Vector U loop in patients with idiopathic cardiomyopathy

The U loops of vectorcardiograms were recorded in 50 normal subjects, 10 patients with dilated cardiomyopathy (DCM group), and 83 patients with hypertrophic cardiomyopathy (HCM group). The HCM group was divided into three subgroups: those with obstructive hypertrophic cardiomyopathy (HOCM), nonobstructive hypertrophic cardiomyopathy (HNCM), and apical hypertrophy (APH). The spatial characteristics of the U loop were examined qualitatively and quantitatively and were correlated with echocardiographic findings. The magnitude of the U loop was significantly larger in the HCM group, especially in the APH subgroup, than in the normal subjects, but it was not larger in the DCM group. The maximum U vector was significantly displaced anteriorly and to the right in the DCM and HCM groups, especially the APH and HNCM subgroups. In the HNCM and APH subgroups, the magnitude of the U loop correlated significantly with the thickness of the posterior wall of the left ventricle, but not with that of the interventricular septum. These findings suggest that the U loop is related to hypertrophy of the apex and the posterior wall of the left ventricle.     

肥厚型心肌病的节段性室壁运动异常11例报告

目的：报告11例肥厚型心肌病（HCM）伴节段性室壁运动异常（SWMA），以提高对HCM特殊表现的认识。方法：11例均做胸部X线摄片、常规12导联心电图、二维超声心动图、心脏磁共振成像、左室造影和选择性冠状动脉（CA）造影，并对其结果进行对比分析。结果：在11例HCM伴SWMA患者，CA造影均正常，心室肥厚部位在心尖部5例，前壁或前侧壁及室间隔2例，前壁及心尖部1例，前壁1例，普遍性肥厚2例。SWMA位于肥厚部位10例，非肥厚部位1例。结论：SWMA不是冠心病特有的表现，HCM可以引起SWMA。HCM伴SWMA需与冠心病鉴别。     

Hypertrophic cardiomyopathy in the Saudi Arabian population: Clinical and echocardiographic characteristics and outcome analysis

Background

Current published literature on hypertrophic cardiomyopathy (HCM) comes primarily from Western populations. There is no published data on clinical and echocardiographic characteristics and long-term outcome of HCM in an Arab population.

Methods

We conducted a retrospective analysis of all patients 16 years or older diagnosed with HCM at our institution. Detailed clinical and echocardiographic data were collected and outcome was analyzed.

Results

A total of 69 patients were identified as having HCM. The mean age was 42 ± 16 years with 71% male patients. All patients were Saudi citizens with Arab ancestry. Details about family history and presenting symptoms were available for 44 and 48 patients consecutively. Nine (18%) patients were asymptomatic and were diagnosed based on abnormal cardiac auscultation. The commonest presenting symptoms were dyspnea with or without chest pain and palpitations occurring in 40 (81%) patients. Only four (9%) of 44 patients had a family history of HCM and /or sudden cardiac death (SCD). The most common ECG abnormality was left ventricular hypertrophy (LVH) present in 60 (86%) patients. The commonest septal hypertrophy morphology was mid-septal (catenoid) in 30 (43%) followed by neutral in 23 (33%), basal septal (sigmoid) in 3 (4%) and apical in 6 (8%) patients. Twenty (28%) patients had evidence of resting left ventricular cavity gradient of ⩾30 mmHg. Eleven (16%) patients had evidence of biventricular hypertrophy. Left ventricular ejection fraction was normal in 65 (94%) patients. Over a median (25–75 percentile) follow-up of 7 years (4.5–10), only three patients died, all of non-cardiac causes. There were no cases of SCD during the follow-up period. Six patients required an implantable cardioverter-defibrillator (ICD); five for primary prevention and one for secondary prevention. Only one patient progressed to end stage dilated cardiomyopathy.

Conclusion

The natural history of hypertrophic cardiomyopathy in the Saudi population appears to be benign with catenoid morphology being the most common septal hypertrophy pattern. Risk of SCD appears to be quite low in this population.     

Relationship between the QT indices and the microvolt-level T wave alternans in cardiomyopathy.

