Pathophysiology and Treatment of Hypertrophic Cardiomyopathy

Interventions in Hypertrophic Obstructive Cardiomyopathy

Obstructive hypertrophic cardiomyopathy is the most common genetically transmitted cardiomyopathy that is associated with significant morbidity and mortality. Despite contemporary treatments and interventions, the management of patients with obstructive hypertrophic cardiomyopathy remains poorly defined compared with other branches of cardiology. In this review, we discuss established and novel therapeutic interventions in patients with obstructive hypertrophic cardiomyopathy with a focus on percutaneous and surgical strategies including surgical myectomy, mitral valve repair or replacement, percutaneous alcohol septal ablation, pacemaker and cardioverter-defibrillator implantation, septal embolization, radiofrequency endocardial catheter ablation, and percutaneous intramyocardial septal radiofrequency ablation.

Isolated discrete upper septal thickening in a non-referral cat population of senior and young cats

INTRODUCTION/OBJECTIVES

Discrete upper septal thickening (DUST) is a phenotype of elderly people. The cardiac phenotype in senior cats has been incompletely described. We aimed to characterize the echocardiographic phenotype of senior cats, specifically to determine prevalence of DUST and hypertrophic cardiomyopathy (HCM).

ANIMALS

One hundred and forty-nine healthy, normotensive cats.

MATERIALS AND METHODS

Prospective cross-sectional study. Senior (≥9 years) and young (<6 years) cats were recruited from non-referral population. We defined DUST as an isolated basilar septal bulge, and HCM as left ventricular wall thickness ≥6 mm. An interventricular septum ratio (basal-to-mid septal thickness ratio) was calculated. We assessed for associations between clinical and echocardiographic variables and DUST. Data are presented as mean (±SD), median (range), or frequency (percentage).

RESULTS

One-hundred and two senior and 47 young cats were enrolled. Aortoseptal angle (AoSA) was steeper in senior cats (137° (±14.5) vs. 145° (±12.3) in young cats, P=0.002). Eighteen cats had DUST (18/149, 12%), fourteen senior, and four young cats (P=0.4). Cats with DUST had steeper AoSA (125° (±8.3) vs. 142° (±13.7), P<0.0001) and higher interventricular septum ratio (1.4 (1.2-2.0) vs. 1.0 (0.7-1.8)). Univariable analysis showed decreased odds of DUST with greater AoSA (OR 0.9, P<0.0001), age was not associated with DUST. Twenty-nine senior cats had HCM (28.4%).

DISCUSSION/CONCLUSIONS

Prevalence of DUST was 12%. There was no association between age and DUST. Smaller/steeper AoSA was the main factor associated with DUST. There was a high prevalence of HCM in this senior population.

Prevalence and Prognosis of Atenolol-Responsive Systolic Anterior Motion of the Septal Mitral Valve Leaflet in Young Cats with Severe Dynamic Left Ventricular Outflow Tract Obstruction

BACKGROUND

Severe dynamic left ventricular outflow tract obstruction (DLVOTO) secondary to the systolic anterior motion of the septal mitral valve leaflet (SAM) can result either from congenital mitral valve disorders or left ventricular concentric hypertrophy of any cause, in cats commonly hypertrophic cardiomyopathy (HCM). Though HCM cannot be reversed, the question remains whether atenolol can cure cats with severe DLVOTO resulting from a presumed mitral valve dysplasia.

METHODS

In this retrospective case series, client-owned asymptomatic cats younger than 1.5 years with echocardiographic evidence of SAM and severe DLVOTO were included. Oral atenolol therapy and recheck echocardiography after 2-3 months were recommended. The owners and referring veterinarians were called for long-term follow-up information.

RESULTS

Of the 28 included cats, 23 were treated with atenolol. Recheck echocardiography performed in 17 cats showed a resolution of SAM in 47%. In the long term, SAM remained absent in only 9% of the treated cats. Cardiac-related death occurred in 26% of the atenolol-treated cats.

CONCLUSIONS

The long term benefit of twice-daily atenolol therapy was documented in 9% of cats. Whether the cats where atenolol failed to resolve DLVOTO on long-term had HCM, or a therapy-resistant congenital primary mitral valve disorder remains unclear.

