The changes in regional myocardial surface area during coronary occlusion and reperfusion

Summary For the analysis of regional myocardial function, the measurement of regional myocardial surface area (RMA) was performed on the epicardial surface of myocardial segment lengths in a direction parallel to the superficial myocardial fibers (SLa) and at right angles to the first (SLb). In eight anesthetized dogs with opened-chests, measurements were done during a 60 s left anterior descending coronary artery occlusion and reperfusion. In the ischemic region, coronary occlusion resulted in dyskinesis in RMA, and the reduction of it during the ejection phase (ERA) decreased significantly at 10 s (p<0.05) and thereafter (p<0.01). Regional myocardial work (EWA) from the pressure-area loops during the ejection phase also decreased significantly at 10 s (p<0.05) and thereafter (p<0.01). The end-diastolic RMA (EDRMA) increased significantly at 30 s (p<0.01) and thereafter (p<0.01). In the non-ischemic region, compensatory changes were shown, namely ERA, EWA and EDRMA, increased significantly during occlusion. After reperfusion, recovery to the control level was prompt, and only EDRMA remained the increased value after 30 s (p<0.01). Between SLa and SLb, characteristics differed from each other, which suggested that the directional differences of SLs should be considered when regional myocardial function is assessed from unidirectional SL. The changes in RMA reflect both changes of SLa and SLb during coronary occlusion and reperfusion, and were more marked than each SL. Thus, the usefulness of RMA to assess regional myocardial function was demonstrated during coronary occlusion and reperfusion.     

Contrast echocardiography can assess risk area and infarct size during coronary occlusion and reperfusion: experimental validation

OBJECTIVES: We sought to validate the ability of real-time myocardial contrast echocardiography (MCE) measures of opacification defect and contrast refilling parameters to estimate risk area (RA) and infarct area (IA) during coronary occlusion and reperfusion. BACKGROUND: No data exist establishing the accuracy of MCE in determining RA and IA size. We hypothesized that in the setting of coronary occlusion, MCE should identify RA as a perfusion defect early after bubble destruction, collateral flow to viable myocardium as opacification late during refilling and IA as absent opacification. METHODS: Three hours of coronary occlusion and reperfusion were each produced in 11 dogs in which real-time MCE was performed during intravenous infusion of Sonovue (Bracco). Real-time contrast echocardiography was performed at baseline, during occlusion and reperfusion. Early (BEGIN) and end (END) images from a FLASH refilling sequence were acquired, as well as late refilling images (LATE) 1 min after FLASH. Real-time contrast echocardiography defect size and quantitative refilling parameters were compared with RA and IA determined by tissue staining. RESULTS: During occlusion, defect size varied with refilling time; defects from BEGIN images correlated best to RA and those from LATE images to IA. Refilling parameters, but not LATE peak intensity, did not predict the IA size during occlusion. During reperfusion, defects from BEGIN images were well correlated to RA and END images to IA, whereas peak plateau intensity and refilling slope parameters predicted IA size. CONCLUSIONS: Real-time contrast echocardiography defect size varies throughout microbubble refilling. Appropriately selected defect sizes and refilling parameters provide estimates of RA and IA during coronary occlusion and reperfusion.     

Proximal coronary hemodynamic changes evaluated by intracardiac echocardiography during myocardial ischemia and reperfusion in a canine model

BACKGROUND: The purpose of this study was to assess whether the dynamic changes in coronary flow velocity and coronary flow velocity reserve (CFVR) by intracardiac echocardiography (ICE) within proximal coronary arteries are related to myocardial perfusion status and infarct size in a myocardial ischemia-reperfusion injury model. METHODS: In 14 dogs, left anterior descending coronary artery (LAD) was ligated for 2 hours followed by 2 hours reperfusion. Coronary flow velocity was obtained by ICE within coronary arteries at baseline, and at the end of both occlusion and reperfusion period. The CFVR was calculated as the ratio of hyperemic to resting peak diastolic velocity (PDV). Myocardial perfusion was evaluated by real time myocardial contrast echocardiography (MCE). The infarct area was detected by triphenyltetrazolium chloride (TTC) staining and expressed as the percentage of the whole left ventricular (LV) area. RESULTS: CFVR significantly decreased both in proximal LAD and left circumflex (LCx) artery at the end of occlusion, and did not recover at the end of reperfusion. However, no significant difference in flow parameters was observed between dogs with myocardial perfusion defect and those without. CFVR in LAD at the end of reperfusion did not correlate with the infarct size (r =-0.182, P = NS) either. CONCLUSIONS: Decreased CFVR detected by ICE occurs both in ischemic and in nonischemic proximal arteries during myocardial ischemia and early stage of reperfusion. This change in CFVR has poor correlation with the extent of microvascular impairment and cannot be used to predict infarct size.     

