Improvement In Wall Thickening Research Articles

Myocardial adaptation after surgical therapy differs for aortic valve stenosis and hypertrophic obstructive cardiomyopathy

Surgical therapies in aortic valve stenosis (AVS) and hypertrophic obstructive cardiomyopathy (HOCM) aim to relief intraventricular pressure overload and improve clinical outcome. It is currently unknown to what extent myocardial adaptation concurs with restoration of intraventricular pressures, and whether this is similar in both patient groups. The aim of this study was to investigate changes in myocardial adaptation after surgical therapies for AVS and HOCM. Ten AVS and ten HOCM patients were enrolled and underwent cardiac magnetic resonance cine imaging and myocardial tagging prior to, and 4 months after aortic valve replacement (AVR) and septal myectomy, respectively. Global left ventricular (LV) analyses were derived from cine images. Circumferential strain was assessed from myocardial tagging images at the septal and lateral wall of the mid ventricle. Pressure gradients significantly decreased in both AVS and HOCM after surgery (p < 0.01), with a concomitant decrease in left atrial volume (p < 0.05) suggesting lower diastolic filling pressures. Also, LV volumes, mass and septal wall thickness decreased in both, but to a larger extent in AVS than in HOCM patients. AVR improved wall thickening (p < 0.05) and did not change systolic strain rate. Myectomy did not affect wall thickening and reduced septal systolic strain rate (p = 0.03). Both AVR and myectomy induced positive structural remodeling in line with a reduction of pressure overload. A concomitant recovery in systolic function however was found in AVR only. The systolic functional deterioration in HOCM patients seems to be inherent to myectomy and the ongoing and irreversible disease.

Long-term left ventricular remodelling after revascularisation for ST-segment elevation myocardial infarction as assessed by cardiac magnetic resonance imaging

ObjectiveLeft ventricular remodelling following a ST-segment elevated myocardial infarction (STEMI) is an adaptive response to maintain the cardiac output despite myocardial tissue loss. Limited studies have evaluated long term ventricular...

MDCT abnormalities of small- and medium-sized bronchus in active tuberculosis: a new angle on an old disease

The incidence and findings of tuberculous invasion of the peripheral bronchus have not been fully investigated with MDCT. Purpose To evaluate the prevalence and findings of MDCT abnormalities of small- and medium-sized bronchus (SMB) in active pulmonary tuberculosis (TB). Using multiplanar reformation, 35 consecutive MDCT scans (follow-up exams available in 14 patients with a mean interval of 8.1 months) were assessed for following abnormalities of SMB: bronchial impaction (BI), wall thickening, dilatation, peribronchial cuff of soft tissue, and bronchocavitary fistula. It was also assessed whether tree-in-buds (TIB) have a tendency to distribute in the territories of diseased SMB, and whether SMB abnormalities are present in patients with relatively mild disease. SMB abnormalities were observed in 23 (65.7%) patients with active TB. The most frequent finding was wall thickening (n = 18, 51.4%), followed by BI (n = 13, 37.1%; zigzag-shaped in four), dilatation (n = 11, 31.4%), amputated appearance of air column (n = 11, 31.4%), peribronchial cuff of soft tissue (n = 10, 28.6%), and bronchocavitary fistula (n =8, 22.9%). TIB (n = 29; absent in two patients with SMB) was mainly within (n = 14) or close to (n = 4) the territory of diseased SMB. Follow-up CT frequently showed improvement of wall thickening (11/12) and persistence of bronchial dilatation (11/13). SMB abnormality was present in all of six patients with mild disease. MDCT shows that tuberculous invasion of the peripheral bronchus may be more frequent than previously thought, of which findings include wall thickening, BI, dilatation, amputated appearance of air column, peribronchial cuff of soft tissue and bronchocavitary fistula.

Does laser type impact myocardial function following transmyocardial laser revascularization?

