Mitral Stenosis for Non-Cardiac Surgery Case File

Mitral Stenosis for Non-Cardiac Surgery Case File

Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 21

A 28-year-old Haitian woman presents to labor and delivery at 38 weeks’ gestation for a repeat elective cesarean section. She has had an uneventful pregnancy with a singleton fetus. The patient’s past medical history is significant for mitral stenosis. During her pregnancy, she noticed dyspnea on exertion with walking one flight of stairs, which has remained stable. She is unable to lay flat in bed, and props herself up on two pillows to sleep. She has taken Coumadin in the past, but has taken lowmolecular- weight heparin since becoming pregnant. With the consent of her cardiologist, she has not taken any anticoagulant for the past 2 days. Her only other medication is prenatal vitamins. She has no known drug allergies, does not smoke, and has not consumed any alcohol since becoming pregnant. The patient is 5 ft 3 in tall and weighs 75 kg. Auscultation of the chest reveals a III/VI diastolic murmur. Her lungs are clear to auscultation, though she has +2 edema of both lower extremities to the knee. She has very mild jugular venous distension.

➤ What additional information should be obtained in the preoperative evaluation?

➤ What are the intraoperative hemodynamic goals?

➤ What special monitors should be considered because of the mitral stenosis?

ANSWERS TO CASE 21:

Mitral Stenosis for Non-Cardiac Surgery

Summary: A 28-year-old woman with mitral stenosis presents for an elective cesarean section.

➤ Preoperative evaluation: The preoperative assessment in the patient with mitral stenosis should include questions to elicit any signs and symptoms of pulmonary edema, pulmonary hypertension, or congestive heart failure. It is important to note the patient’s exercise tolerance, as well as medication taken with particular attention to anticoagulant agents. The patient should also have an ECG and transthoracic echocardiogram performed preoperatively.

➤ Intraoperative hemodynamic goals: Maintenance of sinus rhythm if at all possible, the prevention of tachycardia and/or systemic vasodilatation, and the careful maintenance of preload.

➤ Special monitoring: An arterial line and possibly a pulmonary artery catheter. If she has a general anesthetic, a transesophageal echocardiography probe should also be considered. This is in addition to the standard monitors specified by the American Society of Anesthesiologists.

ANALYSIS

Objectives

1. Understand the pathophysiology and etiology of mitral stenosis.

2. Become familiar with the signs and symptoms of mitral stenosis.

3. Know the intraoperative hemodynamic goals of mitral stenosis.

4. Be able to formulate an anesthetic plan for the patient with aortic stenosis presenting for non-cardiac surgery.

Considerations

Besides the need to monitor the cardiovascular status, the patient in this case is happily complicated by an impending birth. So, many medications administered to the mother could affect the fetus as well. Routine caesarean sections are usually performed under spinal and/or epidural anesthesia to minimize the circulating concentrations of anesthetics which might cause fetal depression. However, both spinal and epidural anesthesia cause sympathectomy, which in turn reduces preload and afterload, neither of which are well tolerated in patients with mitral disease. However, for patients with mild or moderate disease, an epidural with its indwelling catheter, can be intermittently dosed to gradually achieve the desired sensory level, while concomitantly administering alpha blockers to control preload and afterload.

The general anesthetic for a typical cesarean section is characterized by the administration of an induction anesthetic agent before the patient is paralyzed and incubated. No additional anesthetic is administered until the baby has been delivered. The period between induction and delivery of the infant is often marked by classic signs of “light” anesthesia such as tachycardia and hypertension, neither of which is well tolerated by a patient with mitral stenosis.

Whatever the choice, monitoring is an important consideration. Simply measuring central venous pressure may not provide sufficient information regarding a possible increase in pulmonary artery pressure, which could lead to pulmonary edema. Although it has not been shown to alter mortality, pulmonary artery pressure monitoring should be considered. If a general anesthetic is used, a transesophageal echocardiogram (TEE) probe can provide superior information. However, the TEE probe cannot remain in place throughout the postoperative period.

APPROACH TO

Mitral Stenosis for Non-Cardiac Surgery

The incidence of mitral stenosis has decreased drastically in the United States over the past 50 years; however, it continues to remain a major health problem in developing countries. Patients with mild mitral disease have a minimally increased risk of adverse cardiac outcomes in the setting of non-cardiac surgery. However, patients with severe disease or associated pulmonary hypertension (PHT) have a significantly increased risk of perioperative morbidity. Two-thirds of patients with mitral stenosis are women.

Etiology

Mitral stenosis can be congenital, but the vast majority of cases are acquired, most commonly from rheumatic fever. The most common etiology of acquired mitral stenosis is rheumatic fever. In susceptible individuals, inflammatory changes following a group A Streptococcus infection can lead to valvular disease as a delayed complication. After the widespread institution of antibiotic treatment for group A streptococcal infection was initiated in the United States, the incidence of this complication has decreased dramatically. Other less common causes of acquired mitral stenosis include infective endocarditis, connective tissue disorders, rheumatoid arthritis, atrial myxoma, carcinoid disease, sarcoidosis, and iatrogenic stenosis after mitral valve surgery. Congenital mitral stenosis is rare and usually associated with a more complex cardiac malformation such as hypoplastic left heart syndrome.