Changes in regional myocardial cross-sectional area during brief coronary occlusion and reperfusion in conscious dogs

The effect of a brief period of coronary occlusion on a regional myocardial cross-sectional area was studied in 6 conscious dogs. Subendocardial segment length and wall thickness were continuously measured with a sonomicrometer in the central ischemic area perfused by the left circumflex coronary artery during a 2-min circumflex occlusion and subsequent reperfusion. Measurements were repeated before and after collateral development induced by 180 +/- 30 (SEM) 2-min circumflex occlusions (20 +/- 3 days). In order to evaluate the changes in regional myocardial volume, end-diastolic regional cross-sectional area was calculated as a product of end-diastolic segment length and wall thickness. Before collateral development, end-diastolic regional cross-sectional area transiently decreased 1.4 +/- 0.6% (NS) at 10 sec following sudden coronary occlusion, thereafter gradually increased to 3.7 +/- 1.0% (P less than 0.05) at the end of a 2-min occlusion. At 10 sec of reperfusion, end-diastolic regional cross-sectional area further increased to 7.0 +/- 1.1% (P less than 0.05) probably due to increased intravascular volume. Increase in end-diastolic regional cross-sectional area was still 2.5 +/- 0.6% (NS) at 3 min after the release of occlusion. After collateral development, the changes in end-diastolic regional cross-sectional area were 0.1 +/- 0.1% (NS), 0.4 +/- 0.3% (NS), 1.0 +/- 0.6% (NS) and 0.2 +/- 0.4% (NS), respectively. Thus, a significant increase in the regional myocardial cross-sectional area occurs during a brief period of coronary occlusion and reperfusion.     

Quantification of area at risk during coronary occlusion and degree of myocardial salvage after reperfusion with technetium-99m methoxyisobutyl isonitrile

Serial myocardial imaging with technetium-99m methoxyisobutyl isonitrile (99mTc-MIBI) has been proposed for evaluating myocardial salvage after reperfusion. To define 99mTc-MIBI uptake before and after reperfusion, 17 open-chest dogs underwent 3 hours of left anterior descending artery occlusion and 3 hours of reperfusion. 99mTc-MIBI was injected during occlusion (group 1) or after 90 minutes of reperfusion (group 2). Myocardial 99mTc-MIBI activity was correlated with microsphere flow during occlusion and reperfusion. Anatomic risk area and infarct area were defined by postmortem vital staining and correlated with the perfusion defects defined by analysis of 99mTc-MIBI macroautoradiographs and gamma camera images of myocardial slices. The left ventricle was divided into 96 segments for gamma well counting. Flow and 99mTc-MIBI activity were normalized to nonischemic values. Myocardial segments were grouped, based on occlusion flow, into zones: severely ischemic (less than or equal to 30% nonischemic), moderately ischemic (greater than 30%, less than or equal to 60% nonischemic), mildly ischemic (greater than 60%, less than or equal to 90% nonischemic), and nonischemic (greater than 90%, less than or equal to 120% nonischemic). Among dogs injected with 99mTc-MIBI during coronary occlusion (group 1), myocardial 99mTc-MIBI activity correlated linearly with occlusion flow for both endocardial (r = 0.91) and transmural (r = 0.91) segments. The risk area defined by 99mTc-MIBI autoradiography (group 1) correlated with the postmortem risk area (rho = 0.94) but was 29% smaller than the anatomic risk area (p = 0.03), reflecting the contribution of collateral flow. Among dogs injected with 99mTc-MIBI after reperfusion (group 2), myocardial 99mTc-MIBI did not correlate with reperfusion flow in either endocardial or transmural segments. Among group 2 dogs, myocardial 99mTc-MIBI activity was significantly less than reperfusion flow at the time of injection in the severely ischemic (25 +/- 5% versus 74 +/- 24% nonischemic, p = 0.002), moderately ischemic (54 +/- 12% versus 96 +/- 15% nonischemic, p = 0.001), and mildly ischemic (84 +/- 6% versus 93 +/- 3% nonischemic, p = 0.002) zones. The defect area defined by 99mTc-MIBI autoradiography (group 2) correlated very closely with the postmortem infarct area (rho = 0.98). Thus, the myocardial uptake of 99mTc-MIBI during coronary occlusion correlates with occlusion flow and reflects the "area at risk." When 99mTc-MIBI was given after 90 minutes of reperfusion following 3 hours of coronary occlusion, the myocardial activity was significantly reduced compared with reperfusion flow in both necrotic and perinecrotic regions, reflecting myocardial viability more than the degree of reperfusion.     

