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Critical Care Nurse. 2008;28: 44-52
Copyright © 2008 by the American Association of Critical-Care Nurses.
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Clinical Article
CE Article

Systolic Heart Failure in a Patient With Hypertrophic Obstructive Cardiomyopathy

A Potentially Life-Threatening Complication

Shannon Etheridge Whitten, MS, NP-C, ARPN, BC, CCRN

Shannon Etheridge Whitten is a family nurse practitioner with experience in internal medicine, critical care, and cardiology. She currently practices at Quality of Life Internal Medicine in Charlotte, North Carolina and Tennille Community Center in Tennille, Georgia.

To purchase electronic or print reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 809-2273 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, reprints{at}aacn.org.

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To learn more about hypertrophic obstructive cardiomyopathy, read "Cardiogenic Shock in a Patient With Hypertrophic Obstructive Cardiomyopathy After Insertion of a Pacemaker" by Anna Barkman and Judy McCay in the American Journal of Critical Care, 2002;11:537–542[Free Full Text] . Available at www.ajcconline.org.

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Financial Disclosures
None reported.

This article has been designated for CE credit. A closed-book, multiple-choice examination follows this article, which tests your knowledge of the following objectives:

  1. Identify the pathophysiologic characteristics of hypertrophic obstructive cardiomyopathy (HOCM)
  2. Describe common signs and symptoms of HOCM
  3. Discuss the diagnostic and treatment modalities for HOCM

Corresponding author: Shannon Etheridge Whitten, MS, NP-C, ARPN, BC, CCRN, PO Box 372, Tennille, GA 31089 (e-mail: Shannon8633{at}hotmail.com).


CASE STUDY

LB, a 61-year-old man, well known in our cardiology practice, came to the emergency department early one morning after experiencing 24 hours of profound weakness and increasing dyspnea out of proportion to his usual shortness of breath. He had a history of hypertrophic obstructive cardiomyopathy and paroxysmal atrial arrhythmias. He said he had no personal or family history of coronary artery disease (CAD), and a recent coronary angiogram showed no evidence of CAD. Coincidentally, he was scheduled to return later the same day for a septal ablation because his signs and symptoms were not improving with aggressive medical therapy that included the use of high-dose β-blockers and calcium channel blockers. An echocardiogram 1 week earlier had revealed an ejection fraction of 70%, an asymmetric thickening of the intracardiac septum, and marked systolic outflow obstruction with a gradient of almost 100 mm Hg on exertion. On arrival in the emergency department, LB was diaphoretic with a systolic blood pressure of 60 mm Hg, a low-grade fever, and sinus tachycardia with a heart rate of 122/min. His dual-chamber, inhibited response, adaptive rate pacemaker was functioning appropriately. LB had not experienced any chest discomfort or had any indications of infection that could explain this precipitous exacerbation in his signs and symptoms.

Physical examination revealed diffuse crackles throughout all lung fields and profound dyspnea with an oxygen saturation of 87%. He had a harsh IV/VI systolic ejection murmur that intensified when he performed the Valsalva maneuver. An echocardiogram revealed an ejection fraction of 15% to 20% with anterior septal, apical, and lateral wall hypokinesis. LB was clearly in cardiogenic shock of unknown origin. The acute care nurse practitioner made arrangements for urgent transfer to the coronary care unit for stabilization because LB was decompensating quickly.

Laboratory results indicated a white blood cell count of 11000/uL, a creatine kinase level of 2034 U/L (to convert to microkatals per liter, multiply by 0.0167), an MB fraction of 53 ng/mL, and a troponin level of 23.6 ng/mL. His renal function was stable, with a creatinine level of 1.3 mg/dL (to convert to micromoles per liter, multiply by 88.4). Blood, urine, and sputum cultures showed no growth of microorganisms, so the leukocytosis and fever were suspected to be a reactive process. Electrocardiography (ECG) revealed left ventricular hypertrophy, and 1-mm ST-segment depression was present in all the precordial leads. Comparison with an earlier ECG confirmed that the ST-segment depression was a new finding. A pulmonary artery catheter was placed for continuous hemodynamic monitoring, and administration of dopamine was started for treatment of hypotension. Intravenous furosemide (Lasix) was started cautiously to treat the pulmonary edema.