The relationship between the QT indices and microvolt-level T wave alternans (TWA) is unknown in cardiomyopathy, so the present study examined 86 patients with cardiomyopathy who experienced TWA during exercise testing (EXT). The QT interval (QT), duration from the Q wave to the peak of the T wave (QTp), duration from the peak to the end of the T wave and the dispersion of these parameters were measured by 12-lead electrocardiogram at rest and during EXT. In dilated cardiomyopathy (DCM), TWA was positive (TWA+) in 19 patients and negative (TWA-) in 17. No significant difference was observed between the TWA+ and TWA- groups in any parameter. In hypertrophic cardiomyopathy (HCM), TWA was positive in 24 patients and negative in 12. Max QTc, max QTpc and mean QTpc during EXT in the TWA+ group were significantly longer than those in the TWA- group. The sensitivity of TWA for ventricular tachycardia (VT) was high in DCM and HCM, and that of max QTc >500 ms during EXT for VT was high in HCM (93%). TWA is a useful predictor for VT in DCM and HCM, and prolonged max QTc during exercise has a prognostic value in HCM. Repolarization abnormality during exercise plays an important role in the genesis of VT in cardiomyopathy.     

Rare association of hypertrophic cardiomyopathy and complete atrioventricular block with prompt disappearance of outflow gradient after DDD pacing.

Although arrhythmias are common in hypertrophic cardiomyopathy (HCM), complete atrioventricular (AV) block is very unusual. A 27-year-old female presented with a recent history of syncope and exercise intolerance. ECG demonstrated complete AV block. Two-dimensional Doppler echocardiography revealed HCM with a 60 mmHg left ventricular outflow tract (LVOT) gradient. A temporary transvenous ventricular pacemaker was inserted urgently, and subsequently replaced by a permanent DDD pacemaker. All symptoms were eliminated. This symptomatic improvement was associated with complete disappearance of LVOT gradient at the time of implantation. No gradient was observed during early follow-up and at 6 months after DDD pacemaker implantation.     

Luminal narrowing of coronary capillaries in human hypertrophic hearts: an ultrastructural morphometrical study using endomyocardial biopsy specimens

Background—Abnormal microcirculation has been suggested in hearts with pathological conditions, particularly in hypertrophic hearts, even in the presence of normal epicardial coronary arteries. However, the morphology of coronary capillaries has not been well investigated in those hearts.
Methods—Ultrastructural morphometry of the capillaries in 47 endomyocardial biopsy specimens taken from 30 patients was performed.
Patients—Six patients had hypertrophic cardiomyopathy with dilated cardiomyopathy-like features (DCM-like HCM), six had HCM, six had DCM, five had postmyocarditis, and seven were normal subjects.
Results—The short axial diameters of capillaries were similar among the groups. Abnormal stenosis of more than 90% luminal narrowing was found in 31% of capillaries of the DCM-like HCM group, 16% of the HCM group, 13% of the DCM group, 11% of the postmyocarditis group, and 2% of the normal subjects. Mean (SD) stenosis of the lumen was most severe in DCM-like HCM (78(8)%), and more severe in HCM (67(9)%), DCM (66(8)%), and postmyocarditis (68(4)%) than normal subjects (56(8)%). The mean cross sectional areas of capillaries were similar among the groups; however, the endothelial cellular area was significantly (p < 0.05) greater in DCM-like HCM (24.2 (8.2) µm²) than in normal subjects (14.7 (1.8) µm²), indicating that capillary narrowing was due to the increased volume of capillary endothelial cells. The endothelial cells of the stenosed capillaries showed severely oedematous changes of the cytoplasm wholely or partially, but the cytoplasmic organelles and nuclei appeared intact.
Conclusion—Narrowing of the coronary capillaries may be of pathophysiological significance in microcirculatory abnormality in hypertrophic hearts, particularly in patients with DCM-like HCM.

Keywords: capillary;  hypertrophy;  cardiomyopathy;  ultrastructure     

肥厚型心肌病心律失常与心肌离子通道突变的关系

目的:探讨肥厚型心肌病(HCM)患者是否存在与心律失常有关的通道改变。方法:以PCR加SSCP方法对24例HCM患者心肌离子通道IKr、IKs和INa的编码基因KvLQT1、HERG、SCN5A进行筛查。正常对照100例。结果:在其中伴严重室性心律失常(短阵室性心动过速及因室性心动过速频发而安装ICD)的12例HCM患者中发现2例存在KvLQT1基因突变,分别为Pro448Arg突变和Val607Ala/Ile608Leu/Met619Leu三突变串联,后一种突变为首次报道。在其余无明显心律失常的12例HCM患者和正常对照中未发现突变。结论:心肌离子通道突变可能是部分HCM患者发生严重心律失常的机制之一。     