Pathophysiology

Mitral stenosis occurs when thickening, fibrosis, or calcification of the valve leaflets, or fusion of the leaflet commissures obstruct flow from the left atrium to the left ventricle. The normal mitral valve orifice is 4 to 6 cm2. Symptoms generally occur when the orifice is narrowed to less than 2.5 cm2. Patients may initially develop symptoms only during exercise, or other states which increase cardiac output. However, as the disease progresses and the valve narrows to less than 1.5 cm2, mitral stenosis is considered severe and patients often have symptoms at rest.

A stenotic mitral valve limits diastolic inflow of blood from the left atrium to the left ventricle. As a result, a pressure gradient develops between the two chambers and left atrial pressures increase to maintain flow across the valve. The increase in left atrial pressure decreases pulmonary venous inflow, thereby increasing pulmonary vasculature pressure. Over time, pulmonary hypertension can result and ultimately, right ventricular failure. A second consequence of the increased left atrial pressure is chamber dilation. As the left atrium dilates, atrial fibrillation often develops. An enlarged left atrium is also susceptible to areas of stasis, and thus thrombus formation. Because of the obstruction to inflow, in mitral stenosis the left ventricular end-diastolic volume is low resulting in low stroke volume and cardiac output.

Signs and Symptoms

Patients with mitral valve abnormalities due to rheumatic disease tend to present with symptoms in the third to fourth decades of life: most commonly, dyspnea and orthopnea. Pregnancy, which also occurs during these decades, produces hemodynamic changes that may unmask previously undiagnosed disease. Rarely, patients may have hemoptysis due to rupture of dilated bronchial veins. With severe mitral disease, patients have signs of right ventricle failure such as peripheral edema and jugular venous distension.

Preoperative Evaluation

The preoperative evaluation of a patient with mitral stenosis presenting for non-cardiac surgery focuses on identifying high-risk patients. Parturients with severe PHT can have mortality rates of up to 40% during pregnancy and in the postpartum period. A careful history should be obtained to search for symptoms of dyspnea, orthopnea, paroxysmal nocturnal dyspnea, arrhythmias, or peripheral edema. The patient’s functional capacity and exercise tolerance should be determined, since a patient with good exercise tolerance and functional capacity can undergo low-risk surgery without further invasive testing. In parturients, 

Table 21–1 MODIFIED NEW YORK HEART ASSOCIATION FUNCTIONAL CLASSIFICATION OF HEART DISEASE
CLASS	DESCRIPTION
I II III IV	Asymptomatic except during severe exertion Symptomatic with moderate activity Symptomatic with minimal activity Symptomatic at rest

the prepregnancy classification using The New York Heart Association functional class (Table 21–1) has been strongly associated with both maternal and fetal complications during childbirth.

On physical examination, a characteristic low-pitched, rumbling diastolic murmur at the left ventricular apex is heard with the patient lying in the left lateral decubitus position. In patients with mild disease, this murmur may only be heard when the heart rate is elevated and the flow across the mitral valve is increased. The preoperative physical examination also focuses on uncovering signs of heart failure. Auscultation of the chest may reveal rales, wheezing, or an S3 gallop, examination of the neck may reveal jugular venous distension, and examination of the extremities and abdomen may reveal pitting edema or ascites.

The severity of mitral valve stenosis should be determined prior to any elective surgery. Doppler and two-dimensional transthoracic echocardiography are valuable tools to assess the pathology and grade the severity of mitral stenosis. Echocardiography will also detail other cardiac valvular lesions, as well as providing information with regard to right ventricular function and detecting left atrial thrombus formation if present. A current ECG should be obtained and may reveal atrial fibrillation. A chest radiograph may be warranted to rule out pulmonary edema if signs of congestive heart failure are present on examination.

Anesthetic Management

The intraoperative management of patients with mitral stenosis is based upon preventing tachycardia, maintaining afterload, and carefully maintaining of preload. Attention to preload and intravascular volume is most important to minimize exacerbation of pulmonary vascular congestion. In patients with PHT, it is also of critical importance to avoid further increasing pulmonary vascular resistance, by preventing hypercarbia and hypoxemia. In the presence of severe pulmonary hypertension, agents that cause pulmonary vascular vasodilation may also need to be employed.

Premedication for an anxious patient may be indicated to prevent tachycardia. However, over-sedation should be avoided as this can precipitate hypoxemia and hypercarbia thereby worsening PHT. SpO2 should be monitored continuously, and supplemental oxygen provided. Rate control medications such as beta blockers, calcium channel blockers, and digoxin should be continued until the time of surgery. To promote intraoperative hemostasis, Coumadin should be discontinued preoperatively and a heparin bridge instituted if necessary. 