LB was taken to the cardiac catheterization laboratory and, as expected, did not have any evidence of coronary artery stenosis or thrombus. Because of the normal findings on the coronary angiogram, the cause of the cardiogenic shock was thought to be myocardial stunning. An intra-aortic balloon pump was successfully placed at a ratio of 1:2, providing further hemodynamic stabilization. The intravenous infusion of heparin started in the catheterization laboratory was continued, and LB returned to the coronary care unit. On his second day in the unit, atrial fibrillation with a rapid ventricular response developed. Treatment with β-blockers was resumed for rate control, and intravenous infusion of digoxin was started to provide positive inotropic stimulation for the diminished left ventricular function. LB was weaned off the balloon pump, mechanical ventilation, and dopamine, which were eventually discontinued without complications.

Two weeks later, a repeat echocardiogram revealed an ejection fraction of 50% with midanterior apical hypokinesis that was clearly an improvement and an indication that the myocardium was stunned, not infarcted. Systolic anterior motion of the mitral valve was evident, and the peak systolic outflow gradient was 55 mm Hg at rest. LB was taken to the catheterization laboratory for reevaluation. His resting systolic gradient increased when he performed the Valsalva maneuver and peaked at 100 mm Hg with a dobutamine challenge. On the basis of these additional findings, a decision was made to proceed with percutaneous transluminal septal myocardial ablation (PTSMA). Per protocol, 98% ethanol (3 mL) was injected into a large first septal perforator artery with the catheter balloon inflated to prevent untoward effects. The septal ablation was successful; the left ventricular outflowgradient decreased to 40 mm Hg.

LB returned to the coronary care unit for observation overnight, which is standard. The same evening, a paroxysmal atrial flutter with a rapid ventricular response developed. With the addition of intravenous amiodarone, LB’s cardiac rhythm converted to normal sinus rhythm. His pacemaker was reprogrammed to reduce the sensitivity of the rate response to allow for his own intrinsic beats. The rationale was that the atrial kick of late diastole produced by his intrinsic rhythm would allow more effective diastolic filling. At discharge to home, he was taking a long-acting β-blocker, amiodarone, and warfarin. Arrangements were made for follow-up with his primary cardiologist 1 week after discharge.

 


   Discussion
Top
 Discussion
Findings on Physical Examination
 Summary
 PRIME POINTS
 References
 
Epidemiology
Hypertrophic obstructive cardiomyopathy (HOCM) is a genetically transmitted disease that affects approximately 0.2% to 4% of the US population.1 It is the result of a mutation in multiple genes that encode protein in the cardiac sarcomere, the primary contractile unit of the cardiac muscle.2 HOCM is typically inherited in an autosomal manner, with variable penetrance and variable expressivity.3 Approximately half of all cases of HOCM have an autosomal dominant pattern; the rest are the result of sporadic gene mutations.3,4 Recently, HOCM was linked to the cardiac myosin heavy-chain genes on chromosome 14 in some families, suggesting genetic heterogeneity.5 The age at which clinical manifestations become apparent varies. The existence of different disease genes or mutations in a gene may account for the differences in genotypic and phenotypic expressions.3

Morphological evidence of disease is visible on echocardiograms in approximately 25% of first-degree relatives of patients with HOCM.2,5 Genetic testing is still in its early stages; however, it can be used to detect asymptomatic family members with the same mutation. Patients with a known family history of HOCM should be considered for noninvasive screening, especially children and adolescents up to 18 years old, because HOCM is more progressive in children and young adults.2,3 An echocardiogram will usually suffice as an initial screening tool in this population.2

