Percent Systolic Wall Thickening Research Articles

MRI native T1 and T2 mapping of myocardial segments in hypertrophic cardiomyopathy: tissue remodeling manifested prior to structure changes.

The aim of this study was to examine the local myocardial segments in hypertrophic cardiomyopathy (HCM) by MRI T1 and T2 mapping, and to investigate how tissue remodeling correlates with structural and functional remodeling in HCM. 47 patients with HCM and 19 healthy volunteers were enrolled in this study. All subjects underwent cardiac MRI at 3.0 T. Native T1 and T2 values, end-diastolic wall thickness (EDTH), and percentage of systolic wall thickening (PSWT) were assessed in the left ventricular segments according to the American Heart Association model. Myocardial segments were categorized as normal, non-hypertrophic, mild-hypertrophic, moderate-hypertrophic, and severe-hypertrophic based on EDTH. The difference among all five groups, and the correlation between native T1 and T2 values, EDTH, and PSWT were evaluated. Native T1 and T2 values were significantly elevated in both non-hypertrophic and hypertrophic segments of HCM patients compared to controls (both p < 0.001). PSWT was preserved in non-hypertrophic segments (p = 0.838), while significantly impaired (p < 0.001) in hypertrophic segments. Native T1 value of severe hypertrophic segments in HCM was significantly higher than segments of mild and moderate hypertrophy (p < 0.05). In HCM patients, the non-hypertrophic myocardial segments already demonstrated significantly elevated T1 and T2 values, despite normal wall thickness and preserved contraction function. The finding suggests that tissue remodeling may precede morphological and functional remodeling in HCM. MRI native T1 and T2 mapping can provide additional value for HCM diagnosis at an early stage. Myocardial tissue remodeling, as detected by MRI native T1 and T2 mapping, occurs earlier than morphological and functional changes in HCM patients.

Quantitative assessment of myocardial strain with displacement encoding with stimulated echoes MRI in patients with coronary artery disease

To determine the diagnostic performance and reproducibility of strain assessment with displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR) in identifying contractile abnormalities in myocardial segments with late gadolinium enhancement (LGE). DENSE CMR was obtained on short-axis planes of the left ventricle (LV) in 24 patients with suspected coronary artery disease. e1 and e2 strains of LV wall were quantified. Cine MRI was acquired to determine percent systolic wall thickening (%SWT), followed by (LGE) CMR. The diagnostic performance of e1, e2 and %SWT for predicting the presence of LGE was evaluated by receiver operating characteristics (ROC) analysis. Myocardial scar on LGE CMR was observed in 91 (24 %) of 384 segments. The area under ROC curve for predicting the segments with LGE was 0.874 by e1, 0.916 by e2 and 0.828 by %SWT (p = 0.001 between e2 and %SWT). Excellent inter-observer reproducibility was found for strain [Intraclass correlation coefficient (ICC) = 0.962 for e1, 0.955 for e2] as compared with %SWT (ICC = 0.790). DENSE CMR can be performed as a part of routine CMR study and allows for quantification of myocardial strain with high inter-observer reproducibility. Myocardial strain, especially e2 is useful in detecting altered abnormal systolic contraction in the segments with myocardial scar.

Quantitative assessment of left ventricular systolic wall thickening using multidetector computed tomography

Background Multidetector computed tomography (MDCT) of the heart provides both anatomical and functional information. The objective of this study was to evaluate the accuracy of quantitative assessment of left ventricular contractile function in relation to two-dimensional transthoracic echocardiography (TTE). Materials and methods Sixty-four patients with known or suspected coronary artery disease underwent ECG-gated 64-slice MDCT and TTE. Regional left ventricular contractile function was measured by percent systolic wall thickening (SWT) in 16 myocardial segments using MDCT, and compared with visual evaluation of wall motion score (WMS) by TTE. Global SWT by MDCT was calculated as the mean SWT of all myocardial segments and compared with wall motion index (WMI) by TTE. Results Eight hundred and eleven segments (81%) were classified as normokinetic, 142 (14%) as hypokinetic, 41 (4%) as akinetic and 5 (0.5%) as dyskinetic by TTE. A significant inverse linear trend was found between regional SWT by MDCT and WMS by TTE ( p < 0.001). Sensitivity and specificity for the identification of regional abnormalities of contractile function were 76% and 78%, respectively. A linear correlation between global SWT by MDCT and WMI by TTE was found ( r = −0.8, p < 0.001). Sensitivity and specificity for the identification of WMI > 1.5 using global SWT was 91% and 94%, respectively. Conclusion Quantification of systolic wall thickening by MDCT provides functional information, which is well correlated to visual assessment of global left ventricular contractile function by TTE.

