How to Image Hypertrophic Cardiomyopathy.

Abstract

HomeCirculation: Cardiovascular ImagingVol. 10, No. 7How to Image Hypertrophic Cardiomyopathy Free AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplemental MaterialFree AccessReview ArticlePDF/EPUBHow to Image Hypertrophic Cardiomyopathy Martin S. Maron, MD, Ethan J. Rowin, MD and Barry J. Maron, MD Martin S. MaronMartin S. Maron Search for more papers by this author , Ethan J. RowinEthan J. Rowin Search for more papers by this author and Barry J. MaronBarry J. Maron Search for more papers by this author Originally published12 Jul 2017https://doi.org/10.1161/CIRCIMAGING.116.005372Circulation: Cardiovascular Imaging. 2017;10:e005372A 48-year-old man, with only a history of mild systemic hypertension, was initially evaluated after presenting with symptoms of exertional dyspnea occurring predominantly with inclines. At that time, an abnormal 12-lead ECG was obtained demonstrating left ventricular hypertrophy by conventional voltage criteria, prompting additional testing with a 2-dimensional echocardiogram that showed normal systolic function (ejection fraction=65%), with 14-mm ventricular septal thickness and 12 mm in the posterolateral wall, and mild systolic anterior motion (SAM) of the mitral valve (bend of anterior leaflet into outflow tract without septal contact). A stress nuclear stress test showed no myocardial ischemia at rest or at peak exercise with a normal blood pressure response and no arrhythmias or ST-T changes during exercise or in recovery. The patient was prescribed a β-blocker for treatment of systemic hypertension.During the next 2 years, the patient developed more limiting exertional symptoms with routine activities. β-Blocker dosage was increased, and a repeat echocardiogram demonstrated similar findings to the initial study, borderline left ventricular (LV) wall thickness despite well-controlled blood pressure. The abnormal ECG, and mild SAM at rest, raised consideration for a diagnosis of hypertrophic cardiomyopathy (HCM) and management for limiting heart failure symptoms.Diagnosis and Phenotypic CharacterizationHCM is often suspected in a patient based on the presence of cardiovascular symptoms, detection of abnormal ECG, systolic ejection murmur on routine examination, or as part of pedigree screening.1,2 Abnormalities on ECG are present in >90% of patients with HCM, although no specific ECG pattern is pathognomonic.1 Clinical diagnosis of HCM can reliably be made in the majority of patients with 2-dimensional transthoracic echocardiography by imaging increased LV wall thickness (≥15 mm) with a nondilated cavity in the absence of any disease known to cause LV hypertrophy of that magnitude (ie, systemic hypertension or aortic stenosis).1–5 In certain situations, mild increases in LV wall thickness can be considered diagnostic (13–14 mm), including in relatives of patients with HCM.1,2 Increased RV wall thickness is present in over one third of HCM patients (ie, ≥8 mm), although its prognostic significance is uncertain.6 The superior spatial resolution of cardiovascular magnetic resonance (CMR) can provide reliable determination of RV hypertrophy, although particular care should be taken to exclude epicardial fat, pericardium, and trabeculations.Maximal LV wall thickness measurements should be assessed perpendicular to the ventricular septum in either the parasternal long-axis or short-axis imaging planes, and the measurement derived from the LV segment with greatest thickness within the chamber.3,4 Overestimation of LV wall thickness can occur if the crista supraventricularis, a prominent right ventricular (RV) muscle structure that originates in the RV apex and transects the cavity to insert on the ventricular septum, is not recognized and included in the transdimensional measurement of basal ventricular septal thickness.6 The crista is often identified with echocardiography (and particularly with CMR) on the basal short-axis images and observed to separate from the septum in systole allowing the endocardial borders of the ventricular septum to be clearly delineated, thereby providing accurate assessment of septal wall thickness.6Occasionally, a diagnosis of HCM is suspected based on a patient’s clinical profile but imaging with echocardiography is technically suboptimal or LV wall thickness measurements are borderline. CMR should be performed in these situations to clarify diagnosis by providing the opportunity for precise and reliable wall thickness measurements by virtue of sharp contrast between bright blood and dark myocardium with high spatial resolution imaging (Figure 1).5,7,8 Particularly in those HCM patients with increased wall thickness confined to the anterolateral wall, apex, and posterior septum.5,7,8 In patients in whom distal LV chamber is not well visualized or there is concern for increased apical wall thickness, and CMR is not available, contrast echocardiography should be performed (Figure 2).3,4Download figureDownload PowerPointFigure 1. Advantage of cardiovascular magnetic resonance (CMR) compared with 2-dimensional echocardiography (2DE). A, 2DE. Anterolateral left ventricular (LV) free wall is 18 mm; epicardial border and adjacent extracardiac structures are not well defined (asterisks). B, CMR in the same patient shows well-delineated border of anterolateral LV wall (arrowheads), which is massively thickened (35 mm), creating a SD risk factor. C, 2DE. Posterior ventricular septal (VS) thickness is 21 mm (asterisk). D, CMR in same patient; massive hypertrophy (41 mm; asterisk) creating a SD risk marker. E, 2DE. Maximal LV wall thickness measurement is ambiguous as anterior LV wall border not well defined. F, CMR in same patient clearly delineates LV border providing reliable measurement of massive hypertrophy (30 mm) of anterior wall. Reprinted from Maron8 with permission of the publisher. Copyright © 2012. SD indicates sudden death; RV, right ventricle; and VS, ventricular septum.Download figureDownload PowerPointFigure 2. Morphological abnormalities of the left ventricular (LV) apex more reliably identified by contrast echocardiography and cardiovascular magnetic resonance (CMR) in patients with hypertrophic cardiomyopathy (HCM), implications for management. A–E, Lower risk apical hypertrophy. A, Abnormal 12-lead ECG pattern. B, Four-chamber echocardiogram shows normal LV wall thickness. C, In the same patient, opacification of LV chamber with echocardiographic contrast demonstrates regional area of increased wall thickness at apex of 16 mm (asterisks). D, High-resolution CMR imaging confirms apical hypertrophy (asterisks). E, Contrast CMR images show no late gadolinium enhancement (LGE), consistent with the absence of myocardial scarring, associated with lower risk for sudden death events. F–J, Higher risk LV apical aneurysm. F, Abnormal 12-lead ECG pattern; G, Four-chamber echocardiogram shows increased LV wall thickness at mid-LV level but no apical aneurysm (arrow heads). H, In same patient, opacification of LV chamber with echocardiographic contrast demonstrates medium-sized thin-wall apical aneurysm (arrowheads) with associated hour-glass–shaped LV chamber with regional area of increased wall thickness at mid-LV level of 16 mm (asterisks). I, High-resolution CMR imaging confirms apical aneurysm (arrowheads). J, Contrast CMR images show transmural LGE of aneurysm rim (arrowheads) with contiguous extension into the inferior (short arrow) and anterior LV walls (long arrow), a potential nidus of monomorphic VT. In addition, marked signal intensity contrast between the bright aneurysm rim and hypointense mass (yellow arrow) confirms presence of a thrombus in the apical aneurysm that was not seen on echocardiography, raising consideration for stroke prophylaxis with anticoagulation. LA indicates left atrium; RV, right ventricle.HCM Versus Hypertensive CardiomyopathyDifferentiation of phenotypes corresponding to HCM or alternatively to pressure overload conditions (eg, systemic hypertension) can be challenging solely from an imaging standpoint with echocardiography and CMR, given the considerable morphological overlap between the 2 conditions.9 However, LV wall–thickening patterns that are clearly asymmetrical, in which all or most LV segments do not demonstrate the same or similar thicknesses, is most consistent with HCM, particularly when noncontiguous areas of focal hypertrophy are evident with CMR.8On the contrary, pressure overload most often produces more symmetrical (or concentric) patterns of LV wall thickness in which all segments of the wall seem to have identical or similar thicknesses. A limitation for reliably making this diagnostic distinction of asymmetrical versus symmetrical hypertrophy is the lack of consensus criteria for this morphological differentiation.9 Nevertheless, useful features that can favor the HCM phenotype versus systemic hypertension are LV wall thickness >18 mm and mitral valve systolic anterior motion with septal contact.8,9 Also, treatment with antihypertensive drugs producing regression of LV hypertrophy would favor a diagnosis of hypertensive heart disease.– CMR can be used to clarify HCM diagnosis or the extent of wall thickness in those patients in whom LV hypertrophy measurements remain uncertain or borderline with 2-dimensional echocardiography, whereas contrast echocardiography considered in patients in whom there is concern for apical hypertrophy and CMR is not available.