Effect of infarct stiffness on non-infarcted left and right ventricular tissue remodeling: a computational study based on myocardial mechano-transduction

Background/Introduction

The mechanical properties of infarcted myocardium are important determinants of cardiac pump function and risk of developing heart failure following myocardial infarction (MI).

Purpose

To better understand the effects of infarct stiffness on compensatory hypertrophy and dilation of non-infarcted tissue in the left (LV) and right ventricle (RV), by using a computational model.

Methods

The CircAdapt computational model of the human heart and circulation was applied to simulate an acute MI involving 20% of LV wall mass. The simulation was validated using previously published experimental data. Subsequently, two degrees of increased infarct stiffness were simulated. In all three simulations, a model of structural myocardial adaptation of the non-infarcted tissue was applied, based on sensing of mechanical loading of myocytes and extracellular matrix (ECM).

Results

Mild and severe stiffening of the infarct reduced the increase of LV end-diastolic volume (EDV) from +23 mL to +17 mL and +16 mL, respectively, and the increase of LV non-infarcted tissue mass from +31% to +21% and +18%. RV EDV decreased after adaptation, and mild and severe infarct stiffening reduced the decrease of RV EDV from −21 mL to −12 mL and −10 mL, respectively. Increase of RV tissue mass was reduced from +13% to +8% and +7% with mild and severe infarct stiffening. In the LV, reduced dilation and hypertrophy were driven mainly by a reduction of maximum stress in the ECM and a higher stress between the myocytes and ECM following infarct stiffening. The decreased RV hypertrophy, but not EDV reduction, was caused by a reduction of maximum RV ECM stress and maximum RV active myofiber stress.

Conclusions

Model simulations predicted that a stiffened LV infarct reduces both LV and RV non-infarcted tissue hypertrophy as well as LV dilation. In LV remodeling, maximum ECM stress and stress between myocyte and ECM played a more prominent role than in RV remodeling, while maximum active stress was more important in the RV.

Overview of all model simulations

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): This work was funded by the Netherlands Organisation for Scientific Research and the Dutch Heart Foundation.

Baseline left atrial strain is associated with clinical outcomes following cardiac resynchronization therapy in patients with intermediate electrocardiographic criteria

Background

Guidelines favor patient selection by left bundle branch block (LBBB) with QRS width ≥150 ms for cardiac resynchronization therapy (CRT). However, predicting response to CRT patients with QRS width 120 to 149 ms or non-LBBB remains difficult. Speckle tracking left atrial (LA) strain is a novel means to assess cardiac function, however its applications to CRT patients remains unclear.

Purpose

To test the hypothesis that baseline LA strain has prognostic value in CRT patients with intermediate ECG criteria.

Methods

We studied 195 patients with heart failure (HF) who underwent CRT based on routine indications: ejection fraction ≤35% and QRS width ≥120 ms. GLS was assessed using the 3 standard apical views. LA longitudinal strain was based on 12 segments from the 2 and 4-chamber apical view. Peak LA strain, a measure associated with the reservoir function of the LA, was defined as the average of peak longitudinal strain from all segments. The predefined combined clinical endpoint was death, heart transplant or left ventricular assist device (LVAD) over 4 years after CRT.

Results

LA strain was feasible in 162 (83%) of the candidates for CRT: age 64±11 years, 72% male, QRS duration 156±26 ms, 39.5% had LBBB with QRS ≥150ms, 60.5% had intermediate ECG criteria. Median LA strain was 11.0% [1.3% - 36.8%]. High LA peak strain was associated with more favorable event-free survival and Low LA Peak strain was associated with worse clinical outcome following CRT (FIGURE, p<0.001). Patients with intermediate ECG criteria for CRT (non-LBBB or QRS width 120 to 149 ms) and high peak LA strain had similar outcome to those with Class I indications for CRT (LBBB and QRS≥150 ms). Multivariable analysis revealed that LA strain had independent prognostic value (hazard ratio 0.98 per LA strain %, p<0.01) even after adjusted for other clinical, electrophysiological and echocardiographic covariates including QRS morphology and duration, ischemic cardiomyopathy, LVEF and global longitudinal strain.

Conclusions

Baseline peak LA strain had important prognostic value in HF patients who are candidates for CRT. Prognostic value of LA strain was most significant in CRT patients with intermediate ECG criteria (QRS 120 to 149ms or non-LBBB) and has promise for clinical applications.

LA strain and clinical outcome after CRT

Funding Acknowledgement

Type of funding source: None

P2724Diagnosis of transthyretin versus light chain cardiac amyloidosis by apical sparing strain ratio in patients with clinically suspected disease

Background

Apical sparing by longitudinal strain imaging has reported utility for the diagnosis of cardiac amyloidosis. However, potential differences in the apical sparing pattern in light chain (AL) versus transthyretin (ATTR) amyloidosis in patients with high clinical suspicion for cardiac amyloidosis is not clear.

Purpose

Our objective was to test the hypothesis that echocardiographic strain imaging could determine differences in patients with clinically suspected AL and ATTR cardiac amyloidosis.

Methods

We studied 206 patients, aged 64±11, with clinically suspected cardiac amyloidosis. Routine longitudinal strain imaging analyses was performed (EchoPAC, GE Healthcare) with bulls-eye plots. After 27 exclusions (8 arrhythmia/frame rate, 19 missing/poor images), there were 179 patients. Included were 129 patients with cardiac amyloid: 42 by endomyocardial biopsy, 4 by technetium pyrophosphate scan, 65 by non-cardiac biopsy with suggestive cardiac imaging (interventricular septal thickness ≥1.2cm by echocardiography or characteristic cardiac MRI findings), 15 with multiple myeloma and suggestive cardiac imaging, and 3 by autopsy; 50 patients had a negative endomyocardial biopsy or autopsy for cardiac amyloid. The apical sparing ratio by strain imaging was calculated as the (average of apical segments) / (average of mid segments + average of basal segments).

