should be delayed for acute hepatitis, as there is a significantly increased risk of morbidity. As with any patient presenting for surgery, the presence of chronic liver disease can lead to abnormalities with coagulation. With significantly impaired hepatic function, there will be decreased ability to generate clotting factors and coagulation studies should be ordered. These patients are at greater risk of requiring transfusion of plasma perioperatively. Platelet function can also be impaired. It may be beneficial to obtain a preoperative thromboelastogram to help determine the degree and type of coagulation abnormalities present.

e. Neurologic:

As with any patient presenting for surgery, a full history and physical should be performed and the patient should be assessed for any coexisting neurologic disease. Any new or acute neurologic symptoms should prompt evaluation prior to elective surgery. As there is risk of postoperative cerebrovascular accident with cardiac surgery, any history of cerebrovascular accident or transient ischemic attack should be thoroughly assessed and deficits noted.

f. Endocrine

Diabetes mellitus

Patients should be assessed for the presence of type 1 and type 2 diabetes mellitus. Hemoglobin A1c levels should be obtained and oral medication or insulin regimens should ideally be optimized prior to surgery. Diabetics are at an increased risk for postoperative infections and cardiovascular events. Perioperative glucose control helps to minimize cardiovascular risk, and although the absolute target is a point of contention, a glucose goal of less than 150 mg/dL is reasonable. Other means of minimizing the diabetic patient’s risk of cardiovascular events include administration of beta-blockers, statins, and ACE inhibitors. Diabetic patients also often have neuropathy and should be assessed for the presence of autonomic instability. They should be expected to have delayed gastric emptying and are at an increased risk of aspiration.

Thyroid disease

Patients should be assessed for thyroid disease and thyroid function should be assessed if the patient is on thyroid medication or untreated disease is suspected clinically.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

Carotid artery disease

Patients with significant carotid disease are at an increased risk of postoperative stroke. All patients should be queried for a history of transient ischemic attacks or visual loss and assessed for the presence of bruits. Most of these patients will undergo ultrasound assessment of the carotid arteries and if there is greater than 80% stenosis they may benefit from carotid endarterectomy prior to elective cardiac surgery. It can be particularly useful to monitor cerebral oximetry in the patient with cerebrovascular disease and adjust the mean arterial pressures as necessary to maintain optimal cerebral perfusion.

Coagulation disorders

All patients should obtain preoperative laboratory tests including platelet count, prothrombin time, and partial thromboplastin time to assess for underlying coagulation abnormalities. Any unexplained results should be investigated and corrected prior to elective surgery. Any platelet coagulation factor disorders should be thoroughly evaluated prior to elective surgery as these patients are at risk for significant bleeding with cardiopulmonary bypass.

Patients with AS also have an acquired von Willebrand syndrome that is thought to be related to the high shearing forces applied to the platelets traversing the stenotic valve and is directly related to the severity of stenosis. Intraoperative desmopressin may be useful in improving platelet function in these patients after cardiopulmonary bypass.

Anemia

The risk of perioperative blood transfusion is greatly increased if the patient presents to surgery with a low hematocrit. Elective surgical patients can be optimized preoperatively with iron and erythropoietin to help minimize the need for perioperative blood transfusion.

4. What are the patient's medications and how should they be managed in the perioperative period?

Beta-blockers should be taken on the day of surgery and continued throughout the perioperative period if the patient tolerates them. Statins should be taken throughout the perioperative period as well. Diabetic patients should cut their dose of insulin on the day of surgery and avoid taking metformin. Perioperative glucose control should continue via insulin infusion while the patient is in the intensive care unit. Patients coming for elective AVR should stop taking antiplatelet medications prior to surgery. The duration of cessation will depend on the duration of action of the drug (e.g., clopidogrel should be stopped 1 week prior to surgery, whereas the longer-acting ticlodipine should be stopped for 2 weeks). Platelet function assays may be obtained to determine the degree of platelet inhibition present after stopping the drugs. All herbal supplements that impact platelet function or coagulation should similarly be stopped a minimum of 1 week prior to surgery.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Any medications that impact platelet function or coagulation are of concern in the patient undergoing AVR as they are at significant risk for bleeding after cardiopulmonary bypass. Antidysrhythmics and antihypertensives should be continued prior to elective AVR surgery, in an attempt to maintain hemodynamic stability.

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac: The patient should continue all cardiac medications prior to surgery, including antihypertensives, antidysrhythmics, and beta-blockers.

Pulmonary: The patient should continue all pulmonary medications prior to surgery.