Minimally invasive right infra-axillary thoracotomy for transaortic septal myectomy

Extended left ventricular septal myectomy remains the gold standard for the treatment of hypertrophic obstructive cardiomyopathy (HOCM) with refractory symptoms. On the basis of traditional modified transaortic Morrow myectomy, we innovatively performed a minimally invasive, video-assisted single-port thoracotomy through the right infra-axillary region. Our procedure can provide good visualization of the left ventricular outflow tract and hypertrophic ventricular septum for accurate resection. It also ensures optimal exposure of the mitral valve in the presence of complex mitral subvalvular structures.

Preintervention imaging and intraoperative management care of the hypertrophic obstructive cardiomyopathy patient

With an estimated overall mortality of less than 1 percent per year, hypertrophic cardiomyopathy, is the most common genetic cardiomyopathy. Intraoperative transesophageal echocardiography is the standard of care for assessing patients with hypertrophic obstructive cardiomyopathy undergoing surgical septal myectomy, allowing surgical planning, intraoperative hemodynamic monitoring, and postprocedural assessment of the repair, including detection of immediate complications. At various phases during surgical septal myectomy, the changing hemodynamic conditions may lead to worsening or improvement in left ventricle outflow tract obstruction by change in preload or afterload, systolic anterior motion of the mitral valve, or sympathetic stimulation. These characteristics represent unique challenges in the management of these patients, requiring a comprehensive understanding of the management of all the conditions required to decrease the left ventricle outflow tract gradient avoiding obstruction, which include the maintenance of sinus rhythm, adequate rate avoiding tachycardia and bradycardia, and avoidance of systemic hypotension preserving preload and afterload, with adequate vasoactive agents. The aim of this review is to summarize the perioperative assessment and management of patients undergoing hypertrophic obstructive myopathy surgery.

[Hypertrophic cardiomyopathy]

Hypertrophic cardiomyopathy is the most common genetically determined cardiac disease with a prevalence of 0.2-0.6%. The most important pathophysiological phenomenon is dynamic obstruction predominantly of the left ventricular outflow tract in 70% of the patients. Clinical symptoms (e.g. dyspnea, angina pectoris and syncope) are extremely variable depending on changes in preload and afterload and an increased risk of sudden cardiac death particularly in younger patients. The diagnostic measures should be carried out with respect to a prognostic and symptomatic treatment with implantation of an implantable cardioverter defibrillator (ICD) in cases of increased risk of sudden cardiac death. When medication treatment fails, first-line treatment consists of septal ablation and surgical myectomy as a supplementary measure, depending on the underlying morphology and experience of the surgeon.

Borisov K, Seggewiß H. Hypertrophic Obstructive Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by mutations in a number of genes. Its prevalence is 0.2% to 0.6%.

METHODS

This review is based on publications retrieved by a selective literature search and on the authors' clinical experi- ence.

RESULTS

70% of patients with HCM suffer from the obstructive type of the condition, clinically characterized by highly dynamic and variable manifestations in the form of dyspnea, angina pectoris, and stress-dependent presyncope and syn- cope. Younger patients are at particular risk of sudden cardiac death; thus, all patients need not only symptomatic treatment, but also risk assessment, which can be difficult in individual cases. Left ventricular obstruction, which usually causes symptoms, is treated medically at first, with either a beta- blocker or verapamil. If medical treatment fails, two invasive treatments are available, surgical myectomy and percu- taneous septum ablation. Both of these require a high level of expertise. If performed successfully, they lead to sustained gradient reduction and clinical improvement. Septum ablation is associated with low perioperative and peri-interventional mortality but necessitates permanent pacemaker implantation in 10-20% of patients.

CONCLUSION

In the absence of evidence from randomized comparison trials, a suitable method of reducing the gradient should be determined by an HCM team in conjunction with each individual patient. Important criteria for decision-making include the anatomical findings and any accompanying illnesses.