Results

Cardiac amyloidosis patients were 79% with AL and 21% with ATTR. Applying the previously published apical sparing ratio cut-off of 1.0 for longitudinal strain imaging, sensitivity and specificity were 29% and 78%, respectively, for diagnosis of cardiac amyloidosis. Applying a ratio cut-off of 0.81 improved sensitivity to 72% with specificity of 64% and area under the curve (AUC) of 0.66. Positive and negative predictive values were 85% and 46%, respectively, at this ratio cut-off. The apical sparing ratio was significantly higher in AL and ATTR as compared to the biopsy negative group (p<0.001). Furthermore, the apical sparing ratio was significantly higher in ATTR as compared to AL (p<0.05).

Apical sparing pattern and ratio

Conclusions

Among patients with high clinical suspicion for cardiac amyloidosis, the apical sparing ratio by echocardiographic strain imaging can demonstrate differences for AL and ATTR cardiac amyloidosis and has potential for clinical utility.

Dynamic effects of positive-pressure ventilation on canine left ventricular pressure-volume relations

Positive-pressure ventilation (PPV) may affect left ventricular (LV) performance by altering both LV diastolic compliance and pericardial pressure (Ppc). We measured the effect of PPV on LV intraluminal pressure, Ppc, LV volume, and LV cross-sectional area in 17 acute anesthetized dogs. To account for changes in lung volume independent of changes in Ppc and differences in contractility, measures were made during both open- and closed-chest conditions, during closed chest with and without chest wall binding, and after propranolol-induced acute ventricular failure (AVF). Apneic end-systolic pressure-volume relations (ESPVR) were generated by inferior vena caval occlusions. With the open chest, PPV had no effects. With the chest closed, PPV inspiration decreased LV end-diastolic volume (EDV) along its diastolic compliance curve and decreased end-systolic volume (ESV) such that the end-systolic pressure-volume domain was shifted to a point left of the LV ESPVR, even when referenced to Ppc. The decrease in EDV was greater in control than in AVF conditions, whereas the shift of the ESV to the left of the ESPVR was greater with AVF than in control conditions. We conclude that the hemodynamic effects of PPV inspiration are due primarily to changes in intrathoracic pressure and that the inspiration-induced decreases of LV EDV reflect direct effects of intrathoracic pressure on LV filling. The decreases in LV ESV exceed the amount explained solely by a reduction in LV ejection pressure.

Color-coded tissue Doppler assessment of the effects of acute ischemia on regional left ventricular function: comparison with sonomicrometry

Echocardiographic assessment of regional left ventricular (LV) function usually consists of subjective visual inspection of endocardial movement and wall thickening. Color-coded tissue Doppler (TD) is a potential means to quantify regional LV function more objectively. Accordingly, in this study, color-coded TD was used to assess the regional effects of acute ischemia in an open-chest canine model of coronary occlusion, with implanted sonomicrometry length crystals as a standard of reference. Eight dogs were studied during baseline conditions and during left anterior descending coronary artery occlusion. Midventricular short-axis images were used to guide the color TD M-mode cursor through circumflex (septal) and left anterior descending (anterolateral) perfusion zones. Off-line conversion of endocardial time-velocity maps was performed. Peak systolic endocardial velocity by TD decreased from 4.4 +/- 1.4 cm/s to 1.8 +/- 1.5 cm/s with coronary occlusion (P < .05 versus baseline). Similar significant decreases in calculated systolic velocity by sonomicrometry occurred with ischemia from 11.1 +/- 3.8 mm/s to 8.2 +/- 1.2 mm/s (P < .05 versus baseline). Peak systolic velocity by TD was inversely correlated with end-systolic length by sonomicrometry as a measure of regional function (r = -0.77, P < .001). Time to peak systolic velocity increased with ischemia from 154 +/- 60 ms to 286 +/- 67 ms by TD and 200 +/- 60 ms to 320 +/- 30 ms by sonomicrometry (P < .05 versus baseline). The delay in time to peak systolic velocity by TD and sonomicrometry were correlated (r = 0.75, P < .001). In conclusion, color-coded TD echocardiography has the potential to quantify regional LV function during coronary ischemia.

Effects of aging on left atrial reservoir, conduit, and booster pump function: a multi-institution acoustic quantification study

OBJECTIVE

To assess the feasibility of measuring left atrial (LA) function with acoustic quantification (AQ) and then assess the effects of age and sex on LA reservoir, conduit, and booster pump function.

PATIENTS AND SETTING

165 subjects without cardiovascular disease, 3-79 years old, were enrolled by six tertiary hospital centres.

INTERVENTIONS

Continuous LA AQ area data were acquired and signal averaged to form composite waveforms which were analysed off-line.

MAIN OUTCOME MEASURES

Parameters of LA performance according to age and sex.

RESULTS

Signal averaged LA waveforms were sufficiently stable and detailed to allow automated analysis in all cases. An age related increase in LA area was noted. LA reservoir function did not vary with age or sex. All parameters of LA passive and active emptying revealed a significant age dependency. Overall, the passive emptying phase accounted for 66% of total LA emptying ranging from 76% in the youngest to 44% in the oldest decade. LA contraction accounted for 34% of atrial emptying in all subjects combined with the older subjects being more dependent on atrial booster pump function. When adjusted for atrial size, there were no sex related differences in LA function.

CONCLUSIONS

LA reservoir, conduit, and booster pump function can be assessed with automated analysis of signal averaged LA area waveforms. As LA performance varies with age, establishment of normal values should enhance the evaluation of pathologic states in which LA function is important.