Quantitative assessment of regional left ventricular wall thickness and thickening using 16 multidetector-row computed tomography: comparison with cine magnetic resonance imaging

The purpose of this study was to investigate the feasibility of retrospective electrocardiography-gated multidetector-row computed tomography (MDCT) in the assessment left ventricular (LV) wall thickness and thickening and to test its validity compared to cine magnetic resonance imaging (MRI) as a standard of reference. We enrolled 19 patients who underwent both cardiac MDCT and cine MRI. End-diastolic wall thickness (EDWT) and end-systolic wall thickness (ESWT) were measured in 16 myocardial segments. Percent systolic wall thickening (%SWT) was generated from the EDWT and ESWT. Nondiagnostic myocardial segments were excluded. Correlation and agreement between MDCT and cine MRI were analyzed. Segmental assessability values were 86.2% (262/304) and 92.1% (280/304) for MDCT and cine MRI, respectively. In assessable segments by both modalities (80.9%, 246/304), a significant correlation between MDCT and MRI was found (r = 0.89, 0.85, and 0.61, for EDWT, ESWT, and %SWT, respectively; all P < 0.05). Mean EDWT and ESWT values by MDCT were slightly lower than those by cine MRI (9.8 +/- 3.6 vs. 10.0 +/- 3.7 mm and 13.8 +/- 4.4 vs. 14.1 +/- 4.3 mm, respectively; both P < 0.01). Bland-Altman analysis revealed acceptable limits of agreement between MDCT and Cine MRI. MDCT is a feasible method to assess regional LV wall thickness and systolic thickening.

Expression of the MDR-1 Gene-encoded P-glycoprotein in Cardiomyocytes of Conscious Sheep Undergoing Acute Myocardial Ischemia Followed by Reperfusion

We have recently reported that in chronic myocardial ischemia, adult mammalian cardiomyocytes express P-glycoprotein (P-gp). We now investigate if P-gp is also expressed in acute regional ischemia followed by reperfusion. Adult conscious sheep underwent 12-min occlusion of the mid-left anterior descending artery (inflatable cuff). Successful ischemia-reperfusion was confirmed by monitoring percent systolic left ventricular anterior wall thickening (sonomicrometry) during the whole ischemic period and every 10 min over 2 hr following cuff deflation. At 3, 24, and 48 hr after reperfusion, P-gp expression was investigated by immunohistochemistry and Western blot and MDR-1 mRNA by RT-PCR. Cardiomyocytes in the occluded artery territory (but not those in remote areas) consistently expressed P-gp at their sarcolemma. Whereas at 3 and 24 hr P-gp was mainly observed in the T tubules, at 48 hr it predominated in intercalated discs and gap junctions. RT-PCR and Western blot revealed higher expression in ischemic than in control myocardium. We conclude that in adult sheep with acute myocardial ischemia, the MDR-1 gene-encoded P-gp is expressed at the sarcolemma of the cardiomyocytes from 3 hr up to at least 48 hr after reperfusion.

Usefulness of Automated Quantitation of Regional Left Ventricular Wall Motion by a Novel Method of Two-Dimensional Echocardiographic Tracking

A novel 2-dimensional (2-D) echocardiographic tracking method enables the automated tracking of displacement between 2 points of interest in echocardiographic images. The purpose of this study was to evaluate whether this 2-D tracking method could be used to measure left ventricular (LV) wall thickness and percent systolic wall thickening (%WT) in parasternal short-axis views, in comparison with conventional manual measurement, and to determine whether this system can be used to quantitatively assess regional LV wall motion in echocardiography. In 24 subjects (12 with LV wall motion abnormalities), 6 segments in the short-axis images were assessed by this method. Two sample points at the endocardium and epicardium were tracked automatically during 1 cardiac cycle. Then, LV wall thickness and %WT were calculated. In 50 subjects (32 with LV wall motion abnormalities), average %WT as an average of all %WT in every degree of angle in each of the 6 segments was measured by this method, and the results were compared with the visual assessment of LV wall motion scores. There was excellent agreement between the 2-D tracking and manual methods for LV wall thickness (r = 0.99) and %WT (r = 0.97). The mean differences in LV wall thickness and %WT were 0.1 +/- 0.4 mm and 0 +/- 5.4%, respectively. Average %WT was significantly decreased in the regions of hypokinetic or akinetic wall motion compared with those of normal motion (18 +/- 4% and 4 +/- 4% vs 39 +/- 10%, p <0.001). In conclusion, this 2-D tracking method can be used for the noninvasive, automated quantitation of LV wall motion in 2-D echocardiography.