17例肥厚型心肌病病人心电I图特点分析

目的提高对肥厚型心肌病的诊断识别.方法对1996年～2000年确诊为肥厚型心肌病17例病人的临床资料进行分析.结果全部病人心电图均有T波异常,9例心尖肥厚型心肌病病人表现为I、aVL、V2～6导联T波倒置,V1～3导联R波幅度明显增加,其中2例伴完全右束支传导阻滞者亦有左胸导联T波明显倒置;5例普遍肥厚型心肌病病人表现为T波倒置导联较心尖肥厚型心肌病病人范围小(V3～6导联伴或不伴I、aVL导联轻度倒置),V1～3导联R波幅度增加不如心尖肥厚型心肌病病人明显;2例间隔肥厚梗阻型心肌病病人有V1～3导联ST段抬高,T波直立,V1～3导联R波不增加与前两型不同;1例间隔肥厚型心肌病伴完全右束支传导阻滞者表现为V1导联呈qR形态,与心尖肥厚型心肌病伴完全右束支传导阻滞者的rsR'亦不相同.结论重视临床和心电图变化采取进一步的检查措施可以最大限度的减少该病的误诊.     

An initial study on left ventricular diastolic function in patients with hypertrophy cardiomyopathy using single-beat, real-time, three-dimensional echocardiography

Objectives To assess the regional diastolic function in patients with hypertrophic cardiomyopathy (HCM) by using single-beat, real-time, three-dimensional echocardiography (RT-3DE). Methods Sixty-five patients with HCM in sinus rhythm together with fifty age- and gender-matched normal controls were studied by two–dimensional echocardiography (2DE) and RT-3DE. The parameters analyzed by RT-3DE included: left ventricular (LV) volumes, left ventricular ejection fraction (LVEF), end diastolic sphericity index (EDSI), diastolic dyssynchrony index (DDI), dispersion end diastole (DISPED), and normalized 17 segmental volume-time curves. Results LVEF was slightly lower evaluated by RT-3DE compared with 2DE (63.2 ± 6.8% vs. 59.1 ± 6.4%, P < 0.0001). Normal subjects had relatively uniform volumetric curves for all LV segments. In HCM patients, the segmental volumetric curves were dyssynchronous. Increased DDI and DISPED in end diastole were observed in patients with HCM (9.95 ± 3.75, 41.76 ± 17.19, P < 0.0001), not all abnormal volumetric segments occurred in the hypertrophic regions. Conclusions Patients with HCM have presented regional diastolic dyssynchrony in the diastole phase, and this preclinical lesion can be recognized by single-beat RT-3DE.     

肥厚型心肌病患者临床症状及超声心动图特点

目的　总结肥厚型心肌病患者临床症状及超声心动图特点 ,探讨二者之间的关系。方法　收集 10 3例肥厚型心肌病患者的病史、体征、心电图和超声心动图结果并进行统计学分析。结果　 1、肥厚型心肌病患者的症状以劳力性呼吸困难为多见 ,与舒张功能异常有关 (P<0 .0 5 ) ,2、心电图异常者占 93% ,3、超声心动图显示 :(1)非对称型肥厚 74 % ,对称型肥厚 2 6 % ,心尖肥厚型 4例 ;(2 )非梗阻型 72 % ,梗阻型 2 8% ;(3)全部病例左心室射血分数均正常 ,舒张功能受损占 5 0 % ;(4 )梗阻组左心室腔明显缩小 ,室间隔明显增厚 ,有二尖瓣前叶收缩期前向运动 (SAM)现象者占 6 6 % ,与非梗阻组比较有显著性差异 (P<0 .0 5 )。结论　肥厚型心肌病临床症状、心电图表现无特异性 ,结合超声心动图可确诊 ;左心室流出道梗阻的发生与室间隔肥厚的程度有关 ;劳力性呼吸困难与舒张功能异常有关     

Effect of biventricular pacing on symptoms and cardiac remodelling in patients with end-stage hypertrophic cardiomyopathy