Normal values of regional left ventricular endocardial motion: multicenter color kinesis study

Our goal was to establish normal values for quantitative color kinesis indexes of left ventricular (LV) wall motion over a wide range of ages, which are required for objective diagnosis of regional systolic and diastolic dysfunction. Color-encoded images were obtained in 194 normal subjects (95 males, 99 females, age 2 mo to 79 yr) in four standard views. Quantitative indexes of magnitude and timing of systolic and diastolic function were studied for age- and gender-related differences. Normal limits of all ejection and filling indexes were in a narrow range (< or =25% of the mean), with no major gender-related differences. Despite invariable ejection fractions, both peak filling and ejection rates decreased with age (30 and 20%, correspondingly) with a concomitant increase in mean filling and ejection times, resulting in five- and twofold increases in the late to early filling and ejection ratios, correspondingly. Diastolic asynchrony increased with age (from 4.7 +/- 2.0 to 6.4 +/- 3.2 from the 2nd to 7th decade). The normal values of color kinesis indexes should allow objective detection of regional LV systolic and diastolic dysfunction.

Tissue Doppler echocardiography

Tissue Doppler echocardiography (TDE) is a relatively recent addition to the diagnostic ultrasonographic examination. This is similar to routine Doppler ultrasonography to assess blood flow, but technologic features focus on lower velocity frequency shifts. Two techniques are used to assess myocardial function: pulsed TDE and color-coded TDE. A great deal of data has been generated on TDE over the last 5 years, and this review allows for only a small portion of these emerging data to be discussed. One clinical application is to assess peak systolic mitral annular velocity from the apical windows as an index of global ventricular function. The six-site average for peak systolic mitral annular velocity by the color-coded TDE method of greater than 5.4 cm/sec is predictive of an ejection fraction greater than 50% with an 88% sensitivity and a 97% specificity. An emerging application is to use pulsed-TDE to assess ventricular filling pressures. The mitral annular to inflow ratio (E/Ea) greater than 10 is predictive of a mean pulmonary capillary wedge pressure greater than 15 mm Hg with a 92% sensitivity and 80% specificity. Another application is to use peak early diastolic velocity to help differentiate constrictive pericarditis from restrictive cardiomyopathy. Peak early diastolic velocity is blunted with restrictive cardiomyopathy and preserved with constrictive pericarditis. These are just a few of the many evolving clinical applications of this new quantitative diagnostic ultrasonographic method.

Evaluation of the potential role of color-coded tissue Doppler echocardiography in the detection of allograft rejection in heart transplant recipients

BACKGROUND

Color-coded tissue Doppler (TD) echocardiography can noninvasively quantify alterations in left ventricular (LV) systolic and diastolic function. The objective of this study was to test the hypothesis that TD may play a role in the detection of LV dysfunction associated with allograft rejection in heart transplant recipients.

METHODS AND RESULTS

Seventy-eight consecutive transplant recipients underwent 89 TD studies of posterior wall myocardial velocity gradient and mitral annular velocity within 1 hour of endomyocardial biopsy. Color TD echocardiographic images were digitized for semiautomated computer analysis. Histologic analysis revealed no significant rejection in 75 biopsies and significant rejection in 14. TD posterior wall peak systolic and diastolic velocity gradients were reduced significantly with rejection: 3.9 +/- 2.0 s(-1) versus 2.6 +/- 0.9 s(-1) and 5.4 +/- 2. 4 s(-1) versus 3.5 +/- 1.6 s(-1), respectively (P <.05 vs the nonrejecting group). Peak systolic and diastolic mitral annular velocities by TD were also reduced with rejection: 63 +/- 14 mm/s versus 49 +/- 12.4 mm/s and 90 +/- 23 mm/s versus 60 +/- 21 mm/s, respectively (P <.001 vs the nonrejecting group). A TD peak-to-peak mitral annular velocity >135 mm/s had 93% sensitivity, 71% specificity, and 98% negative predictive value for detecting rejection. Although TD was unable to discriminate between rejection and other causes of low velocity values, high TD velocity values were supportive of excluding rejection.

CONCLUSIONS

These data suggest that color-coded TD may play a potential role as a screening test to exclude rejection in heart transplant recipients. Although this method has the potential to decrease the number of biopsies, further testing in a larger series of transplant recipients with rejection is warranted.

Assessment of left internal mammary artery graft patency and flow reserve after minimally invasive direct coronary artery bypass

Despite its merits, minimally invasive direct coronary artery bypass surgery (MIDCAB) has been criticized for variable left internal mammary artery (LIMA) graft patency rates, prompting the frequent use of postoperative LIMA angiography. Noninvasive transthoracic Doppler interrogation of LIMA grafts has recently been shown to have utility for assessing patency and flow reserve after conventional bypass surgery, but data after MIDCAB has been limited. The objective of this study was to assess LIMA graft anatomy and physiology in 54 patients after MIDCAB using angiography and noninvasive LIMA Doppler imaging. The right internal mammary artery (RIMA) was studied as a control. LIMA flow reserve in response to adenosine was evaluated in a subgroup of 18 randomly chosen patients with patent grafts. LIMA angiographic patency was 93%. Forty-four patients (81%) had obtainable LIMA Doppler data. Patent grafts had a diastolic dominant flow pattern with a peak diastolic/systolic velocity ratio of 1.3 +/- 0.6 and a percent diastolic time-velocity integral (TVI) of 70 +/- 11%. These data were significantly different than the RIMA control values of 0.2 +/- 0.1 and 30 +/- 10%, respectively (p <0.05). Occluded grafts had absent flow or a systolic dominant pattern. Adenosine-induced increases in LIMA peak diastolic velocity from 48 +/- 20 to 105 +/-28 cm/s (p <0.05 vs baseline) and diastolic TVI from 21 +/- 10 to 37 +/- 19 cm (p <0.05 vs baseline), yielding adenosine/baseline ratios of 2.4 +/- 0.9 and 2.0 +/- 0.7, respectively, which was consistent with normal flow reserve. The diastolic flow velocity reserve response was inversely related to baseline diastolic flow (r = -0.69). In conclusion, MIDCAB can be associated with a high rate of LIMA potency and favorable physiologic Doppler flow patterns. Correlation of these findings to long-term patient outcome after MIDCAB is warranted.

