Study design

We performed a retrospective analysis of the entire HCM cohort ( overall cohort , n = 728) to assess sex-specific differences in cardiac phenotype, degree of LV myopathy, genetics and adverse outcomes. In order to eliminate the confounding effect of age on outcomes, a sub-group of age-matched HCM patients ( age-matched subgroup ) was selected from the overall cohort using individual matching study design. The age difference in each pair was ±4 years, and a total of 200 pairs (N = 400) were selected ( Supplemental Table 1 ).

All echocardiographic and cardiac magnetic resonance (CMR) measurements reported in the manuscript, were performed at the time of the first clinic visit. Myocardial perfusion imaging by positron emission tomography (PET) was performed at follow up, in patients with symptoms of angina, ventricular arrhythmias or exertional dyspnea despite optimal therapy.

Degree of LV myopathy was assessed by measuring LV mass, LV ejection fraction (LVEF), LV global peak longitudinal systolic strain (LV-GLS), LV diastolic function (E/A, E/e′), late gadolinium enhancement in the LV (LV-LGE) and myocardial blood flow (MBF) at rest and following vasodilator-stress.

Conventional and stress echocardiography

Transthoracic echocardiography was performed using a GE Vivid 7 or E-9 ultrasound machine (GE Ultrasound, Milwaukee, WI) and a multi-frequency phased-array transducer, at baseline and following maximum exercise on a treadmill. Indexed maximum wall thickness (MWT) was defined as MWT divided by body surface area to represent the degree of hypertrophy relative to body size. Biplane left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV) and ejection fraction (LVEF) were calculated using modified Simpson’s method. Mitral inflow early diastole (E) and atrial contraction (A) waves were measured by Doppler echocardiography. Tissue Doppler peak early diastolic wave (e′) was derived from the apical four-chamber view at the basal septal wall and used to compute E/e′. LVOT pressure gradients were measured in the apical views by continuous-wave Doppler echocardiography under resting conditions and during provocative maneuvers including Valsalva, amyl nitrite inhalation, following treadmill exercise in order to elicit latent obstruction, as previously reported. Peak resting and stress (exercise, amyl nitrite, valsalva) pressure gradients were used to define HCM as non-obstructive (<30 mmHg at rest and stress), labile obstructive (< 30 mmHg at rest, ≥30 mmHg with stress), or obstructive (≥30 mmHg at rest and stress).

Deformation analysis by echocardiography

Echocardiographic images for speckle tracking strain analysis were prospectively acquired at frame rates of 50 to 90 Hz, and longitudinal systolic strain was analyzed from the apical two-, three-, and four-chamber views using EchoPAC 112 (GE Vingmed Ultrasound AS, Horten, Norway). Peak longitudinal systolic strain was measured in all 18 segments of the LV, and averaged to obtain a global value (LV-GLS). Poorly tracking segments or images, which could not be optimized, were excluded from analysis. Patients with at least four unanalyzable segments were excluded from analysis.

Cardiac magnetic resonance imaging and data analysis

Cardiac magnetic resonance imaging was performed in a 1.5 T system (MAGNETOM Avanto; Siemens Healthcare, Erlangen, Germany). The contrast agent, gadopentetate dimeglumine was used at 0.2 mmol/kg (Magnevist; Bayer Schering, Berlin, Germany). Good quality, complete CMR data were available in 76% (555/728) of HCM patients. Left ventricular mass and late gadolinium enhancement (LV-LGE) were quantified using QMASS software (QMASS 7.4; Medis, Leiden, The Netherlands). Images for LGE quantification were assessed in short axis views. A region of interest was placed in an area of normal appearing nulled myocardium, typically the basal lateral wall. Pixels with signal intensity greater than six standard deviations higher than the mean of normal myocardium were considered abnormal, as described previously.

Positron emission tomography (PET) imaging and analysis

HCM patients (n = 145) were referred for perfusion-PET if they had symptoms of angina, ventricular arrhythmias or exertional dyspnea despite optimal therapy. Cardiac PET/CT imaging was performed using a GE Discovery VCT PET/CT System (GE Healthcare, Waukesha, Wisconsin) and a 1-day rest/stress protocol, as described previously. Approximately 370 MBq (10 mCi) of ¹³ N-ammonia was injected intravenously, followed by PET acquisition in two-dimensional list mode for 20 minutes. Vasodilator stress was induced approximately 60 minutes after injection of the rest dose. Semi-automated analysis of the resulting myocardial perfusion images was performed using QPET (Cedars Sinai, Los Angeles, California). The summed stress score (SSS), the summed rest score (SRS), and the summed difference score (SDS) (SSS − SRS = SDS) were computed to assess the degree of inducible ischemia in each patient. Global myocardial blood flow (MBF in ml/min/g) at rest and during peak vasodilator stress were quantified using QPET software as previously described. For regional MBF analysis, the LV wall was divided into 5 regions: septum, apex, anterior, inferior, and lateral walls. Vasodilator-induced transient left ventricular cavity dilation (LVCD) was assessed using the PET-LVCD-index. The PET-LVCD-index was computed by dividing the LV volume during peak vasodilator stress by the LV volume at rest. Patients with an index >1.13 were considered to have LVCD.

Definition of cardiovascular outcomes and follow-up

The primary outcome was defined as a composite endpoint, that included new onset AFib, new sustained VT (VT rate ≥130 bpm, >30 sec duration) or VF, new onset or worsening HF to New York Heart Association functional class III or IV requiring hospitalization, and all-cause mortality. Individual adverse cardiovascular events (AFib, VT/VF, HF, death) were defined as the secondary outcome. Only the first adverse outcome in each patient was included in the primary and secondary endpoint calculation. An outcome that occurred prior to enrollment and recurred during follow-up, or a second adverse outcome during follow-up was not included in the primary and secondary endpoint calculation. All-cause mortality statistics for our study population were obtained by linking our database to the Social Security Death Index. Patients who underwent septal reduction therapy (septal myectomy, alcohol septal ablation) during follow up, but prior to any adverse event were considered as censored 1 day prior to septal reduction therapy. Patients who remained event-free until June 30, 2016 were censored; longest duration of follow up in our cohort was 10 years.