Chapter 10. Hypertrophic Obstructive Cardiomyopathy and Cardiac Masses

• Previous chapters have discussed how fixed obstructions to blood flow through the heart can lead to significant morbidity and mortality. Aortic and mitral stenosis are two examples of lesions, which may prevent the heart from effectively pumping blood. Hypertrophic cardiomyopathy (HCM) likewise can prevent the heart from pumping blood but in a dynamic rather than fixed way. With each beat the hypertrophied septum of the HCM patient together with the anterior mitral valve leaflet prevent the heart from ejecting blood as they obstruct the left ventricular outflow tract (LVOT) (Figure 10–1). Hence, this condition in the past was known as hypertrophic obstructive cardiomyopathy (HOCM). Failure to eject enough blood from the heart leads to syncope, dyspnea, and, at times, sudden death.
  Figure 10–1.Graphic Jump Location

  

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  The midesophageal long-axis view is presented here in outline form. As a consequence of the hypertrophied interventricular septum, flow patterns within the heart are altered such that the anterior leaflet of the mitral valve is drawn during ventricular systole into the LVOT producing obstruction. This is known as systolic anterior motion of the mitral valve (SAM).

• Although rare, cardiac tumors and other masses can interfere with valve function, produce emboli, and dynamically obstruct blood flow through the heart and prevent ejection into the systemic circulation. This chapter will examine these different conditions, which are nonetheless linked by their dynamic ability to prevent the heart from properly functioning.

HCM is an autosomal dominant trait; roughly one-half of the patients have a blood relative afflicted with HCM.1 The disease can affect both males and females. It is estimated that HCM presents in 1:500 of the general adult population and that these patients are at increased risk for sudden cardiac death (SCD).2 Certainly, many patients with HCM are not detected and can present with SCD as the first manifestation of their cardiac disease.

Symptoms of HCM include: dyspnea, exercise intolerance, palpitations, syncope, chest pain, and SCD. HCM can manifest in both the left and the right heart; however, it is overwhelmingly a disease of the left ventricle. HCM can occur with and without LVOT obstruction.3 In non-obstructive HCM disease the patients develop a hypertrophied myocardium with diastolic dysfunction. As previously discussed in Chapter 2, diastolic dysfunction occurs when the heart is unable to normally relax during diastolic filling. Subsequently, impaired ventricular compliance leads to an increased left ventricular end-diastolic pressure (LVEDP), elevated pulmonary arterial pressures, increased pulmonary congestion, and decreased coronary perfusion pressure (CPP). Such patients can develop angina, dysrhythmias, systolic heart failure, and sudden death in the absence of any LVOT obstruction. Nonetheless, patients in whom HCM disease produces an obstruction of the LVOT are at a significantly increased risk of death and/or severe heart failure.3

Clinically, the diagnosis of HCM with dynamic LVOT obstruction is made by the auscultation of a late systolic murmur. The murmur is heard in late systole as the anterior leaflet of the mitral valve abuts the hypertrophied septum during systole (Videos 10–1 and 10–2). This systolic anterior motion (SAM) of the mitral valve provides the source of dynamic systolic obstruction in these patients (Figure 10–2A and 2B). Various clinical maneuvers can be employed to increase the murmur by reducing the venous return to the heart (eg, Valsalva maneuver). By reducing venous return to the heart, the ventricles fill to a lesser degree. In the HCM patient, the fuller the heart, the less likely it is that during systole the mitral valve will be able to obstruct the LVOT. In the underloaded heart, however, the anterior leaflet of the mitral valve can more readily obstruct the ejection of blood.