Focalized Contractile Impairment at Hypertrophied Myocardium Proven in Consideration of Wall Stress in Patients With Hypertrophic Cardiomyopathy

In hypertrophic cardiomyopathy (HCM) a hyperkinetic state is sometimes observed in spite of impaired systolic function in the hypertrophied myocardium. The aim of the present study was to determine the mechanism of this paradox. Seventeen patients with HCM and 10 normal subjects underwent cine magnetic resonance (MR) imaging to measure percent systolic wall thickening and percent fractional shortening. The ratio of systolic radial wall stress of the LV at the hypertrophied myocardium over that at the nonhypertrophied myocardium was evaluated to describe the focal advantageous condition for wall thickening. The ratio was 0.66 +/- 0.36 at the start of contraction and 0.78 +/- 0.31 at early-systole, indicating consistently smaller radial wall stress at the hypertrophied myocardium. Although the condition for contraction was favorable (a ratio less than 1.00), percent systolic wall thickening at the hypertrophied myocardium (23.0 +/- 11.8%) was smaller than that at the nonhypertrophied myocardium (70.5 +/- 32.3%). Smaller end-diastolic dimension (HCM group; 45.2 +/- 4.2 mm, reference group; 48.9 +/- 4.1 mm, P = 0.04) with a statistically identical value of systolic decrease in intraventricular dimension (HCM group; 19.7 +/- 3.9 mm, reference group; 18.9 +/- 3.2 mm, P = 0.60) yielded high percent fractional shortening in patients with HCM (43.5 +/- 7.6%). Although contractile impairment was proven at the hypertrophied region with low radial wall stress in the HCM group, the smaller end-diastolic dimension in this group resulted in high percent fractional shortening.

Relation of ultrasonic tissue characterization with integrated backscatter to contractile reserve in patients with chronic coronary artery disease.

Previous studies have shown that viable but stunned myocardium displays contractile reserve and exhibits cardiac cycle-dependent variations of integrated backscatter (CVIB), whereas infarcted myocardium does not. This study was designed to clarify whether assessment of the acoustic properties of the myocardium can predict contractile reserve in patients with chronic coronary artery disease (CAD). In all, 21 patients with chronic CAD and 19 normal control subjects were studied. The magnitude of CVIB of the myocardium was measured in the basal and mid segment of the anterior septum and posterior wall of the left ventricle, using a real-time, two-dimensional integrated backscatter imaging system. The results were compared with the percent systolic wall thickening and the wall motion before and after revascularization. The wall motion was graded as normal, hypokinetic, or akinetic, and contractile reserve was considered present when an akinetic or hypokinetic segment improved after revascularization. The average magnitude of CVIB was lower among dysfunctional segments of CAD than among normal segments of controls (3.73 +/- 1.71 vs. 6.35 +/- 0.69, p < 0.001). Of the 77 segments examined, 38 showed reversible dysfunction. Before revascularization, percent systolic wall thickening was similar among segments showing contractile reserve compared with those with persistent dysfunction myocardium (17.97 +/- 8.41 vs. 16.83 +/- 6.37%, p = 0.19), and the mean CVIB was significantly greater in segments with than in those without contractile reserve (4.73 +/- 1.47 vs. 2.75 +/- 1.31, p < 0.001). The CVIB above 3 dB before percutaneous transluminal coronary angioplasty predicted segments with contractile reserve with a sensitivity and specificity of 84.2 and 79.5%, respectively. Cardiac cycle-dependent variations of integrated backscatter reflected myocardial contractility and functional capacity of the myocardium. They predicted segmental contractile reserve in patients with CAD.