Transmyocardial laser revascularization (TMR) is currently clinically performed with either a CO(2) or Ho:YAG laser for the treatment of severe angina. While both lasers provide symptomatic relief, there are significant differences in the laser-tissue interactions specific to each device that may impact their ability to enhance the perfusion of myocardium and thereby improve contractile function of the ischemic heart. A porcine model of chronic myocardial ischemia was employed. After collecting baseline functional data with cine magnetic resonance imaging (MRI) and dobutamine stress echo (DSE), 14 animals underwent TMR with either a CO(2) or Ho:YAG laser. Transmural channels were created with each laser in a distribution of 1/cm(2) in the ischemic zone. Six weeks post-treatment repeat MRI as well as DSE were obtained after which the animals were sacrificed. Histology was preformed to characterize the laser-tissue interaction. CO(2) TMR led to improvement in wall thickening in the ischemic area as seen with cine MRI (40.3% vs. baseline, P < 0.05) and DSE (20.2% increase vs. baseline, P < 0.05). Ho:YAG treated animals had no improvement in wall thickening by MRI (-11.6% vs. baseline, P = .67) and DSE (-16.7% vs. baseline, P = 0.08). Correlative semi-quantitative histology revealed a significantly higher fibrosis index in Ho:YAG treated myocardium versus CO(2) (1.81 vs. 0.083, P < 0.05). In a side-by-side comparison CO(2) TMR resulted in improved function of ischemic myocardium as assessed by MRI and echocardiography. Ho:YAG TMR led to no improvement in regional function likely due to concomitant increase in fibrosis in the lasered area.

Sequential Changes of Myocardial Microstructure in Patients Postmyocardial Infarction by Diffusion-Tensor Cardiac MR

Background— We used diffusion-tensor cardiac MR to investigate myocardial microstructure changes, including tissue integrity (mean diffusivity [MD], fractional anisotropy) and fiber architecture (helix angles) in patients with recent myocardial infarction (MI). This study aimed to investigate the sequential changes of myocardial microstructure and its relationships with changes of macrostructure and function of the left ventricle post-MI. Methods and Results— Seventeen patients (age, 55.1�11.5 years; all men) participated in the follow-up study. Diffusion-tensor cardiac MR, cine gradient echo for left ventricle function, and late gadolinium enhancement for viability were measured from recent to chronic MI (median interval, 191 days). When compared with the remote zone, the infarct-adjacent zone showed overall increase of MD (2-way MANOVA, F 1,16 =36.3; P &lt;0.001), decrease of fractional anisotropy (F 1,16 =5.8; P =0.029), and decrease of mean helix angles (F 1,16 =62.0; P &lt;0.001). From recent to chronic MI, there was overall sequential decrease of MD (F 1,16 =22.6; P &lt;0.001) and increase of fractional anisotropy (F 1,16 =7.8; P =0.013). Multiple linear regression showed that the improvement of wall thickening in the infarct-adjacent zone correlated with sequential decrease of MD in the infarct-adjacent zone ( r =−0.70; P =0.002) and increase of mean helix angles (ie, more right-handed helical myofiber reorientation, predominantly subendocardial location) in the remote zone ( r =0.60; P =0.011). Likewise, wall thickening in the remote zone correlated with MD in the remote zone ( r =−0.72; P =0.001) and mean helix angles in the infarct-adjacent zone ( r =0.72; P =0.001). Conclusion— Diffusion-tensor cardiac MR suggests that sequential zonal improvement of tissue integrity and fiber architecture remodeling both associate with sequential recovery of zonal wall thickening of the left ventricle from recent to chronic MI.

Injection of Adeno-associated Viral Vector–Encoding Vascular Endothelial Growth Factor Gene in Infarcted Swine Myocardium: MR Measurements of Left Ventricular Function and Strain

