NEW YORK (Reuters Health) – Individual variations in the membranous septum and in the rotation of the aortic root could have implications for transcatheter aortic valve replacement (TAVR).
“The most interesting finding was the correlation of clockwise aortic root rotation with lengthening of the central fibrous body under the aortic root, and hence increased fibrous as opposed to muscular support of the aortic root,” Dr. Justin T. Tretter from Cincinnati Children’s Hospital Medical Center, in Ohio, told Reuters Health by email. “We presume that this variability in aortic root rotation also directly correlates to the length of the atrioventricular conduction axis which courses underneath the aortic root before bifurcating into the bundle branches, variability which may leave those with a clockwise-rotated aortic root at higher risk for conduction damage following left-ventricular outflow tract and aortic root manipulation.”
New or worsened conduction abnormalities commonly follow TAVR, but the precise anatomical basis for this complication is poorly understood.
Dr. Tretter and colleagues used 26 autopsy specimens of normal hearts and 78 CT data sets from adults (mean age, 64) to measure the dimensions of the membranous septum, to assess the influence played by rotation of the aortic root and to infer the relationship to the atrioventricular conduction axis.
The aortic root was centrally located in 14 hearts (54%), rotated clockwise in four (15%), and rotated counterclockwise in eight (31%), according to the November 16 online report in Heart.
The dimensions and position of the membranous septum were independent of aortic root rotation.
When the aortic root was located centrally, the septal myocardium supported the mid-portion of the left coronary leaflet and extended rightward to include the entire right coronary leaflet, whereas fibrous tissue supported the entire non-coronary leaflet and extended leftward to the mid-portion of the left coronary leaflet.
The extent of fibrous support increased with increasing clockwise rotation and decreased with increasing counterclockwise rotation of the aortic root.
CT results from the 78 adults paralleled the findings of the autopsy studies. The median rotation of the aortic root was 15.5 degrees, with a range from -32 degrees to +44.7 degrees, and the dimensions of the membranous septum were independent of aortic root rotation.
Elongation of the central fibrous body associated with clockwise rotation of the aortic root could place the atrioventricular bundle, which penetrates the atrioventricular component of the septum as it extends to reach the left-ventricular outflow tract, at increased risk during instrumentation or TAVR.
“This novel understanding of variation in the aortic root and its underlying support, and the described methods to assess this by CT assessment, may allow for better preprocedural and preoperative planning,” Dr. Tretter said. “The variability in structural support may affect valve function and durability, while the variability in the central fibrous body and membranous septum dimensions may predispose certain patients to an increased risk of conduction damage (i.e., those with a clockwise-rotated aortic root). However, these theories require further investigations in disease-specific populations.”
Dr. Arash Salemi and Dr. Adham Elmously from Weill Cornell Medicine/New York Presbyterian Hospital, New York, who have examined various aspects of aortic valve replacement, told Reuters Health by email, “Multidetector CT imaging has completely revolutionized the TAVR practice by aiding in annular sizing, which reduced the rate of postprocedure aortic regurgitation, by identifying annular calcification, and by determining the ‘horizontality’ or angle of the ventricular outflow tract. Establishing a protocol which estimates variation in the location of the atrioventricular conduction axis may prove to be beneficial in decreasing post-TAVR pacemaker requirements.”
“The ability to identify a relationship on CT between the aortic root and the atrioventricular conduction axis will have an important role in determining appropriate TAVR implant and implantation depth, which will hopefully diminish the need for permanent pacemaker implantation,” they conclude.
SOURCE: http://bit.ly/2zZpp3C
Heart 2017.
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