BACKGROUND: Biventricular (BiV) pacing is an established therapy for heart failure in ischaemic and dilated cardiomyopathy. Its effects in end-stage hypertrophic cardiomyopathy (HCM) are unknown. AIMS: To assess the potential benefits of BiV pacing in patients with symptomatic end-stage HCM. METHODS: Twenty patients with non-obstructive HCM (12 male, mean age 57+/-13 years), left bundle branch block and symptoms of heart failure refractory to medical therapy underwent implantation of a BiV device. NYHA class, echocardiographic parameters and exercise capacity were assessed before and after implantation. RESULTS: At a mean follow-up of 13+/-6 months, an improvement of at least one NYHA class was reported in 8 (40%) patients. A clinical response was associated with an increase in ejection fraction (from 41+/-14% to 50+/-12%, p=0.009), and reductions in left ventricular end-diastolic diameter (from 57+/-6 mm to 52+/-7 mm, p=0.031) and left atrial diameter (from 65+/-8 mm to 57+/-6 mm, p=0.005). Percentage predicted peak oxygen consumption was unchanged in responders but significantly declined in non-responders (p=0.029). CONCLUSIONS: BiV pacing improved heart failure symptoms in a significant proportion of patients with end-stage HCM. Symptomatic improvement was associated with reverse remodelling of the left atrium and ventricle.     

超声检查对肥厚型梗阻性心肌病起搏治疗血液动力学变化的探讨

用超声技术探讨起搏器对肥厚型梗阻性心肌病 (HCM)的作用机理。观察 4例HCM(左心导管和造影检查确诊 )患者的如下指标 :①起搏器置入前、后左室梗阻部位形态及运动变化情况 ;②不同起搏间期对左室心肌各部位收缩期运动顺序的影响 ;③观察自主心律与起搏心律对心功能的影响。结果 :①起搏后左室流出道动力性梗阻减轻 (76 .3± 5 2 .8vs 16 1.5± 47.4mmHg ,P <0 .0 5 )。但起搏后 ,肥厚的心肌收缩期梗阻左室流出道现象依然存在。②双腔起搏时 ,左室心肌激动顺序未见变化 ,但传导时限延长 (6 2 .5± 7.4vs 45 .5± 7.7ms,P <0 .0 5 )。③起搏后左室收缩、舒张诸项指标下降。结论 :起搏干扰心肌传导、激动和收缩的正常过程 ,使得其同步性劣于窦性心律时 ,由此可导致左室收缩压力以及狭窄处压力梯度的下降     

β-methyl-p-(123I)-iodophenyl pentadecanoic acid single-photon emission computed tomography in cardiomyopathy

-Methyl-p-(123I)-iodophenyl pentadecanoic acid (BMIPP) is one of the branched-chain free fatty acids, which has suitable characteristics for myocardial SPECT because of higher uptake and longer retention in the myocardium. Recent advances of BMIPP myocardial SPECT for evaluating cardiomyopathy were reviewed. BMIPP defects were observed in 80% patients with hypertrophic cardiomyopathy (HCM). Moreover, BMIPP uptake was reduced at sites that corresponded with hypertrophic areas, where thallium uptake was increased. The correlations between severity score and septal wall thickness and LV function were better with BMIPP SPECT, suggesting that BMIPP is more suitable for the assessment of myocardial integrity in HCM. The dissociation between BMIPP and thallium defects was not observed frequently in dilated cardiomyopathy (DCM). We carried out BMIPP myocardial SPECT to evaluate the therapeutic effects of co-enzyme Q10 on DCM patients. Hearts to the mediastinum ratio and BMIPP defect scores were significantly decreased after co-enzyme Q10 treatment. BMIPP myocardial SPECT was confirmed to be sensitive in evaluating the therapeutic effect for the perspective of metabolic SPECT imaging. Recently, a lack of myocardial uptake of BMIPP has been found in a small subset of patients (0.3%–1.2%). Cardiac radionuclide imaging using BMIPP and 18F-FDG were performed on patients with type I CD36 deficiency. The percent dose uptake of 18F-FDG was significantly higher than in normal controls. CD functions as a major myocardial long-chain fatty acid transporter and its absence may lead to a compensatory up-regulation of myocardial glucose uptake. An increased frequency of CD36 deficiency was demonstrated in cardiomyopathy. Therefore, fatty acid transport proteins and their related gene defects in relation to BMIPP uptake may become an important issue in the future.     