Hypertrophic Obstructive Cardiomyopathy: Surgical Myectomy and Septal Ablation

Hypertrophic cardiomyopathy is a genetic disorder characterized by marked hypertrophy of the myocardium. It is frequently accompanied by dynamic left ventricular outflow tract obstruction and symptoms of dyspnea, angina, and syncope. The initial therapy for symptomatic patients with obstruction is medical therapy with β-blockers and calcium antagonists. However, there remain a subset of patients who have continued severe symptoms, which are unresponsive to medical therapy. These patients can be treated with septal reduction therapy, either surgical septal myectomy or alcohol septal ablation. When performed by experienced operators working in high-volume centers, septal myectomy is highly effective with a >90% relief of obstruction and improvement in symptoms. The perioperative mortality rate for isolated septal myectomy in most centers is <1%. Alcohol septal ablation is a less invasive treatment. In many patients, the hemodynamic and clinical results are comparable to that of septal myectomy. However, the results of alcohol septal ablation are dependent on the septal perforator artery supplying the area of the contact between the hypertrophied septum and the anterior leaflet of the mitral valve. There are some patients, particularly younger patients with severe hypertrophy, who do not uniformly experience complete relief of obstruction and symptoms. Both techniques of septal reduction therapy are highly operator dependent. The final decision as to which approach should be selected in any given patient is dependent up patient preference and the availability and experience of the operator and institution at which the patient is being treated.

Hypovolemia induced systolic anterior motion of the mitral valve in two dogs

Systolic anterior (septal) motion of the mitral valve (SAM) is a common secondary phenomenon in hypertrophic cardiomyopathy (HCM) in people and cats. In humans, it is increasingly recognized that SAM may be found in other cardiac and non-cardiac disease states. In small animal cardiology, SAM unassociated with HCM has been described in dogs with mitral valve dysplasia and right ventricular pressure overload. In this report, we describe two cases of dogs where transient SAM was caused by hypovolemia. When SAM was present both dogs showed pseudohypertrophy and tachycardia. Important factors in the genesis of SAM in this scenario are probably hypovolemia induced changes in left ventricular geometry affecting the orientation of the mitral valve apparatus combined with elevated catecholamine levels. SAM associated with increased wall thickness is not pathognomonic of HCM; this observation is of particular clinical importance when extrapolated to species where HCM is highly prevalent, e.g., cats. An echocardiographic diagnosis should always be evaluated together with full clinical assessment of history and physical examination.

Minimally invasive septal myectomy for the treatment of hypertrophic obstructive cardiomyopathy and intrinsic mitral valve disease

OBJECTIVE

Transaortic left ventricular septal myectomy described by Morrow is a classical procedure for the treatment of systolic anterior motion of the mitral apparatus associated with hypertrophic obstructive cardiomyopathy (HOCM). We aimed to review our results of transmitral septal myectomy and mitral valve repair/replacement in patients with intrinsic mitral valve disease associated with HOCM, operated on through a minimally invasive approach.

METHODS

Between 2005 and 2014, 19 patients [7 men (37%); mean (SD) age, 69.4 (14.5) years] were treated with minimally invasive approach for degenerative mitral regurgitation and HOCM. Preoperative peak left ventricular outflow tract (LVOT) gradient was 66 (24) mm Hg. Severe mitral regurgitation was diagnosed in 16 cases (84%). New York Heart Association functional class III to IV heart failure was present in 13 patients (68%).

RESULTS

Fifteen patients (79%) underwent mitral valve replacement, and four patients (21%) underwent mitral valve repair. Left ventricular outflow tract obstruction was corrected directly in all patients via the mitral valve with septal myectomy/myotomy, avoiding aortotomy in majority of the patients. No significant prolongation of extracorporeal circulation/aortic cross-clamping times was observed (P = 0.41 and P = 0.67, respectively) when compared with a similar population without HOCM. No iatrogenic ventricular septal defect developed in treated patients. No hospital mortality occurred. Resting LVOT gradient reduced at discharge to 13 (22) mm Hg (P = 0.025).

CONCLUSIONS

Transmitral left ventricular septal myectomy in patients with degenerative mitral valve disease is quite a simple, feasible, and effective technique and does not require aortotomy in most cases. It can be performed with low early mortality and satisfactory resolution of LVOT obstruction in a minimally invasive setting.

Mechanical aberrations in hypetrophic cardiomyopathy: emerging concepts

Hypertrophic cardiomyopathy is the most common monogenic disorder in cardiology. Despite important advances in understanding disease pathogenesis, it is not clear how flaws in individual sarcomere components are responsible for the observed phenotype. The aim of this article is to provide a brief interpretative analysis of some currently proposed pathophysiological mechanisms of hypertrophic cardiomyopathy, with a special emphasis on alterations in the cardiac mechanical properties.