Room C, 10/16/2000 2: 00 PM - 4: 00 PM (PS) Comparison of Quantitative Intraoperative Assessment of Regional Systolic Ventricular Function: Pulsed Tissue Doppler Imaging Vs. Percentage of Systolic Wall Thickening

Room C, 10/16/2000 2: 00 PM - 4: 00 PM (PS) Comparison of Quantitative Intraoperative Assessment of Regional Systolic Ventricular Function: Pulsed Tissue Doppler Imaging Vs. Percentage of Systolic Wall Thickening

Quantitative evaluation of left ventricular regional wall motion using a real-time wall thickness curve system with two-dimensional echocardiography

The real-time wall thickness curve system was newly developed for recording left ventricular (LV) wall thickening (WT) on a 2-dimensional echocardiogram recorded in an arbitrary direction because of the scarcity of quantitative data on wall motion change during dobutamine-induced ischemia. This study tested the feasibility of this system for quantitative evaluation of wall motion. In normal subjects, accuracy and reproducibility of measurements were evaluated by comparison with measurements on a conventional M-mode echocardiogram and examination of inter- and intraobserver variability. In 28 patients with coronary artery disease, percent systolic wall thickening (%WT) was measured during dobutamine infusion in incremental doses of 6 μg/kg/min, from 6 to 30 μg/kg/min. Percent change in %WT by dobutamine was compared with percent coronary stenosis derived from quantitative coronary angiography. Analysis of the mean difference and 95% confidence intervals demonstrated good accuracy and reproducibility: 0.0 mm and intervals of −0.5 to 0.5 mm in diastolic wall thickening of LV posterior wall (PW) between both methods, −1% and −4% to 2% in %WT of IVS and LVPW between both observers, and −1% and −3% to 2% in that between both measurements. During dobutamine infusion, the percent change in %WT was significantly correlated with percent stenosis (r = 0.75, p <0.0001). The WT curve system enabled us to assess regional wall function as %WT and was available for quantitative observation of wall motion change during pharmacologic intervention. This system may reduce the effects of heart movement and may be of great clinical benefit in evaluating regional wall function.

Intraoperative Low-dose Dobutamine Echocardiography Predicts the Post-pump Response of Dysfunctioning Myocardial Segments to Coronary Artery Bypass Grafting

Background:Low dose dobutamine echocardiography has recently been introduced for use in identification of viable myocardium in patients with acute myocardial infarction and prediction of the response of dysfunctioning myocardial segments to coronary angioplasty. The aim of this study was to evaluate whether this test could be used to predict the early response of dysfunctioning myocardial segments to coronary artery bypass grafting(CABG. Methods:We studied in 23 patients with multi-vessel disease during CABG. Myocardial segments were monitored by intraoperative transesophageal echocardiography(TEE in the transgastric short-axis view at papillary muscle level. The left ventricle was divided into five segments and sixty eight myocardial segments in 23 patients were analyzed. Percentage of systolic wall thickening(PSWT was calculated in each segment for three times:at baseline(early after pericardiectomy; before bypass during dobutamine infusion(3-5ug/kg/min; and after seperation from cardiopulmonary bypass. Segments showing baseline PSWT ≥30% were considered normal and those <30% were dysfunctional. Segments showing an increase in PSWT ≥10% during dobutamine infusion were considered responders and those <10% nonresponders. Results:At baseline, 24(36% of 68 segments had PSWT ≥30%(normal and (4468% had * 본 논문의 일부는 가톨릭 중앙의료원의 보조로 이루어졌음.

Low-dose dobutamine echocardiography predicts the early response of dysfunctioning myocardial segments to coronary artery bypass grafting

