Interventricular septal and free wall dynamics in hypertrophic cardiomyopathy

Retrofitting the Heart: Explaining the Enigmatic Septal Thickening in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is the most common genetic cardiac disease and is characterized by left ventricular hypertrophy. Although this hypertrophy often associates with sarcomeric gene mutations, nongenetic factors also contribute to the disease, leading to diastolic dysfunction. Notably, this dysfunction manifests before hypertrophy and is linked to hypercontractility, as well as nonuniform contraction and relaxation (myofibril asynchrony) of the myocardium. Although the distribution of hypertrophy in hypertrophic cardiomyopathy can vary both between and within individuals, in most cases, it is primarily confined to the interventricular septum. The reasons for septal thickening remain largely unknown. In this article, we propose that alterations in muscle fiber geometry, present from birth, dictate the septal shape. When combined with hypercontractility and exacerbated by left ventricular outflow tract obstruction, these factors predispose the septum to an isometric type of contraction during systole, consequently constraining its mobility. This contraction, or more accurately, this focal increase in biomechanical stress, prompts the septum to adapt and undergo remodeling. Drawing a parallel, this is reminiscent of how earthquake-resistant buildings are retrofitted with vibration dampers to absorb the majority of the shock motion and load. Similarly, the heart adapts by synthesizing viscoelastic elements such as microtubules, titin, desmin, collagen, and intercalated disc components. This pronounced remodeling in the cytoskeletal structure leads to noticeable septal hypertrophy. This structural adaptation acts as a protective measure against damage by attenuating myofibril shortening while reducing cavity tension according to Laplace Law. By examining these events, we provide a coherent explanation for the septum's predisposition toward hypertrophy.

Development and validation of a new method to diagnose apical hypertrophic cardiomyopathy by gated single-photon emission computed tomography myocardial perfusion imaging

AIM

The aim of this study is to develop and validate a new method to diagnose apical hypertrophic cardiomyopathy (AHCM) by the integral quantitative analysis of myocardial perfusion and wall thickening from gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI).

PATIENTS AND METHODS

Twenty-two consecutive patients, who showed T wave inversion of at least 3 mm in precordial leads and sinus rhythm in ECG, were enrolled. All the patients underwent cardiac magnetic resonance (CMR), gated rest SPECT MPI and echocardiography. According to CMR diagnostic results, 13 patients were categorized as in the AHCM group and the remaining nine patients were categorized as in the non-AHCM group. Operators who were blinded to the CMR diagnosis independently performed the diagnosis by gated SPECT MPI. The regions of interest inside the apical hotspots on the perfusion polar map were drawn and the mean values of wall thickening in the drawn region of interests were calculated. Using MRI diagnosis as the gold standard, AHCM was diagnosed based on receiver operating characteristic analysis of the mean wall thickening in the apical perfusion hotspot. The area under curve, sensitivity, specificity, and accuracy of our method were 0.97, 100%, 89%, and 95%, respectively.

CONCLUSION

Our new method has high sensitivity, specificity, and accuracy against CMR diagnosis. It has great promise to become a clinical tool in the diagnosis of AHCM.

Subendocardial motion in hypertrophic cardiomyopathy: assessment from long- and short-axis views by pulsed tissue Doppler imaging

BACKGROUND

Tissue Doppler imaging (TDI) is a recently developed technique that allows the instantaneous measurement of intrinsic regional myocardial motion velocity. Pulsed TDI is capable of separately assessing left ventricular (LV) regional motion velocity caused by circumferential and longitudinal fiber contraction. This particular feature of function is still controversial in patients with hypertrophic cardiomyopathy (HC).

METHODS

To better characterize intrinsic circumferential and longitudinal LV systolic myocardial function in HC, we used pulsed TDI to measure short- and long-axis LV motion velocities, respectively. The subendocardial motion velocity patterns at the middle of the LV posterior wall (PW) and ventricular septum (IVS) in LV parasternal and apical long-axis views were recorded by pulsed TDI in 19 patients with nonobstructive HC and in 21 normal controls (NC).

RESULTS

Peak short- and long-axis systolic subendocardial velocities in both the LV PW and IVS were significantly smaller in the HC group than in the NC group, and the time to peak velocity was significantly delayed. Furthermore, peak PW systolic velocity was significantly greater along the long axis than along the short axis in the NC group (8.8 +/- 1.5 cm/s vs 8.2 +/- 1.4 cm/s, P <.05), whereas the opposite was observed in the HC group (6.1 +/- 1.2 cm/s vs 7.5 +/- 1.0 cm/s, P <.0001). No significant differences were found in either group between the long- and short-axis IVS velocities (HC: 5.9 +/- 1.4 cm/s vs 5.5 +/- 1.3 cm/s; NC: 7.8 +/- 1.3 cm/s vs 7.9 +/- 1.6 cm/s).