Hypertrophic cardiomyopathy: a clinical and genetic update

This article presents an overview of hypertrophic cardiomyopathy (HCM) and the associated clinical findings, treatment, and management for nurse practitioners. Topics include an overview of the condition, major and minor criteria for diagnosis, clinical course and pathophysiology, genetic inheritance and testing, and dysrhythmias associated with HCM.

Can pharmacologic gradient reduction decrease mortality in hypertrophic cardiomyopathy?

Pharmacologic therapy is the first line approach to relieve symptoms in obstructive hypertrophic cardiomyopathy. There are no randomized trials to evaluate their effect on prognosis. Gradient reduction by surgical septal myectomy is associated with excellent prognosis, but not all patients have symptoms severe enough to require surgery; and, guidelines recommend operation only for patients with high gradients and symptoms unresponsive to pharmacologic therapy. The combination of disopyramide and beta-blockade is effective in reducing resting gradients (though not to the extent of surgery). This review examines the question of whether pharmacologic reduction of gradient in asymptomatic patients or those with milder symptoms might decrease HCM-related mortality.

Echocardiography to individualize treatment for hypertrophic cardiomyopathy

Treatments for hypertrophic cardiomyopathy are largely selected based on patient symptoms and echocardiographic findings. Moreover, all the advanced treatments for heart failure symptoms depend on such imaging for planning and monitoring response to therapy. Risk of sudden death correlates with maximum left ventricular (LV) wall thickness. Massive LV thickening of 30 mm or more is an indication for primary prevention of sudden death with an implanted defibrillator. In this review, we will underscore potential pitfalls in echocardiographic diagnosis. Also we will review, a newly appreciated pathophysiologic mechanism in obstruction dynamic systolic dysfunction due to gradient.

Dual chamber pacing relieves obstruction in Japanese-variant hypertrophic cardiomyopathy

Japanese-variant or apical hypertrophic cardiomyopathy (HCM) is a specific type of HCM, first described in Japan and initially thought to carry a benign prognosis. However, current evidence suggests that these patients experience severe symptoms and are at increased risk of ventricular arrhythmias and death, especially in the presence of an apical akinetic chamber. The management of patients who do not respond to medical therapy is challenging. We describe a patient with Japanese-variant HCM, with an apical akinetic chamber and severe symptoms who failed medical therapy. The use of dual chamber pacing relieved obstruction and significantly improved the patient's symptoms.

Comparison of acute reduction in left ventricular outflow tract pressure gradient in obstructive hypertrophic cardiomyopathy by disopyramide versus pilsicainide versus cibenzoline

Negative inotropic agents are often administered to decrease the left ventricular (LV) pressure gradient in patients with obstructive hypertrophic cardiomyopathy (HC). Little information is available regarding comparisons of the effects on LV pressure gradient among negative inotropic agents. The present study compared the decrease in the LV pressure gradient at rest in patients with obstructive HC after treatment with pilsicainide versus treatment with disopyramide or cibenzoline. The LV pressure gradient and LV function were assessed before and after the intravenous administration of each drug. In 12 patients (group A, mean pressure gradient 90 ± 24 mm Hg), the effects of disopyramide, propranolol, and verapamil were compared. In another 12 patients (group B, mean pressure gradient 98 ± 34 mm Hg), a comparison was performed among disopyramide, cibenzoline, and pilsicainide. In group A, the percentage of reduction in the LV pressure gradient was 7.7 ± 9.9% with verapamil, 19.0 ± 20.2% with propranolol, and 58.6 ± 15.0% with disopyramide, suggesting that disopyramide was more effective than either verapamil or propranolol. In group B, the percentage of reduction in the LV pressure gradient was 55.3 ± 26.6% with disopyramide, 55.3 ± 20.6% with cibenzoline, and 54.7 ± 15.4% with pilsicainide, suggesting an equivalent effect on the LV pressure gradient for these 3 agents. In conclusion, these results indicate that the acute efficacy for the reduction of the LV pressure gradient at rest by pilsicainide (a pure sodium channel blocker) was equivalent to that of disopyramide or cibenzoline (combined sodium and calcium channel blockers). Accordingly, sodium channel blockade might be more important for reducing the LV pressure gradient at rest in patients with obstructive HC than calcium channel blockade or β blockade.

