The study population was comprised of 36 patients with HCM (20 males; mean age, 57±10 years; 31 patients with non-obstructive HCM) and 21 age- and gender-matched control subjects with normal left ventricular thickness. The subjects with left ventricular systolic dysfunction (left ventricular ejection fraction <55%), significant valvular disease, arrhythmia, coronary artery disease, or renal insufficiency (serum creatinine >1.4 mg/mL) were excluded. Each subject provided informed, written consent to the protocol that had been approved by our Institutional Review Board.

The ratio between procollagen type I N-terminal peptide (PINP) and collagen type I pyridinoline cross-linked C-terminal telopeptide (ICTP), PINP/ICTP, which is known as the degree of synthesis and degradation of type I collagen, was 9.1±7.8 in the control group and 10.9±6.5 in the HCM group. Patients with HCM (n=36) were divided into the following two groups based on the median value of the PINP/ICTP: the lower group (PINP/ICTP < median value; n=18; 10 males) and the higher group (PINP/ICTP ≥ median value; n=18; 10 males) for analysis. A comparison was made between the 3 groups (the control group, the HCM group with a lower PINP/ICTP, and the HCM group with a higher PINP/ICTP).

Standard 2-dimensional measurements (left ventricular diastolic and systolic dimensions, ventricular septum and posterior wall thickness, left atrial volume, and left ventricular outflow tract) were obtained with the subjects in the left decubitus position. The left ventricular ejection fraction was calculated by the modified method of Quinones et al.15) After obtaining the rest images from the standard parasternal and apical views, a multistage supine bicycle exercise testing was performed with a variable load bicycle ergometer (Medical Positioning Inc., Kansas City, MO, USA). Subjects pedaled at constant speed beginning at a workload of 25 W with an increment of 25 W every 3 minutes. Echocardiography was performed using an ultrasound system (System 7; GE Vingmed, Horten, Norway) with a 2.5-MHz transducer during rest, each stage of exercise, and recovery in the sequence described as follows. From the apical window, a 1-2-mm pulsed Doppler sample volume was placed at the mitral valve tip, and mitral flow velocities from 5-10 cardiac cycles were recorded. The mitral inflow velocities were traced and the following variables were obtained: peak velocity of early (E) and late (A) filling, and deceleration time of the E wave velocity. Tricuspid regurgitant jet velocity was also obtained to estimate pulmonary artery systolic pressure using continuous wave Doppler, if measurable. Mitral annular velocity was measured by Doppler tissue imaging using the pulsed wave Doppler mode. The filter was set to exclude high-frequency signals, and the Nyquist limit was adjusted to a range of 15-20 cm/s. Gain and sample volume were minimized to allow for a clear tissue signal with minimal background noise. E' and systolic (S') velocities of the mitral annulus were measured from the apical 4-chamber view with a 2-5-mm sample volume placed at the septal corner of the mitral annulus. Stroke volume (SV) was measured from the left ventricular outflow tract diameter and the pulse wave Doppler signal, as previously described.16) To provide a continuous variable that might estimate Ed, the E/E' ratio was used as an estimation of mean left atrial pressure. Operant Ed was estimated as E/E' divided by the volume SV of filling during diastole, based on a previous study.17) These measurements were performed at baseline, at each stage of exercise, and recovery in the same sequence. All data were stored digitally and measurements were made at the completion of each study.

To assess collagen markers, we measured serum levels of peptides released during collagen synthesis and degradation. Peripheral venous blood samples were centrifuged at 4℃. Aliquots of serum were immediately stored at -70℃ until the assay.

The measurement of serum PINP, procollagen type III amino terminal peptide (PIIIINP), and ICTP was performed using a commercially available radioimmunoassay (Farmos Diagnostica, Oulu, Finland), all of which were indicators reflecting collagen synthesis and degradation. The accuracy of this method has been reported to have an inter- and intra-assay variation <10%.

All the results were expressed as the mean±standard deviation. To compare the categorical variables, a chi-square test was used. For comparison of the continuous variables, analysis of variance (ANOVA) was performed. Serum biochemical markers indicating myocardial fibrosis did not follow a normal distribution, which were converted to logarithms for statistical analysis. Statistical significance was defined as <.05. Statistical analysis was performed using Statistical Package for Social Science (SPSS) 13.0 for Windows (SPSS, Inc., Chicago, IL, USA).

The baseline characteristics of clinical variables and serum collagen markers are shown in Table 1. The age and gender distribution was not different between the three groups. The left ventricular end-diastolic and end-systolic dimensions were significantly lower in the HCM group, especially in the HCM group with a higher PINP/ICTP ratio. The myocardial thickness of the interventricular septum and posterior wall were increased in the HCM group. The HCM group had a significantly larger left ventricular volume index, but there were no differences in the left ventricular systolic function. There were no significant differences in the duration of exercise between the three groups. Of the serum biochemical markers indicating myocardial fibrosis, the log PINP and log PINP/ICTP were significantly higher in the HCM group. Furthermore, the patients with HCM with a higher PINP/ICTP ratio had significantly higher levels of log PINP and log PINP/ICTP due to the study design.

The changes in systolic blood pressure, diastolic blood pressure, and heart rate during exercise are shown in Table 2. In the three groups, the blood pressure and heart rate were increased gradually during exercise; however, there were no significant differences between the three groups in hemodynamic variables at rest and with exercise.

As shown in Table 3, Doppler echocardiographic parameters were compared at rest and each stage of exercise between the three groups. At rest, the E' velocity was significantly lower in the patients with HCM as compared with the control subjects. Interestingly, the HCM group with a higher PINP/ICTP revealed lower E' velocities, a higher E/E' ratio, and lower S' velocities than the HCM group with lower PINP/ICTP. From these results, we know that the left ventricular longitudinal diastolic and systolic function at rest were significantly impaired in patients with HCM who had a higher PINP/ICTP ratio.

At each stage of exercise, the E' velocity, E/E' ratio, and S' velocity were significantly lower in the HCM group than the control group, and the values were elevated to a similar extent during exercise. Thus, the magnitude of changes in E' velocity, E/E', and S' velocity from rest to each stage of exercise was not different between the three groups. Therefore, the presence of HCM or the higher PINT/ICTP ratio were not associated with a significant decrease in diastolic functional reserve during exercise, even though there was significant left ventricular diastolic dysfunction at rest.