Determinants of aortic pressure variation during positive-pressure ventilation in man

STUDY OBJECTIVES

To define the relation between systolic arterial pressure (SAP) changes during ventilation and left ventricular (LV) performance in humans.

DESIGN

Prospective repeat-measures series.

SETTING

University of Pittsburgh Medical Center Operating Room.

PATIENTS

Fifteen anesthetized cardiac surgery patients before and after cardiopulmonary bypass when the mediastinum was either closed or open.

INTERVENTIONS

Positive-pressure ventilation.

MEASUREMENTS AND RESULTS

SAP and LV midaxis cross-sectional areas were measured during apnea and then were measured for three consecutive breaths. SAP increased during inspiration, this being the greatest during closed chest conditions (p < 0.05). Changes in SAP could not be correlated with changes in either LV end-diastolic areas (EDAs), end-systolic areas, or stroke areas (SAs). If SAP decreased relative to apnea, the decrease occurred during expiration and was often associated with increasing LV EDAs and SAs. SAP often decreased after a positive-pressure breath, but the decrease was unrelated to SA deficits during the breath. Increases in SAP were in phase with increases in airway pressure, whereas decreases in SAP, if present, followed inspiration. No consistent relation between SAP variation and LV area could be identified.

CONCLUSIONS

In this patient group, changes in SAP reflect changes in airway pressure and (by inference) intrathoracic pressure (as in a Valsalva maneuver) better than they reflect concomitant changes in LV hemodynamics.

Assessment of left ventricular contractile state by preload-adjusted maximal power using echocardiographic automated border detection

OBJECTIVES

We sought to assess the ability of preload-adjusted maximal power measured by echocardiographic automated border detection (ABD) to quantify left ventricular (LV) contractility by determining the effects of alterations in preload, afterload and contractile state.

BACKGROUND

Preload-adjusted maximal power can reflect LV contractile state relatively independent of changes in loading conditions.

METHODS

Eight anesthetized dogs had placement of aortic electromagnetic flow probes, LV and arterial pressure catheters and inferior vena caval (IVC) occluders; four had placement of thoracic aortic balloon occluders. Echocardiographic ABD measures of cross-sectional area were used as a surrogate for LV volume, and flow was estimated as the first derivative of area with respect to time. Power was calculated as the product of flow and pressure.

RESULTS

Preload independence during vena caval occlusions was achieved by preload adjustment (1/[end-diastolic area]3/2). Afterload independence was demonstrated by preload-adjusted maximal power being unaffected by acute increases in LV systolic pressure induced by aortic occlusion. ABD preload-adjusted maximal power reflected changes in contractile state: increasing with dobutamine infusion from 36+/-14 to 70+/-15 mW/cm4 (p < 0.05 vs. control) and decreasing with propranolol infusion from 35+/-13 to 17+/-7 mW/cm4 (p < 0.05 vs. control). These changes were significantly correlated with calculations of preload-adjusted maximal power using aortic flow (r = 0.90, SEE 10.5 mW/cm4) and load-independent measures of end-systolic elastance from pressure-area loops (r = 0.90, SEE 10.6 mW/cm4). Calculations of normalized preload-adjusted maximal power using arterial pressure were also closely correlated with similar calculations using LV pressure (r = 0.99, SEE 3%).

CONCLUSIONS

Preload-adjusted maximal power using echocardiographic ABD can predict LV contractile state relatively independent of loading conditions and has potential for clinical application.

Heterogeneous immediate effects of partial left ventriculectomy on cardiac performance

BACKGROUND

Partial left ventriculectomy (PLV) is a novel surgical treatment for severe heart failure consisting of resection of a large wedge of myocardium to reduce wall stress and restore the normal mass-volume ratio. Although ejection fraction (EF) has been shown to improve after PLV, few other physiological data describing its immediate effects on left ventricular (LV) performance are available.

METHODS AND RESULTS

Eight patients, 58+/-5 years old, with severe clinical heart failure and EF of 12+/-3% were studied before and immediately after PLV. LV performance was assessed by the predominantly load-insensitive measures of pressure-area relations with high-fidelity pressure catheters and transesophageal automated echocardiographic measures of cross-sectional area as a surrogate for volume. LV end-diastolic volume decreased from 200+/-60 to 89+/-17 mL, EF increased from 12+/-3% to 41+/-8%, and right ventricular (RV) fractional area change increased from 24+/-12% to 37+/-16% (all P<.05 versus before). Changes in pressure-area relations were variable: end-systolic elastance, 6.5+/-3.4 to 4.3+/-2.5 mm Hg/cm2 and preload recruitable stroke work, 33+/-16 to 34+/-19 mm Hg (P=NS versus before). End-diastolic stiffness increased from 0.13+/-0.06 to 0.19+/-0.07 mm Hg/cm2 (P<.05 versus before). Improvement in LV performance was inversely correlated with semiquantitative histological assessment of myocardial fibrosis and positively correlated with nuclear enlargement and hyperchromasia, indicative of myocyte hypertrophy. No long-term follow-up data were available.

CONCLUSIONS

PLV resulted in reductions in LV volumes, increases in EF and RV ejection, but increases in LV stiffness. Estimates of LV performance revealed variable results associated with the degree of myocardial fibrosis. Further study of these effects in relation to patient outcome is warranted.

