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Biomedical subjects

A F Bolger

Publications and source records attributed to A F Bolger.

51 records · Page 3Linked to original sources
PubMed1995

Exploring better methods to preserve the chordae tendineae during mitral valve replacement.

BACKGROUND: It is not known how best to resuspend the mitral chordae tendineae during mitral valve replacement to optimize postoperative left ventricular (LV) systolic and diastolic function. METHODS: Six different techniques to preserve the chordae during mitral valve replacement were compared in 12 dogs using a nondistorting isovolumic technique: conventional, all chordae severed; anterior, all chordae preserved anteriorly; partial, anterior papillary muscle chordae preserved anteriorly; posterior, all chordae preserved posteriorly; oblique, anterior papillary muscle chordae directed anteriorly and posterior papillary muscle chordae posteriorly; and counter, opposite of oblique chordal direction. Control measurements (no chordal tension) were recorded between each experimental condition. RESULTS: The oblique method tended to have the best LV systolic function versus the conventional method (Emax = 4.0 +/- 1.8 versus 3.3 +/- 1.2 mm Hg/mL [mean +/- standard deviation]; p = 0.08 by repeated-measures analysis of variance; physiologic intercept Ees100 = 20.3 +/- 8.6 mL [p < 0.05 versus control]), with no major change in LV diastolic stiffness. The posterior method had a lower Emax (3.3 +/- 1.2 mm Hg/mL) than the oblique method, but a similar Ees100 (20.8 +/-8.1 mL; p < 0.05 versus control) and the best diastolic LV performance (LV diastolic stiffness = 0.46 +/- 0.23 mm Hg/mL). The counter method also had good systolic function (Emax = 3.8 +/- 1.2 mm Hg/mL; Ees100 = 19.7 +/- 7.5 mL; p < 0.05 versus control), but had less favorable diastolic properties (0.65 +/- 0.37 mm Hg/mL; p < 0.05 by repeated-measures analysis of variance versus posterior). CONCLUSIONS: In this isovolumic preparation in normal canine hearts, the oblique method of chordal resuspension was associated with the best LV systolic function, whereas the counter technique impaired LV diastolic function. These preliminary results warrant further study in ejecting and failing hearts to determine conclusively which chordal orientation best preserves LV performance after mitral valve replacement.

Animals↗
PubMed1994

Left atrial pressure-clamp servomechanism demonstrates LV suction in canine hearts with normal mitral valves.

A novel technique is presented to study suction of the in situ left ventricle in open-chest experimental animals without requiring cardiopulmonary bypass or disturbing the native mitral valvular apparatus. In 17 dogs, left ventricular pressure (LVP) and left atrial pressure (LAP) were measured, the left atrium was cannulated and connected to a servo pump, and LAP was controlled to a setpoint near 0 mmHg by withdrawing blood from the left atrium. Heart rate [103 +/- 17 (SD) min-1], peak pressure (100 +/- 13 mmHg), minimum pressure (1.4 +/- 0.8 mmHg), and maximum rate of change of pressure with respect to time during isovolumic contraction and relaxation (2,506 +/- 775 and -1,761 +/- 855 mmHg/s, respectively) were normal. Servo control of LAP was possible to +/- 1 mmHg. LV suction was demonstrated in each heart (mean negative LVP -2.3 +/- 1.1 mmHg; P < 0.0001). This new technique demonstrates that the left ventricle can generate negative diastolic suction pressures when examined in vivo and in situ with an undisturbed mitral valve and physiologically normal preload and afterload. This adds to a growing body of evidence that, under appropriate circumstances, the heart can suck blood into itself and thereby aid in its own filling.

Animals↗
PubMed1994

Dynamics of normal and ischemic canine papillary muscles.