Diagnosis and treatment of congestive heart failure secondary to hypertrophic cardiomyopathy in a kinkajou (Potos flavus)

An adult castrated male pet kinkajou (Potos flavus) presented with dyspnea due to congestive heart failure and was diagnosed with hypertrophic cardiomyopathy (HCM) and suspected pulmonary arterial hypertension. Diagnosis was based on history, clinical signs, clinical pathology, radiographs, abdominal ultrasonography, abdominal fluid analysis, electrocardiography, and echocardiogram. An undetermined hepatopathy also was found at presentation and resolved after metronidazole antimicrobial treatment. Cardiopulmonary medical treatment, including a loop diuretic, an angiotensin-converting enzyme inhibitor, a beta-adrenergic receptor blocker, and a bronchodilator provided improvement of the clinical signs. To the best of our knowledge, this is the first reported case of antemortem diagnosis and treatment of congestive heart failure and cardiomyopathy in a member of the family Procyonidae, suggesting that HCM should be considered as a differential diagnosis in kinkajous displaying clinical signs of dyspnea and exercise intolerance.

Solution structure of human cardiac troponin C in complex with the green tea polyphenol, (-)-epigallocatechin 3-gallate

Heart muscle contraction is regulated by Ca(2+) binding to the thin filament protein troponin C. In cardiovascular disease, the myofilament response to Ca(2+) is often altered. Compounds that rectify this perturbation are of considerable interest as therapeutics. Plant flavonoids have been found to provide protection against a variety of human illnesses such as cancer, infection, and heart disease. (-)-Epigallocatechin gallate (EGCg), the prevalent flavonoid in green tea, modulates force generation in isolated guinea pig hearts (Hotta, Y., Huang, L., Muto, T., Yajima, M., Miyazeki, K., Ishikawa, N., Fukuzawa, Y., Wakida, Y., Tushima, H., Ando, H., and Nonogaki, T. (2006) Eur. J. Pharmacol. 552, 123-130) and in skinned cardiac muscle fibers (Liou, Y. M., Kuo, S. C., and Hsieh, S. R. (2008) Pflugers Arch. 456, 787-800; and Tadano, N., Yumoto, F., Tanokura, M., Ohtsuki, I., and Morimoto, S. (2005) Biophys. J. 88, 314a). In this study we describe the solution structure of the Ca(2+)-saturated C-terminal domain of troponin C in complex with EGCg. Moreover, we show that EGCg forms a ternary complex with the C-terminal domain of troponin C and the anchoring region of troponin I. The structural evidence indicates that the binding site of EGCg on the C-terminal domain of troponin C is in the hydrophobic pocket in the absence of troponin I, akin to EMD 57033. Based on chemical shift mapping, the binding of EGCg to the C-terminal domain of troponin C in the presence of troponin I may be to a new site formed by the troponin C.troponin I complex. This interaction of EGCg with the C-terminal domain of troponin C.troponin I complex has not been shown with other cardiotonic molecules and illustrates the potential mechanism by which EGCg modulates heart contraction.

Indications for ICD and cardiac resynchronization therapy for prevention of sudden cardiac death

The implantable cardioverter-defibrillator (ICD) is used for primary and secondary prophylaxis of sudden cardiac death in high-risk patients. While several trials have demonstrated the superiority of ICD over standard medical therapy or antiarrhythmic medication in this population, a few trials have not shown survival benefit. The Multicenter Automatic Defibrillator Implant Trial II study revealed that ICD reduces mortality in patients with ischemic cardiomyopathy. The Sudden Cardiac Death-Heart Failure Trial demonstrated that the ICD prevents sudden cardiac death and all-cause mortality in high-risk patients with moderate ischemic and nonischemic cardiomyopathy and heart failure. The ICD is also recommended for high-risk patients with inherited arrhythmia or cardiomyopathy. Cardiac resynchronization therapy reduces mortality and heart failure class as compared with optimal medical therapy in advanced heart failure. The high economic cost of widespread ICD use must also be considered. Therefore, it is prudent to identify a high-risk population who will benefit most from these devices.

