Summary
Background
Hypertrophic cardiomyopathies (HCM) are often associated with left ventricular (LV) outflow tract obstruction, which can explain symptoms and impact prognosis.
Aims
To better understand the mechanisms that link obstruction and LV shape in HCM.
Methods
Patients with HCM who underwent cardiac magnetic resonance (CMR) imaging were included retrospectively. Obstructive HCM was defined as LV outflow gradient more than 30 mmHg at rest by transthoracic echocardiography. The LV shape and mitral angle were assessed by CMR. Results were compared with control subjects.
Results
Mean LV-mitral angle was smaller in patients with obstructive HCM ( n = 29) than in patients with non-obstructive HCM ( n = 15) or control subjects ( n = 15) (80 ± 5° vs 87 ± 7° [ P = 0.0002] and 89 ± 2° [ P < 0.0001]). Mean mitral papillary muscles angle was greater in patients with non-obstructive HCM than in patients with obstructive HCM or control subjects (136 ± 17° vs 123 ± 16° [ P = 0.007] and 118 ± 10° [ P = 0.002]). Patients with non-obstructive HCM had a greater mean LV-aortic root angle than patients with obstructive HCM or control subjects (139 ± 6° vs 135 ± 7° [ P = 0.04] and 133 ± 7° [ P = 0.03]).
Conclusion
There is a relation between morphological and functional parameters in HCM within which the mitral valve is probably part of pathophysiogenesis.
Résumé
Contexte
Les cardiomyopathies hypertrophiques (CMH) sont souvent associées à une obstruction intraventriculaire gauche qui peut expliquer les symptômes et modifier le pronostic.
Objectif
Mieux comprendre les mécanismes qui relient l’obstruction intraventriculaire et la géométrie ventriculaire dans la CMH.
Méthodes
Les patients porteurs d’une CMH et ayant été explorés par imagerie par résonance magnétique (IRM) cardiaque ont été rétrospectivement inclus. La CMH obstructive était définie par un gradient intraventriculaire gauche supérieur à 30 mmHg au repos en échocardiographie transthoracique. La géométrie ventriculaire gauche et l’angle de la valve mitrale avec le ventricule gauche ont été explorés par IRM. Les résultats ont été comparés à ceux de sujets témoins.
Résultats
L’angle mitral moyen était plus petit chez les patients porteurs d’une CMH obstructive ( n = 29) que chez les patients porteurs d’une CMH non obstructive ( n = 15) ou chez les sujets témoins ( n = 15) (80 ± 5° contre 89 ± 2° [ p < 0,0001] et 87 ± 7° [ p = 0,0002]). L’angle interpapillaire moyen était plus important chez les patients porteurs d’une CMH non obstructive que chez les patients porteurs d’une CMH obstructive ou chez les sujets témoins (136 ± 17° contre 123 ± 16° [ p = 0,007] et 118 ± 10° [ p = 0,002]). Les patients porteurs d’une CMH non obstructive avaient un angle aortique moyen plus grand que les patients porteurs d’une CMH obstructive ou que les sujets témoins (139 ± 6° contre 135 ± 7° [ p = 0,04] et 133 ± 7° [ p = 0,03]).
Conclusion
Il existe une relation entre les paramètres morphologiques et fonctionnels du myocarde dans la CMH, dans laquelle la valve mitrale intervient probablement dans la physiopathologie.