– Overestimation of LV wall thickness can occur if RV muscle structures are included in ventricular septal measurement, while high spatial resolution imaging with CMR can reliably aid in differentiating these structures and provide accurate LV wall thickness measurements.Sudden DeathAfter confirmatory diagnosis, assessment of sudden death risk is a critical component of the routine evaluation of all HCM patients (Figure 3). Currently, 2011 ACC/AHA expert consensus guidelines recommend identification of high-risk patients based on the presence of noninvasive conventional risk factors.1 With particular relevance for the cardiovascular imager is the requirement to provide reliable wall thickness measurements because massive LV hypertrophy (≥30 mm) is a risk factor that can itself be sufficient, even in the absence of other conventional risk markers, to consider a patient to be at unacceptably high risk and offer primary prevention implantable cardioverter defibrillator therapy (Figure 3).1–4,10 In addition, the linear relationship between wall thickness and sudden death risk in HCM10 also suggests that less extensive wall thickness measurements, which approach 30 mm, can inform sudden death risk.1 In this regard, consideration should be given to incorporating CMR into the initial evaluation of HCM patients to ensure accurate wall thickness measurements, particularly because in some patients extent and magnitude of hypertrophy can be underestimated by echocardiography, particularly when present in the anterolateral wall or apex (Figures 1 and 2).1,2,5,7,8 Calculated LV mass has not emerged as an independent predictor of sudden death events.11Download figureDownload PowerPointFigure 3. Flow diagram outlining the role of imaging in hypertrophic cardiomyopathy (HCM) management strategies. *Patients without LV outflow tract gradient (<30 mm Hg) at rest should undergo stress (exercise) echocardiography. †No data on benefit of pharmacological therapy, although β-blockers are often administered prophylactically in clinical practice. **β-Blockers, calcium channel antagonists, and possibly diuretics administered judiciously. ‡Usually, β-blockers or calcium channel antagonists (verapamil), or disopyramide. ΩCalcium channel antagonists or alternatively β-blockers. αGenerally regarded as ≥30 mm Hg outflow gradient, but ≥50 mm Hg when septal reduction intervention is considered (ie, septal myectomy and alcohol ablation). βNo or trivial (<30 mm Hg) outflow gradient at rest and with exercise. ¥≥15% of total LV mass. €Assessment of LV filling pressures should take into account transmitral Doppler flow velocities, pulmonary venous flow velocity, mitral deceleration time, estimated pulmonary artery pressures, left atrial size, and myocardial strain imaging. §Includes anomalous papillary muscle insertion directly into anterior mitral leaflet and aberrant LV muscle bundles. ASA indicates alcohol septal ablation; LGE, late gadolinium enhancement; LVOT, left ventricular outflow tract; and MV, mitral valve. Reprinted from Maron and Maron5 with permission of the publisher. Copyright © 2015.More recently, the European Society of Cardiology has promoted a novel score for risk stratification,2 which takes into account many clinical variables some of which are not considered in the ACC/AHA guidelines, including assessment of outflow tract obstruction. However, the US/Canadian guidelines have emphasized the difficulty in using obstruction as an independent risk marker in HCM, given the highly dynamic nature of gradients and the fact they can be mitigated or eliminated with drug therapy or invasive treatment.1 Left atrial size assessed with transdimensional measurement is also included in the ESC risk score, although the independent relationship between left atrial size and sudden death risk in HCM is unresolved and therefore itself is not a measurement used to dictate management decisions for sudden death prevention.1A relatively uncommon but important phenotypic subgroup, which falls outside the traditional risk stratification algorithm, are HCM patients with LV apical aneurysm formation (sometimes associated with midcavity hypertrophy and outflow obstruction).12 Aneurysms are considered a high-risk phenotype based on increased likelihood of adverse disease-related consequences, including sudden death and thromboembolism (Figure 2). Because imaging the distal portion of the LV chamber may be limited with echocardiography in some patients, a high index of suspicion is required for detection of the aneurysm and potential apical thrombus, requiring CMR, or if not available, contrast echocardiography(Figure 2).12More recently, there has been increasing interest in identifying patients at risk for sudden death by imaging the underlying abnormal myocardial substrate of fibrosis with contrast-enhanced CMR.13–17 After intravenous injection, gadolinium will accumulate in areas of expanded extracellular space within the myocardium (Figure 4), likely representing myocardial fibrosis,18 imaged as late gadolinium enhancement (LGE), and expressed as percent of LV mass. Cross-sectional studies have demonstrated a strong association between LGE and increased risk for ambulatory nonsustained ventricular tachyarrhythmia,13 suggesting that LGE may represent a structural nidus for ventricular tachyarrhythmias in HCM (Figure 4). Many longitudinal studies assessing LGE in HCM