Quantification of the myocardial response to low-dose dobutamine using tissue Doppler echocardiographic measures of velocity and velocity gradient

Low-dose dobutamine echocardiography has been clinically useful in myocardial viability studies, although routine visual assessment of wall motion is subjective. The objective was to quantify the incremental myocardial response to low-dose dobutamine infusion using a new semiautomated tissue Doppler (TD) analysis system and to compare these data with routine echocardiographic measures in the same subjects. Twelve subjects had TD and routine echocardiographic studies at baseline and during 10-minute stages of dobutamine infusion at 1, 2, 3, and 5 microg/kg/min. Color TD video data were converted to a digital velocity matrix (4.5 velocity data points/mm at 500 Hz) for analysis of mitral annular velocity, endocardial velocity, and velocity gradient at each stage. Posterior wall percent thickening and ejection fraction were calculated from the routine images. Mitral annular peak systolic velocity significantly increased with only 1 microg/kg/min of dobutamine from 69 +/- 9 to 77 +/- 7 mm/s (p <0.05 vs baseline), and further incremental increases occurred with each subsequent dose. Anteroseptal and posterior wall peak endocardial velocity increased with 2 microg/kg/min of dobutamine from 33 +/- 7 to 46 +/- 15 mm/s and 50 +/- 9 to 61 +/- 10 mm/s, respectively (p <0.01 vs baseline) and further increased with 5 microg/kg/min (p <0.0001 vs 3 microg/kg/min). Posterior wall peak systolic gradient also increased with 2 microg/kg/min of dobutamine from 3.1 +/- 0.6 to 5.4 +/- 1.6 s(-1) (p <0.05 vs baseline). Routine measures of percent wall thickening or ejection fraction did not detect increases until the 3 microg/kg/min dose. TD can detect subtle alterations in contractility induced by low-dose dobutamine and has the potential to quantify regional ventricular function objectively.

Resource utilization for minimally invasive direct and standard coronary artery bypass grafting

BACKGROUND

Minimally invasive direct coronary artery bypass grafting (MIDCABG) has been recently reintroduced into the cardiac surgical armamentarium for selected patients with suitable coronary anatomy. We hypothesized that MIDCABG had the potential for similar immediate results with decreased perioperative morbidity and decreased resource utilization compared with standard coronary artery bypass grafting (CABG).

METHODS

From January 1996 to August 1996, 17 MIDCABG patients were compared with 33 patients with left ventricular ejection fraction greater than 0.50 who underwent CABG with standard technique. No significant differences were observed between the two groups for preoperative variables that are known to affect cost and resource utilization. Length of stay in the hospital was 2.5 +/- 0.8 days for MIDCABG and 5.9 +/- 2 days for CABG (p < 0.0001); length of stay in the intensive care unit was 12.3 +/- 3.3 hours for MIDCABG compared to 32.3 +/- 12.6 hours for the CABG group (p < 0.0001).

RESULTS

Forty-one percent of MIDCABG patients were extubated in the operating room and 59% were discharged home on the first or second postoperative day versus none in the CABG group (p < 0.0001). Significantly less morbidity was observed in the MIDCABG group compared with CABG. Total ratio of cost-to-charge was $12,885 +/- $1,511 for MIDCABG and $21,260 +/- $5,497 for CABG (p < 0.0001), with an average savings of $8,375.

CONCLUSIONS

Minimally invasive CABG is associated with significant reduction of resource utilization and morbidity related to inital hospitalization compared with CABG.

Quantitative assessment of alterations in regional left ventricular contractility with color-coded tissue Doppler echocardiography. Comparison with sonomicrometry and pressure-volume relations

BACKGROUND

Tissue Doppler imaging (TDI) is a novel method of color-coding myocardial velocity on-line. The objective of the present study was to evaluate endocardial velocity with TDI as a method of objectively quantifying alterations in regional contractility over a wide range induced by inotropic modulation.

METHODS AND RESULTS

Myocardial length crystals were used to simultaneously assess regional left ventricular (LV) function, and high-fidelity pressure and conductance catheters were used to assess global LV contractility by pressure-volume relations in nine open-chest dogs. Mid-LV M-mode and two-dimensional color TDI images were recorded during control and inotropic modulation stages with dobutamine and esmolol. Predicted significant increases in TDI indices occurred with dobutamine: peak systolic velocity of 4.41 +/- 1.07 to 6.67 +/- 1.07 cm/s*, systolic time-velocity integral (TVI) of 0.43 +/- 0.12 to 0.62 +/- 0.10 cm*, and diastolic TVI of 0.49 +/- 0.11 to 0.71 +/- 0.17 cm*. Opposing significant decreases occurred with esmolol: peak systolic velocity of 4.46 +/- 0.94 to 2.31 +/- 0.81 cm/s*, systolic TVI of 0.47 +/- 0.12 to 0.19 +/- 0.11 cm*, and diastolic TVI of 0.55 +/- 0.11 to 0.33 +/- 0.11 cm* (*all P < .001 versus control). Changes in TDI peak systolic velocity were correlated with changes in fractional shortening (r = .88) and shortening velocity (r = .87) by sonomicrometry. Changes in TDI peak velocity from multiple mid-LV sites also correlated significantly with maximal elastance (r = .85 +/- .04) from pressure-volume relations.

CONCLUSIONS

TDI measures reflect directional and incremental alterations in regional and global LV contractility and have the potential to quantify regional LV function.

Quantitative evaluation of the segmental left ventricular response to dobutamine stress by tissue Doppler echocardiography

Tissue Doppler imaging displays color-coded myocardial velocity on-line and has potential to objectively quantify regional left ventricular function. Sixty patients, aged 56 +/- 10 years, were studied to determine the normal and abnormal segmental endocardial velocity response to dobutamine stress, and the sensitivity, specificity, and accuracy of tissue Doppler imaging for detecting abnormal wall motion at peak stress as defined by routine visual interpretation. Separate 2-dimensional routine gray scale and color tissue Doppler image sets were acquired at rest and peak dobutamine stress in a digital cineloop format. Routine wall motion interpretation from gray scale images and color-coded peak systolic endocardial velocity from tissue Doppler images were determined independently. Twenty-two patients who reached their target heart rate and had normal wall motion at peak stress served as a control group. There were 19 patients who had wall motion abnormalities at peak stress. Segmental peak endocardial velocities increased significantly in all segments in the control group. Endocardial velocity was significantly lower at peak stress in the pooled abnormal segments than in the pooled normal segments: 3.1 +/- 1.2 versus 7.2 +/- 1.9 cm/s, respectively (p < 0.05 vs normal control). However, the velocity response of abnormal apical segments could not be distinguished from normal controls by tissue Doppler imaging. Excluding apical segments, a peak velocity of < or = 5.5 cm/s with peak stress had an average sensitivity of 96%, specificity of 81%, and accuracy of 86% for identifying abnormal segments at peak stress as defined by routine 2-dimensional criteria. Tissue Doppler imaging has the potential to quantify regional left ventricular function during dobutamine stress.