Not surprisingly, echocardiography is best suited to make the diagnosis of HCM disease.1 When ventricular wall thickness in diastole is greater than 14 mm the patient is thought to have HCM disease assuming there are no other conditions that would produce ventricular hypertrophy (eg, aortic stenosis or systemic hypertension). Symptomatic patients routinely have thickened interventricular septums of 20 to 30 mm.1

HCM is a genetic disease. Mutations in the genes, which code for the cardiac sarcomeres and their supporting proteins, have been implicated as causes of HCM.1,2 Mutations in the beta-myosin heavy chain and myosin-binding protein C represent upward of 50% of the genotyped patients.2 However, other cardiac protein mutations can also be associated with HCM. Additionally, the phenotypic expression of the HCM patient is variable. Thus, even in families with the same mutation, the variations in phenotypic expression can lead to radically different outcomes.1

At the cellular level, the myocardium of the HCM is a mix of oddly shaped myocytes and fibrotic tissue. The myocytes of the HCM patient lack the neat parallel array of normal ventricular muscle tissue.1

This abnormal myocardium can become quite noncompliant leading to diastolic dysfunction. As the LVEDP increases, pressure is transmitted through the left atrium to the pulmonary vasculature resulting in elevated pulmonary arterial pressures (PAP). The HCM patient can develop dyspnea with minimal exertion. Thus, HCM patients can be symptomatic without having LVOT obstruction.

Systolic function is often initially maintained in the HCM patient. However, over time in a small percentage of patients, the heart's systolic pumping ability fails.3 In HCM patients especially if LVOT obstruction is present, the increased LV work to overcome elevated pressures will lead to increased wall stress, ischemia, cell death, ventricular fibrosis, and heart failure.3

Mitral regurgitation frequently occurs in HCM with obstruction of the LVOT. Some of the causes responsible for the development of mitral regurgitation are elevated intraventricular pressures, systolic anterior motion (SAM) of the mitral leaflets in the presence of LVOT obstruction, abnormally positioned papillary muscles, and redundant mitral leaflets. Mitral regurgitation may result in left atrial dilatation, atrial fibrillation, decreased stroke volume, and further impairment of the ventricular function (Figure 10–3).

SCD is one of the most dreaded complications of HCM.4 Consequently, many patients with this condition are provided with an implantable cardioverter defibrillator (ICD) after a risk stratification and selection process.

The majority of patients with HCM are managed medically when symptoms warrant.1 Asymptomatic patients are routinely managed expectantly; however, ICD placement may be considered in those with a strong family history of SCD. Medical therapy is centered primarily upon determining the nature of HCM encountered. The non-obstructive HCM patient presents with signs and symptoms of diastolic dysfunction.1 Both beta-blockers and calcium antagonists have been used in this setting with variable results. It is possible that these agents improve symptoms by reducing the incidence of myocardial ischemia in the HCM patient. Patients presenting with signs of heart failure in the non-obstructive HCM patient can be treated with judicious administration of diuretics to relieve symptoms of pulmonary congestion. However, reduced ventricular volumes could prove problematic as the noncompliant, dysfunctional ventricle requires an adequate SV to generate an acceptable cardiac output. Rhythm disturbances such as atrial fibrillation should also be corrected in order to permit adequate LV filling during diastole.

Patients with obstructive HCM can develop intraventricular pressure gradients during systole. Gradients across the LVOT of over 100 mm Hg can be detected between different regions of the LV cavity (Video 10–3). Indeed, the presence of obstruction with gradients as low as 30 mm Hg is predictive of worse outcomes and increased mortality in the HCM patient population.3 Therapy is aimed at reducing myocardial contractility in order to reduce the LVOT gradient during systole. Beta-blockers, verapamil, and disopyramide are employed to this end. These agents have negative inotropic effects and reduce the systolic gradient. Likewise, efforts are made to maintain a large, well-filled left ventricle. Any situation leading to a reduction in the size of the left ventricle (eg, hypovolemia, increased myocardial contractility, and decreased systemic vascular resistance) will increase the dynamic obstruction during ventricular systole.

HCM patients can be symptomatic whether they have the obstructive form or the non-obstructive form of cardiomyopathy. It is important to realize that both presentations can lead to perioperative complications resulting from arrhythmia, hypotension, and even sudden cardiac death. Although the cardiac anesthesiologist is likely to encounter that subset of obstructive HCM patients not amenable to medical therapy, it is critical to understand that the HCM patient may undergo a variety of procedures and have varying anesthetic requirements.

What differentiates the obstructive form of HCM from the non-obstructive form is the dynamic development of a pressure gradient across the LVOT.