cohorts have been analyzed in a pooled manner, demonstrating a strong relationship between the amount of LGE and risk of a sudden death event (Figure 4).14 On the basis of these observations, extensive LGE occupying ≥15% of LV mass may identify HCM patients at increased risk for sudden death (even without conventional risk factors) and who may benefit from primary prevention therapy (Figure 3); absent or focal LGE associated with low risk.5,14,15 In addition, extensive LGE can act as an arbitrator to resolve decision making on ICDs in patients who reside in a gray area of ambiguity in which future risk is difficult to define precisely, with extensive LGE swaying toward a decision of ICD and no or minimal LGE potentially away from device therapy (Figure 3).5,15Download figureDownload PowerPointFigure 4. Relationship between late gadolinium enhancement and sudden death risk in hypertrophic cardiomyopathy (HCM). A and B, Contrast-enhanced cardiovascular magnetic resonance (CMR) images in 2 different HCM patients, each with extensive late gadolinium enhancement (LGE) throughout the ventricular septum (arrows). C, NSVT on 24-h Holter ECG is 7-fold more common in HCM patients with LGE as compared with those without LGE. D, Relation between extent of LGE and sudden death events in 1293 patients with HCM. Reprinted from Chan et al15 with permission of the publisher. Copyright © 2014. LA indicates left atrium; LV, left ventricle; and RV, right ventricle.Of note, the pattern of LGE in HCM is diverse, and therefore, it is not possible to predict outcome based on LGE distribution. LGE confined to areas of confluence between RV and septum is limited in size and is associated with lower risk for sudden death, similar to patients with no LGE. This observation is likely because of the fact that LGE localized to this area does not represent myocardial scarring but rather an expanded extracellular matrix because of confluence of intersecting LV and RV myofibrils.17.T1 mapping is a novel, emerging CMR technique, which provides a noninvasive assessment of expanded extracellular space within the myocardium.19 Extracellular volume fraction has emerged as a promising measure of the extracellular matrix and is calculated by measuring longitudinal relaxation (T1) of the myocardium before (native T1) and after injection of gadolinium. Currently, many small-scale studies have found significant correlations between extracellular volume fraction values and collagen volume fraction quantified from histopathology obtained from LV tissue obtained from patients with HCM.19The early clinical experience with T1 mapping in HCM has largely been confined to differentiating HCM from other cardiovascular disease. Extracellular volume fraction values have been found to be significantly higher in HCM patients compared with patients with LV hypertrophy secondary to cardiac amyloidosis or Fabry disease.20,21 However, in the absence of clinical outcome studies, there is currently no role for T1 mapping in risk assessment. Further clarification of many of these CMR-based issues in HCM will emerge from the international multicenter HCMR study (Hypertrophic Cardiomyopathy Registry).22– Massive LV wall hypertrophy is an important marker of increased risk for sudden death in HCM, and consideration should be given to CMR to provide reliable measurements of wall thickness.– HCM patients with LV apical aneurysm represent a high-risk subgroup, and CMR, or alternatively contrast echocardiography, should be performed for reliable identification.– Extent of LGE by contrast-enhanced CMR may help identify high-risk patients who have none of the traditional risk markers and help resolve complex ICD decision making in patients whose high-risk status remains uncertain after assessment with the traditional risk markers.Special Considerations: CMR in HCMThe last decade has seen enormous penetration of CMR into routine clinical cardiovascular practice, although some challenges still persist with regard to image analysis and interpretation when applying CMR to a complex, heterogeneous genetic heart disease such as HCM. There is currently no expert consensus on standardization in 2 key areas: (1) protocol for CMR image acquisition in HCM and (2) analysis and interpretation of clinically relevant morphology, the most visible of which is LGE. Specific examples include– Determination of wall thickness in all regions of the LV chamber can be impacted by interobserver reader interpretation, which may involve differentiating morphological structures such as crista supraventricularis and LV papillary muscles/trabeculations from the LV wall.– Considerations related to quantification of LGE can be more complex. The study by Chan et al15 established the management principle for LGE in HCM and sudden death risk stratification—that is, that it is not the presence of LGE that is important, but rather the extent and distribution of LGE in the LV as expressed by the percent of LV mass. Quantification of LGE was formulated using a standardized core laboratory study design to establish reproducible measurements.