Pathophysiology
HOCM is the obstructive subvariant of hypertrophic cardiomyopathy. It is characterized by left ventricular hypertrophy, a hyperdynamic left ventricle, systolic anterior motion of the mitral valve, and outflow obstruction in the absence of other identifiable diseases.6,7 Mutations in the myocardial sarcomere proteins result in muscle disarray and fibrosis, ultimately causing inappropriate left ventricular hypertrophy.1,3 The term HOCM is preferred to the older term idiopathic hypertrophic subaortic stenosis because hypertrophy can occur in any segment of the ventricle and interventricular septum, not just the subaortic septum.5

Hypertrophy of the subaortic septum alone or in combination with systolic anterior motion of the mitral valve produces obstruction of the left ventricular outflow tract (LVOT) that results in decreased cardiac output. Bulging of thickened septum into the outflow tract during systole causes anterior apposition of the mitral valve leaflet, further narrowing the outflow tract and creating an amplifying feedback loop whereby obstruction begets more obstruction1,8 (Figure 1Go). This obstruction increases left ventricular systolic pressure, decreases coronary perfusion pressure, and increases left ventricular end-diastolic pressure (LVEDP) in the absence of increased volume.10 Most patients with HOCM have a thick hypercontractile left ventricle and impaired diastolic relaxation. Ventricular hypertrophy is usually out of proportion to the hemodynamic load, meaning the LVEDP is elevated even with normal left ventricular volume.11 The abnormally elevated LVEDP may lead to backward failure with pulmonary congestion, dyspnea, and even heart failure. In most cases, heart failure is due to diastolic dysfunction (Figure 2Go). Systolic function is usually preserved, even in advanced cases; importantly, the LVOT obstruction in HOCM is not fixed, and therefore a sudden variation in the amount of obstruction can lead to serious complications,10 such as the systolic failure in this case study. The obstruction varies considerably from day to day even in patients in stable condition and can change with the slightest alteration in physiological state, such as with exercise or illness.


Figure 1
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  		Figure 1 Classic features of hypertrophic obstructive cardiomyopathy. Long-axis view of obstruction of the left ventricular outflow tract by a thickened interventricular septum. Note the systolic anterior motion of the mitral valve obstructing the left ventricular outflow tract.

 

Figure 2
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  		Figure 2 Pathophysiology of hypertrophic obstructive cardiomyopathy.

 
LB had a significant outflow obstruction from asymmetric hypertrophy of the subaortic septum that was further compromised by systolic anterior motion of the mitral valve. In his case, the cardiogenic shock was attributed to myocardial stunning, the result of a critical change in the LVOT obstruction. Myocardial stunning is a phenomenon in which short recurrent, reversible episodes of ischemia result in prolonged depression of cardiac function that eventually recovers with time.4 The stunning is the result of oxidative stress, namely, the production of oxygen-derived free radicals during reperfusion of an ischemic myocardium.4 The exact incidence of myocardial stunning is unknown, but it is generally well tolerated in patients with normal structure and function of the left ventricle.4,12

LB’s manifestation was unique because his ejection fraction decreased precipitously from 70% to approximately 15% to 20%, not allowing time for compensation. Myocardial stunning in a patient whose cardiac output was already compromised by obstruction only complicated matters by further reducing cardiac output, leading to pulmonary congestion and cardiogenic shock.

Clinical Manifestations
Most patients with HOCM are asymptomatic or only minimally symptomatic; the most common findings are dyspnea and chest pain, in that order.6 Shortness of breath usually correlates with the heart’s inability to increase cardiac output, particularly upon exertion.13 Orthopnea and paroxysmal nocturnal dyspnea are less common and are thought to be due to pulmonary venous congestion.

The cause of chest pain is less clear but it may stem from decreased perfusion in the microcoronary circulation.14 This perfusion defect is thought to be the result of phasic compression of intramural vessels and dynamic coronary bridges by the hypercontractile left ventricle.8 Myocardial ischemia has been linked to the increase in oxygen demand associated with small-vessel coronary artery disease. Chest pain typically occurs in response to activity or strenuous exercise but may occur at rest.8 The pain varies in quality from pressure to crushing pain and typically improves with rest or cessation of the offending activity.