To prospectively investigate the long-term effect of adeno-associated viral (AAV) vector-encoding vascular endothelial growth factor gene (VEGF) (AAV-VEGF) on left ventricular (LV) mass and volumes, as well as on regional contractility and circumferential strain, in a swine model of reperfused myocardial infarction. All experimental procedures received approval from the institutional committee on animal research. Of 16 pigs subjected to reperfused myocardial infarction, six were treated, six were controls, and four died during the ischemic intervention. In six animals, cardiac-specific AAV-VEGF was injected into the periinfarcted and infarcted myocardium 1 hour after reperfusion. Magnetic resonance (MR) imaging was performed at 3 days and 8 weeks after infarction by using cine, tagged, and delayed enhancement (with gadoterate meglumine) sequences to measure global and regional LV function and infarct size. At postmortem examination, tissue samples stained with isolectin B4, Masson trichrome, and hematoxylin-eosin were used to characterize injured myocardium. Two-tailed Student t test was used for statistical analysis. Six treated animals showed no change in mean LV ejection fraction after 8 weeks (40.3%+/-0.9 [standard error of the mean] vs 41.0%+/-0.7) in contrast to a decrease measured in six control animals (41.4%+/-0.7 vs 36.1%+/-0.6, P<.001). AAV-VEGF improved wall thickening and circumferential strain in periinfarcted and remote myocardium. A greater reduction in gadoterate meglumine-enhanced infarct area was measured in treated animals (18.6%+/-1.5 of the LV mass at 3 days vs 9.8%+/-1.0 of the LV mass at 8 weeks, P<.001) compared with control animals (17.7%+/-2.0 vs 14.8%+/-1.0, P=.008). Findings at histopathologic evaluation indicated an increase in vascular density and a decrease in myocyte diameter in the periinfarcted myocardium of treated, compared with control, animals. Angiogenesis and arteriogenesis induced by VEGF genes improved regional myocardial strain and wall thickening and preserved ejection fraction after infarction.

Positive effect of darbepoetin on peri-infarction remodeling in a porcine model of myocardial ischemia–reperfusion

Erythropoietin (Epo) has anti-apoptotic and pro-angiogenic effects in rodent models of myocardial infarction (MI). We tested the hypothesis that a long-acting Epo derivative (darbepoetin) has a beneficial effect on infarct size and peri-infarct remodeling in a clinically relevant large animal model of ischemia–reperfusion. A human acute MI scenario was simulated in 16 domestic pigs by inflating an angioplasty balloon in the proximal left circumflex (LCx) artery for 60 min. The animals were randomized to darbepoetin 30 μg/kg iv or placebo (saline) at the time of reperfusion. Treatment with darbepoetin did not lead to a reduction in the infarct size at 2 weeks as assessed by histology (30.3 ± 1.8% of the volume at risk for placebo vs. 33.2 ± 2.5% for darbepoetin). However, significant effects were seen in the peri-infarct region. Histological evaluation revealed decreased interstitial fibrosis (6.8 ± 0.7% of myocardial sections area vs. 9.6 ± 0.7%, p = 0.02) and increased average capillary area (106 ± 3% of the non-infarcted myocardium vs. 89 ± 4%, p = 0.003) in the treatment arm in the absence of significant cardiac hypertrophy. This resulted in preserved regional wall motion as assessed by tissue Doppler-derived radial strain (subepicardial radial strain 90.1 ± 21.2% for darbepoetin vs. 20.3 ± 10.1% for placebo, p < 0.05). However, this did not translate to improved wall thickening (126.5 ± 6.0% of diastolic thickness for darbepoetin vs. 119.8 ± 5.4% for placebo, p = NS). Beneficial effects of darbepoetin to peri-infarct remodeling were observed in a clinically relevant model of ischemia–reperfusion. Although the infarct size was not reduced, there was a limited decrease in interstitial fibrosis, increased capillary area and regional functional improvement in darbepoetin-treated animals.

The Relationship between Transmural Extent of Infarction on Contrast Enhanced Magnetic Resonance Imaging and Recovery of Contractile Function in Patients with First Myocardial Infarction Treated with Thrombolysis

Background: The aim of the current study was to assess the utility of transmurality of delayed enhancement on cardiac magnetic resonance imaging (MRI) in predicting functional recovery in patients with first ST-elevation myocardial infarction (MI) who had received thrombolysis. Methods: Nineteen patients underwent cine and contrast-enhanced MRI 3 days and 8 weeks after MI. The transmural extent of infarction (TEI) was determined from the late enhancement component of the first scan. Segmental wall thickening was scored from the cine components of both the initial and follow-up scans. Results: The TEI was inversely related to the likelihood of improvement in wall thickening; χ² test for trend = 53.9, p < 0.0001. Delayed enhancement with >50% transmurality predicted a lack of recovery with 82% sensitivity and 54% specificity. The equivalent values for >75% transmurality were 57 and 77%, respectively. The proportion of the left ventricular segments exhibiting functional recovery was related to the percentage of the left ventricle that was severely dysfunctional but had ≤50% TEI (r = 0.49, p = 0.03). In a backward conditional regression model this was the only independent predictor. Conclusion: These data suggest that TEI, determined by contrast-enhanced cardiac MRI, is a useful predictor of the likelihood, or otherwise, of functional recovery following acute MI treated with thrombolysis.