Dobutamine echocardiography has recently been introduced for use in identification of viable myocardium in patients with acute myocardial infarction and prediction of the response of dysfunctioning myocardial segments to coronary angioplasty. The aim of this study was to evaluate whether this test may be used to predict the early response of dysfunctioning myocardial segments to surgical revascularization. We studied 30 patients with three-vessel disease and chronic, stable angina pectoris during coronary artery bypass grafting (CABG). Patients were monitored by intraoperative transesophageal echocardiography in the transgastric short-axis view at the papillary muscle lvel. The left ventricle was divided into eight segments; and 240 myocardial segments were analyzed. Percentage of systolic wall thickening (PSWT) was calculated in each segment at baseline (early after pericardiectomy), before bypass during dobutamine infusion (5 μg/kg/min), and after separation from cardiopulmonary bypass. Segments showing PSWT <30% at baseline were considered dysfunctional. Segments showing an increase in PSWT >10% during dobutamine infusion were considered responders. Segments showing an increase in PSWT <10% during dobutamine infusion were considered nonresponders. At baseline, 161 (67%) of 240 segments had PSWT <30% (dysfunctioning segments). During dobutamine, 98 (60%) of 240 segments had PSWT >10% (from 11.3% ± 7.6% to 24.2% = 12.0%, p < 0.01; responder segments), and 63 (40%) increased PSWT <10% (from 10.2% = 4.9% to 8.3% ± 5.5%, p value not significant [NS]; nonresponder segments). After CABG, responder segments showed a significant increase in PSWT in comparison with baseline values (from 11.3% ± 7.6% to 24.4% ± 14.0%; p < 0.01). Segments not responding to dobutamine showed no significant changes in PSWT after CABG (from 10.2% ± 4.9% to 9.3% ± 6.6%; p = NS). Seventy-nine normal segments (PSWT 43.9% ± 12.6%) showed a slight but significant reduction in wall thickening both during dobutamine (PSWT 33.6% ± 14.0%, p 0.01 vs baseline) and after CABG (PSWT 32.8% ± 14.6%; p < 0.01 vs baseline), suggesting that compensatory hyperfunction was present at baseline. Estimation of clinical accuracy for transesophageal echocardiography dobutamine-stress test yielded to 91% sensitivity, 93% specificity, 97% positive predictive value, 79% negative predictive value, and 92% overall accuracy. In responder segments there was a correlation between PSWT during dobutamine infusion and after CABG ( r = 0.62).

Regional myocardial function during contiguous ischaemia in an anaesthetized canine model: comparison of six methods of measurement

During acute myocardial ischaemia, the function of the unaffected muscle is the primary determinant of residual cardiac performance. We compared six methods of measuring regional function in the remaining non-ischaemic segment after acute ligation of the left anterior descending (LAD) coronary artery in 16 dogs. Preparation included left ventricular micromanometers, regional sonomicrometer transducers to measure segment length and wall thickness, caval occluders and left atrial catheters for injection of radioactive microspheres to measure regional blood flow. Pulmonary artery, central venous and systemic arterial pressures were measured and regional coronary venous blood was collected for direct myocardial oxygen consumption (VO2) calculations. Under basal high-dose fentanyl-neuromuscular blocker anaesthesia, the LAD was occluded after addition of halothane or isoflurane at 0.5 or 1.5 MAC concentrations. Regional myocardial function of the non-ischaemic segment was assessed by the following computer-derived indices: percent systolic wall thickening (% WT), velocity of shortening (vs), percent systolic shortening (%SS), regional stroke work (RSW), regional preload recruitable stroke work (RPRSW) and regional end-systolic elastance (Ees). No index demonstrated enhanced function in the non-ischaemic segment after LAD ligation and all monitors, except Ees, were sensitive to depression of function represented by a decrease in values after administration of halothane and isoflurane (P < 0.05). Ees values increased with the addition of isoflurane and remained constant with halothane. Circulating concentrations of catecholamines were unchanged after ischaemia, while inhalation agents caused a decrease in the concentrations of adrenaline and dopamine (P < 0.05), but not noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging during dobutamine stress for detection and localization of coronary artery disease. Quantitative wall motion analysis using a modification of the centerline method.