Background
Hypertrophic cardiomyopathy (HCM) is a relatively common genetic cardiac disease with a prevalence of 1/500 and a heterogeneous phenotype. Left ventricular (LV) outflow tract obstruction is of great concern in the exploration and management of HCM because of the association with poor outcome and symptoms . Mechanisms that underlie the obstruction are complex and require special LV hypertrophy and systolic anterior motion of the anterior leaflet of the mitral valve. After several years dedicated to the description of abnormal myocardium, including LV hypertrophy and LV outflow tract, the emergence of new imaging techniques now allows the role of the mitral apparatus in the genesis of LV outflow tract obstruction to be highlighted . Abnormalities of the mitral valve have previously been described, including increased mitral leaflet areas, decreased mobility of the posterior mitral leaflet, increased numbers and mass of papillary muscles and abnormal positions of papillary muscles . Providing a good contrast and a high spatial resolution, cardiac magnetic resonance (CMR) imaging allows a precise assessment of LV geometry and mitral apparatus . The purpose of our work was to study the relation between left ventricular shape, mitral valve angle and left ventricular outflow tract obstruction at rest using CMR.
Methods
Sample
We retrospectively studied 44 consecutive patients with HCM who underwent CMR between January 2006 and February 2012 in the Cardiac Imaging Centre at Rangueil University Hospital, Toulouse, France. The clinical diagnosis of HCM was based on the demonstration by bi-dimensional echocardiography of a non-dilated and hypertrophied left ventricle (maximum left wall thickness ≥ 15 mm) in the absence of another cardiac or systemic disease that could produce a similar degree of hypertrophy . During the same period, 15 control subjects without cardiomyopathy were retrospectively recruited from consecutive referrals to our Cardiac Imaging Centre for persantin CMR to detect silent myocardial ischaemia. Any patients with clinical evidence of coronary artery disease were excluded, including patients with a clinical history and typical electrocardiogram associated with biochemical, angiographic or CMR evidence of previous myocardial infarction. Patients with a positive stress magnetic resonance imaging (MRI) test were also excluded. Demographic data, cardiovascular risk factors and medications were extracted from medical records.
Echocardiography
Transthoracic bi-dimensional echocardiography was performed using the commercially available system Philips IE33 (Philips Healthcare, Best, The Netherlands). The peak instantaneous LV outflow tract gradient was measured at rest with continuous-wave Doppler in the apical five-chamber view with the simplified Bernoulli equation. Obstructive HCM was defined by a peak instantaneous LV outflow gradient greater or equal to 30 mmHg at rest .
Cardiovascular magnetic resonance
CMR (Siemens Avanto 1.5-T, Erlangen, Germany, n = 25 and Philips Intera 1.5-T, Eindhoven, The Netherlands, n = 19) was performed using cine steady-state free precession breath-hold sequences (echo time [TE]/repetition time [TR] = 1.5/25 ms, flip angle 80°, matrix 192 × 156, field of view = 350 × 350 mm, temporal resolution 35 ms for the Siemens scan; and TE/TR = 1.5/3.5 ms, flip angle 60°, matrix 160 × 146, field of view 350 × 350 mm, temporal resolution 35 ms for the Philips scan) in four-chamber, long-axis and LV outflow track views; and sequential 8-mm short-axis views (no gap) from the atrioventricular ring to the apex. The late gadolinium enhancement images were acquired 10 minutes after intravenous gadolinium-diethylenetriamine pentaacetic acid (0.2 mmol/kg) in identical short-axis planes using an inversion-recovery gradient echo sequence. Inversion times were adjusted to null normal myocardium (typically 320–440 ms). In all patients, imaging was repeated for each short-axis image in two separate phase-encoding directions to exclude artefacts. Late gadolinium enhancement was assessed visually and was only deemed to be present when the area of signal enhancement could be seen in a cross-cut long-axis image by the independent observers.
Ventricular volumes and function were measured using standard techniques and analysed using semi-automated software (Argus software, Siemens, Erlangen, Germany and ViewForum software, Philips, Eindhoven, The Netherlands). LV mass was indexed to body surface area. LV shape and mitral angles were measured in end-diastole at rest using the open source software Osirix ( http://www.osirix-viewer.com ). The LV-mitral angle (LVMa) was defined as the angle between the LV axis and the mitral annulus in the four-chamber view ( Fig. 1 A , left panel). The mitral papillary muscles angle (MPMa) was defined as the angle between the middle of the base of both mitral papillary muscles and the centre of the left ventricle in the LV short-axis view ( Fig. 1 B, left panel). As previously described, the LV-aortic root angle (LVARa) was defined as the angle between the LV inflow and outflow tract by tracing a line between the apex and the middle of the mitral annulus and a line passing through the long axis of the aortic root in the three-chamber view ( Fig. 1 C, left panel).