CONCLUSIONS

By using the capability of pulsed TDI for the evaluation of intrinsic myocardial velocity instantaneously in a specific region and direction, we found impairment of LV myocardial systolic function in patients with HC not only in the hypertrophied IVS but also in the nonhypertrophied LV PW. We also found a greater decrease in LV PW velocities along the long axis than the short axis, suggesting greater impairment of long-axis contraction in patients with HC. Because our HC patients did not appear to have excessive intracavitary pressure, these results suggest that the relatively normal-appearing PW is directly affected by the HC pathologic process.

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.

Hypertrophic cardiomyopathy: functional aspects by tagged magnetic resonance imaging

Studies addressing the issue of regional function in hypertrophic cardiomyopathy patients (HCM) are reviewed. The relationship between regional wall thickness and function in these patients was studied by three dimensional (3D) tagged magnetic resonance imaging (MRI) utilizing the volume-element approach. Regional function was indexed by myocardial thickening and circumferential shortening and related to the local thickness and wall stress index. An inverse relationship was found between wall thickening and thickness as well as between circumferential shortening and wall thickness. Lower stresses were obtained for thicker myocardial segments. Function of the normal-thickness regions was enhanced in the HCM patients relative to the normal subjects. Thicker segments in patients with HCM are thus characterized by reduced systolic function, which occurs at segments with relatively low stress levels. This pattern is consistent with the hypothesis that the thick myocardial segments have reduced contractile activity, probably due to recently identified mutations in the gene responsible for production of beta heavy chain myosin as well as other contractile proteins.

Left ventricular wall thickness and regional systolic function in patients with hypertrophic cardiomyopathy. A three-dimensional tagged magnetic resonance imaging study

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.

Echocardiography in coronary artery disease

Echocardiography has a major role in the evaluation of patients with CAD. To obtain the maximal amount of information using this technique, certain basic principles relating to regional myocardial mechanics during ischemia and flow-function relations are required. In addition, a detailed knowledge of cardiac anatomy and the three-dimensional orientation of the heart within the chest cavity is required to access meaningful information from two-dimensional planes. Furthermore, skill is also required in acquiring data in proper imaging planes and in separating true (actual pathology) from the false (artifacts, etc.). Echocardiography is not a "mature" technology. It is still developing and it is sometimes difficult to keep up with the advances. However, keeping abreast of these developments is essential to fully exploit the advantages of this technique. In addition, knowledge of the ever-changing aspects of CAD is required in order to correctly interpret visual information in context of a particular patient. Finally, more clinical studies are needed to further define the role of echocardiographic techniques in patients with CAD.

Prevalence and mechanisms of mitral regurgitation in the absence of intrinsic abnormalities of the mitral leaflets

Two hundred nineteen consecutive patients referred for echocardiography were analyzed to determine the occurrence of mitral regurgitation (MR) in the absence of intrinsic abnormalities of the mitral leaflets. MR was assessed by means of the pulsed-Doppler technique. There was a higher incidence of MR associated with absence of mitral leaflet abnormalities compared to the presence of these abnormalities (59% vs 41%, p less than 0.01). The most common causes of MR were mitral annular calcification (MAC) and incomplete mitral leaflet closure (IMLC). The extent of calcific deposit in patients with MAC and the distance from the mitral leaflet coaptation point to the mitral annular plane in systole patients with IMLC correlated well with the severity of MR by Doppler technique (rho = 0.91 and 0.71, respectively). To determine the mechanisms of MR in these two conditions, 29 consecutive patients with MAC and 28 with IMLC were referred to the echocardiography laboratory, and 10 age-matched control subjects were prospectively analyzed. Patients with MAC had a 50% reduction in the sphincteric action of the mitral anulus in systole compared to control subjects. All patients with IMLC had poor left ventricular systolic function; most had left ventricular, mitral annular, and left atrial dilation, and only eight had regional wall motion abnormalities. When discriminant function analysis was used, poor left ventricular systolic function was the principal variable that separated patients with IMLC from normal subjects (F = 81.6, p less than 0.0001). We conclude that: (1) MR in adults occurs most commonly in the absence of intrinsic abnormalities of the mitral leaflets, primarily those resulting from MAC and IMLC; (2) MR in patients with MAC results from a reduced sphincteric action of the mitral anulus in systole; and (3) IMLC results from poor left ventricular systolic function, irrespective of the cause.

