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Dr. Irena Peovska Mitevksa
Echocardiography is an invaluable tool in the diagnosis, prognosis, management strategy and follow-up of patients with HCM. This review briefly profiles the practical use of established echocardiography techniques and discusses the evolving role of novel echocardiography imaging modalities in the assessment of patients with hypertrophic cardiomyopathy.
HCM is a common genetic cardiovascular disease with the overall prevalence estimated between 0.05-0.2% of the population (1). HCM is a disease state characterised by unexplained, marked and asymmetric left ventricular (LV) hypertrophy associated with non dilated ventricular chambers in the absence of another cardiac or systemic disease capable of producing the magnitude of hypertrophy evident in a given patient (2). Clinically, HCM is usually recognised by a maximal LV wall thickness >15 mm. However, it should be underscored that in principle, any degree of wall thickness is compatible with the presence of the HCM geneticsubstrate.
In order to establish the diagnosis of HCM, a systematic echocardiography approach is necessary. The echocardiographic examination should include.
Additional novel echocardiographic modalities add for better understanding of subclinical LV damage. Transthoracic echocardiography is recommended as a component of the screening algorithm for family members of patients with HCM.
Hypertrophy preferentially involves the interventricular septum in the basal LV segments but often extends into the lateral wall, posterior septum and LV apex. Although HCM is typically characterised by asymmetric septal hypertrophy (ASH), almost any myocardial segment may be involved. The following two-dimensional (2D) echocardiographic criteria are used to aid diagnosis:
Nevertheless, genotype positive adults (including those who die suddenly) may have normal or near normal wall thickness. Assessing the extent and severity of hypertrophy must include the measurement of maximal wall thickness in all LV segments from base to apex, ensuring that the wall thickness is recorded at mitral, mid-LV and apical levels. It is important to recognise however, that asymmetric left ventricular hypertrophy (LVH) in itself is not pathognomonic of HCM but may be encountered in a variety of congenital or acquired conditions, including right ventricular hypertension, systemic hypertension, aortic stenosis, septal sarcomas, Fabry disease, Freidreich's ataxia, mucopolysaccharide or glycogen storage disorders and amyloidosis.
Associated abnormalities of left ventricular outflow tract:The pathophysiology of HCM is complex and consists of multiple interrelated abnormalities, including LVOT obstruction, diastolic dysfunction, mitral regurgitation, myocardial ischemia, and arrhythmias (4). It is clinically important to distinguish between the obstructive and nonobstructive forms of HCM because management strategies are largely dependent on the presence or absence of symptoms caused by obstruction. For HCM, it is the peak instantaneous LV outflow gradient rather than the mean gradient that influences treatment decisions. Up to one third of patients with HCM will have obstruction under basal (resting) conditions (defined as gradients ≥30 mm Hg). Another one third will have labile, physiologically provoked gradients (<30 mm Hg at rest and ≥30 mm Hg with physiologic provocation) (5). The final one third will have the nonobstructive form of HCM (gradients <30 mm Hg at rest and with provocation). Marked gradients ≥50 mm Hg, either at rest or with provocation, represent the conventional threshold for surgical or percutaneous intervention if symptoms cannot be controlled with medications. The presence of SAM is documented using M-mode echocardiography and is characterised by mid-systolic notching of the aortic valve and contact of the anterior mitral valve leaflet/chordae with the septum. In obstructive HCM, IVS is much wider, with smaller LV cavity, and greater incidence of mitral insufficiency, generally directed towards the posterior wall of the left atrium, and a larger tendency to calcify the mitral annulus. Obstruction to LV outflow is dynamic, varying with loading conditions and contractility of the ventricle. Increased myocardial contractility, decreased ventricular volume, or decreased afterload increase the degree of subaortic obstruction. Most recent studies that explain the mechanism of the outflow tract gradient in HCM emphasise that during ventricular systole, flow against the abnormally positioned mitral valve apparatus results in drag force on a portion of the mitral valve leaflets, which pushes the leaflets into the outflow tract. When a gradient is detected in the LV cavity, it is important to systematically exclude obstruction that is unrelated to SAM, including sub-aortic membranes, mitral valve leaflet abnormalities and mid-cavity obstruction, particularly when interventions to relieve LV outflow obstruction are contemplated.