Renal: The patient should continue all renal medications prior to surgery and if on chronic hemodialysis should undergo hemodialysis within 24 hours prior to elective surgery.

Antiplatelet: The patient should stop taking antiplatelet medications prior to surgery, with the exception of aspirin that should be continued until the day of surgery.

Psychiatric: The patient should continue all psychiatric medications prior to surgery.

j. How To modify care for patients with known allergies

Potential allergens should be avoided in the perioperative period.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

N/A

l. Does the patient have any antibiotic allergies? (common antibiotic allergies and alternative antibiotics)

Avoid administering antibiotics to which the patient has an allergy and choose appropriate alternatives (e.g., the patient allergic to cefazolin may receive vancomycin).

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Documented: Avoid all trigger agents such as succinylcholine and inhalational agents. Follow a proposed general anesthetic plan: adequate flushing of the anesthetic machine, changing of the anesthesia circuit, and plan for total intravenous anesthesia with propofol ± opioid infusion ± nitrous oxide. Ensure an MH cart is available [MH protocol] and MHAUS telephone numbers available.

Family history or risk factors for MH: Best to proceed with nontriggering anesthetic as in the patient with documented MH above.

Local anesthetics/muscle relaxants: Avoid local anesthetics and muscle relaxants to which the patient has a documented allergy.

5. What laboratory tests should be obtained and has everything been reviewed?

Common laboratory normal values will be same for all procedures, with a difference by age and gender.

  • Hemoglobin levels

  • Electrolytes: Sodium, potassium, chloride, bicarbonate, BUN, creatinine, glucose, calcium

  • Coagulation panel: PT/INR, PTT, platelets

  • Imaging: Echocardiogram, cardiac stress test and cardiac catheterization if indicated, possible cardiac perfusion scan, carotid ultrasound

  • Other tests: HbA1c if diabetic, thyroid tests if thyroid disease present

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

The only option for anesthetic management of AVR is a general anesthetic with cardiopulmonary bypass.

a. Regional anesthesia

Regional anesthesia is not an option for AVR.

b. General anesthesia

General anesthesia is the only anesthetic option for the patient undergoing AVR using cardiopulmonary bypass. The patient is positioned supine and the arms are typically tucked at the patient’s sides. This minimizes the anesthesiologist’s access to the patient once surgery has commenced. Care must be taken to pad all pressure points and tape the eyes closed to avoid corneal abrasions. All lines and invasive monitoring should be placed prior to prepping for surgery.

Airway: Endotracheal intubation is necessary as is controlled ventilation.

Arterial pressure monitoring: Recommended to place arterial line prior to induction, typically in the radial artery. This allows for continuous blood pressure monitoring and is essential throughout the procedure and in the postoperative period. If radial artery access is unavailable, then brachial or femoral arteries can be used.

Central venous access: Central venous access is necessary for administration of inotropes and vasoactive medications and monitoring of central venous pressures. Typically the internal jugular is accessed as the anesthesiologist is positioned at the head of the bed, but subclavian or femoral venous access will also suffice.

Pulmonary artery catheter:Pulmonary artery catheters may be placed to monitor pulmonary artery pressures, cardiac output, and systemic vascular resistance. These are placed through an introducer sheath placed in most often in the internal jugular vein.

Transesophageal echocardiography:Intraoperative TEE is essential for AVR. It is used to assess the severity of aortic valve disease, ventricular function, other cardiac and valvular lesions, measure dimensions important for surgical repair, and assess the integrity of the replaced valve after cardiopulmonary bypass.

c. Monitored anesthesia care

Monitored anesthesia care (MAC) is not an option for AVR.

6. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

The typical patient should receive cefazolin, cefuroxime, or vancomycin prophylactically. If the patient has an allergy to beta-lactam antibiotics, vancomycin and clindamycin are acceptable alternatives. Patients with a history or MRSA infection should receive vancomycin. Prophylactic antibiotics should be administered within the 30 minutes prior to incision, with the exception of vancomycin that should be administered within the 90 minutes prior to incision. These are 2011 recommendations for patients undergoing cardiac surgery from the Surgical Care Improvement Project (SCIP).

What do I need to know about the surgical technique to optimize my anesthetic care?