What is the Optimal Channel Density for Transmyocardial Laser Revascularization?

Background Transmyocardial laser revascularization (TMR) has demonstrated reproducible relief of angina in patients with end-stage coronary disease. However, the optimum dose or channel density has not been elucidated. Methods Using a porcine model of chronic myocardial ischemia, 14 animals were treated with CO 2 TMR and randomized as follows: group 1 was 1 channel per 2 cm 2; group 2 was 1 channel per 1 cm 2; and group 3 was 2 channels per 1 cm 2. Left ventricular myocardial viability and function were assessed by magnetic resonance imaging (MRI) and echocardiography pretreatment, and repeated 6 weeks later. Results The MRI assessment of group 1 (1 channel/2 cm 2) and group 2 (1 channel/cm 2) demonstrated similar improvement in segmental contractility posttreatment of 12.11% ± 5.15% and 12.47% ± 9.51%, respectively. In contrast, group 3 (2 channels/cm 2) showed significantly worse segmental contractility posttreatment: −18.52% ± 7.16% ( p = 0.01). Echocardiographic imaging revealed significant improvements in wall thickening in the ischemic zone for group 1 at 0.91 ± 0.07 cm pretreatment versus 1.30 ± 0.09 cm posttreatment, ( p = 0.01); and for group 2 at 0.93 ± 0.11 cm versus 1.42 ± 0.18 cm, ( p = 0.01). No significant improvement in wall thickening was seen in group 3 (0.84 ± 0.06 cm versus 0.88 ± 0.09 cm, p = n.s.). Conclusions These data corroborate the empiric finding of an effective therapeutic dose range for TMR, 1 channel per 1 to 2 cm 2. These results also demonstrate a detrimental effect when channel density is increased above the clinical standard of 1 channel per cm 2 to a density of 2 channels per 1 cm 2.

Low-level exercise echocardiography detects contractile reserve and predicts reversible dysfunction after acute myocardial infarction: Comparison with low-dose dobutamine echocardiography

OBJECTIVESThe aim of this study was to evaluate low-level exercise echocardiography (LLEE) in detecting contractile reserve and predicting functional improvement of akinetic myocardium early after acute myocardial infarction (AMI).BACKGROUNDExperimental and clinical studies have shown that low-dose dobutamine enhances contractile function of dyssynergic but viable myocardium in patients with recent AMI. We hypothesized that endogenous catecholamines produced during a LLEE test could serve as a myocardial stressor to elicit contractile reserve.METHODSFifty-two consecutive patients with first AMI and ≥2 akinetic segments in the infarct-related territory underwent 5 ± 2 days after AMI low-dose dobutamine echocardiography (LDDE) (5, 10 and 15 μg/kg/min) and LLEE (25 W during 3 min on a supine bicycle, with continuous echocardiographic recording). Both tests were performed on the same day, in random order. Follow-up echocardiography was obtained one month later. Regional wall thickening was semi-quantitatively assessed using a 16-segment, 5-grade scale model. Contractile reserve was defined as improvement in wall thickening of ≥1 grade.RESULTSMean increase in heart rate during stress tests was 15 ± 7 beats/min with LLEE and 13 ± 6 beats/min with LDDE (p = NS). Contractile reserve was detected in 119 (55%) of 217 akinetic segments at LLEE and in 137 (63%) segments at LDDE. At follow-up study, functional improvement was identified in 139 (64%) segments. Sensitivity, specificity and positive and negative predictive values for predicting functional recovery were 81%, 92%, 95% and 73%, respectively, for LLEE, and 91%, 86%, 92% and 84%, respectively, for LDDE. Moreover, there was a good correlation between systolic wall thickening measured in the center of the dyssynergic area during stress tests and at follow-up study: r = 0.77, p < 0.001 with exercise testing and r = 0.73, p < 0.001 with dobutamine testing.CONCLUSIONSLow-level exercise echocardiography provides a promising alternative to LDDE for identifying myocardial viability and predicting reversible dysfunction early after AMI.

