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‘How I do’ CMR in HCM. Dr Sanjay Prasad, Royal Brompton Hospital London, UK. For SCMR August 2006 This presentation is posted for members of scmr as an educational guide – it represents the views and practices of the author, and not necessarily those of SCMR. s.prasad@rbht.nhs.uk.
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‘How I do’ CMR in HCM Dr Sanjay Prasad, Royal Brompton Hospital London, UK. For SCMR August 2006 This presentation is posted for members of scmr as an educational guide – it represents the views and practices of the author, and not necessarily those of SCMR. s.prasad@rbht.nhs.uk
Hypertrophic Cardiomyopathy: Clinical Aspects • Characterized by myocyte disarray, hypertrophy, and interstitial fibrosis • 90% of pts have familial disease • 10% de novo mutations • Increased risk of SCD • Adult prevalence 1:500 (Autosomal Dominant) • 1st degree-relatives -1:2 risk gene carrier
HCM: Diagnosis • Unexplained hypertrophy • Measured wall thickness exceeds 2SD for gender-,age-, and BSA-matched populations • ≥ 1.5cm in absence of a recognized cause • There may be associated systolic anterior motion of the mitral valve leaflets and outflow tract obstruction • Multiple causative mutations in at least 10 different sarcomeric proteins • Variable phenotype and clinical outcome Seidman et al 2002; Chien 2003
HCM – HistopathologyMyocyte Disarray Here with some associated fibrosis
In addition to asymmetric hypertrophy, there is often extensive fibrosis HCM and Fibrosis
CMR Evaluation of HCM • The first important aspect is determining LV and RV volumes, ejection fractions, maximal wall thickness and mass • We recommend the modified Simpson’s method rather than biplanar assessment since it makes no assumptions on cardiac morphology and is both more accurate and reproducible. • After piloting the 4ch and VLA views, retrospectively gated gradient echo cine slices are taken from the base to apex • Typically 7mm slices with a 3mm gap. • Usually myocardial coverage is achieved in 9-10 slices
CMR Quantification See the presentation ‘how I do’ LV volumes Downloadable from www.scmr.org
HCM: Cine Imaging • The key questions to address are: - • Presence, distribution, and severity of LVH and RVH. LV/RV mass and wall thickness • Extent of septal involvement • Distribution of hypertrophy in the variant forms of hypertrophic cardiomyopathy
Functional Assessment • Cine images are then acquired to determine if there is SAM and LVOTO. • SSFP images with retrospective gating recommended
HCM: LVOTO Assessment • In-plane followed by through plane breath-hold flow mapping is performed to look at the peak velocity at the outflow tract (red-bar) and at the level of the aortic valve.
Assessment of Fibrosis • The presence of replacement fibrosis can be detected using the inversion recovery late enhancement technique following gadolinium-DTPA administration. • After all, fibrosis is the main component of chronic MI which is visible with the late enhancement technique
HCM fibrosis imaging? Fibrosis imaging in HCM Gd infarct imaging
HCM – a wide variety of scar 2 patients. For the lower patient, scar is present and invisible without Gd-DTPA. Many patients have no detectablescar
Fibrosis -not like IHD Picro sirius red stains collagen red. In-vivo vs exvivo match
Detection of Fibrosis: Inversion Recovery Sequence • Dosage of Gd-DTPA: 0.1-0.2mmol/kg • At 0.1mmol/kg, images are usually acquired after about 5 minutes with a TI starting at ~340ms (every other heart beat). • At 0.2 mmol/kg, scans are acquired after about 15 minutes with a TI starting at ~250ms.
HCM: Detection of Fibrosis • LGE is predominantly seen in a patchy distribution and correlates with wall thickness. • Unlike in IHD, the subendocardium is not necessarily affected. • Unlike DCM, the distribution is typically more diffuse and not specific to mid-wall circumferential fibres.
Detection of Fibrosis: Inversion Recovery Sequence • Tips to confirm fibrosis and not artefact: • Phase swap each slice • If mid-wall enhancement is seen, ensure TI is optimal and if need be, repeat the slice with a different TI • Cross-cut through any areas of suspected mid-wall enhancement • If subendocardial enhancement is seen, reconsider the diagnosis or assess if this reflects ‘bystander’ coronary disease • It is common to see some fibrosis around the LVOT and at the RV/LV septal insertion points
Assessment of Fibrosis late enhancement in the septum reflecting fibrosis
RV insertion point enhancement 2 spots of enhancement at RV insertion points • The 3rd point is artefact – Present AP phase encoding, disappears head-foot. This is artefact ghosting across the image.
Other techniques: perfusion Rest Perf Late Gd Perfusion defects in HCM – uncertain significance; here matching enhancement
Summary • Evaluate function, volumes, maximal wall thickness, distribution of hypertrophy and overall mass index. • Flow mapping to assess LVOTO • Presence of fibrosis important using inversion-recovery Gd-DTPA s.prasad@rbht.nhs.uk