Effects of exercise on the duration of diastole and on interventricular phase differences in patients with hypertrophic cardiomyopathy: relationship to cardiac output reserve

BACKGROUND

Our study sought to characterize the effect of exercise on the duration of left ventricular (LV) diastole and interventricular dyssynchrony in patients with hypertrophic cardiomyopathy (HCM). We hypothesized that an abnormally shortened diastolic time may adversely affect cardiac performance.

METHODS

We studied 49 symptomatic patients with HCM during incremental exercise. Twenty-nine patients had obstructive disease (HOCM) and 20 no resting or provocable gradient (HNCM). Right heart catheterization and high temporal resolution radionuclide angiography were simultaneously performed. The loss of diastolic time per beat (LDT(RR)) was quantified using a regression equation obtained from a healthy control group (n = 30).

RESULTS

During rest and peak exercise, a significant shortening of the relative duration of LV diastole (35.6 +/- 5 vs. 38.0 +/- 3 s/min and 29.3 +/- 6 vs. 32.4 +/- 3 s/min; P < or = .02) and an increased interventricular phase delay were evident in patients with HOCM compared to controls. Baseline and peak exercise LDT(RR) values were inversely related to cardiac output reserve and exercise duration. In multivariate analysis, LDT(RR) at peak exercise was identified as an independent predictor of cardiac output reserve.

CONCLUSIONS

In HOCM, baseline abnormalities of the relative duration of LV systolic and diastolic time aggravate during exercise. The disproportionate shortening of diastolic time may significantly impair cardiac efficiency by restricting diastolic filling.

Preliminary clinical investigation of 99mTc-methoxyisobutylisonitrile washout rate in hypertrophic cardiomyopathy

OBJECTIVE

The aim of this study was to investigate the changes in early and late washout rates of 99mTc-methoxyisobutylisonitrile (MIBI) in hypertrophic cardiomyopathy (HCM), and to analyze the relationships between early and late washout rates and the hypertrophic thickness of left ventricular (LV) wall.

METHODS

The patients who were clinically diagnosed as positive for HCM underwent 99mTc-MIBI static planar and gated single-photon emission computed tomography (SPECT) imaging. Early (90 min after the intravenous injection) and late (4 h after the intravenous injection) washout rates of 99mTc-MIBI between HCM group and normal control group were compared. Linear correlation analysis was made between early and late washout rates and the hypertrophic thickness of LV wall measured by gated SPECT.

RESULTS

The early and late washout rates of 99mTc-MIBI in normal control group were (18.90+/-3.70) and (31.27+/-4.04)%, respectively; and the washout rates in HCM group were (27.77+/-2.60) and (42.66+/-3.30)%, respectively. Significant statistical differences were observed in the early and late washout rates of 99mTc-MIBI between HCM group and normal control group (t=-7.320 and t=-8.069, both P<0.01). Correlations between early and late washout rates and the maximal hypertrophic thickness of LV wall obtained by gated SPECT were excellent (r=0.611, P<0.05; r=0.873, P<0.01, respectively).

CONCLUSION

The early and late washout rates of 99mTc-MIBI in HCM group were significantly higher than those in normal control group, and both the early and late washout rates correlated well with the hypertrophic thickness of LV wall.

Anesthetic Considerations in the Patient With Valvular Heart Disease Undergoing Noncardiac Surgery

Valvular heart disease can be an important finding in patients presenting for noncardiac surgery. Valvular heart disease and resulting comorbidity, such as heart failure or atrial fibrillation, significantly increase the risk for perioperative adverse events. Appropriate preoperative assessment, adequate perioperative monitoring, and early intervention, should hemodynamic disturbances occur, may help prevent adverse events and improve patient outcome. This review article aims to guide the practitioner in the various aspects of anesthetic management in the perioperative care of patients with valvular heart disease. The pharmacological approach to optimization of patient outcome with drugs, such as βblockers and lipid-lowering medications (statins), is an evolving field, and recent developments are discussed in this article.

Indications for implantable cardioverter defibrillator use for primary prevention of sudden cardiac death

The implantable cardioverter defibrillator (ICD) is used for primary and secondary prophylaxis of sudden cardiac death in high-risk patients. Although several trials have demonstrated the superiority of ICD over standard medical therapy or antiarrhythmic medication in this population, a few trials have not shown survival benefit. This review examines the major ICD trials that provide the basis for current therapy in this rapidly changing and very important area of cardiology.