Identification of LVOTO is important in the management of symptoms and assessment of sudden cardiac death risk. 2D and Doppler echocardiography during a Valsalva manoeuvre in the sitting and semi-supine position—and then on standing, if no gradient is provoked—is recommended in all patients (6,7). Exercise stress echocardiography is recommended in symptomatic patients if bedside manoeuvres fail to induce LVOTO ≥50 mm Hg. Pharmacological provocation with Dobutamine is not recommended, as it is not physiological and can be poorly tolerated. Similarly, nitrates do not reproduce exercise induced gradients and should be reserved for patients who cannot perform physiologically stressful procedures. Midsystolic notching, coarse systolic fluttering of the aortic valve, and fibrotic septal changes at the level of leaflet- septal contact are related echocardiographic features in obstructive HCM.
Systolic anterior motion of the mitral valve nearly always results in failure of normal leaflet coaptation and mitral regurgitation, which is typically mid-to-late systolic and inferolaterally oriented. The presence of a central- or anteriorly directed jet of mitral regurgitation should raise suspicion of an intrinsic mitral valve abnormality and prompt further assessment with TOE if necessary.
Left atrial (LA) volume is largely determined by the presence of diastolic dysfunction, mitral regurgitation, and atrial myopathy. Although LA enlargement as assessed from linear dimensions was shown to independently predict long-term prognosis in patients with HCM, it is important to recognize that linear dimensions, may misrepresent true LA size, because this chamber frequently remodels asymmetrically. The American Society of Echocardiography/EAE recommends indexing LA volume (derived from biplane area length or method of disks) to body surface area for quantification of LA size (normal indexed LA volume = 22 ± 6 ml/m2). LA volume has been found to be a long-term independent indicator of functional capacity and an LA volume index of >34 ml/m2 has been shown to be predictive of a greater degree of LVH, severity of diastolic dysfunction, and adverse cardiovascular outcomes.
Ejection fraction usually is preserved despite significant impairment of longitudinal c contractile function, evidenced by attenuation in sy stolic annular velocities, strain and strain rate. With the use of strain imaging, it is now possible to identify regional heterogeneity in contractile function, an important advance in our understanding of myocardial mechanics in HCM. Terminally in the disease process, myocardial fibrosis may result in progressive impairment of systolic function end-stage HCM. Deterioration of systolic function has also been associated with increased mortality (up to 11% per year) and sudden cardiac death. A thorough assessment of systolic function by means of a biplane Simpson’s ejection fraction and tissue Doppler imaging (TDI)-derived systolic velocities should be performed in the basal inferoseptal and anterolateral walls routinely in all patients at initial diagnosis and on subsequent scans. In patients with HCM systolic function is typically normal or supernormal regardless of the presence of LVOT obstruction.
Assessment of diastolic function: Patients with HCM often have diastolic dysfunction, mostly indicating impaired myocardial relaxation regardless of symptoms or presence of LV outflow obstruction. Assessment of LV filling pressures is helpful in the evaluation of symptoms and disease staging. Doppler echocardiographic parameters are sensitive measures of diastolic function, but are influenced by loading conditions, heart rate and age. Therefore, a comprehensive evaluation of diastolic function, including Doppler of mitral valve inflow, tissue Doppler velocities at the mitral annulus, pulmonary vein flow velocities, pulmonary artery systolic pressure and LA size and volume is recommended as part of the routine assessment of HCM. Patients with a restrictive LV filling pattern may be at higher risk for adverse outcome, even with a preserved ejection fraction (EF).
TDI has become standard in most tertiary centres managing patients with cardiomyopathies. Systolic velocities are attenuated in HCM despite a preserved or supranormal ejection fraction, even in myocardial segments which do not demonstrate overt hypertrophy. The early-diastolic mitral annular velocity (Ea) is reduced in HCM patients with the degree of attenuation related to the magnitude of hypertrophy. TDI may also help in the differentiation of various conditions resulting in LVH, with demonstrable differences in TDI velocities between conditions of physiological hypertrophy (athlete’s heart) and pathological hypertrophy. Mean systolic annular motion Sa <9 cm/s is parameter for differentiating pathological LVH (HCM/hypertensive LVH) from physiological LVH (diagnostic accuracy of 92%). In a recent report of patients with established HCM, low lateral mitral annular systolic velocity (<4 cm/s) was found to have prognostic value and independently predicted death or hospitalization for worsening heart failure. However, tissue Doppler imaging is angle-dependent technique, influenced by cardiac translational motion and tethering. The evolution of newer echocardiographic technologies such as strain imaging, speckle tracking, and 3D echocardiography (3D-E) has revolutionized the assessment of cardiac performance from assessment of ejection fraction to a more sophisticated assessment of regional cardiac mechanics. These advances have facilitated preclinical diagnosis, improved risk stratification and our understanding of therapeutic options for HCM.