This investigation was designed to elucidate the dynamics of the left ventricular (LV) papillary muscles. Miniature tantalum myocardial markers were placed on the tip and base of each papillary muscle in six dogs. Markers were also implanted into the LV myocardium to define two orthogonal equatorial diameters and the long-axis dimension. Two weeks later, after recovery from thoracotomy, markers were visualized by biplane fluoroscopy, and video images were recorded during control conditions, after autonomic blockade, after inotropic stimulation with calcium, after methoxamine infusion (to increase afterload), and after blood volume augmentation (to increase preload). Two days later, radiographic recordings were made before and after occlusion of the left circumflex coronary artery. Computer-aided analysis of the video recordings was used to determine three-dimensional coordinates of the markers. It was found that before circumflex coronary occlusion, the dynamics of both papillary muscles closely mimicked the dynamics of the LV as a whole. The papillary muscles shortened during ejection and lengthened during diastole. Their lengths changed minimally during the isovolumic periods, and this behavior was not altered by any of the interventions except coronary occlusion. During circumflex coronary artery occlusion, the ischemic posterior papillary muscle lengthened during isovolumic contraction and most of ejection and shortened only when LV pressure began to fall. Hence, we believe that previous studies demonstrating papillary muscle lengthening during isovolumic contraction and shortening during isovolumic relaxation may have been confounded by coexistent myocardial ischemia or stunning.

Animals↗
PubMed1992

Rigid ring fixation of the mitral annulus does not impair left ventricular systolic function in the normal canine heart.

BACKGROUND: Previous studies suggest that rigid fixation of the mitral annulus with an annuloplasty ring may impair left ventricular (LV) systolic performance. We used load-insensitive indexes of global and regional LV contractile mechanics to test the hypothesis that rigid fixation of the mitral annulus alters LV systolic function. METHODS AND RESULTS: Global and regional LV systolic mechanics were compared in 10 dogs during two mitral annular conditions: rigidly fixed and freely mobile. Carpentier-Edwards annuloplasty rings (20-24 mm) were inserted using a special buttressing suture technique that permitted alternate cinching of the ring down onto the annulus and subsequent removal away from the annulus. Aortic flow was measured with an electromagnetic flow probe, LV pressure by a micromanometer, and LV wall thickness and three near-orthogonal LV endocardial chamber dimensions using piezoelectric crystals during four sequential ring conditions: 1) down, 2) away, 3) down, and 4) away. The following parameters were analyzed during each ring condition to assess global LV systolic function: end-systolic chamber elastance (end-systolic pressure-volume relation), fiber elastance (end-systolic stress-volume relation), preload recruitable stroke work, and myocardial stress-strain relation. Additionally, regional LV systolic performance was assessed using the end-systolic pressure-diameter relation and a regional analog of preload recruitable stroke work. No significant differences in any of these measurements of LV systolic mechanics were observed between the two mitral annular conditions. CONCLUSIONS: Rigid fixation of the mitral annulus alters neither global nor regional LV systolic function in anesthetized, open-chest dogs with normal ventricles.

Animals↗
PubMed1991

Mitral valve replacement in dilated canine hearts with chronic mitral regurgitation. Importance of the mitral subvalvular apparatus.

The importance of the mitral subvalvular apparatus in terms of left ventricular (LV) mechanics and energetic efficiency in the chronically dilated canine heart was assessed in nine dogs with surgically induced mitral regurgitation. Miniature radiopaque tantalum markers were implanted into the myocardium to measure LV volume. Biplane cinefluoroscopic images obtained 1 week and 3 months after creation of mitral regurgitation confirmed the presence of LV dilatation. Mitral valve replacement with preservation of all chordae tendineae was then performed. LV systolic function and derived energetics were then assessed during transient caval occlusion both before and after chordal division by using exteriorized snares. Global LV systolic mechanics, as assessed by the slopes of the end-systolic pressure volume (Ees) and end-systolic stress volume (Ms) relations, fell by 46% (11.7 +/- 2.8 versus 6.3 +/- 1.4 mm Hg/ml, p less than 0.001) and 33% (17.8 +/- 4.0 versus 12.0 +/- 5.1 kdyne/cm5, p = 0.0001), respectively, when the chordae were divided. Chordal severing also increased systolic LV wall stress or LV afterload. In terms of calculated myocardial energetics, the slopes of the stroke work-end-diastolic volume and pressure volume area-end-diastolic volume relations declined significantly by 20% (85 +/- 14 versus 68 +/- 16 mm Hg) and 11% (116 +/- 20 versus 104 +/- 20 mm Hg) after cutting the chordae, thereby indicating reduced external stroke work and mechanical energy generated at any given level of preload. Moreover, the efficiency of energy transfer from pressure volume area to external stroke work fell by 19% (p less than 0.001). Since effective systemic arterial elastance (Ea) did not change, the Ea/Ees ratio (index of ventriculoarterial [V-A] coupling) increased from 0.93 +/- 0.27 to 1.67 +/- 0.62 (p = 0.006). Therefore, chordal division in dilated dog hearts due to chronic mitral regurgitation resulted not only in deterioration of systolic LV mechanics but also deleterious changes in calculated LV energetics and efficiency due to exacerbated mismatch in V-A coupling between the left ventricle and the systemic arterial bed, unfavorable loading conditions, and exhaustion of preload reserve. These observations in the low-pressure, volume-overloaded heart due to chronic mitral regurgitation underscore the importance of the mitral subvalvular apparatus for optimal LV systolic performance and energetic efficiency.