Dobutamine-atropine stress echocardiography for risk stratification in patients with chronic left ventricular dysfunction

ObjectiveTo assess the prognostic value of sustained improvement, scar and inducible ischemia with or without viability in patients with chronic left ventricular dysfunction (LVD).BackgroundDobutamine-atropine stress echocardiography (DASE) accurately detects scar, reversible dysfunction and the extent of coronary artery disease in LVD.MethodsThree hundred fifty consecutive patients (age 62 ± 13 years, mean ± SD, 215 men/135 women) with moderate to severe LVD (LVEF < 40%, mean 30 ± 8%) underwent DASE and were followed for ≥18 months. Dobutamine-atropine stress echocardiographic findings were classified according to sustained improvement in all vascular territories, scar, inducible ischemia (worsening wall motion at peak dose only or biphasic responses) and their extent.ResultsSustained improvement occurred in 83 patients (24%), scar alone in 99 (28%) and inducible ischemia in 168 (48%, with biphasic responses in 104). Ischemia was induced in all vascular territories in 26 patients. Patients with sustained improvement or scar alone were treated medically, whereas 46% (78/168) with inducible ischemia were revascularized (coronary bypass surgery, n = 67 or angioplasty, n = 11). There were 76 hard events including cardiac death in 59, nonfatal myocardial infarction in 11, and resuscitated sudden death in 6. Hard events were rare in sustained improvement (5%, 4/83), uncommon in scar (13%, 13/99) and common (p < 0.01) in medically treated patients with inducible ischemia (59%, 53/90). Cardiac deaths were especially common (p < 0.01) in patients with biphasic responses (55%, 28/51). Inducible ischemia independently predicted hard events (χ2= 75.35, p < 0.001) along with reduced LVEF at peak dose (χ2= 8.38, p = 0.004). Hard cardiac events were uncommon (8%, 6/78, p < 0.001) in patients with inducible ischemia who underwent early revascularization.ConclusionsInducible ischemia during DASE was the major determinant of outcome in LVD and independent of clinical data and left ventricular function. Improved wall thickening alone and scar alone predicted good outcome. Survival of patients with inducible ischemia was better after revascularization.

Reversal of reflex-induced myocardial ischemia by median nerve stimulation: a feline model of electroacupuncture.

Acupuncture is reported to reduce myocardial ischemia, arrhythmias, and hypertension. To investigate the physiological mechanisms underlying these observations, a model of reflex-induced, reversible myocardial ischemia was developed to test the effects of median nerve stimulation as a surrogate for electroacupuncture. Chloralose-anesthetized cats were instrumented to measure arterial blood pressure, left ventricular pressure, left ventricular dP/dt, heart rate, left anterior descending (LAD) coronary blood velocity, and regional wall motion. The LAD artery either was partially occluded or a small diagonal branch was ligated. Subsequently, transient reflex activation of the cardiovascular system was evoked by application of bradykinin (typically 1 microg/mL) to the gallbladder, which significantly increased myocardial oxygen demand (double product), left ventricular dP/dt, and coronary blood velocity and caused ischemia-induced regional dysfunction, evidenced by significant (P<.05) reduction in normalized wall thickening (10.7+/-4.2% versus -23.6+/-2.9%; control versus ischemia; n=7). However, when median nerves were stimulated with low frequency (5 Hz) to mimic electroacupuncture, bradykinin-induced change in normalized wall thickening was significantly improved (-23.6+/-2.9% versus 9.8+/-4.9%; ischemia versus median nerve stimulation, P<.05) and remained augmented > or = 1 hour. Results were similar in partial and complete occlusion groups. Significant improvement in wall thickening was associated with unchanged increment of coronary blood velocity and significantly diminished increments of double product and diastolic blood pressure. These results suggest that stimulation of the median nerve to mimic electroacupuncture diminishes regional myocardial ischemia triggered by a sympathetically mediated increase in cardiac oxygen demand. The mechanism of this effect is related to reduction in cardiac oxygen demand, secondary to a diminished pressor response. These data provide the first documentation of the physiological mechanisms underlying the possible beneficial effect of electroacupuncture in the context of restricted coronary blood flow and augmented myocardial oxygen demand.