2D strain allows spatial and temporal tracking of longitudinal, circumferential and radial myocardial deformation. Its ability to provide angle-independent measures of LV strain is advantageous. Studies in patients with HCM have demonstrated a reduction in longitudinal strain with basal to apical gradient, an increase in circumferential strain, normal systolic twist or torsion, and reduction in untwisting in diastole. Another study showed significantly decreased longitudinal, circumferential, and radial strains in patients with HCM compared to a healthy control group (23.3±17% vs. 27.2±14.9%, 16.8±7.1% vs.19.65.2%, 25.2 ±13.9% vs. 36.8 ±17.2%, respectively. Significant reductions in strain in the septal segments (particularly the mid-septal segment), correlate with the septal/posterior wall ratio (10). Longitudinal deformation abnormalities are often focal or subsegmental and may be underestimated if careful spatial mapping is not used. Because of its intrinsic ability to provide angle-independent strain data, 2D strain holds a unique advantage over tissue Doppler-derived strain, which is particularly important for myocardial deformation analysis in the apical LV segments.
3D-echocardiography has provided insights into the mechanics of SAM and deformational geometry of the LV outflow tract. This method facilitates the assessment of LVOT area after intervention for septal reduction,surgical myectomy, volumetric estimates of left atrial mechanical function, and accurate estimation of LV ejection fraction as well as LV mass in hypertrophied hearts (comparing favorably with CMR imaging).
Transoesophageal echocardiography should be considered in patients with poor transthoracic echo windows, as an alternative or complementary investigation to CMR. It is particularly useful in patients with LVOTO if the mechanism is unclear, when assessing the mitral valve apparatus before a septal reduction procedure, and when severe mitral regurgitation caused by intrinsic valve abnormalities is suspected. In patients undergoing septal myectomy, perioperative TEE should be used to guide the surgical strategy and to detect surgical complications (ventricular septal defect and aortic regurgitation (AR)) and residual LVOTO. Following myectomy, intraoperative TEE studies can confirm the adequacy of myectomy and quantitate residual gradients, severity of mitral and aortic regurgitation, ventricular function, and development of a ventricular septal defect (8).
Contrast echocardiography currently is used to enhance endocardial definition, Doppler signals, and to evaluate myocardial perfusion. Myocardial contrast echocardiography can help anticipate the location and delineate the extent of septal infarct (selective injection of contrast into septal perforators) before alcohol septal ablation.
Interventricular and intraventricular delays are commonly present in patients with HCM, despite the absence of conduction abnormalities on the electrocardiogram, and appear to correlate to the degree of septal LVH and the presence of LV outflow obstruction. The prevalence and degree of LV dyssynchrony was significantly greater in patients with HCM compared with hypertensive LVH and age-matched control patients. Another study of 123 patients with HCM found that an intraventricular delay of >45 ms, predicted an increased risk for ventricular tachyarrhythmias and sudden cardiac death at 5-year follow-up (85.5% sensitivity; 90.4% specificity; positive predictive value: 66.9%; negative predictive value: 96.7%; test accuracy: 88.8%) (11,12).
Several echocardiographic parameters given below, are also important for prediction of unfavourable outcome in HCM patients (13).
Differential diagnosis between HCM and physiologic non-pathologic left ventricular (LV) hypertrophy associated with physical training (commonly referred to as ‘‘athlete’s heart’’) has important implications, because identification of cardiovascular diseases associated with sudden death may be the basis for disqualification from competition to minimize risk. Conversely, improper over-diagnosis of cardiac disease may lead to unnecessary withdrawal from athletics. Echocardiography is one of the most important methods for differentiation between pathologic and physiologic left ventricular hypertrophy (14).