Right ventricular performance and left ventricular assist device filling

BACKGROUND

Right ventricular (RV) function is believed to be an important determinant of left ventricular assist device (LVAD) filling. This study was designed to demonstrate this relation in patients.

METHODS

To demonstrate the interaction between RV ejection and LVAD filling, 10 patients (mean age, 49 +/- 13 years) supported with an LVAD were studied. Right ventricular pressure-area loops from cross-sectional area using transesophageal echocardiographic automated border detection and high-fidelity RV pressure were recorded simultaneously with LVAD volume during intraoperative inferior vena cava occlusion. Beat-by-beat RV ejection phase indices were calculated: stroke area, peak ejection rate, and stroke work. The LVAD filling rate was calculated as the first derivative of the volume, and the peak filling rate and the mean filling rate during RV systole were determined for each cardiac cycle.

RESULTS

Right ventricular stroke area, peak ejection rate, and stroke work were closely correlated with LVAD peak filling rate (r = 0.87 +/- 0.09, r = 0.83 +/- 0.09, and r = 0.85 +/- 0.10, respectively). Also, baseline LVAD mean filling rate correlated with RV stroke work (r = 0.77) and LVAD peak filling rate with RV peak ejection rate for the group (r = 0.75).

CONCLUSIONS

These correlations demonstrate predictable associations of RV ejection with LVAD filling.

Left ventricular performance assessed by echocardiographic automated border detection and arterial pressure

Automated echocardiographic measures of left ventricular (LV) cavity area are closely correlated with changes in volume and can be coupled with LV pressure (PLV) to construct pressure-area loops in real time. The objective was to rapidly estimate LV contractility from end-systolic relationships of cavity area (as a surrogate for LV volume) and central arterial pressure (Pa) (as a surrogate for PLV) in a canine model using automated algorithms. In eight anesthetized mongrel dogs, we simultaneously measured PLV, LV area, and Pa (fluid-filled catheter). End-systolic pressure-area relationships in terms of pressure-area elastance (E'es)] from pressure-area loops during inferior vena caval occlusions were determined during basal conditions (control), dobutamine infusion (5-10 micrograms.mg-1.min-1), and after bolus propranolol (2 mg/kg) with both PLV and Pa by semiautomated and automated iterative regression methods. E'es increased during dobutamine infusion and decreased after propranolol infusion in all animals and with all iterative methods. Estimates of Ees from Pa were closely correlated with E'es from PLV by both the semiautomated and automated methods (r = 0.93; P < 0.01). The relationship between E'es obtained from Pn for the two methods was also closely correlated. Although the automated methods displayed larger differences from the semiautomated iterative technique by Bland-Altman analysis, the change in E'es with all techniques during dobutamine infusion and after propranolol infusion was of similar magnitude and direction among the three techniques. Greater variability with the dobutamine runs was partially due to abnormally conducted ventricular beats that minimized the number of consecutive beats that could be used for these analyses. We conclude that on-line Pa recordings from fluid-filled catheters can be used with echocardiographic automated border detection to rapidly calculate E'es as a means to estimate LV contractility.

Right ventricular performance and contractile reserve in patients with severe heart failure. Assessment by pressure-area relations and association with outcome

BACKGROUND

Right ventricular (RV) performance appears to be important in patients with severe heart failure. Although clinical assessments of RV function previously have been limited to load-dependent ejection phase indices, a new method has been developed using the relatively load-insensitive concepts of pressure-volume relations with automated echocardiographic measures of RV cross-sectional area as a surrogate for volume.

METHODS AND RESULTS

Sixteen patients with New York Heart Association functional class IV heart failure and group mean left ventricular ejection fraction of 20 +/- 5% were studied. RV pressure-area loops were recorded on-line from echocardiographic measures of RV area and high-fidelity pressure during transient inferior, vena caval balloon occlusions. RV contractile reserve was assessed as its functional response to an increase in dobutamine from 5.7 +/- 4.1 to 13.1 +/- 4.7 micrograms/kg per minute. Complete data sets were available in 13 patients. Group mean RV end-systolic elastance (E'es) and maximal elastance (E'max) increased with augmented dobutamine infusion (2.9 +/- 1.5 to 5.5 +/- 3.3 mm Hg/cm2 and 3.3 +/- 1.6 to 6.4 +/- 3.9 mm Hg/cm2, respectively; P < .01 versus baseline), although individual responses were variable. During a 30-day follow-up, 9 patients remained unstable, requiring continuous intravenous inotropic therapy; 6 of these had profound deterioration requiring mechanical circulatory support. The remaining 4 patients had a comparatively good short-term outcome with clinical stability. A 100% increase in RV E'es or E'max was associated with a good short-term outcome (P < .05).

CONCLUSIONS

RV performance can be assessed by pressure-area relations in patients with heart failure. RV contractile reserve in response to increases in dobutamine was associated with a good short-term outcome and may be of prognostic value in patients with severe heart failure.