Nitroglycerin Enhances the Ability of Dobutamine Stress Echocardiography to Detect Hibernating Myocardium

A biphasic response of wall thickening with initial improvement and subsequent deterioration during dobutamine stress echocardiography (DSE) has been increasingly used for detection of hibernating myocardium. However, the improvement of wall thickening at low-dose DSE may be limited in hibernating myocardium by severe hypoperfusion. Nitroglycerin (NTG) improves myocardial perfusion, reduces oxygen demand, and may enhance low-dose dobutamine to improve wall thickening. A pig model of myocardial hibernation of 24 hours to 7 days was created through severe left anterior descending coronary artery stenosis with coronary flow reductions of approximately 40%, producing severe regional left ventricular dysfunction but no infarction in seven pigs. Myocardial infarction was produced in five pigs with occlusion of the artery. DSE was performed with incremental doses with and without an NTG infusion of 50 to 100 microg/min. In the hibernating group, NTG alone improved wall thickening in the hibernating region modestly from 11.4+/-7.2% at baseline to 19.1+/-7.0%. The improvement was associated with increased regional coronary flow from 0.46+/-0.12 to 0.55+/-0.13 mL x beat(-1) x 100 g myocardium(-1) (P<.05). There was an additive effect of NTG to low-dose (2.5 to 5 microg x kg(-1) x min(-1)) dobutamine on wall thickening in the hibernating region. The improvement of wall thickening of hibernating myocardium with NTG and dobutamine, from 23.7+/-11.1% to 31.1+/-8.9% (P<.001), was associated with an increase in regional coronary flow (P<.01). NTG did not prevent high doses of dobutamine from inducing deterioration of wall thickening in hibernating myocardium. In the infarcted group, no improvement in wall thickening was observed in infarcted regions during NTG infusion, dobutamine infusion, or the combination. NTG enhances the improvement of wall thickening at low-dose dobutamine and does not prevent high-dose dobutamine from inducing ischemia in hibernating myocardium. Thus, NTG augments the biphasic response of wall thickening and improves the accuracy of DSE for detecting viable myocardium.

Dobutamine echocardiography and thallium-201 imaging predict functional improvement after revascularisation in severe ischaemic left ventricular dysfunction.

To evaluate the concordance between thallium-201 uptake and echocardiographic wall thickening, which are both indicators of potentially reversible myocardial dysfunction, in patients with chronic ischaemic left ventricular failure and to assess their relative contribution to predicting improvement in regional function after revascularisation in a subgroup. 45 patients with chronic ischaemic left ventricular dysfunction (mean (SD) ejection fraction 25 (8)%) underwent echocardiography before and after dobutamine infusion (10 micrograms/kg/min). Of these, 22 patients underwent rest echocardiography at a mean (SD) of 9 (1) weeks after revascularisation. 201Tl imaging was performed during dobutamine echocardiography and at rest, 1, and 4 h after treatment with sublingual glyceryl trinitrate on two separate days. Potentially reversible dysfunction was thought to be present when a myocardial segment contained a Tl score of > or = 3 (ascending score 1-4), or showed improved wall thickening of a dysynergic segment during dobutamine stimulation. Of the 201Tl protocols, the redistribution scan 1 h after treatment with glyceryl trinitrate best demonstrated myocardial viability. Concordance between 201Tl and dobutamine induced wall thickening was 82% (kappa = 0.59) for detecting potentially reversible myocardial dysfunction before revascularisation (n = 45). Regional function improved in 18 of 22 patients after revascularisation. There were 168 dysynergic segments before intervention. The sensitivity of echocardiography and 201Tl imaging for detecting "recoverable" or viable segments after revascularisation was 87% and 92% respectively and specificity was 82% and 78% respectively (P = NS). Dobutamine echocardiography and 201Tl imaging may be used to predict mechanical improvement in dysynergic segments after revascularisation in patients with chronic ischaemic left ventricular dysfunction.

