Hypertrophic obstructive cardiomyopathy-left ventricular outflow tract shapes and their hemodynamic influences applying CMR

Abstract

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic cardiac disorders and is characterized by different phenotypes of left ventricular hypertrophy with and without obstruction. The effects of left ventricular outflow tract (LVOT) obstruction based on different anatomies may be hemodynamically relevant and influence therapeutic decision making. Cardiovascular magnetic resonance (CMR) provides anatomical information. We aimed to identify different shapes of LVOT-obstruction using Cardiovascular Magnetic Resonance (CMR). The study consisted of two parts: An in-vivo experiment for shape analysis and in-vitro part for the assessment of its hemodynamic consequences. In-vivo a 3D depiction of the LVOT was created using a 3D multi-slice reconstruction from 2D-slices (full coverage cine stack with 7 slices and a thickness of 5-6 mm with no gap) in 125 consecutive HOCM patients (age = 64.17 +/- 12.655; female n = 42). In-vitro an analysis of the LVOT regarding shape and flow behavior was conducted. For this purpose, 2D and 4D measurements were performed on 3D printed phantoms which were based on the anatomical characteristics of the in-vivo study, retrospectively. The in-vivo study identified three main shapes named K- (28.8%), X- (51.2%) and V-shape (10.4%) and a mixed one (9.6%). By analyzing the in-vitro flow measurements every shape showed an individual flow profile in relation to the maximum velocity in cm/s. Here, the V-shape showed the highest value of velocity (max. 138.87 cm/s). The X-shape was characterized by a similar profile but with lower velocity values (max. 125.39 cm/s), whereas the K-shape had an increase of the velocity without decrease (max. 137.11 cm/s). For the first time three different shapes of LVOT-obstruction could be identified. These variants seem to affect the hemodynamics in HOCM.

Keywords: Cardiovascular magnetic resonance; Hemodynamics; Hypertrophic cardiomyopathy; Hypertrophic obstructive cardiomyopathy; Left ventricular outflow obstruction; Shape analysis.

Fig. 1

Study cohort with the results of the shape differentiation

Fig. 2

(a) short axis package (SAX) covering the entire LVOT with seven slices; (b) Cine images showing the LVOT without (left) and with contours (right); (c) exemplary short axis cross sections with marked LVOT

Fig. 3

a-c three chamber view of the different shapes; (a) K-shape; (b) X-shape; (c) V-shape; (d) O-shape

Fig. 4

Distribution of hypertrophy types by shape of obstruction

Fig. 5

outlined experimental setup of the phantom circuit

Fig. 6

(a) 3D LVOT phantoms; control = “healthy” O-shape; (b) schematic illustration of the LVOT with the set-up of segmentation

Fig. 7

(a) 2D Flow CMR results with the parameter maximum velocity in cm/s in every single slice; (b) Velocity values per cross section categorized by the four different shapes

Fig. 8

4D Flow CMR visualization of the four phantom models with the path lines which includes the cross sections of each shape next to the velocity visualizations; in order: O-shape, K-shape, X-shape, V-shape; (b) 4D Flow CMR patterns of the different cross sections

Fig. 9

a-d 4D Flow CMR-visualization with streamlines showing the helical and vortical character of the flow; (a) O-shape with laminar flow corresponds with grade 0; (b) K-shape with helical flow corresponds with grade 2; (c) X-shape with helical flow grade 1; (d) V-shape with helical flow grade 1