Syncope and presyncope are common and may occur as the result of both atrial and ventricular arrhythmias, heart block, decreased cerebral perfusion, or even abnormal reflex vasodilatation during or after physical activity.8,10 Congestive heart failure is usually the result of increasing LVOT obstruction and impaired diastolic relaxation that lead to increased filling pressures, which in turn cause pulmonary and systemic congestion.

Palpitations are sometimes just the patient’s sensation of strong contractions; however, atrial or ventricular arrhythmias are more often the real culprit.3 Arrhythmias are thought to be the product of ventricular remodeling, decreased cardiac output, microcoronary ischemia, and hypotension.10 Arrhythmias generally are not well tolerated because they further contribute to reductions in cardiac output. The most common arrhythmias seen in HOCM are atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia, and heart block of various degrees. Sudden cardiac death from ventricular arrhythmias is not uncommon and, in fact, is the leading cause of sudden cardiac death in patients age 35 years or younger.3,10


   Findings on Physical Examination
Top
 Discussion
 Findings on Physical Examination
Summary
 PRIME POINTS
 References
 
Physical examination of a patient with HOCM should be focused on arterial pulsations and auscultation.3 The most common finding is a systolic ejection murmur that varies in intensity and is best heard at the sternal border and/or apex.5 As a rule of thumb, anything that increases venous return decreases the murmur’s intensity, and anything that decreases venous return increases the murmur’s intensity. The murmur usually increases with standing, with exercise, or when the Valsalva maneuver is performed, and it decreases with squatting, gripping the hand, or use of vasopressors. The holosystolic murmur of mitral regurgitation is best heard at the apex and axilla, and it is often heard in patients with significant LVOT obstruction.2,10 Other common findings include the S4 gallop of ventricular noncompliance and paradoxical splitting of the second heart sound from delayed closure of the aortic valve (Table 1Go).


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  		Table 1 Clinical manifestations and findings on physical examination of patients with hypertrophic obstructive cardiomyopathy

 
A bifid apex and a bifid carotid pulse may also be detected on physical examination. A bifid apex is a powerful systolic impulse or thrust created by the increased muscle mass of the hypertrophied left ventricle and may be detected on palpation.5,10 A bifid pulse may be evident particularly in the carotid arteries. The cause is the rapid increase in pressure through the outflow tract in early systole, followed by a decrease during midsystole as the gradient increases, and finally followed by another increase in pressure during late systole.10 Common hemodynamic findings in a patient with HOCM include decreased cardiac output and increased LVEDP. Pulmonary artery pressures may be elevated in those patients with diastolic and systolic heart failure.

Diagnosis
Echocardiography is the test of choice for the initial diagnosis.15 Most patients with HOCM have echocardiographic evidence of septal hypertrophy, and this test has a sensitivity of 90% for detection of HOCM.3 Table 2Go gives additional diagnostic echocardiographic findings.5,10 A chest radiograph may reveal an enlarged cardiac silhouette. ECG changes are seen in up to 95% of patients with HOCM.3 The classic ECG findings include typical left ventricular hypertrophy with or without strain in leads V2 through V6, marked left-axis deviation; deep, narrow q waves in the leftward-oriented leads (aVL and V6); and left atrial enlargement as indicated by terminal P-wave negativity in lead V1.17


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  		Table 2 Echocardiographic findings in patients with hypertrophic obstructive cardiomyopathy

 
Cardiac catheterization is another useful test but is usually reserved for patients who are not responding to medical therapy. Catheterization can be used to assess the degree of outflow obstruction in patients with refractory disease.2 It is also useful to determine coronary anatomy before intervention. Electrophysiology studies are rarely used in diagnosis but can be useful to determine which patients are at high risk for life-threatening ventricular arrhythmias.3 Finally, exercise testing is not routinely used in patients with HOCM because of the increased risk for syncope, hypotension, and arrhythmias.5