Augmentation of left ventricular slow filling in hypertrophic cardiomyopathy]

To investigate the significance of augmentation of left ventricular slow filling, trans-mitral flow (TMF) was echocardiographically observed through pulsed Doppler method in 116 patients with hypertrophic cardiomyopathy (HCM), 74 with dilated cardiomyopathy (DCM), 27 with mitral regurgitation (MR), 86 with old myocardial infarction (OMI) and 80 normal controls (C). The slow filling-wave (SFW) in TMF was defined as the filling wave with obvious peak velocity during slow filling phase. The peak velocities (E, A, S) of the early filling, the atrial contraction and the slow filling waves were measured. The SFW was divided into two patterns according to the S and E ratio: large SFW (S/E greater than or equal to 1/2) and small SFW (S/E less than 1/2). 1) The small SFW was more frequently, but not significantly, observed patients with MR (37%) than in normal subjects (18%), patients with HCM (10%), DCM (4%) and OMI (7%). However large SFW was observed in 16 patients (14%) with HCM, but not in normal subjects and patients with other cardiac diseases excluding one patient with DCM. 2) In normal subjects and patients with DCM, OMI and MR, those with small SFW had larger E and smaller A/E than those without small SFW. However in patients with HCM, there was no difference in these indices (E and A/E) according to whether the patients were with or without SFW. 3) In HCM, patients with large SFW had significantly smaller E and significantly larger isovolumic relaxation time than those without SFW. Thus, appearance of the large slow filling wave, which might be caused by abnormal relaxation of the left ventricle, was frequently observed in patients with HCM.     

R-wave amplitude response to myocardial ischemia in hypertrophic cardiomyopathy

Background and Purpose

R-wave amplitude change during exercise has been reported to enhance diagnostic value for myocardial ischemia in coronary heart disease.

Methods

We summed up R-wave amplitude in all the 12 leads during exercise testing and correlated the results with regional myocardial ischemia or diffuse subendocardial ischemia as detected by scintigraphy in 49 patients with hypertrophic cardiomyopathy (HCM) and 16 controls.

Results

The sum of R-wave amplitude decreased during exercise in patients with HCM (mean, 12.4 mV to 11.7 mV, P < .01) as well as in controls (8.0 mV to 7.7 mV, P < .05). Percent changes in the sum of R-wave amplitude did not differ between 4 subgroups of patients with HCM: one having both regional and subendocardial ischemia, one only the former, one only the latter, and one neither of them (mean, 6.5%, 7.7%, 4.6%, and 5.1%; P = .79).

Conclusions

R-wave amplitude response to exercise failed to demonstrate myocardial ischemia in our patients with HCM.     

Chronotropic incompetence and its relation to exercise intolerance in hypertrophic cardiomyopathy

Background

Diminished functional capacity is common in hypertrophic cardiomyopathy (HCM), although the underlying mechanisms are complicated. We studied the prevalence of chronotropic incompetence and its relation to exercise intolerance in patients with HCM.

Methods

Cardiopulmonary exercise testing was performed in 68 patients with HCM (age 44.8 ± 14.6 years, 45 males). Chronotropic incompetence was defined by chronotropic index (heart rate reserve)/(220-age-resting heart rate) and exercise capacity was assessed by peak oxygen consumption (peak Vo₂).

Results

Chronotropic incompetence was present in 50% of the patients and was associated with higher NYHA class, history of atrial fibrillation, higher fibrosis burden on cardiac MRI, and treatment with β-blockers, amiodarone and warfarin. On univariate analysis, male gender, age, NYHA class, maximal wall thickness, left atrial diameter, peak early diastolic myocardial velocity of the lateral mitral annulus, history of atrial fibrillation, presence of left ventricular outflow tract obstruction (LVOTO) at rest, and treatment with beta-blockers were related to peak Vo₂. Peak heart rate during exercise, heart rate reserve, chronotropic index, and peak systolic blood pressure were also related to peak Vo₂. On multivariate analysis male gender, atrial fibrillation, presence of LVOTO and heart rate reserve were independent predictors of exercise capacity (R² = 76.7%). A cutoff of 62 bpm for the heart rate reserve showed a negative predictive value of 100% in predicting patients with a peak Vo₂ < 80%.

Conclusions

Blunted heart rate response to exercise is common in HCM and represents an important determinant of exercise capacity.     