The LVOT provides the pathway for oxygenated blood as it leaves the LV cavity and is ejected out of the aortic valve. The systolic anterior motion of the mitral valve in the LVOT is the most common cause of dynamic obstruction generating significant pressure gradients (> 50 mm Hg) across the LVOT. The hypertrophied bulge of the intraventricular septum at the level of the LVOT may direct the flow in the heart in such a way that it drags the anterior leaflet into the LVOT producing obstruction.5 The development of increased LV intracavitary pressure can soon lead to mitral valve incompetence and worsening symptoms of systolic and diastolic heart failure.

Only a minority of HCM patients is brought to surgery for myectomy and/or mitral valve replacement. Many patients will nonetheless require anesthesia at some point for noncardiac surgery. Management is directed at minimizing the degree of outflow obstruction, lessening the impact of diastolic dysfunction, and controlling arrhythmias. Both general and neuraxial anesthesia techniques can produce wide swings in hemodynamics. As mentioned, during anesthesia induction in the patient with a fixed obstruction to systolic ejection, such as aortic stenosis, it often becomes necessary to administer fluids and vasoconstrictors to prevent hemodynamic instability. In the patient with dynamic obstruction, the greater the decrease in venous return the worse the degree of obstruction. Agents, which decrease sympathetic tone and peripheral vascular resistance, likewise can increase the degree of dynamic obstruction, as the heart is free to contract against less resistance. An increase in heart rate associated with laryngoscopy, intubation, and surgical stimulation should be avoided, as this will decrease the time of LV diastolic filling and systolic ejection resulting in worsening of the degree of dynamic obstruction and hypotension. Consequently, these patients are frequently managed with fluid and vasopressor administration at the time of induction and intraoperative arterial and TEE monitoring. Short-acting beta-blockers such as esmolol can be used to reduce myocardial contractility, decrease the heart rate, and counteract the effects of increased catecholamine release during intubation, emergence, and other periods associated with surgical stress.

Neuraxial anesthesia approaches can be employed2 in these patients and have also been used in the patient with HCM for labor analgesia.2 The decrease in sympathetic tone with its associated reduction in venous return and decrease in peripheral vascular resistance makes the use of neuraxial techniques potentially deleterious. Careful titration of local anesthetic to obtain the appropriate level of anesthesia is clearly important if these approaches are to be safely employed. Likewise, invasive monitoring may prove helpful in this setting in order to detect acute deteriorations. Regional techniques which leave sympathetic tone relatively unaffected (eg, peripheral nerve blocks) could be of use where indicated in the HCM patient.

HCM patients frequently have undergone the placement of an ICD. The perioperative management of these devices is discussed in Chapter 15.

Anesthetic management may be further complicated by diastolic dysfunction. Additionally, patients often have some degree of mitral regurgitation, which further increases LAP, PCOP, and pulmonary congestion. Treatment is aimed at reducing the degree of dynamic obstruction, favoring adequate systolic ejection and thereby, reducing MR and pulmonary congestion. Although diuresis to unload the heart might be desirable in the patient with a high grade of diastolic dysfunction, care must be taken not to reduce ventricular volume as to worsen the obstruction across the LVOT.

For those patients who do not benefit from medical management, there are surgical approaches to relieve dynamic obstruction and restore adequate mitral valve function. Anesthetic management remains centered upon minimizing the degree of LVOT obstruction during the hemodynamic shifts associated with general anesthesia. Monitoring is similar to that employed in any cardiac surgical case requiring CPB. The utility of the PA catheter in this setting is unproven. However, TEE is essential to the performance of the operation. In this procedure, TEE is not merely a monitor of ventricular function or an additional surveillance tool—it is essential for the surgical management of the patient.5,6 There is close interaction between the anesthesiologist and the surgeon during the surgery.

A variety of induction and maintenance agents can be employed in these patients. More important than the drug choice for anesthesia induction is directing therapy toward maintaining an adequately volume-loaded and less-contractile heart. Catecholamine release associated with inadequate anesthetic depth can increase obstruction secondary to tachycardias and augmented myocardial contractility.