Quantitative measurement of wall motion is essential to assess objectively the functional significance of coronary artery disease. We developed a quantitative wall thickening analysis on stress magnetic resonance images. This study was designed to assess the clinical value of magnetic resonance imaging (MRI) during dobutamine stress for detection and localization of myocardial ischemia in patients with suspected coronary artery disease. Thirty-nine consecutive patients with clinically suspected coronary artery disease referred for coronary arteriography and 10 normal volunteers underwent gradient-echo MRI at rest and during peak dobutamine stress (infusion rate, 20 micrograms.kg-1.min-1). MRI was performed in the short-axis plane at four adjacent levels. Display in a cine loop provided a qualitative impression of regional wall motion (cine MRI). A modification of the centerline method was applied for quantitative wall motion analysis by means of calculation of percent systolic wall thickening. Short-axis cine MRI images were analyzed at 100 equally spaced chords constructed perpendicular to a centerline drawn midway between the end-diastolic and end-systolic contours. Dobutamine MRI was considered positive for coronary artery disease if the percent systolic wall thickening of more than four adjacent chords was < 2 SD below the mean values obtained from the normal volunteers. The overall sensitivity of dobutamine MRI for the detection of significant coronary artery disease (diameter stenosis > or = 50%) was 91% (30 of 33), specificity was 80% (5 of 6), and accuracy was 90% (35 of 39). The sensitivity for identifying one-vessel disease was 88% (15 of 17), for two-vessel disease 91% (10 of 11), and for three-vessel disease 100% (5 of 5). The sensitivity for detection of individual coronary artery lesions was 75% for the left anterior descending coronary artery, 87% for the right coronary artery, and 63% for the left circumflex coronary artery. Dobutamine MRI clearly identifies wall motion abnormalities by quantitative analysis using a modification of the centerline method. Dobutamine MRI is an accurate method for detection and localization of myocardial ischemia and may emerge as a new noninvasive approach for evaluation of patients with known or suspected coronary artery disease.

Effects of diltiazem on perioperative ischemia, arrhythmias, and myocardial function in patients undergoing elective coronary bypass grafting

A prospective, randomized study was performed on 120 patients undergoing elective coronary bypass grafting to define the effect of the calcium channel blocker diltiazem on perioperative ischemia, arrhythmias, and myocardial function. Patients received a continuous 24-hour perioperative infusion of either diltiazem (0.1 mg/kg per hour, n = 60) or nitroglycerin (1 μg/kg per minute, n = 60). Perioperative monitoring included hemodynamic measurements, three-channel Holter monitoring, repeated assessment of 12-lead electrocardiograms, and analysis of ischemia-specific laboratory parameters (creatine kinase, creatine kinase-MB, and creatine kinase-MB-mass and troponin-T). Global and regional systolic function and diastolic compliance were assessed by means of transesophageal echocardiography. The two groups did not differ with respect to preoperative and operative data. Except for a significant reduction in perioperative heart rate, diltiazem had no influence on hemodynamic parameters. The number (17 ± 9 versus 25 ± 5, p < 0.05) and the duration (69 ± 47 versus 104 ± 87 minutes, p < 0.05) of transient ischemic events were significantly reduced as compared with the nitroglycerin group. In addition, peak values of all assessed laboratory parameters except creatine kinase were significantly lower in the diltiazem group. Patients treated with diltiazem had a lower incidence of perioperative atrial fibrillation (5% versus 18%, p < 0.05) and lower numbers of ventricular premature beats per hour (10 ± 8 versus 19 ± 22, p < 0.05) and ventricular runs per hour (5 ± 17 versus 32 ± 38, p < 0.05). Postoperatively, the percent fractional area of contraction and percent systolic wall thickening of the anterior wall were significantly improved in the diltiazem group but not in the nitroglycerin group. In addition, the postoperative diastolic flow/velocity ratio was significantly lower in the nitroglycerin group than in the diltiazem group (0.949 ± 0.391 versus 1.331 ± 0.475, p < 0.001). It is concluded that perioperative infusion of the calcium antagonist diltiazem has no adverse effect on perioperative hemodynamics and systolic myocardial function and provides potent antiischemic and antiarrhythmic protection in patients undergoing coronary bypass grafting. (J THORAC CARDIOVASC SURG 1994;107:811-21)

Accurate systolic wall thickening by nuclear magnetic resonance imaging with tissue tagging: Correlation with sonomicrometers in normal and ischemic myocardium