Surgical technique for AVR can be done through a traditional median sternotomy or with a minimally invasive approach (e.g., mini thoracotomy, robotic surgery). Although the principles of the surgical repair are similar, access to the patient and invasive lines may differ. If a minimally invasive approach is planned, then typically the anesthesiologist may place additional neck lines to allow for left ventricular venting and delivery of cardioplegia via the coronary sinus. The surgical approach and plan are developed in conjunction with the cardiac surgeon and should occur prior to surgery. Aortic valve surgery can be divided into three main phases: pre cardiopulmonary bypass, cardiopulmonary bypass, and post cardiopulmonary bypass.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Good communication skills are key, as the roles of the cardiac anesthesiologist, cardiac surgeon, and perfusionist are intimately linked.Careful assessment of the patient via TEE is essential and all information obtained should be conveyed to the team, as it may alter the surgical plan.Cell saver should be used to maximize recovery of the patient’s blood.

Cardiac complications

Cardiac complications are the most common intraoperative complications with AVR. There may be cardiac collapse on induction of general anesthesia if the patient’s preoperative cardiac function was severely compromised (e.g., acute severe AR), and careful titration of medications is paramount. Median sternotomy may injure the right ventricle leading to life-threatening exsanguination, particularly if the patient has had previous cardiac surgery and scar tissue is present. Surgical care should be taken in these situations and the anesthesiologist should be prepared with medications and blood products to optimize hemodynamics until the patient can safely be placed on cardiopulmonary bypass. Aortic dissection can occur with placement of the aortic cannula for cardiopulmonary bypass, and it is best to decrease the systolic blood pressure below 100 mm Hg at the time of cannulation to help avoid this disastrous complication. Perhaps more commonly, the newly replaced aortic valve can have perivalvular leaks that are noted at the end of cardiopulmonary bypass that are detected by TEE, necessitating return to cardiopulmonary bypass and repair of the leaks. Finally, if there is residual air within the left ventricle after cardiopulmonary bypass, air emboli can lodge in the coronary arteries, causing cardiac ischemia or in the cerebral vasculature causing stroke. This devastating complication can be avoided by assessing for air within the LV chamber via TEE prior to coming off cardiopulmonary bypass and taking measures to evacuate the air if necessary.

Pulmonary complications

Pulmonary complications can occur intraoperatively and may be more common with single lung ventilation, which may be necessary in some of the minimally invasive surgical techniques. There may be difficulties with ventilation and oxygenation, particularly if hypoxic vasoconstriction is impaired. The circulating inflammatory mediators associated with cardiopulmonary bypass, as well as increased duration of cardiopulmonary bypass runs, may increase the risk of postoperative pulmonary complications.

Neurologic complications

The most common and devastating neurologic complication with aortic valve surgery is stroke. This can happen with air embolism at the end of cardiopulmonary bypass as mentioned above in the cardiac section. It is best to avoid coming off cardiopulmonary bypass until the air has been minimized, and it is best to place the patient in the Trendelenberg position after removal of the aortic cross-clamp to minimize cerebral air emboli. Aortic calcifications can also embolize to the cerebrovascular system if disturbed during aortic cannulation, cross-clamp, or manipulation. Epiaortic scanning can help define areas of atheromatous disease that can then be avoided during aortic cannulation and cross-clamping.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

The patient who underwent AVR should have the same criteria for extubation as any other patient in the ICU postoperatively.

c. Postoperative management

What analgesic modalities can I implement?

Postoperative analgesia is typically achieved with parenteral opioids, intrathecal opioids, or a combination of the two.

What level bed acuity is appropriate?

An ICU bed is necessary as the patient is intubated, sedated, and potentially hemodynamically unstable.

What are common postoperative complications, and ways to prevent and treat them?

Postoperative complications include reexploration for bleeding, stroke, and renal failure. Postoperative bleeding is best avoided by stopping antiplatelet medication prior to surgery and treating any baseline coagulation deficits, ensuring there are no areas of surgical bleeding prior to closure of the surgical site, and treatment of any intraoperative coagulopathies as they arise in the operating room. Stroke can best be prevented by minimizing the patient’s risk of cerebrovascular embolism intraoperatively as mentioned above, by minimizing intracardiac air prior to separation from cardiopulmonary bypass and avoiding manipulation of aortic atheromas. Renal failure can be minimized by optimizing the patient’s renal function prior to surgery, minimizing the cardiopulmonary bypass time, and maintaining adequate mean arterial pressures both on and off cardiopulmonary bypass to ensure adequate renal blood flow.

What's the Evidence?

Baumgartner, H, Hung, J, Bermejo, J. "Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice". J Am Soc Echocardiogr. vol. 22. 2009. pp. 1-23.

(Assessment of AS.)

Zoghbi, WA, Enriquez-Sarano, M, Foster, E. "Recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography". J Am Soc Echocardiogr. vol. 16. 2003. pp. 777-802.

(Assessment of AR.)
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