Treatment Strategies
The treatment goal for patients with HOCM is to improve signs and symptoms by decreasing heart rate, decreasing outflow obstruction, decreasing oxygen demand, improving left ventricular and septal relaxation, improving filling parameters, and preventing major complications.10 β-Blockers, nondihydropyridine calcium channel blockers such as verapamil, disopyramide (Norpace), and amiodarone are the preferred medications to treat this disease.1 β-Blockade is useful in preventing an exercise-related increase in pressure gradient but is less helpful in reducing high resting gradients.10 Furthermore, β-blockade can markedly decrease outflow obstruction by promoting septal relaxation. Disopyramide, on the other hand, is used to reduce resting gradients and is best used in combination with a β-blocker.10,18 Amiodarone was selected for LB in an attempt to convert his rhythm to sinus rhythm and to decrease the risk for sudden cardiac death from arrhythmias.

Surgical myectomy and PTSMA are invasive procedures usually reserved for patients in whom medical management is unsuccessful.17 Surgical myectomy involves excision of a rectangular part of the thickened subaortic septum. For patients with minimal septal hypertrophy (15–18 mm), a mitral valve replacement is preferred over myectomy because of the risk of septal perforation.1 Surgical myectomy ameliorates signs and symptoms in about 70% of patients and is the preferred procedure for patients who have concomitant cardiac disease that requires surgery.11

PTSMA is a nonsurgical alternative for patients in whom traditional medical therapy has not been helpful or who are deemed too high risk for surgery. PTSMA is indicated for symptomatic patients with New York Heart Association class III heart failure; however, patients with less severe signs and symptoms are considered if they have high outflow tract gradients or documented risk factors for sudden cardiac death. An outflow tract obstruction is considered significant if the gradient is greater than 50 mm Hg at rest or is 30 mm Hg at rest and increases to 80 mm Hg under stress.1,13 PTSMA involves injection of ethanol into 1 or more septal perforator arteries, producing a controlled infarction of the myocardial septum. A successful PTSMA results in septal thinning with reduction in the LVOT obstruction. Abolishing the gradient during the procedure is not necessary because remodeling after ablation shrinks the subaortic septum further.19 Although the long-term safety of PTSMA has been established in clinical trials, the risk for mortality is 1.1% to 4%, and the procedure is slightly less effective than myectomy for long-term control of signs and symptoms.13 Furthermore, up to 10% of patients require a permanent pacemaker/defibrillator after PTSMA because of arrhythmias or heart block.20

Finally, dual-chamber, inhibited response, adaptive rate pacemakers may be used to decrease septal contractility, but at best provide only modest improvements in LVOT obstruction.2 Even so, pacemakers may have another useful role in HOCM. A recent study21 suggests left ventricular endocardial temporary pacing may be useful in predicting patients’ response to PTSMA. Implantable cardiac defibrillators with or without the use of amiodarone are another useful treatment and do prevent cardiac death in high-risk populations.3,10 Adolescents, children, and patients more than 65 years old are considered high risk.3

Contrary to the standard medical management of HOCM, digoxin, vasopressors, and a balloon pump were required in LB’s case to maintain adequate filling pressures and forward flow. Vasodilators, diuretics, positive isotropic medications, and balloon pumps normally would increase the LVOT obstruction in a patient with HOCM and therefore should be avoided; however, they were necessary to treat the cardiogenic shock in LB.

Nursing Considerations
Critical care nurses must understand the pathophysiology, management (Table 3Go), and dynamic features of HOCM to individualize a plan of care for patients and to prevent potential life-threatening complications. Nursing care after myectomy is similar to postoperative care of any patient undergoing invasive heart surgery.