As mentioned in the previous section, hemodynamic derangements such as hypotension or tachycardia at the time of induction should be treated promptly using vasoconstrictors, fluids, or short-acting beta-blockers. Antiarrhythmics and beta-blockers should be continued perioperatively. Intraoperative therapeutic interventions may be monitored using TEE guidance to demonstrate relief of obstruction and reduced pressure gradient.

Video 10–3 demonstrates the LVOT being obstructed by the anterior leaflet of the mitral valve abutting the bulging septum. The deep gastric view is employed and as such there is a good alignment between the LVOT and the Doppler beam. Using continuous wave Doppler (CWD), it is possible to determine the velocity of flow across the obstruction. Video 10–3 displays the time-velocity integral of a patient with a severe dynamic gradient. Using Bernoulli equation, it is possible to calculate the peak gradient present across the LVOT:

Pressure gradient = 4V2

where V is the peak blood flow velocity.

As can be seen the gradient can be rather significant.

Patients with severe gradients can quickly deteriorate perioperatively developing profound hypotension. Additionally, these patients have a significantly elevated LVEDP. Recalling, the formula for coronary perfusion pressure:

CPP = DBP − LVEDP

The combination of profound systemic hypotension and elevated LVEDP will result in a reduced CPP in patients with HCM leading to a downward spiral of ischemia, hypotension, arrhythmias, and eventually cardiac arrest.

Surgery is directed at reducing the muscle mass of the intraventricular septum in the region where it contacts the anterior leaflet of the mitral valve (Figure 10–2B).5,6 After institution of cardiopulmonary bypass (CPB) and heart arrest by administration of cardioplegia, the aorta is opened and then the surgeon carefully retracts the leaflets of the aortic valve. Looking down the LVOT the surgeon is able to identify the muscle mass and reduce its size. Measurements obtained by TEE in the operating room assist the surgeon in guiding the repair. The echocardiographer determines the thickness of the septum and the distance from the aortic valve to the point where the mitral valve leaflet makes contact with the septum during systole. Additionally, TEE is used to determine the competency of the mitral valve. Should the mitral valve be deformed or incompetent it may have to be repaired or replaced. Primarily, however, surgery is directed at removing the bulge in the ventricular septum.5 By removing the septal bulge, the drag forces which push the anterior leaflet of the mitral valve into the LVOT are removed and the coaptation point of the mitral valve moves more posteriorly in relationship to the LVOT. Consequently, the systolic anterior motion of the mitral valve is relieved and the gradient across the LVOT reduced (Figure 10–2B). Figure 10–3D demonstrates the broad area of septum removed in order to reduce drag force on the mitral valve and thereby relieve SAM.

Once the surgical repair is completed, the aorta is closed and the patient weaned from CPB in the usual fashion. TEE is again employed to make sure the surgeon has not created a ventricular septal defect (VSD) during the repair by cutting out too much of the intraventricular septum. Additionally, the mitral and aortic valves are examined by TEE to be sure that any mitral repair is competent and that the aortic leaflets have not been damaged during retraction to expose the LVOT.

Often a dobutamine challenge is performed to determine the adequacy of the repair. In this setting dobutamine (5-10 −g/kg/min) is administered to the patient. This will cause increases in heart rate and contractility, conditions which both can increase the likelihood of LVOT obstruction, as well as a decrease in peripheral vascular resistance. The LVOT is examined for signs of dynamic obstruction and any residual gradients measured. In addition to creation of VSD, heart block requiring pacemaker insertion can be necessary in upward of 10% of these patients.5

Alcohol septal ablation (ASA) is also employed to reduce the size of the septal bulge. In this catheter-based technique, the left anterior descending artery (LAD) is entered and a septal branch located. The area of distribution of flow from the branch is determined and if confined to the septum, absolute alcohol is injected producing a controlled myocardial infarction. Risks include spread of the alcohol outside of the septum, ventricular arrhythmias, and heart block. The infarcted septum gradually reduces in size upon healing and changes the flow patterns in the ventricle reducing drag on the anterior leaflet of the mitral valve and relieving obstruction.