Left ventricular ejection dynamics in hypertrophic cardiomyopathy and aortic stenosis: comparison with the use of Doppler echocardiography

Left ventricular ejection dynamics of 15 patients with hypertrophic cardiomyopathy (nine obstructive, six nonobstructive) were compared to those in 12 age-matched normal subjects and 10 patients with valvular aortic stenosis by means of combined two-dimensional and Doppler echocardiography. Doppler peak flow velocities in obstructive (HOCM, 2.5 +/- 1.3 m/sec) and nonobstructive (HNCM, 2.6 +/- 0.6 m/sec) hypertrophic cardiomyopathy, as well as in patients with aortic stenosis (AS, 3.6 +/- 1.3 m/sec) were significantly higher than in the normal population (1.0 +/- 0.2 m/sec; p less than 0.001 for all comparisons), but did not differ from each other. The HOCM patients had time to peak velocity (154 +/- 55.7 msec) that was higher than that in both HNCM (86 +/- 8.4 msec) and normal groups (84.5 +/- 8.9 msec; p less than 0.001 for both comparisons), but did not differ from those in AS (117 +/- 52.5 msec). The total ejection time did not differ between HOCM (348.2 +/- 91.1 msec) and AS (328.8 +/- 30.4 msec) groups, but was prolonged in HOCM compared to HNCM (198 +/- 21.0 msec) and normal groups (233 +/- 28.3 msec; p less than 0.001 for both comparisons). The normal and HNCM groups did not differ in time to peak or total ejection time measurements. The percent of flow velocity present in the initial third of the systolic velocity integral for HOCM (44.5% +/- 5.9) and HNCM (49.4% +/- 2.5) groups was greater than for normals (36.2% +/- 5.4; p less than 0.05 for both comparisons), but HOCM values did not differ from HNCM values.(ABSTRACT TRUNCATED AT 250 WORDS)

The interventricular septum in health and disease

The interventricular septum constitutes a major part of the heart and contributes to both left and right ventricular function. It is directly affected in certain disease states which can be diagnosed by echocardiographic examination of the septum. The septum also demonstrates characteristic patterns in cardiac conditions that do not directly affect it. These abnormal patterns have physiologic and diagnostic value. As a general rule, no matter what the diastolic configuration of the interventricular septum, it tries to assume its characteristic concave shape in systole. The significant exception is the presence of right ventricular pressure overload. The introduction of echocardiography has greatly increased our understanding of the interventricular septum in both health and disease.

Clinical improvement in hypertrophic cardiomyopathy after inferior myocardial infarction

In cases of hypertrophic cardiomyopathy, the pathophysiologic role of the systolic pressure gradient across the left ventricular outflow tract is the subject of continued controversy. A patient with this disorder is described whose symptoms and provokable intraventricular gradient disappeared after inferior myocardial infarction. Diastolic left ventricular pressures were essentially unchanged, the isovolumic relaxation period became prolonged and the ejection fraction decreased from 0.77 to 0.61 after infarction. The peak ejection rate was unchanged, but the disappearance of systolic anterior motion of the mitral valve leaflet and obstructive manifestations may have resulted from enlarged mid to late systolic ventricular volumes. This case suggests a direct relation between symptoms and intraventricular pressure gradient in certain patients with hypertrophic cardiomyopathy.

Echocardiographic analysis of ventricular septal dynamics in hypertrophic cardiomyopathy and other diseases

It has been suggested that the adynamic or hypokinetic appearance of the ventricular septum is a unique echocardiographic feature of hypertrophic cardiomyopathy (HC). To determine how characteristic of HC the adynamic septum is, 70 patients with this disease, and 31 with other cardiac diseases that produce left ventricular (LV) hypertrophy and pressure overload (aortic valvular stenosis or systemic hypertension), and 25 subjects with normal hearts were studied by echocardiography. On M-mode echocardiography, 53 of 70 patients (75%) with HC had an abnormally low value for percent systolic thickening of the septum associated with either reduced or normal septal excursion; however, 17 patients (25%) showed normal septal dynamics. Twenty of 31 patients (64%) with other cardiac diseases that produce pressure overload showed normal septal thickening and excursion, while 11 (36%) had reduced systolic thickening associated with either diminished or normal excursion. Greatly reduced values for percent systolic thickening of the septum were present both in patients with HC (13 +/- 1%) and in patients with other cardiac diseases (21 +/- 2%). However, differences in systolic septal thickening between the 2 groups were largely a manifestation of the greater absolute diastolic septal thickness in patients with HC. When values for percent systolic thickening were normalized for diastolic septal thickness, or when systolic thickening was compared in only patients with similar diastolic septal thicknesses, differences in septal thickening between patients with HC and those patients with other cardiac diseases were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)