Potential influence of intraluminal thrombus on abdominal aortic aneurysm as assessed by a new non-invasive method

Intraluminal thrombus may play a role in abdominal aortic aneurysm pathogenesis and rupture. The purpose of this work was to demonstrate the feasibility of a new non-invasive method for the determination of the biomechanical features of the aortic wall and luminal boundary in abdominal aortic aneurysm containing intraluminal thrombus. Automated ultrasonographic measures of infrarenal aortic cross-sectional area (A) were obtained on-line along with non-invasive arterial pressure (p) from eight patients of mean (s.e.m.) age 74(3) years, with abdominal aortic aneurysm (mean dimensions 5.9(0.4) x 5.3(0.5) cm) containing intraluminal thrombus. Luminal boundary and abdominal aortic aneurysm wall were scanned separately. Compliance (C) was computed as C = (Amax - Amin)/[Amax(Pmax - Pmin)], where 'max and 'min' represent maximum and minimum values, respectively. Mean compliance was lower for the abdominal aortic aneurysm wall alone than for the luminal surface enclosed by intraluminal thrombus: 4.0(0.9) x 10(-4)/mmHg versus 9.8(1.7) x 10(-4)/mmHg (P < 0.01). Intraluminal thrombus area was nearly constant over the cardiac cycle, indicating that the thrombus is virtually incompressible. This noninvasive method to assess biomechanical features of abdominal aortic aneurysm has potential to further the understanding of the influences of intraluminal thrombus on aneurysm disease.

Color-coded measures of myocardial velocity throughout the cardiac cycle by tissue Doppler imaging to quantify regional left ventricular function

TDI is a new echocardiographic technique that calculates and displays color-coded myocardial velocity on-line. To determine the feasibility of endocardial velocity throughout the cardiac cycle as a means to quantify regional function, 20 normal subjects aged 30 +/- 5 years and 12 patients with heart disease aged 62 +/- 17 years were studied with a prototype TDI system. TDI M-mode images were acquired by using a multicolored velocity map (display range, -30 to 30 mm/sec; temporal resolution, 90 Hz). Color-coded velocity data were then converted to numeric values off-line at 50 msec intervals. Posterior wall velocities throughout the cardiac cycle by TDI were closely correlated with velocity calculations from the first derivative of routine digitized M-mode tracings (group mean r = 0.88 +/- 0.03, SEE = 7.0 +/- 1.1 mm/sec). Anteroseptal TDI color-coded systolic velocity occurred 164 +/- 84 msec from the onset of the electrocardiographic QRS compared with 203 +/- 33 msec in the posterior wall (P < 0.05) in normal subjects, consistent with normal electrical activation. Significant differences in systolic and diastolic posterior wall TDI velocity data were observed in patients with hypokinetic or akinetic segments assessed by independent routine study when compared with normal controls. Calculated systolic and early diastolic posterior wall TDI indexes correlated significantly with percentage of wall thickening. Of abnormal anteroseptal segments, TDI systolic time velocity integrals were significantly different than normal and correlated with percentage of wall thickening. TDI has potential to quantitatively assess regional left ventricular function.

Mitral annular descent velocity by tissue Doppler echocardiography as an index of global left ventricular function

Mitral annular descent has been described as an index of left ventricular (LV) systolic function, which is independent of endocardial definition. Echocardiographic tissue Doppler imaging is a new technique that calculates and displays color-coded cardiac tissue velocities on-line. To evaluate mitral annular descent velocity as a rapid index of global LV function, we performed tissue Doppler imaging studies in 55 patients, aged 56 +/-15 years, within 3 hours of radionuclide ventriculographic ejection fraction. Tissue Doppler M-mode studies were obtained from each of 6 mitral annular sites, as follows: inferoseptal and lateral from apical 4-chamber views, anterior and inferior from apical 2-chamber views, and anteroseptal and posterior from apical long-axis views. Only 1 patient with severe mitral annular calcification was excluded. The group mean 6-site average peak mitral annular descent velocity was 5.5 +/- 1.9 cm/s (range 2.4 to 10.5), and the group mean ejection fraction was 49 +/- 18% (range 17 to 80%). The 6-site average peak annular descent velocity correlated linearly with LV ejection fraction (r = 0.86, SEE = 1.02 cm/s): LV ejection fraction = 8.2 (average peak mitral annular descent velocity) + 3%. The 6-site peak mitral annular descent velocity average >5.4 cm/s was 88% sensitive and 97% specific for ejection fraction >50%. The peak mitral annular descent velocity from the apical 4-chamber view (average from inferoseptal and lateral sites) correlated most closely with the LV ejection fraction (r = 0.85) as an individual view. Peak mitral annular descent velocity by tissue Doppler imaging has the potential to estimate rapidly the global LV function.

Improvement in pulmonary function and elastic recoil after lung-reduction surgery for diffuse emphysema

BACKGROUND

Pulmonary function may improve after surgical resection of the most severely affected lung tissue (lung-reduction surgery) in patients with diffuse emphysema. The basic mechanisms responsible for the improvement, however, are not known.

METHODS

We studied 20 patients with diffuse emphysema before and at least three months after either a unilateral or a bilateral lung-reduction procedure. Clinical benefit was assessed by measurement of the six-minute walking distance and the transitional-dyspnea index, which is a subjective rating of the change from base line in functional impairment and the threshold for effort- and task- dependent dyspnea. Pressure-volume relations in the lungs were measured with static expiratory esophageal-balloon techniques, and right ventricular systolic function was assessed by echocardiography.

RESULTS

The patients had significant improvement in the transitional-dyspnea index after surgery (P<0.001). The mean (+/-SD) coefficient of retraction, an indicator of elastic recoil of the lung, improved (from 1.3+/-0.6 cm of water per liter before surgery to 1.8+/-0.8 after, P<0.001). Sixteen patients with increased elastic recoil had a greater increase in the distance walked in six minutes than the other four patients, in whom recoil did not increase (P=0.02). The improved lung recoil led to disproportionate decreases in residual volume as compared with total lung capacity (16 percent vs. 6 percent), but the decreases in both values were significant (P<0.001). Forced expiratory volume in one second increased (from 0.87+/-0.36 to 1.11+/-0.45 liters, P<0.001). End-expiratory esophageal pressure also decreased (P=0.002). These improvements in lung mechanics led to a decrease in arterial partial pressure of carbon dioxide form 42+/-6 to 38+/-5 mm Hg (P=0.006). Furthermore, the fractional change in right ventricular area, an indicator of systolic function, increased from 0.33+/-0.11 to 0.38+/-0.010 (P=0.02).