Animals↗
PubMed1991

Freehand allograft aortic valve replacement and aortic root replacement. Utility of intraoperative echocardiography and Doppler color flow mapping.

UNLABELLED: Seventeen consecutive patients undergoing 20 planned aortic valve replacements with allograft valves at Stanford University Medical Center were studied with intraoperative epicardial echocardiography and Doppler color flow mapping before and after cardiopulmonary bypass. Native aortic valves were replaced in 12 of the 20 patients, and eight patients underwent second aortic valve procedures. In 17 of 20 patients allograft selection was guided by prebypass echocardiographic estimates of annular diameter and/or length of allograft aortic root required. Other prebypass findings included unanticipated severe mitral regurgitation in one patient (which precluded allograft aortic valve replacement), left-to-right shunts in five patients, ascending aortic dissection in one, and aortic root disease necessitating coronary reimplantation or bypass in two. Postbypass echocardiography demonstrated acceptable competency of 18 of 19 allograft valves (mild or no aortic insufficiency). Postbypass echocardiography also documented successful repair of four of five shunts and mild mitral regurgitation in 15 of 19 patients (versus 11 of 19 before bypass). CONCLUSIONS: Intraoperative echocardiography-Doppler mapping is a useful adjunct for allograft aortic valve or aortic root replacement; it allows confident selection of appropriate tissue size before aortic cross clamping, which minimizes delay from allograft thawing procedures. It also provides helpful information about the extent of aortic root disease and coronary ostial anatomy before bypass, confirms allograft competency after bypass, and detects accompanying valvular and other hemodynamic lesions before and after allograft valve replacement.

Adult↗
PubMed1990

Intraoperative echocardiography and Doppler color flow mapping in freehand allograft aortic valve and root replacement.

Intraoperative epicardial echocardiography and color flow Doppler were performed before and after cardiopulmonary bypass in 17 consecutive patients undergoing 20 freehand allograft aortic valve replacements. Native aortic valves were replaced in 12, and prostheses in 8 patients. Precardiopulmonary bypass echocardiography estimates of annular diameter guided allograft selection and predicted length of allograft aortic root required, defined coronary situs, and revealed other cardiac abnormalities. These included unanticipated severe mitral regurgitation (which precluded allograft aortic valve replacements in one patient), left-to-right shunts in the membranous septum, ascending aortic dissection, and aortic root pathology requiring coronary reimplantation or bypass. Postcardiopulmonary bypass echocardiography demonstrated acceptable competency of 18/19 allograft valves (mild or no aortic insufficiency), and successful repair of 3/4 shunts. Mild mitral regurgitation was detected more often at postcardiopulmonary bypass than precardiopulmonary bypass (15 vs 11 cases) and postcardiopulmonary bypass estimates of mitral regurgitation severity corollated well with subsequent postoperative follow-up. IOE allows selection and thawing of the allograft valves prior to aortic cross clamping, minimizing cross-clamp time. It detects important concomitant cardiac abnormalities, and predicts postoperative allograft valve and mitral competency. Intraoperative echocardiography Doppler, is therefore, a useful adjunct for allograft aortic valve replacements or aortic root replacement.