Statistical analysis
Baseline characteristics are summarized using means and standard deviations (SDs) for continuous variables, and numbers and percentages for categorical variables. Associations between categorical variables were investigated using the Fisher’s exact test; and the mean values of continuous variables were compared using a Mann-Whitney test. Spearman’s correlation co-efficient was used to assess the association between angles and peak instantaneous LV outflow tract gradients. Reproducibility was assessed in 10 randomly selected patients and expressed as the absolute difference between two paired measurements divided by their average. The statistical difference was considered to be significant when P -values were < 0.05. All analyses were performed using Statview (SAS Institute Inc., Version 5).
Results
Population
Among the 44 patients with HCM explored by CMR imaging between January 2006 and February 2012, 24 (55%) were men and the mean age was 55 ± 15 years. Of these 44 patients, 29 (66%) had LV outflow tract obstruction at rest (mean peak instantaneous LV outflow tract gradient 62 ± 57 mmHg). All of the patients with obstructive HCM had a systolic anterior motion of the mitral valve. Among the 15 patients without LV outflow tract obstruction, two (5%) patients had peak instantaneous LV outflow tract gradients of 12 and 18 mmHg at rest. The other patients without LV outflow tract obstruction had no gradient at rest. The mean indexed LV mass of all 44 patients was 95 ± 27 g/m 2 . Thirty-four patients (77%) with HCM had symptoms: 21 (48%) and 13 (30%) of patients were New York Heart Association (NHYA) stages II and III, respectively. HCM patients and control subject characteristics are shown in Table 1 .
| Control subjects ( n = 15) | Non-obstructive HCM ( n = 15) | Obstructive HCM ( n = 29) | |
|---|---|---|---|
| Age (years) | 53 ± 14 | 50 ± 17 | 57 ± 14 |
| Men | 13 (87) | 9 (60) | 15 (52) † |
| Body mass index (kg/m 2 ) | 26 ± 3 | 26 ± 4 | 27 ± 4 |
| NYHA functional class | 1.1 ± 0.4 | 1.8 ± 1.0 | 2.2 ± 0.6 ††† |
| NYHA class | |||
| I | 13 (87) | 7 (47) † | 3 (10) ††† ,* |
| II | 2 (13) | 3 (20) | 18 (62) †† ,* |
| III/IV | 0 | 5 (33) †† | 8 (28) † |
| Family history of HCM | 0 | 5 (33) †† | 4 (14) |
| Maximum LV thickness (mm) | 10 ± 2 | 21 ± 7 ††† | 21 ± 4 ††† |
| Indexed LV mass (g/m 2 ) | 62 ± 17 | 92 ± 18 ††† | 97 ± 31 ††† |
| Late gadolinium enhancement | 0 | 14 (93) ††† | 12 (41) †† ,*** |
| LVEF (%) | 62 ± 10 | 63 ± 7 | 69 ± 8 † |
| Medical history | |||
| Smoking habit | 1 (7) | 0 | 2 (7) |
| Hypertension | 6 (40) | 3 (20) | 7 (24) |
| Diabetes | 1 (7) | 3 (20) | 2 (7) |
| Hyperlipidaemia | 3 (20) | 4 (27) | 9 (31) |
| Medications | |||
| Diuretic | 3 (20) | 6 (40) | 10 (34) |
| ACEI or ARB | 5 (67) | 4 (27) | 7 (24) |
| Beta-blocker | 3 (20) | 11 (73) †† | 28 (97) ††† ,* |
| Calcium channel blocker | 1 (7) | 2 (13) | 3 (10) |
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