Hypertrophic cardiomyopathy

Dynamic magnetic resonance imaging assessment of the effect of ventricular wall curvature on regional function in hypertrophic cardiomyopathy

We hypothesized that contraction within the ventricular septum in hypertrophic cardiomyopathy (HC) may be related to its abnormal morphology because ventricular wall stress is related to wall curvature by the Laplace equation. To test this, we studied 17 HC patients with various septal morphologies using dynamic magnetic resonance imaging techniques. Short- and long-axis curvatures of the basal septal and basal lateral walls were determined on cine images as the reciprocal of the radius of the arc best fit to the endocardial contour, which was negative if the wall was convex to the cavity of the left ventricle. Endocardial and epicardial intramyocardial circumferential shortening (% circumferential shortening) was measured in the septal and lateral walls on basal short-axis myocardial tagging images. Septal walls were flatter in the short-axis plane and more convex toward the left ventricular cavity in the long-axis plane than lateral walls, as indicated by smaller short- and long-axis curvatures. Septal percent circumferential shortening was significantly lower than the lateral percent circumferential shortening, suggesting reduced septal contraction. Endocardial and epicardial percent circumferential shortening showed significant positive correlations with wall curvatures. Multiple stepwise linear regression analysis revealed that both short- and long-axis curvatures significantly contributed to percent circumferential shortening (r=0.87 for endocardial and r=0.70 for epicardial, both p<0.0001). In conclusion, wall curvature is related to wall function in HC; the more convex toward the left ventricular cavity the wall is, the less it contracts. Reduced contraction of the septum in HC may be partly due to its abnormal curvature.

New insights into the reduction of mitral valve systolic anterior motion after ventricular septal myectomy in hypertrophic obstructive cardiomyopathy

To determine the mechanism of reduction of mitral valve systolic anterior motion by myectomy, we examined 33 patients with hypertrophic obstructive cardiomyopathy echocardiographically before and after myectomy. Measurements included outflow tract diameter, the direction of ejection streamline (the angle between the ejection flow and the mitral valve), midventricular fractional area change, and papillary muscle inward excursion in the short-axis image. After myectomy, the outflow tract was enlarged (from 1.2 +/- 0.3 cm to 2.1 +/- 0.4 cm; p < 0.001), and the ejection flow became more parallel to mitral leaflets (from 51 +/- 10 degrees to 28 +/- 8 degrees; p < 0.001), whereas hyperdynamic midventricular fractional area change was reduced (81% +/- 14% to 62% +/- 14%; p < 0.001), and papillary muscle excursion decreased (1.3 +/- 0.3 cm to 0.8 +/- 0.3 cm; p < 0.001). Outflow enlargement and reduced ventricular contraction would decrease the Venturi force. Change of ejection streamline and reduced contraction would decrease the drag force onto the mitral leaflets. Blunted papillary motion would increase the mitral leaflet tension and decrease the effect of drag force on both leaflets. Thus myectomy decreases Venturi and drag forces and appears to reduce systolic anterior motion of the mitral valve.

Is there increased sympathetic activity in patients with hypertrophic cardiomyopathy?

OBJECTIVES

This study aimed to assess autonomic nervous system activity in patients with hypertrophic cardiomyopathy.

BACKGROUND

Patients with hypertrophic cardiomyopathy are traditionally thought to have increased sympathetic activity. However, convincing evidence is lacking.

METHODS

Heart rate variability was assessed from 24-h ambulatory electrocardiographic (Holter) recordings in 31 patients with hypertrophic cardiomyopathy and 31 age- and gender-matched normal control subjects in a drug-free state. Spectral heart rate variability was calculated as total (0.01 to 1.00 Hz), low (0.04 to 0.15 Hz) and high (0.15 to 0.40 Hz) frequency components using fast Fourier transformation analysis.

RESULTS

There was a nonsignificant decrease in the total frequency component of heart rate variability in patients with hypertrophic cardiomyopathy compared with that of normal subjects (mean +/- SD 7.24 +/- 0.88 versus 7.59 +/- 0.57 ln[ms2], p = 0.072). Although there was no significant difference in the high frequency component (5.31 +/- 1.14 versus 5.40 +/- 0.91 ln[ms2], p = 0.730), the low frequency component was significantly lower in patients than in normal subjects (6.25 +/- 1.00 versus 6.72 +/- 0.61 ln[ms2], p = 0.026). After normalization (i.e., division by the total frequency component values), the low frequency component was significantly decreased (38 +/- 8% versus 43 +/- 8%, p = 0.018) and the high frequency component significantly increased (16 +/- 6% versus 12 +/- 6%, p = 0.030) in patients with hypertrophic cardiomyopathy. The low/high frequency component ratio was significantly lower in these patients (0.94 +/- 0.64 versus 1.33 +/- 0.55, p = 0.013). In patients with hypertrophic cardiomyopathy, heart rate variability was significantly related to left ventricular end-systolic dimension and left atrial dimension but not to maximal left ventricular wall thickness. No significant difference in heart rate variability was found between 14 victims of sudden cardiac death and 10 age- and gender-matched low risk patients.

CONCLUSIONS

Our observations suggest that during normal daily activities, patients with hypertrophic cardiomyopathy experience a significant autonomic alteration with decreased sympathetic tone.