Adolescent↗
PubMed1990

Importance of the mitral subvalvular apparatus for left ventricular segmental systolic mechanics.

The relative importance of the anterolateral (ANTLAT) and posteromedial (POSTMED) papillary muscle (PM) chordae tendineae for left ventricular (LV) segmental wall function was assessed in 12 in situ ejecting canine hearts. Pairs of piezoelectric crystals were placed in the regions subtending PM insertions and the ANTLAT LV free wall to measure wall thickness. After mitral valve replacement with complete preservation of the subvalvular apparatus, chordal attachments to either the ANTLAT PM or POSTMED PM were randomly severed using exteriorized snares, followed by subsequent division of the remaining chordae tendineae. Segmental wall function in each region was determined at each stage by segmental preload recruitable stroke work (sPRSW, slope of the segmental stroke work-end-diastolic wall thickness relation). The order in which the chordae were severed was unimportant (p greater than 0.530 in all regions). When the ANTLAT PM chordae were severed first, there were significant declines in sPRSW without a change in the wall thickness intercept in both the ANTLAT (-71.0 +/- 18.3 vs. -57.7 +/- 16.8 mmHg, p less than 0.05) and POSTMED (-81.8 +/- 23.1 vs. -65.4 +/- 17.3 mmHg, p less than 0.05) PM insertion sites. No further significant reductions in sPRSW in either region were detected after severing the remaining chordal attachments to the POSTMED PM. sPRSW in the ANTLAT LV free wall decreased progressively, reaching statistical significance when both sets of chordae tendineae were divided (-88.3 +/- 14.3 vs. -74.0 +/- 15.2 mm Hg, p less than 0.05). When the POSTMED PM chordae were severed first, no significant changes in sPRSW or the wall thickness intercept in either region of PM insertion were detected. Subsequent division of the ANTLAT PM chordal attachments reduced sPRSW significantly in both the ANTLAT PM (-65.9 +/- 21.1 vs. -56.1 +/- 22.1 mm Hg, p less than 0.05) and POSTMED PM (-78.8 +/- 24.7 vs. -67.2 +/- 24.0 mm Hg, p less than 0.05) insertion sites, without a shift in the wall thickness intercept. In the ANTLAT LV free wall, sPRSW again fell progressively, achieving statistical significance only when both chordal attachments were severed (-78.6 +/- 14.8 vs. -62.2 +/- 13.7 mm Hg, p less than 0.05). In conclusion, division of the chordae tendineae resulted in a decline in segmental LV function not only in the areas subtending PM insertions but also in remote LV regions. Furthermore, the influence of the ANTLAT PM chordae predominated local LV systolic function at both PM insertion sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Computer analysis of Doppler color flow mapping images for quantitative assessment of in vitro fluid jets.

To determine the ability of Doppler color flow mapping to accurately and reproducibly assess the flow volume and kinetic energy of in vitro fluid jets, a Doppler color flow mapping system was interfaced with an image processing computer. An aliasing correction algorithm was used to extend the upper limit of measurable velocity to 184 cm/s. Images were analyzed for jet area (equal to the total number of image pixels) and jet energy (equal to the sum of all pixel velocities squared), both integrated over all frames of the injection and in single maximal frames. The Doppler flow mapping area and energy measurements were compared with known flow volume and delivered kinetic energy, and the effects of four experimental variables (orifice area, gain setting, chamber compliance and chamber size) were evaluated. Jet area correlated nonlinearly with flow volume and was markedly affected by each of these experimental variables, increasing by 40 to 150% from the smallest to the largest orifice size, 15 to 94% with the highest versus the lowest gain setting, 1 to 54% with greater chamber compliance and 7 to 70% in the large versus the small chamber. In contrast, jet energy correlated linearly with delivered kinetic energy up to 350,000 ergs, at which point velocities started to exceed the extended velocity range and second wrap aliasing occurred. The relation was not affected by orifice area, gain or compliance, and was only minimally affected by chamber size.(ABSTRACT TRUNCATED AT 250 WORDS)

Image Processing, Computer-Assisted↗
PubMed1987

Intraoperative Doppler color flow mapping for assessment of valve repair for mitral regurgitation.