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  		Table 3 Disease management

 
Patients are admitted to the intensive care unit after PTSMA for no less than 24 hours (Table 4Go). Elderly patients and patients with class IV heart failure have a higher risk of complications than others do after the intervention and typically require additional time in the unit.19 Vital signs are monitored every 30 to 60 minutes for 4 hours, and then monitoring is tapered to every 2 hours unless otherwise specified. Patients with overt heart failure may require monitoring of cardiac output, systemic vascular resistance, and pulmonary artery wedge pressures to guide medical therapy. Assessment of catheter insertion sites for bleeding, hematomas, and signs of infection is important. Access sites are managed the same as any site after any catheterization procedure.


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  		Table 4 Nursing protocols after percutaneous transluminal septal myocardial ablation

 
ECG should be performed before ablation, when the patient arrives in the unit, and hourly for 4 hours. An ECG should be ordered if the patient has indications of extension of the myocardial infarction because this change is a potentially life-threatening complication of PTSMA. Serial measurements of cardiac enzyme levels should be done per preference of the cardiologist or per unit protocol. Patients after ablation are experiencing an infarct and require intensive monitoring. They should be assessed for chest pain and dyspnea. Chest pain is common, and management usually involves the use of opiate analgesics such as morphine sulfate, nonsteroidal anti-inflammatory drugs, or both. Patients should be monitored for arrhythmias; any patient who has undergone PTSMA is at increased risk for atrial and ventricular arrhythmias.

To prevent deleterious complications, critical care nurses must be clear on medications that are indicated and contraindicated for patients with HOCM. The use of inotropes, angiotensin-converting enzyme inhibitors, and vasodilators such as nitroglycerin should be avoided and questioned if they are ordered for a patient with HOCM. Nitrates may be ordered for chest pain after PTSMA, but their use should be clarified because nitrates are contraindicated in any patient with a significant gradient. If patients are given antiplatelet or anticoagulant therapy, they must be monitored closely for bleeding complications, drug reactions, and medication interactions.

Patients are typically transferred to a telemetry step-down unit after the initial 24-hour observation period once the transvenous pacemaker has been discontinued, but patients are still at risk for complications and should be monitored closely until discharge. Discharge planning should start when the patient arrives in the unit. Patients must understand which medications they are to continue and which ones they should discontinue, because their disease process may have changed dramatically after successful intervention. Treatment with β-blockers is usually continued after discharge. Patients must be instructed to follow up with their cardiologist or nurse practitioner within 2 to 4 weeks of discharge unless otherwise instructed. Patients with any marked residual obstruction must be counseled to avoid strenuous activity and contact sports because of the risk of sudden cardiac death. Finally, patients should be instructed to seek additional medical attention if they experience any indications of infection, pain, or alteration in temperature/sensation in the catheterized extremity.


   Summary
Top
 Discussion
 Findings on Physical Examination
 Summary
PRIME POINTS
 References
 
HOCM is a genetic disease characterized by LVOT obstruction, ventricular hypertrophy, and volume overload. Its defining characteristics are a hyperdynamic left ventricle with or without septal hypertrophy and dynamic obstruction of the outflow tract. The most common findings include dyspnea, chest pain, and syncope, and these are usually the result of the heart’s inability to increase cardiac output with activity.10 Because HOCM is not curable, the goals of treatment are focused on improving patients’ signs and symptoms and decreasing complications.1

Patients with HOCM require lifelong medical therapy; therefore, medical and interventional therapies are considered complementary, not competitive.19 PTSMA and surgical myectomy are good options for patients with medication-refractory disease, but because of the potential complications, these interventions must be used only in the appropriate patients. Complications of HOCM include, but are not limited to, heart failure, atrial and ventricular arrhythmias, and sudden cardiac death. Although HOCM is a disease typified by diastolic dysfunction, complications may occur with progressive or uncompensated disease, resulting in systolic heart failure as in LB’s case. Critical care nurses’ over-all knowledge of this disease and their ability to detect problems early can make every bit of difference for the patient, as it did in this case. LB has continued to do well without any further complications thanks to the diligence of his health care team.