Objectives. This study examined whether the correlation of systolic wall thickening (%WT) by nuclear magnetic resonance (NMR) imaging with wall thickening by sonomicrometry (SM) is improved by using a three-dimensional volume element model of the left ventricular wall.Background. Left ventricular wall obliquity with respect to the imaging plane causes overestimation of wall thickness by planar imaging techniques. Wall thickness perpendicular to the endocardial surface can be accurately calculated by three-dimensional reconstruction of left ventricular wall segments.Methods. Sonomicrometers were placed transmurally in 11 dogs (left anterior descending artery territory) with an imaging marker, visible on NMR imaging, sewn to the epicardial crystal. Two adjacent NMR short-axis image planes were radially segmented by four perpendicular spin-saturated planes (tags), dividing the myocardium into eight volume elements, one of which contained the sonomicrometer crystal pair. Left ventricular thickness and thickening were calculated by four methods: 1) linear = distance between epicardium and endocardium at midpoint in the segment with the sonomicrometer; 2) planar = area of that segment divided by the mean of the endocardial and epicardial arc lengths; 3) biplanar = average of wall thicknesses calculated by the planar method from the segment with sonomicrometers and the corresponding segment located in the adjacent short-axis imaging plane; and 4) three-dimensional = volume of the element with the sonomicrometers divided by the mean of the endocardial and epicardial surface areas.Results. Regressions for all methods using pooled data from control periods and during ischemia: Linear %WT = 0.59 + 1.31 SM%WT (r = 0.71, SEE = 0.28, p < 0.0002) Planar %WT = 1.43 + 1.62 SM%WT (r = 0.87, SEE = 0.19, p < 0.0001) Biplanar %WT = 2.09+1.46 SM%WT (r = 0.90, SEE = 0.15, p < O.0001) Three-dimensional %WT = 0.19+1.49 SM%WT (r = 0.95, SEE = 0.10, p < 0.0001)Conclusions. Nuclear magnetic resonance imaging with tissue tagging allows accurate noninvasive assessment of systolic wall thickening. The three-dimensional volume element approach, by accounting for obliquity between the image plane and the left ventricular wall, provides the strongest correlation between NMR imaging and percent systolic wall thickening by sonomicrometer crystals.

Quantitation of global and regional left ventricular function by cine magnetic resonance imaging during dobutamine stress in normal human subjects.

Magnetic resonance imaging (MRI) provides high-resolution images of the heart. However, physical exercise during MRI is difficult due to space restriction and motion artefacts. To evaluate the feasibility of MRI during stress conditions, dobutamine was used as an alternative to exercise. Haemodynamics, ventricular volumes and wall thickening were measured at rest and during peak dobutamine infusion (15 micrograms.kg-1 x min-1) in 23 normal human subjects. To calculate left ventricular volumes, eight short-axis views were obtained encompassing the left ventricle from base to apex. At six levels, percent systolic wall thickening (%WTh) was measured in 18 segments (20 degrees intervals). Heart rate, systolic and diastolic blood pressures, stroke index, cardiac output and left ventricular ejection fraction increased significantly during dobutamine infusion (all P values < 0.001). In addition, %WTh increased significantly (P < 0.001) during dobutamine compared to the control state at all levels except in the apical and low-left ventricular levels. Both in control conditions and during dobutamine, segmental wall motion analysis showed the highest %WTh at the posterolateral area and the lowest %WTh at the septal region (P < 0.05). MRI clearly identifies wall motion dynamics and provides calculations of segmental wall thickening and haemodynamic parameters. Dobutamine is a useful stress agent by virtue of its safety, operator control and its effects which resemble physical exercise.

Myocardial function and transmural blood flow during coronary venous retroperfusion in pigs.

