Enhanced regional deformation at the anterior papillary muscle insertion site after chordal transsection

Mitral chordal-leaflet-myocardial interactions in mitral valve prolapse

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.

Importance of preservation of chordal apparatus in mitral valve replacement

Mitral valve replacement often involves disruption of the chordal apparatus with disturbance of the annulo-papillary continuity. This results in significant downgrading of ventricular function. Analyzes various reports to accurately assess the advantages of chordal preservation. This review briefly briefly reviews the surgical techniques. The advantages of chordal preservation are analyzed, with particular emphasis on the technical difficulties and potential complications involved.

Contribution of myocardium overlying the anterolateral papillary muscle to left ventricular deformation

Previous studies of transmural left ventricular (LV) strains suggested that the myocardium overlying the papillary muscle displays decreased deformation relative to the anterior LV free wall or significant regional heterogeneity. These comparisons, however, were made using different hearts. We sought to extend these studies by examining three equatorial LV regions in the same heart during the same heartbeat. Therefore, deformation was analyzed from transmural beadsets placed in the equatorial LV myocardium overlying the anterolateral papillary muscle (PAP), as well as adjacent equatorial LV regions located more anteriorly (ANT) and laterally (LAT). We found that the magnitudes of LAT normal longitudinal and radial strains, as well as major principal strains, were less than ANT, while those of PAP were intermediate. Subepicardial and midwall myofiber angles of LAT, PAP, and ANT were not significantly different, but PAP subendocardial myofiber angles were significantly higher (more longitudinal as opposed to circumferential orientation). Subepicardial and midwall myofiber strains of ANT, PAP, and LAT were not significantly different, but PAP subendocardial myofiber strains were less. Transmural gradients in circumferential and radial normal strains, and major principal strains, were observed in each region. The two main findings of this study were as follows: 1) PAP strains are largely consistent with adjacent LV equatorial free wall regions, and 2) there is a gradient of strains across the anterolateral equatorial left ventricle despite similarities in myofiber angles and strains. These findings point to graduated equatorial LV heterogeneity and suggest that regional differences in myofiber coupling may constitute the basis for such heterogeneity.

Strain-related regional alterations of calcium-handling proteins in myocardial remodeling

BACKGROUND

Cardiac remodeling has been shown to have deleterious effects at both the global and local levels. The objective of this study is to investigate the role of strain in the initiation of structural and functional changes of myocardial tissue and its relation to alteration of calcium-handling proteins during cardiac remodeling after myocardial infarction.

METHODS

Sixteen sonomicrometry transducers were placed in the left ventricular free wall of 9 sheep to measure the regional strain in the infarct, adjacent, and remote myocardial regions. Hemodynamic, echocardiographic, and sonomicrometry data were collected before myocardial infarction, after infarction, and 2, 6, and 8 weeks after infarction. Regional myocardial tissues were collected for calcium-handling proteins at the end study.

RESULTS

At time of termination, end-systolic strains in 3 regionally distinct zones (remote, adjacent, and infarct) of myocardium were measured to be -14.65 +/- 1.13, -5.11 +/- 0.60 (P < or = .05), and 0.92 +/- 0.56 (P < or = .05), respectively. The regional end-systolic strain correlated strongly with the abundance of 2 major calcium-handling proteins: sarcoplasmic reticulum Ca2+ adenosine triphosphatase subtype 2a (r2 = 0.68, P < or = .05) and phospholamban (r2 = 0.50, P < or = .05). A lesser degree of correlation was observed between the systolic strain and the abundance of sodium/calcium exchanger type 1 protein (r2 = 0.17, P < or = .05).

CONCLUSIONS

Regional strain differences can be defined in the different myocardial regions during postinfarction cardiac remodeling. These differences in regional strain drive regionally distinct alterations in calcium-handling protein expression.

Regional myocardial function at the papillary muscle insertion site

The importance of the mitral apparatus to the global left ventricular (LV) function has been suggested in several clinical studies. One recent study reported that chordal transsection induced an unloading of myocardium at the papillary muscle insertion site. We hypothesized that the regional response for afterloading at this site with intact mitral apparatus was different from that at the free wall. We investigated the end-systolic pressure-regional segment length relations (ESPLR) in two anterior LV sites, free wall (FREE) and the papillary muscle insertion site (PAP), during an increasing afterload by aortic occlusion in 7 anesthetized open-chest dogs. To measure the regional segment length at FREE and PAP, two sets of the pair of sonomicrometer crystals were implanted in the same midwall depth at the same circumferential hoop by using an echocardiographic guide. ESPLR both at FREE and PAP were always highly linear in a physiological range (r > or = 0.9). The slope of this relation at FREE (274 +/- 164 mmHg/mm) was significantly steeper than that at PAP (157 +/- 118 mmHg/mm) for each dog (p < 0.05). These data indicate that the regional response for afterloading at PAP loaded by chordal tension is different from that at FREE in the same heart.

Effects of mitral valve replacement on regional left ventricular systolic strain

BACKGROUND

Mitral valve replacement (MVR) with chordal excision impairs left ventricular (LV) systolic function, but the responsible mechanisms remain incompletely characterized. Loss of normal annular-papillary continuity also adversely affects LV torsional deformation, possibly due to changes in myocardial fiber contraction pattern.

METHODS

Twenty-seven dogs underwent insertion of LV myocardial markers and a sham procedure (cardiopulmonary bypass, no MVR, n = 6), conventional MVR with chordae tendineae excision (n = 7), or chordal-sparing MVR with reattachment of the anterior leaflet chordae to the anterior annulus (n = 7) or to the posterior annulus (n = 7). In the anterior, lateral, posterior, and septal LV regions, linear chords were constructed from each region's central marker to its surrounding markers. Percent systolic shortening (regional LV strain) was calculated for each chord, and the chords were assigned to one of four angular groups: I, left-handed oblique (subepicardial fiber direction); II, circumferential (midwall); III, right-handed oblique (subendocardial); or IV, longitudinal. Regional LV strain data were compared before and after MVR.

RESULTS

Sham and anterior chordal-sparing MVR had minimal effects on regional LV strain. With posterior chordal-sparing MVR: anteriorly, left-oblique (I) strain fell (31%, p<0.05), as did circumferential (II) and right-oblique (III) strains (by 49% and 51%, respectively; p<0.01). Laterally, left-oblique (I) strain fell by 36% (p<0.05), as did longitudinal (IV) strain (54% decline, p<0.01). Conventional MVR with chordal excision disrupted regional fiber shortening diffusely, affecting oblique fibers (I and III) in the anterior and septal regions and impairing longitudinal (IV) strain in all regions (45% to 68% fall, p<0.05).

CONCLUSIONS

Sham and anterior chordal-sparing MVR did not substantially alter regional LV strain; however, loss of normal anatomic valvular-ventricular integrity (conventional MVR) or posterior chordal-sparing MVR resulted in pronounced alterations in LV strain, most notably in the longitudinal and oblique fiber directions. These findings demonstrate that the deleterious effects of chordal excision are associated with perturbed internal myocardial systolic deformation, which suggests that chordal disruption distorts myofiber architecture or regional systolic loading.