   PRIME POINTS
Top
 Discussion
 Findings on Physical Examination
 Summary
 PRIME POINTS
References
 


   References
Top
 Discussion
 Findings on Physical Examination
 Summary
 PRIME POINTS
 References
 

  1. Fifer MA. Alcohol septal ablation for hypertrophic obstructive cardiomyopathy. Cardiol Rounds. 2003;7(1). http://www.cardiologyrounds.org/crus/cardious_0103.pdf. Published January 2003. Accessed July 27, 2008.
  2. Lutz JF. Cardiomyopathy. In: Branch WT, Alexander RW, Schlant RC, Hurst JW, eds. Primary Care Cardiology. New York, NY: McGraw-Hill Co; 2000:387–398.
  3. DeLuca M, Tahir T. Hypertrophic cardiomyopathy. Postgrad Med. 2000;107:127–140.[Medline]
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  5. Zevitz ME. Cardiomyopathy, hypertrophic. eMedicine Web site. http://www.emedicine.com/med/topic290.htm. Updated July 18, 2006. Accessed July 27 2008.
  6. Maron B, Dearani J, Ommen, S, et al. The case for surgery in hypertrophic cardiomyopathy. J Am Coll Cardiol. 2004;44:2044–2053.[Abstract/Free Full Text]
  7. Abbas AE, Brewington SD, Dixon SR, Grines CL, O’Neill WW. Alcohol septal ablation for hypertrophic obstructive cardiomyopathy. J Interv Cardiol. 2005;18(3): 155–162.[Medline]
  8. Sherrid MV, Gunsbug D, Sharma A. Medical treatment of hypertrophic cardiomyopathy. Curr Cardiol Rep. 2000;2:148–153.[Medline]
  9. Kaddoura S. Echo Made Easy. Oxford, England: Churchill Livingstone; 2002:84.
  10. Shah P. Hypertrophic cardiomyopathies. In: Crawford MH, ed. Current Diagnosis and Treatment in Cardiology. New York, NY: Lange Medical Books/McGraw-Hill; 2003:179–187.
  11. Braunwald E, Zipes D, Libby P. Heart Disease: A Textbook of Cardiovascular Medicine. 6th ed. Philadelphia, PA: WB Saunders Co; 2001:1760–1774.
  12. Wittstein I, Thiemann D, Lima J, et al. Neurohumoral features of myocardial stunning due to sudden emotional stress. N Engl J Med. 2005;352:539–548.[Abstract/Free Full Text]
  13. Maron B. Surgery for hypertrophic obstructive cardiomyopathy. Circulation. 2005; 111:2016–2018.[Free Full Text]
  14. Krams R, Kofflard MJ, Dunke DJ, et al. Decreased coronary flow reserve in hypertrophic cardiomyopathy is related to remodeling of the coronary microcirculation. Circulation. 1998;97(3):230–233.[Abstract/Free Full Text]
  15. Nishimura R, Holmes D. Hypertrophic obstructive cardiomyopathy. N Engl J Med. 2004;350:1320–1327.[Free Full Text]
  16. Crawford M. Current Diagnosis and Treatment in Cardiology. 2nd ed. New York, NY: McGraw-Hill Co; 2003.
  17. Roberts R, Sigwart U. Current concepts and pathogenesis in the treatment of hypertrophic obstructive cardiomyopathy. Circulation. 2005;112:293–296.[Free Full Text]
  18. Sherrid MV, Barac I, Mckenna WJ, et al. Multicenter study of the efficacy and safety of dysopyramide in obstructive hypertrophic cardiomyopathy. J Am Coll Cardiol. 2005; 45(8):1251–1258.[Abstract/Free Full Text]
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  21. Chen SL, Dai ZL, Li ZQ, et al. Left ventricular endocardial pacing predicts the reduction of left ventricular outflow tract pressure gradient immediately after percutaneous transseptal myocardial ablation in patients with hypertrophic obstructive cardiomyopathy refractory to medication. Chin Med J (Engl). 2007;120(7):562–568.[Medline]




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