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Left ventricular wall thickness and regional systolic function in patients with hypertrophic cardiomyopathy. A
S J Dong1, J H MacGregor, A P Crawley
1Department of Medicine, University of Calgary, Alberta, Canada.
Insights
Regional function in hypertrophic cardiomyopathy (HCM) is impaired, with reduced systolic thickening and shortening in abnormally thickened heart muscle. This impairment is inversely related to local myocardial thickness.
Area of Science:
- Cardiology
- Medical Imaging
- Biomedical Engineering
Background:
- Regional left ventricular (LV) function in hypertrophic cardiomyopathy (HCM) is poorly understood, with conflicting reports on myocardial contractility.
- Variations in imaging modalities and analysis methods contribute to inconsistent findings regarding LV function in HCM.
Purpose of the Study:
- To assess regional systolic function (wall thickening and shortening) in the hypertrophied LV of HCM patients.
- To correlate regional systolic function parameters with end-diastolic myocardial thickness using advanced imaging techniques.
Main Methods:
- Utilized tagged magnetic resonance imaging (MRI) and a three-dimensional (3D) volume-element approach to analyze LV function.
- Obtained short-axis and long-axis images with detailed tagging patterns in 17 HCM patients and 6 healthy volunteers.
- Calculated end-diastolic thickness, fractional thickening, and circumferential shortening for 72 LV volume elements.
Main Results:
- Patients with HCM exhibited significantly greater end-diastolic LV thickness (15.8 mm) compared to healthy subjects (8.6 mm).
- Fractional thickening was significantly reduced in HCM patients (0.31) versus controls (0.56).
- A strong inverse correlation was found between fractional thickening and end-diastolic thickness, independent of hypertrophy type or age.
Conclusions:
- The myocardium in HCM is heterogeneously thickened, with diminished fractional thickening and circumferential shortening.
- Reduced systolic function in HCM is inversely proportional to local myocardial wall thickness.
Background:
Regional performance of the hypertrophied left ventricle (LV) in hypertrophic cardiomyopathy (HCM) is still incompletely characterized with studies variably reporting that the hypertrophied myocardium is hypokinetic, akinetic, or has normal function. Different imaging modalities (M-mode or two-dimensional echocardiography) and methods of analysis (fixed or floating frame of reference for wall motion analysis) yield different results. We assessed regional function in terms of systolic wall thickening and shortening and related these parameters to end-diastolic thickness using tagged magnetic resonance imaging and the three-dimensional volume-element approach.
Methods And Results:
In 17 patients with HCM and 6 healthy volunteers, four parallel short-axis images with 12 radial tags and two mutually orthogonal long-axis images with four parallel tags were obtained at end diastole and end systole. After the LV endocardial and epicardial borders were traced, three-dimensional volume elements were constructed by connecting two matched planar segments in two adjacent short-axis image planes, accounting for translation, twist, and long-axis shortening. A total of 72 such volume elements encompassed the entire LV. From each of these elements, end-diastolic thickness and systolic function (fractional thickening and circumferential shortening) were calculated. The average end-diastolic thickness was 15.8 +/- 4.2 mm in patients with HCM, which was significantly greater than that in healthy subjects (8.6 +/- 2.1 mm, P < .001). Fractional thickening was significantly less in patients with HCM than in healthy subjects (0.31 +/- 0.22 versus 0.56 +/- 0.23, P < .001). There was a highly significant inverse correlation between fractional thickening and end-diastolic thickness that was independent of the type of hypertrophy or age group. Similar inverse relations were observed between circumferential shortening and end-diastolic wall thickness.
Conclusions:
The myocardium in patients with HCM is heterogeneously thickened and the fractional thickening and circumferential shortening of the abnormally thickened myocardium are reduced compared with healthy subjects. The decrease in fractional thickening and shortening is inversely related to the local thickness.