Incremental Doses of Dobutamine Induce a Biphasic Response in Dysfunctional Left Ventricular Regions Subtending Coronary Stenoses

Dobutamine stress echocardiography has been proposed as a diagnostic tool to identify viable myocardium. How regional wall thickening responds to dobutamine in the ischemic or short-term hibernating myocardium has not been adequately defined. We hypothesized that regional wall thickening would improve initially and subsequently deteriorate with incremental doses of dobutamine in viable myocardial regions supplied by a stenotic coronary artery. This study was undertaken to determine whether this biphasic pattern of regional function characterizes the response of ischemic or hibernating myocardium to dobutamine and to explore the factors and mechanisms that determine this response. Twenty-six pigs in four groups were studied: a control group (n = 5) to assess the response of myocardium perfused by nonstenotic coronary artery to incremental doses of dobutamine, and three experimental groups with a left anterior descending coronary artery stenosis producing acute myocardial ischemia (n = 7), short-term myocardial hibernation for 90 minutes (n = 7), and short-term hibernation for 24 hours (n = 7) to determine the functional and metabolic response to dobutamine under these conditions. Regional coronary flow was reduced to 40% to 60% of baseline, with significant reductions of regional wall thickening as measured by two-dimensional echocardiography and sonomicrometers. An incremental dobutamine infusion from 2.5 to 25 micrograms.kg-1.min-1 increased wall thickening and coronary flow without lactate production in the control group. In the other three groups, during the incremental dobutamine infusion, regional wall thickening improved initially, from 11.4 +/- 7.5% to 19.8 +/- 11.4%, P < .01, at dobutamine doses of 2.5 to 10 (4.5 +/- 2.2) micrograms.min-1.kg-1 but deteriorated subsequently to 5.0 +/- 5.8% at the maximal dose of dobutamine of 12.6 +/- 4.1 micrograms.min-1.kg-1. The initial improvement of regional wall thickening was associated with a small increase in regional coronary flow (from 0.53 +/- 0.18 to 0.68 +/- 0.25 mL.min-1.g-1 myocardium, P < .05) and with regional lactate production. High doses of dobutamine did not further increase regional coronary flow but markedly increased lactate production and induced regional myocardial acidosis (pH 7.26 +/- 0.07). The biphasic pattern of response to dobutamine was observed in each of the three experimental groups. Both peak improvement and peak deterioration occurred earlier and at lower dobutamine dose levels in the group with acute ischemia compared with the group with short-term hibernation for 24 hours (P < .05). A biphasic response of wall thickening to incremental dobutamine with initial improvement and subsequent deterioration is characteristic of ischemic or short-term hibernating myocardium. The initial low-dose dobutamine infusion improved wall thickening in the ischemic or hibernating myocardial region to a modest level. This initial modest improvement was transient and at the expense of metabolic deterioration of myocardial ischemia, so that at higher doses during prolonged dobutamine infusion, wall thickening deteriorated, lactate accumulated, and myocardial acidosis developed.

Enhanced detection of myocardial ischemia by stress dobutamine echocardiography utilizing the “biphasic” response of wall thickening during low and high dose dobutamine infusion

We sought to assess the ability of the "biphasic" response (i.e., initial improvement in wall thickening followed by reduced wall thickening) during serial dobutamine stress echocardiography to detect ischemia in patients with a wall motion abnormality. Furthermore, we compared the power of the biphasic echocardiographic response with that of myocardial perfusion imaging for the detection of myocardial ischemia. Stress echocardiography has been shown to be less sensitive than radionuclide perfusion imaging for detecting ischemia in patients with a wall motion abnormality. Peak stress wall thickening in such areas may not give a full account of the intermediate changes, whereas initial improvement (the biphasic response) may enhance diagnosis. Patients with a wall motion abnormality and documented coronary artery disease underwent simultaneous graded dobutamine (5 to 40 micrograms/kg body weight per min) stress echocardiography and radionuclide perfusion imaging with single-photon emission computed tomography using either technetium-99m sestamibi or technetium-99m tetrofosmin. Semiquantitative analyses of image groups were performed in blinded manner by two separate groups of observers. Myocardial ischemia was detected by perfusion imaging in 45 of the 54 patients. High dose dobutamine echocardiography detected ischemia in only 25 (56%) of these patients. However, when the biphasic response was taken into account, ischemia was detected in 44 (98%) of the 45 patients (p < 0.001). Agreement between radionuclide imaging and echocardiographic findings for the detection of ischemia was significantly enhanced (p = 0.03) when the biphasic response was used (89%, kappa = 0.51) instead of high dose stress dobutamine echocardiography (56%, kappa = 0.10). The detection of myocardial ischemia may be significantly enhanced by utilizing the biphasic response during serial stress dobutamine echocardiography in patients with a wall motion abnormality.