CONCLUSIONS

Lung-reduction surgery can produce increases in the elastic recoil of the lung in patients with diffuse emphysema, leading to short-term improvement in dyspnea and exercise tolerance.

Left ventricular pressure-volume relations with transesophageal echocardiographic automated border detection: comparison with conductance-catheter technique

Pressure-volume relations are important means used to assess left ventricular (LV) contractility; however, on-line volume acquisition has been limited to the invasive conductance catheter. The objective was to compare simultaneous measures of LV volume by transesophageal echocardiographic automated border detection (ABD) and conductance catheter and their respective pressure-volume relations during steady state and alterations in preload and contractility. Seven dogs had placement of high-fidelity pressure and conductance catheters, a vena caval balloon occluder, and a transesophageal probe. An automated Simpson's rule volume algorithm was used from the transverse four-chamber view. Inotropic modulation was induced with dobutamine in four dogs and propranolol in three. Relative changes in ABD volume were linearly related to conductance volume at steady state with group mean r = 0.93 +/- 0.03, standard error of estimate (SEE) = 10 +/- 2%. Changes in end-diastolic volume, end-systolic volume, and stroke work with caval occlusion were also significantly correlated:r = 0.93 =/- 0.04, SEE = 3.6 ml; r = 0.89 +/- 0.04, SEE = 3.8 +/- 1.9 ml; and r = 0.86 +/- 0.05, SEE = 40 +/- 21 mJ, respectively. The overall bias was for absolute ABD volume to be less. End-systolic and maximal elastance values by ABD were significantly higher than by the conductance method; baseline group average 4.97 +/- 0.92 mm Hg/ml versus 2.70 +/- 1.15 mm Hg/ml and 6.63 +/- 1.66 mm Hg/ml versus 3.20 +/- 1.37 mm Hg/ml (p<0.05), respectively. However, the direction and relative magnitude of changes in elastance with inotropic modulation were similar.

Immediate effects of lung transplantation on right ventricular morphology and function in patients with variable degrees of pulmonary hypertension

OBJECTIVES

This study sought to determine the immediate effects of lung transplantation on right ventricular morphology and function in patients with variable degrees of pulmonary hypertension and to evaluate these features as potential markers of immediate outcome.

BACKGROUND

Selected lung transplant recipients with severe preoperative pulmonary hypertension have previously been shown to have a reduction in right ventricular size and improved function at follow-up evaluation.

METHODS

Thirty-two consecutive patients (mean [+/- SD] age 44 +/- 11 years) were prospectively classified into three groups according to their pretransplantation pulmonary artery systolic pressure: severe pulmonary hypertensive group > or = 75 mm Hg, intermediate pulmonary hypertensive group 40 to 74 mm Hg and non-pulmonary hypertensive group < 40 mm Hg. Hemodynamic and transesophageal echocardiographic variables were measured immediately before and after lung transplantation.

RESULTS

Pulmonary artery systolic and mean pressures markedly decreased after transplantation in the severe pulmonary hypertensive group (from 115 +/- 26 to 45 +/- 19 mm Hg and from 76 +/- 14 to 31 +/- 11 mm Hg, respectively, both p < 0.05). Mean pulmonary artery pressure decreased in the intermediate group (from 34 +/- 7 to 26 +/- 7 mm Hg, p < 0.05). Right ventricular end-diastolic area, end-systolic area and eccentricity index decreased in the severe pulmonary hypertensive group after transplantation. End-diastolic area also decreased in the intermediate pulmonary hypertensive group. Right ventricular fractional area change was not significantly different between groups and did not change consistently after transplantation. Three patients with severe pulmonary hypertension who had continued depression of right ventricular function after transplantation died in the immediate postoperative period.

CONCLUSIONS

Lung transplantation is associated with an immediate decrease in pulmonary artery pressures and right ventricular size and normalization of septal geometry but variable changes in right ventricular function. Continued depression of right ventricular fractional area change may be a potential marker of poor outcome.

Hemodynamic effects of pyruvate infusion in dogs

PURPOSE

Although pyruvate supplementation enhances endurance in humans and increases cardiac output in dogs, its effects on cardiac and peripheral vascular function are not known. Thus, we assessed the cardiovascular effects of pyruvate infusion.

MATERIALS AND METHODS

Aortic, left ventricular (LV), and pulmonary (Ppa) pressures and LV stroke volume (Svlv; derived from aortic flow probe) were measured after thoracotomy in eight anesthetized dogs. LV area or volume changes were measured using either an epicardial echocardiography (n = 6) or a conductance catheter (n = 2). LV end-systolic elastance (Eeslv) and preload recruitable stroke force (PRSFlv) relations, as estimates of contractility, were generated by transient inferior vena cava occlusion. Simultaneous stroke volume to arterial pressure relations during the occlusions were used to measure arterial elastance (Ea), and steady-state systemic and pulmonary vascular resistances were used as measures of arterial tone. Graded doses of pyruvate (8, 16, and 32 mg/kg/min), dobutamine (positive control) and propranolol (negative control) and placebo (volume control) were sequentially given.

RESULTS

Dobutamine increased Eeslv, PRSFlv, whereas propranolol had the opposite effect on Eeslv and PRSFlv. Pyruvate at 32 mg/kg/min increased heart rate, Ppa, and SVlv and decreased LV end-diastolic area, and systemic vascular resistance without changing arterial pressure, Eeslv, PRSFlv, or Ea.

CONCLUSIONS

We conclude that pyruvate infusion in normal dogs induces venodilation but does not alter either cardiac contractility or arterial tone.