The ability of color Doppler flow mapping to provide intraoperative information about mitral regurgitation (MR) severity and to evaluate adequacy of mitral valve repair was assessed by performing color Doppler echocardiography immediately before and after cardiopulmonary bypass, with the transducer placed directly on the epicardium. In 56 patients, the degree of MR by intraoperative color Doppler correlated well with left ventricular angiography (kappa = 0.80) and with closed-chest preoperative color Doppler (kappa = 0.84) and had good interobserver reproducibility (kappa = 0.88). Good correlation was also seen between closed-chest color Doppler and angiography (kappa = 0.75). After mitral valve repair in 18 patients (15 ischemic MR, 3 cleft valves), color Doppler was used to assess severity of residual MR intraoperatively and postoperatively. Intraoperative color Doppler identified satisfactory repair (MR less than or equal to 2+) in 15 patients and failure (MR greater than or equal to 3+) in 3, whereas conventional surgical assessment of MR by fluid filling of the arrested ventricle failed to provide reliable differentiation. MR severity on subsequent closed-chest color Doppler follow-up did not change significantly compared with intraoperative evaluation after repair. Intraoperative color Doppler provides accurate grading of MR severity, offers instantaneous evaluation of the adequacy of mitral valve repair before chest closure, and appears to predict the degree of postoperative MR seen on subsequent closed-chest follow-up studies.

Blood Flow Velocity↗
PubMed1987

Intraoperative evaluation of mitral regurgitation by Doppler color flow mapping.

Excessive residual mitral regurgitation after mitral valve reconstruction or coronary artery bypass graft surgery may necessitate reoperation. We evaluated a new intraoperative technique for assessment of mitral regurgitation, real-time two-dimensional Doppler color flow mapping, in 96 patients undergoing cardiac surgery. In comparison with technically adequate preoperative left ventriculography (n = 68) obtained at a similar level of afterload (systolic arterial pressure), Doppler color flow mapping demonstrated a sensitivity of 94% (50/53) and specificity of 93% (14/15) for detection of the presence and absence of mitral regurgitation, respectively. Semiquantitative comparison of color Doppler with angiography demonstrated excellent agreement (kappa = .80, p less than .001), differing by more than one grade in two patients (3%). The pulmonary capillary wedge "V" wave pressure (absolute magnitude, and height above mean) correlated poorly with the simultaneously obtained mitral regurgitation grade by color Doppler, both before (r = .37 and .45) and after (r = .04 and -.15, p = NS) cardiopulmonary bypass. No value of the V wave clearly distinguished 3 + or 4 + regurgitation from lesser degrees of regurgitation. In 15 patients who underwent mitral valve repair, fluid filling of the ventricle was falsely positive (leak, with no regurgitation) in 40% (2/5), and falsely negative (no leak, with 2 + to 3 + regurgitation) in 30% (3/10). Regurgitation grade by color Doppler demonstrated a highly significant (p less than .01) dependence on systolic pressure, suggesting that intraoperative changes in afterload conditions importantly influence mitral regurgitation severity. Thus, Doppler color flow mapping provides accurate intraoperative evaluation of mitral regurgitation and may aid surgical decision making.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Vessel Prosthesis↗
PubMedDate not supplied

Understanding continuous-wave Doppler signal intensity as a measure of regurgitant severity.

Continuous-wave Doppler signal intensity is commonly expected to reflect the severity of mitral regurgitation. Physical principles predict that alignment of the imaging beam, flow velocity, and turbulence can also be important or even dominant determinants of continuous-wave Doppler signal intensity. The reliability of tracking regurgitant severity with continuous-wave Doppler signal intensity was assessed in vitro with varying volume, velocity, turbulence, and beam alignment. The conditions wherein continuous-wave Doppler signal intensity increased with regurgitant volume were specific but poorly predictable combinations of orifice size, flow volume, and perfect beam alignment. Under other conditions flow velocity and turbulence effects dominated, and continuous-wave Doppler signal intensity did not reflect changing regurgitant volume. Continuous-wave Doppler signal intensity-based impressions of regurgitant severity may be unreliable and even misleading under some circumstances.

Echocardiography, Doppler↗