In addition to standard ASA monitors, an arterial line may be indicated. In patients with PHT, the placement of a pulmonary artery catheter should be considered although there are no data that demonstrate an improvement in outcome with the intraoperative use of this device. Transesophageal echocardiography may be useful to monitor ventricular function and preload.

A variety of anesthetic techniques can be employed as long as the hemodynamic goals of avoiding tachycardia or pulmonary vasoconstriction and maintaining adequate preload and systemic vascular resistance are met. Spinal and epidural anesthesia are typically well tolerated in patients with mild to moderate disease, but are relatively contraindicated in patients with severe disease. However, with invasive monitoring and careful titration of agents to prevent hypotension, spinal and epidural anesthesia have been safely used in patients with severe mitral stenosis.

For general anesthesia, a balanced technique employing opiates, volatile anesthetics, and muscle relaxants is most often employed. The judicious, careful titration of the induction agent to prevent hypotension is of critical importance. Alpha agonists such as phenylephrine are the agents of choice to treat hypotension, as they increase SVR and may even cause a reflex bradycardia. Beta-adrenergic agents which cause tachycardia and vasodilation are undesirable in patients with mitral stenosis.

Comprehension Questions

21.1. During your preoperative assessment, a 28-year-old woman complains of dyspnea on exertion. Upon auscultation of her heart, you notice a mid-diastolic rumbling murmur. This murmur is most characteristic of which valvular lesion?

A. Mitral stenosis

B. Mitral regurgitation

C. Aortic regurgitation

D. Aortic stenosis

21.2. Which of the following statements about the pathophysiology of mitral stenosis is accurate?

A. Patients with mitral stenosis generally have an under-loaded left ventricle.

B. The increased pressure gradient between the left atrium and left ventricles results in left ventricular hypertrophy.

C. Patients with mitral stenosis have decreased left atrial pressure.

D. Diastolic filling of the left ventricle is increased in mitral stenosis because of the increased pressure gradient between the left atrium and left ventricle.

21.3. What are the intraoperative hemodynamic goals in the management of a pregnant patient undergoing an urgent caesarean section with mitral stenosis?

A. Tachycardia, low systemic vascular resistance, high pulmonary vascular resistance.

B. Tachycardia, avoid marked decreases in systemic vascular resistance, avoid increases in pulmonary vascular resistance.

C. Avoid tachycardia, avoid marked decreases in systemic vascular resistance, and avoid increases in pulmonary vascular resistance.

D. Avoid tachycardia, avoid marked decreases in pulmonary vascular resistance.

ANSWERS

21.1. A. The murmur described is characteristic of mitral stenosis. The murmur of mitral stenosis is a mid-diastolic rumbling murmur, best heard at the apex with the patient in the left lateral position. The murmur of mitral regurgitation is typically a holosystolic murmur that may radiate to the axilla. The murmur associated with aortic regurgitation is a midsystolic ejection murmur generally heard best at the base of the heart and is transmitted to the jugular notch. The murmur associated with aortic stenosis is a mid–systolic crescendodecrescendo murmur that often radiates to the carotids.

21.2. A. The pathophysiology of mitral stenosis involves impaired diastolic filling of the left ventricle because of an obstruction at the level of the mitral valve. This results in a pressure gradient between the left atrium and the left ventricle. Consequently, left atrial pressure rises while the left ventricle is under-filled. As left atrial pressure increases, pulmonary venous return is impaired and pulmonary hypertension with right ventricular failure can occur.

21.3. C. The hemodynamic goals of mitral stenosis include the avoidance of tachycardia, as tachycardia will decrease diastolic filling of the left ventricle and can precipitate pulmonary congestion. Factors that can worsen pulmonary hypertension, such as hypercarbia and hypoxemia, should be avoided. Systemic vascular resistance as well as contractility should be maintained. Lastly, preload or volume status should be maintained carefully to promote stroke volume while minimizing the risk of pulmonary congestion.

Clinical Pearls

➤ Pulmonary hypertension and right ventricular failure are often observed in patients with mitral stenosis and can be precipitated by hypercarbia and hypoxemia. Pharmacological treatment with medications that vasodilate the pulmonary vasculature may be required.

➤ Patients with mitral stenosis often present in atrial fibrillation; however, it is important to remember that tachycardia is poorly tolerated and should be prevented or treated.

➤ As left atrial pressure increases with mitral stenosis, so does pulmonary venous pressure. This increase in pulmonary venous pressure can precipitate pulmonary edema.

References

Cook D, Housmans P, Rehfeldt K. Valvular heart disease. In: Kaplan’s Cardiac Anesthesia. 5th ed. Philadelphia, PA: Saunders Elsevier; 2006:645-690. 

Mends LA, Loscalzo J. Acquired valvular heart disease. In: Andreoli, ed. Cecil Essentials of Medicine. 5th ed. Philadelphia, PA: W.B. Saunders Co; 2001:69-70. 

Mittnacht Alexander JC, Fanshawe M, Konstadt S. Anesthetic considerations in the patient with valvular heart disease undergoing non-cardiac surgery. Semin Cardiothorac Vasc Anesth. 2008;12(33):33-59.

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