– Nevertheless, the persistent challenge lies with translating the core laboratory experience to the many CMR laboratories outside of the academic realm because of the current lack of standardization involving (1) differences in magnetic resonance imaging scanner hardware and software; (2) diverse LGE protocols with lack of agreement on the most appropriate technique to quantify LGE; (3) use of different types and dosage protocols for gadolinium contrast; and (4) inconsistent optimization of inversion times and properly nulled LV myocardium.– On the basis of the data given by Chan et al,15 we use a grayscale threshold 6 SD above the mean signal intensity of nulled myocardium to quantify LGE (Data Supplement), although other methods including full-width at half maximum (ie, pixels that are ≥50% the signal intensity of a hyperenhanced area) have also been shown to have high reproducibility.23 However, qualitative estimation of %LGE by visual interpretation can be useful in many cases when routine quantification seems unnecessary.Identification of HCM Patients at Risk for Heart Failure SymptomsLV Outflow Tract ObstructionSubaortic obstruction in HCM is the most common pathophysiologic mechanism leading to limiting heart failure symptoms in this disease (Figure 5).1,2,24–26 Therefore, once HCM diagnosis is confirmed, determining whether a patient has obstruction is fundamental to clarifying natural history and determining appropriate management strategies because patients with obstruction (at rest or with provocation) are candidates for therapies not available to patients without obstruction (Figure 3). β-Blockers or calcium channel blockers are first-line therapies in symptomatic patients with obstruction, and occasionally, disopyramide can be considered.1,2Download figureDownload PowerPointFigure 5. Clinical significance and implications of left ventricle (LV) outflow tract obstruction. A and B, Apical 2-dimensional echocardiography (2DE) and CW Doppler showing absence of systolic anterior motion (SAM) and obstruction at rest. C and D, Intense exercise provokes SAM–septal contact (arrow) and outflow velocity of 5 m/s (100 mm Hg gradient). E, Changes in LV outflow gradient from rest to postexercise showing physiologically provoked gradients in large consecutive cohort (by mechanism in (C) and (D)). F, Patients with outflow gradients ≥30 mm Hg at rest are at greater risk for HCM-related progressive heart failure or heart failure or stroke death. G, Abolition of LV outflow gradient by surgical septal myectomy is associated with long-term survival (with respect to all-cause mortality) similar to that expected in age- and sex-matched general US population and exceeding that in a comparison group of symptomatic nonoperated patients with obstruction. Reprinted from Maron et al26 with permission of the publisher. Copyright © 2014. CW indicates continuous wave; NYHA, New York Heart Association; and RR, relative risk.With echocardiographic imaging, the typical mechanism of subaortic obstruction in HCM can be reliably defined, with SAM of the mitral valve and septal contact (Figure 6).3,4,24 During SAM–septal contact, incomplete coaptation between the anterior and posterior leaflet of the mitral valve can lead to posteriorly directed mitral regurgitation, which is usually mild to moderate in severity (Figure 6).27Download figureDownload PowerPointFigure 6. Transesophageal echocardiography (TEE) to guide surgical myectomy operative strategy. A–C, Preoperative TEE. A, End-diastolic image demonstrating measurements of ventricular septum to plan depth and extent of muscular resection necessary to achieve optimal relief of outflow obstruction including maximal thickness at point of systolic anterior motion (SAM)–septal contact (red dotted line), length from aortic valve plane to point of septal thinning (yellow dotted line), and wall thickness measurement at point of septal thinning (white dotted line). In addition, mitral valve leaflet is substantially elongated (white line), resulting in SAM–septal contact (arrow) more distal in ventricular septum than typical (B). C, Color Doppler in same view as in (B) demonstrating moderate to severe posterior directed mitral regurgitation (arrows) because of SAM and gap between anterior and posterior mitral valve leaflets. D–F, Postoperative TEE. D, End-diastolic image demonstrating extended septal myectomy trough with basal septal thickness reduced (red dotted-lines) and shortening (ie, plication) of elongated anterior mitral leaflet (white line). E, In midsystole, systolic anterior motion of the mitral valve is absent (arrow). F, In same view as (E), color Doppler imaging demonstrates trace mitral regurgitation (arrow).Continuous-wave Doppler techniques are conventionally used to reliably estimate maximal instantaneous