Mutation in the alpha-cardiac actin gene associated with apical hypertrophic cardiomyopathy, left ventricular non-compaction, and septal defects.

AIMS: The E101K mutation in the alpha-cardiac actin gene (ACTC) has been associated with apical hypertrophic cardiomyopathy (HCM). As prominent trabeculations were described in some carriers, we screened for the E101K mutation in our index patients with HCM, dilated cardiomyopathy (DCM), or left ventricular non-compaction (LVNC). METHODS AND RESULTS: Clinical, echocardiographic, and genetic screening by restriction fragment length polymorphism of the ACTC E101K mutation in 247 families with HCM, DCM, or LVNC. The mutation was found in five index patients (one with LVNC and four with HCM). Clinical and morphological data were obtained from 94 family members. Forty-six individuals had cardiomyopathy (43 with the mutation and three with no genetic study): 23 fulfilled criteria for LVNC, 22 were diagnosed as apical HCM, and one had been diagnosed as restrictive cardiomyopathy. There had been one heart transplant and one congestive heart failure death in patients with severe diastolic dysfunction, and five premature sudden deaths. The E101K mutation was not found in 48 unaffected relatives. Septal defects (eight atrial and one ventricular) were found in nine mutant carriers from four families, and were absent in relatives without the mutation (P = 0.003). CONCLUSION: LVNC and HCM may appear as overlapping entities. The ACTC E101K mutation should be considered in the genetic diagnosis of LVNC, apical HCM, and septal defects.     

超声声学定量技术对肥厚型心肌病患者右心室功能的评价

目的应用声学定量技术(AQ)评价非对称性肥厚型心肌病(包括梗阻性和非梗阻性)患者右室收缩与舒张功能。方法应用声学定量技术分别对2004年7月至2005年10月辽宁省人民医院27例肥厚型梗阻性心肌病(HOCM)患者、35例肥厚型非梗阻性心肌病(HNCM)患者和30例正常对照组人群的标准心尖四腔心切面观进行分析。结果与对照组相比,肥厚型心肌病(包括梗阻型和非梗阻型)右室峰值快速充盈率与右房峰值快速充盈率之比(PRFR/PAFR)、右室快速充盈容积与右房收缩充盈容积之比(RF/AF)明显减低(P<0.05)。而右心室收缩功能指标EF与正常组相比差异无显著性。结论AQ为定量评价肥厚型心肌病患者的右室功能提供了新的方法。     

HLA complex and hypertrophic cardiomyopathy in a European population

HLA tissue typing was performed in 43 unrelated white personswith hypertrophic cardiomyopathy (HCM) living in the northernpart of Belgium. The frequency distribution of the 14-HLA-A,18 HLA-B, 5 HLA-C and 10 HLA-D antigens, which were tested,was similar in patients with obstructive, provocable obstructiveor non-obstructive HCM to that of a control group of 800 normalpersons.     

The role of impaired sympathetic nerve function in enhancing coronary vasoconstriction in patients with hypertrophic cardiomyopathy

Coronary vasospasm and diminished coronary blood flow reserve have often been reported in patients with hypertrophic cardiomyopathy (HCM). However, the mechanism of coronary spasm in HCM is unknown. Thus, coronary endothelial function and sympathetic nerve function in 11 patients with HCM and 11 control patients matched for age and sex were examined. The diameter of the left anterior descending coronary artery was assessed by quantitative coronary angiography, and the change in coronary blood flow was estimated using an intracoronary Doppler flow wire. To assess myocardial sympathetic nerve function, metaiodobenzylguanidine images - 15 min and 180 min after the injection of (123)I-metaiodoben-zylguanidine at a dosage of 111 MBq - were obtained, and the heart to mediastinum (H/M) count ratio and the washout rate (WR) were calculated. The H/M ratio was significantly lower in patients with HCM (2.1+/-0.3) than in control patients (2.6+/-0.4) (P<0.01). In addition, the WR was higher in patients with HCM (35+/-6%) than in control patients (28+/-3%) (P<0.01). The HCM subjects with coronary spasm had lower H/M ratios and higher WRs than HCM subjects without coronary spasm (P<0.05, respectively). In conclusion, impaired sympathetic nerve function may be associated with coronary vasospasm and diminished coronary blood flow reserve in HCM.