Cardiac tumors are rare7-9 but have the potential to create dynamic obstruction in their own right. Cardiac tumors may be primary or secondary, malignant or benign. Primary cardiac tumors are frequently histologically benign (Figure 10–4). Myxomas are the most frequent cardiac tumors; (Video 10–4) other benign tumors include lipomas, fibromas, papillary fibroelastomas, and rhabdomyomas. The most frequent malignant primary cardiac tumors are angiosarcomas; other malignant tumors include rhabdomyosarcoma, liposarcoma, fibrosarcoma, malignant lymphoma.

Metastatic tumors to the heart are far more common than primary tumors, tend not to be intracavitary lesions, and have a grim prognosis. Intraventricular thrombi can develop following myocardial infarction and can be confused with cardiac masses. The incidence of postinfarction thrombi formation has decreased with the routine use of anticoagulating agents' peri-infarction. Nonetheless, intraventricular thrombi can occur and be the source of embolic phenomenon. They are surgically resected if operative therapy is indicated for the patient's primary cardiac disease and if they have become symptomatic. Video 10–5 demonstrates the appearance on echo of intraventricular thrombi.

The clinical presentations, which herald the presence of intracardiac masses, include stroke, dyspnea, and chest pain. Cardiac masses may result in embolization, obstruction, and impairment in ventricular filling or disruption in valvular integrity. Cardiac masses are diagnosed through the use of echocardiography and MRI.

Where indicated surgical management focuses upon removal of the mass and repair or replacement of any valvular structure damaged as a consequence of the lesion.

Anesthetic management of these cases centers upon the primary impact of the lesion on the flow of blood through the heart. Patients whose venous return to the heart is blocked by the mass, will behave similarly to patients with tamponade. These patients are likely to collapse hemodynamically at induction due to vasodilatation and positive pressure ventilation. Patients with obstructing left-sided lesions may develop pressure gradients in the LVOT in a manner similar to that described for the HCM patient. Volume loading and maintenance of vascular tone at the time of induction will help to minimize hemodynamic instability at the time of induction. In certain patients smaller masses may result in valvular insufficiency. Therefore, should a small mass produce aortic or mitral regurgitation, anesthesia is administered to lower systemic resistance and promote forward blood flow. Should the mass produce a restriction to blood flow through the valve, the patient would be managed in a manner similar to that for stenotic valvular lesions.

When cardiac masses present, there is the ever-present risk of embolization. Certainly it is possible perioperatively for a mass to embolize and patients with vegetations due to endocarditis may present with embolization to the bowel, extremities, renal arteries, and brain. Should right-sided lesions be present in addition to tricuspid and pulmonic valvular insufficiency patients are at risk for pulmonary arterial embolization. PA line placement in the presence of right-sided cardiac masses could dislodge vegetation, clot, or other mass leading to perioperative pulmonary embolism.

22-Year-Old Man with Sudden Cardiac Death

A 22-year-old man suffers ventricular fibrillation while playing college football. At the scene cardiopulmonary resuscitation (CPR) is commenced. He is successfully defibrillated at the scene and transported to the emergency room.

Case Questions

What is the differential diagnosis of sudden ventricular fibrillation?

Differential diagnosis includes coronary artery disease, pulmonary embolism, tension pneumothorax, cerebral hemorrhage, and primary dysrhythmias.

In the emergency room, his vital signs are BP 60/40 mm Hg, HR 120 bpm, sinus rhythm, mechanical ventilation, and SaO2 100%. What therapy and evaluation is required?

Physical examination, ECG, and CXR are obtained. Breath sounds are bilateral and CXR is unremarkable. Rhythm appears sinus. Two large-bore IVs are started and an arterial line placed.

A TEE is performed emergently showing the findings in the TEE Video 10–1 What is the diagnosis?

HCM.

What medical therapy is required at this time?

Medical therapy should include beta-blockers to reduce heart rate and myocardial contractility, volume administration, and vasoconstrictors to augment vascular tone.

The patient is scheduled for surgery for myectomy and mitral valve repair. What are the anesthetic concerns for this patient?

Patient requires maintenance of ventricular volume, preservation of vascular tone, and reduction of myocardial contractility.