gradient using the peak LV outflow tract velocity (Figure 5).3,4 Because contamination of the outflow tract Doppler profile by the mitral regurgitation jet will result in overestimation of the outflow tract gradient,24,28 particular care should be taken to differentiating these 2 distinct Doppler profiles. Doppler systolic flow patterns representative of LV outflow gradients characteristically demonstrate gradual increase in velocity in early systole with acceleration and peaking in midsystole (dagger-shaped).28 In contrast, the mitral regurgitation signal begins abruptly at the onset of systole and rapidly establishes markedly increased velocity (usually >6 m/s), which persists throughout systole (bell-shaped).28 Occasionally, HCM patients with typical subaortic obstruction will also have coexistant aortic stenosis, making assessment of aortic valve disease challenging because of altered outflow tract flow dynamics. Planimetry of aortic valve area by TEE can be considered in such situations to clarify severity of aortic stenosis.3In patients with resting outflow tract gradients ≥50 mm Hg, provocative maneuvers appears unnecessary for the purpose of making management decisions and probably contraindicated because the association between substantial gradients and limiting symptoms is already been established.1 For those patients without obstruction under resting conditions, exercise (stress) echocardiography is generally the preferred method for provoking physiological gradients with a symptom-limited Bruce treadmill protocol (Figures 3 and 5).1,2,24 Outflow gradients are assessed in the recovery period while supine, although there seems to be little difference in the magnitude of outflow gradients obtained upright at peak exercise compared with immediately after exercise in the supine position.25 Consideration should be given to holding cardiovascular drugs before assessment of outflow tract gradients to provide a pure assessment of an individual HCM patient’s propensity to generate obstruction. However, in many patients, withdrawal of medication may not be a practical strategy in the clinical arena for a variety of reasons.Pharmacological agents (eg, amyl nitrite, dobutamine, or isoproterenol), administered during the echocardiographic study, or in the catheterization laboratory, to provoke subaortic gradients, are nonphysiological and may not reliably represent gradients incurred by patients during daily physical activities or may well under- or overestimate magnitude of the outflow gradient compared with physiological exercise.29With respect to Valsalva, the one nonphysiological maneuver performed routinely with echocardiography, normal velocities observed with this method do exclude outflow obstruction because ≈50% of such patients will generate gradients with physiological exercise.24 Alternatively, increased Valsalva velocities consistently predict outflow gradients generated with exercise, although the magnitude of gradients are significantly underestimated by Valsalva compared with exercise (by 25–65 mm Hg).24 Therefore, in patients who can exercise, Valsalva does not seem to provide additional management information. However, in selected candidates for septal reduction who cannot perform exercise echocardiography because of comorbidities, a positive Valsalva maneuver can be considered sufficient evidence of the capability to generate outflow tract obstruction.24 With Valsalva maneuver, LV outflow gradients should be acquired ≈5 to 10 seconds after forced expiration, when venous return is significantly reduced and stroke volume is lowest.The presence of an exercise-induced outflow gradient creates treatment options in symptomatic patients aimed at mitigating or eliminating obstruction, including invasive septal reduction therapies, underscoring the importance of performing this test as part of the routine evaluation of HCM patients without rest obstruction (Figure 3).1–3,24,29 This principle can also be extended to asymptomatic HCM patients because an outflow gradient identifies patients who are at greater likelihood of developing limiting symptoms and should be followed longitudinally to anticipate changes in clinical state that could justify therapeutic intervention.24,29 In addition, β-blockers have been demonstrated to mitigate provocable gradients and could be considered for this purpose in asymptomatic obstructive HCM patients with the potential to decrease (or possibly delay onset) future functional disability. Serial assessment of outflow tract gradients should be performed as part of annual evaluations or if there is a change in clinical status that suggests a potential and clinically relevant change in the magnitude of the outflow gradient.1,2Patient Selection and Planning for Septal ReductionHCM patients with outflow tract gradients of ≥50 mm Hg at rest, or with provocation, and drug-refractory advanced heart failure symptoms become candidates for relief of obs