Background
The submitral apparatus maintains annular-papillary continuity and myocardial geometry. In mitral valve prolapse (MVP), elongated chords and redundant leaflets can interact at the region of myocardial attachment, leading to apparent discordant motion of the basal inferolateral wall. The aim of this study was to test the hypothesis that basal inferolateral wall inward motion would occur later in MVP and that this delay is associated with MVP severity.
Methods
Thirty consecutive patients with MVP and matched controls underwent stress echocardiography. Time to peak transverse displacement (TPD) of the inferolateral wall compared with the anteroseptal wall was measured using speckle-tracking echocardiography. The time difference was analyzed as raw data, normalized to the RR interval, and as a percentage of the time to maximal displacement of the anteroseptal segment(s).
Results
Compared with controls, TPD was delayed in patients with MVP both at rest and at peak stress, when evaluating basal segments or basal-mid segments as a unit, both in real time and, more importantly, when correcting for anteroseptal TPD. In patients compared with controls, observed delay at rest and at peak stress was 50 ± 90 versus −30 ± 90 msec ( P = .006) and 70 ± 80 versus −30 ± 60 msec ( P < .0001), respectively; relative to TPD of the anteroseptal segment, the observed delay at rest and at peak stress was 117 ± 24% versus 97 ± 22% ( P = .007) and 144 ± 68% versus 95 ± 21% ( P = .003), respectively. Similar significant findings were observed in basal-mid segments. TPD results were not statistically significant when stratified by prolapse severity. Intraclass correlation coefficients were 0.88 and 0.93, and two-tailed t tests indicated good interobserver and intraobserver variability.
Conclusions
Inferolateral wall TPD is delayed in MVP. TPD is a novel method to characterize chordal-leaflet-myocardial interactions in patients with MVP. Prolapse severity does not predict TPD, likely because of the timing of prolapse and dynamic loading conditions. Implications of this observation include attribution of a perceived wall motion abnormality in MVP during stress echocardiography to a physiologic state and new mechanistic insights into mitral valve physiology.
The mitral chordal apparatus plays a key role in the maintenance of ventricular geometry and performance. Mitral valve prolapse (MVP) is a condition characterized, in part, by elongation of the chordal apparatus and delay in maximal stretch during systole. This delay may influence the timing of myocardial motion in the segment(s) to which the elongated chordae attach and therefore complicate the assessment of left ventricular (LV) systolic function, both at rest and with the enhanced inotropy associated with exercise. A better understanding of this phenomenon may therefore benefit the echocardiographic interpretation of systolic function at rest and after exercise in patients with MVP.
We therefore sought to characterize mitral chordal-leaflet-myocardial (CLM) interactions in MVP using novel applications of speckle-tracking echocardiography. We hypothesized that the delay in mitral chordal-leaflet maximal stretch in patients with MVP will result in delayed maximal inward motion of the basal inferolateral wall compared with the opposing corresponding basal anteroseptal segment and that this delay is associated with MVP severity.
Methods
Study Population
The study population consisted of 30 consecutive patients with MVP meeting the inclusion criteria, who underwent stress echocardiography. Prolapse was defined as maximal end-systolic displacement of the body of the posterior mitral leaflet >2 mm superior to the line connecting the annular hinge points in the parasternal long-axis view. All individuals had posterior mitral leaflet involvement. Inclusion criteria were mitral regurgitation of less than moderate severity, normal LV systolic function, and no LV regional wall motion abnormalities. Thirty age-matched and sex-matched controls were selected from a population of contemporaneous patients referred for stress echocardiography at the same institution.
Exercise Stress Echocardiography
All patients underwent maximal symptom-limited treadmill exercise echocardiography according to the Bruce protocol, as previously outlined by the American Society of Echocardiography. Doppler echocardiography with color flow was performed using a commercially available system (Vivid 7; GE Vingmed Ultrasound AS, Horten, Norway). Images were acquired from standard parasternal and apical views and stored digitally in cine loop format for three consecutive analyzable beats. Offline measurements were performed by a single observer using EchoPAC version 104.3.0 (GE Vingmed Ultrasound AS). Quantification of the extent of MVP was performed by two individuals. To assess intraobserver variability and avoidance of recall bias, the same observer reassessed the amount of prolapse 6 months after initial assessment in 10 randomly selected patients. To assess interobserver variability, a second observer, blinded to the results of the first, performed 10 independent measurements on the same patients for two different parameters on a different reading station.
Speckle-Tracking Strain Analysis
Standard grayscale two-dimensional images were obtained in parasternal and apical views. All images were recorded at frame rates of 70 to 100 Hz and digitally saved in cine loop format. Offline speckle-tracking analysis was performed using software for echocardiographic quantification (EchoPAC version 104.3.0). Endocardial borders of the left ventricle were manually traced within the end-systolic frame. The epicardial tracing was automatically generated by the software algorithm and manually adjusted when necessary. Tracking was accepted only if both visual inspection and EchoPAC software analysis confirmed that it was adequate. Peak transverse displacement in the basal inferolateral, middle inferolateral, basal anteroseptal, and middle anteroseptal walls was assessed in apical long-axis views, and a time-displacement profile was exported to Microsoft Excel 2010 (Microsoft Corporation, Redmond, WA) for quantitative analysis.
Time to peak transverse displacement (TPD) was defined as the time to maximal inward motion of a given myocardial segment ( Figure 1 ). Speckle-tracking consistently tracks pixels within myocardial segments, thus tracking the displacement of myocardial segments at rest and immediately after exercise. By measuring and comparing this parameter in basal and mid inferolateral and anteroseptal segments, the extent of dyssynchrony could be determined in patients with normal mitral valve and ventricular structure and in those with MVP ( Figures 2–4 , Videos 1–4 ; available at www.onlinejase.com ). Because chordal attachments may be variable, we assessed both the relative differences between TPD in basal segments and the average of TPD in all anteroseptal versus inferolateral segments. Both groups were assessed at rest and immediately after exercise. All data were abstracted electronically, using custom-programmed software macros, and checked qualitatively to ensure that computer-derived results were not spurious.
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