The degree of recovery of regional myocardial contraction during coronary venous retroperfusion has not been well established, particularly in the absence of coronary collateral channels. Therefore, the maximal functional benefit attainable with coronary venous retroperfusion was assessed in pigs by means of using selective pump retroperfusion of the left anterior descending vein, with venting of the left anterior descending artery to zero pressure. In eight anesthetized open-chest pigs during selective left anterior descending venous retroperfusion over a range of retroperfusion flows, regional myocardial function (percent systolic wall thickening by sonomicrometry) increased progressively to an average of 62% of control values at a retroperfusion flow rate 200% of control arterial flow. Progressive thickening of the end-diastolic dimension of the anterior wall was observed with increasing retroperfusion flow (from 8.7 +/- 0.9 to 10.7 +/- 2.3 mm, p less than 0.001). Perfusion pressures within the left anterior descending vein increased linearly with increased retroperfusion flow rates (up to 132 +/- 57 mm Hg with retroperfusion flow 200% of control). A gradual increase of retrograde left anterior descending arterial outflow was observed with increasing retroperfusion flows; however, the absolute amount (maximum, 8.3 +/- 4.1 ml/min) was much too low to explain the extent of functional recovery. Transmural myocardial capillary blood flows in the anterior wall with retroperfusion flows of 100% and 200% of control arterial flow were 0.22 and 0.42 ml/min/g with corresponding subendocardial blood flows of 0.14 and 0.29 ml/min/g; ratios of endocardium to epicardium were 0.51 and 0.61, respectively. Thus, capillary blood flows during selective retroperfusion were relatively low despite considerable restoration of regional systolic wall thickening, and a significant difference was noted in the slopes of the relations between regional systolic wall thickening and myocardial blood flow during retroperfusion and anterograde arterial perfusion (p less than 0.05). With retrograde injection of silicone elastomer at different retroperfusion pressures (50, 75, and 100 mm Hg) in three pigs, capillaries were well visualized, and profuse intramyocardial venous anastomotic connections were seen at the highest retroperfusion pressure (100 mm Hg), whereas there was filling of small venules but little capillary filling at the lowest retroperfusion pressure (50 mm Hg). Considerable recovery of regional myocardial function with low regional capillary blood flows were observed during acute venous retroperfusion with high retroperfusion flows with arterial blood. These findings together with low levels of retrograde arterial outflow and visualization of retrograde capillary filling with a rich venous network provide evidence for possible oxygen delivery via the intramyocardial venous plexus.

Effect of changing afterload and inotropic states on inner and outer ventricular wall thickening.

Effect of changing afterload and inotropic states on inner and outer ventricular wall thickening. Am. J. Physiol. 263 (Heart Circ. Physiol. 32): H109-H116, 1992.--To study the differing behaviors of the inner (IH) and outer halves (OH) of the left ventricular (LV) free wall during an increasing afterload and changing inotropic states, we determined the LV pressure (LVP) and transmural (TM) and OH wall thickness (WTTM and WTOH) by sonomicrometry in 11 anesthetized dogs. The percent systolic wall thickening (% delta WT) and the fractional contribution (FC) were calculated. At rest, % delta WT of TM, IH, and OH were 22 +/- 1 (mean +/- SE), 33 +/- 3, and 13 +/- 2 (P less than 0.01 vs. IH), respectively. The FC of IH and OH were 74 +/- 5 and 29 +/- 4% (P less than 0.01 vs. IH), respectively. During increasing afterload by aortic constriction (AC) without drugs, % delta WT in IH was reduced to 22 +/- 2%, associated with unchanged % delta WT in OH (12 +/- 3%), whereas the FC of IH and OH were not altered from resting values. During AC with dobutamine infusion (3 micrograms.kg-1.min-1), the % delta WT and FC in each layer were not reduced from resting values. On the other hand, during AC with propranolol (2 mg bolus iv), the reduction of % delta WT in IH was greater (from 29 +/- 4 to 15 +/- 6%, P less than 0.01) than that in OH (from 11 +/- 2 to 10 +/- 3%; P less than 0.01 vs. IH). The FC in the IH was decreased (56 +/- 16%) by AC with propranolol, so that the difference in FC between IH and OH became insignificant (FCOH 40 +/- 13%, P greater than 0.1 vs. FCIH).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alpha-adrenergic stimulation on regional contractile function and myocardial blood flow with and without ischemia : Miyamoto MI, Rockman HA, Guth BD, et al Circulation 84:1715–1724, 1991

BACKGROUNDThe effect of alpha-adrenergic receptor activation on regional contractile function and transmural myocardial blood flow is controversial. Accordingly, the effects of selective alpha 1-(methoxamine) and alpha 2-(BHT 933) receptor stimulation on regional contractile function and transmural myocardial blood flow distribution were studied in 15 anesthetized open-chest dogs.METHODS AND RESULTSThe alpha-adrenergic agonists were separately infused into the cannulated left circumflex coronary artery during control and ischemic conditions in the same animal. Mean coronary perfusion pressure was held constant by a servocontrolled pump in an extracorporeal circuit. Ischemia was created by reducing coronary perfusion pressure to the level at which percent systolic wall thickening (%WT) decreased by 54%. Contractile function during control conditions was unchanged, whereas under ischemic conditions a further significant decrease in %WT of 27% occurred with either alpha 1- or alpha 2-receptor stimulation wit...