Criteria favoring HCMP:
Common diagnostic challenges include the following:
Conventional echocardiography (TTE) is the most readily accessible and informative tool in making the diagnosis of HCM. It is also the first noninvasive imaging method for risk stratification, treatment selection and follow up of the patients. Two-dimensional strain is a simple, rapid, and reproducible method to early detection of abnormalities in patients with HCM that have apparently normal left ventricular systolic function.
Figure 1. Parasternal long-axis view showing severe asymmetric septal hypertrophy
Figure 2. M-mode across the mitral leaflets showing the presence of systolic anterior motion of the anterior mitral leaflet (SAM)
Figure 3. Late-peaking dynamic left ventricular outflow tract obstruction after the Valsalva maneuver
Figure 4.Two-dimensional strain (quad format) images showing paradoxical apical longitudinal strain and corresponding abnormalities in the color M-mode of the parametric strain map. Loss of base-apex (strain) gradient is present.
1 - 2011 ACCF/AHA Guidelines for the Diagnosis and Treatment of Hypertrophic Cardiomyopathy: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. Gersh BJ, Maron BJ, Bonow RO, et al. J Thorac Cardiovasc Surg. 2011 Dec;142(6):e153-203. 2 - 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy: the Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC). Eur Heart J. 2014 Oct 14;35(39):2733-79. 3 - Echocardiography in hypertrophic cardiomyopathy: the role of conventional and emerging technologies. Afonso LC, Bernal J, Bax JJ, Abraham TP. JACC Cardiovasc Imaging. 2008 Nov;1(6):787-800 4 - Obstructive and non-obstructive hypertrophic cardiomyopathy: clinical, electrocardiographic, and echocardiographic differences. Almenar L et al. Rev Esp Cardiol. 1996 Jun;49(6):423-31. 5 - What is really a nonobstructive hypertrophic cardiomyopathy? The importance of orthostatic factor in exercise echocardiography. Cotrim C, Almeida AR, Lopes L, Fazendas P, João I, et al. (2011) Volume 2011 (2011), Article ID 346797, 4 pages. 6 - Clinical implications of midventricular obstruction in patients with hypertrophic cardiomyopathy. Minami Y, Kajimoto K, Terajima Y, et al. J Am Coll Cardiol. Jun 7 2011;57(23):2346-55. 7. Echocardiography in the treatment of hypertrophic cardiomyopathy. Musat D, Sherrid MV. Anadolu Kardiyol Derg. Dec 2006;6 Suppl 2:18-26 8. Hypertrophic cardiomyopathy: current understanding and treatment objectives. Soor GS, Luk A, Ahn E, Abraham JR, Woo A, Ralph-Edwards A, et al. J Clin Pathol. 2009 Mar;62(3):226-35 9. Differentiation between pathologic and physiologic left ventricular hypertrophy by tissue Doppler assessment of long-axis function in patients with hypertrophic cardiomyopathy or systemic hypertension and in athletes. Vinereanu D, Florescu N, Sculthorpe N, Tweddel AC, Stephens MR, Fraser AG. Am J Cardiol. 2001 Jul 1;88(1):53-8. 10. Global and regional myocardial function quantification by two-dimensional strain: application in hypertrophic cardiomyopathy.Serri K, Reant P, Lafitte M, et al.. J Am Coll Cardiol 2006;47:1175– 81 11. Prognostic value of intra-left ventricular electromechanical asynchrony in patients with mild hypertrophic cardiomyopathy compared with power athletes. D'Andrea A et al. Br J Sports Med. 2006 Mar;40(3):244-50 12. ACC/AHA/HRS 2008 guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: executive summary. Epstein AE, Dimarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. Heart Rhythm. Jun 2008;5(6):934-55 13. Risk stratification for sudden cardiac death in hypertrophic cardiomyopathy: systematic review of clinical risk markers. Christiaans, van Engelen K, van Langen IM, Birnie E, Bonsel GJ, Elliott PM, Wilde AA. Europace. 2010 Mar;12(3):313-21 14. Distinguishing hypertrophic cardiomyopathy from athlete's heart physiological remodelling: clinical significance, diagnostic strategies and implications for preparticipation screening. Maron BJ. Br J Sports Med. 2009 Sep;43(9):649-56
Dr Irena Peovska University Cardiology Clinic Skopje, Macedonia
Author's disclosures: None declared.