The importance of defining left ventricular area at risk in vivo during acute myocardial infarction: an experimental evaluation with myocardial contrast two-dimensional echocardiography

Because the left ventricular "area at risk" is the most important determinant of ultimate infarct size, it would be useful to know the size of the area at risk during acute myocardial infarction to make therapeutic decisions. We therefore performed a series of experiments in four groups of dogs. In group I dogs (n = 15) we attempted to determine whether current methods of assessing left ventricular function during acute myocardial infarction reflect the true size of the area at risk. At each of two to five sequential stages, a more proximal coronary occlusion was performed to produce a larger area at risk until cardiovascular collapse occurred. At each stage, the area at risk (measured by myocardial contrast echocardiography), hemodynamic variables, and left ventricular ejection fraction (LVEF) were measured. Hemodynamic variables became abnormal when the area at risk was large (25% to 40% of the left ventricle), whereas LVEF became abnormal when the area at risk was of moderate size (18%). When cardiac output and LVEF were normalized to baseline values, a close inverse relationship was noted between these variables and area at risk. In contrast, there was a poor relationship between normalized mean arterial pressure and area at risk (r = .42). In group II dogs (n = 9) the area at risk was measured serially over 6 hr after coronary occlusion. The size of the area at risk remained unchanged regardless of the transmural extent of the ultimate infarct. The circumferential endocardial extent of the area at risk closely predicted the circumferential endocardial extent of the infarct at 6 hr in eight of nine dogs that developed an infarct. Group III dogs (n = 7) underwent the same protocol as group II dogs, but the duration of occlusion was 3 hr. The circumferential endocardial extent of the area at risk closely predicted the circumferential endocardial extent of the infarct. Group IV dogs (n = 5) underwent subtotal coronary occlusion. Although regional wall motion abnormalities were noted in this group, no area at risk could be defined. We conclude that although a close inverse relationship is noted between normalized cardiac output and area at risk, the absolute values for cardiac output and other hemodynamic variables become abnormal only when the area at risk is large (25% to 40%); measurement of LVEF may provide a better assessment of the size of the area at risk than hemodynamic variables.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of acute reperfusion on regional myocardial function: serial two-dimensional echocardiography assessment

Serial two-dimensional echocardiography was performed in 23 patients with acute myocardial infarction who received intravenous thrombolytic therapy to evaluate the effect of acute reperfusion on regional wall motion abnormalities. Regional wall motion abnormalities improved in 4 of the 14 patients (29%) with successful reperfusion and in 1 of the 9 (11%) without successful reperfusion. In successfully reperfused patients, the main determinant of improvement in regional wall motion abnormalities was duration from the onset of chest pain to the time of reperfusion (3.3 vs. 6.3 h in successfully reperfused patients without recovery of regional wall motion abnormalities; P less than 0.001).     

Validation of three-dimensional echocardiography for quantifying the extent of dyssynergy in canine acute myocardial infarction: Comparison with two-dimensional echocardiography

Objectives. This study was designed to compare the accuracy of three- and two-dimensional echocardiography for quantifying the extent of abnormal wall motion in experimental acute myocardial infarction, as correlated with the pathologic determination of infarct size.

Background. Two-dimensional echocardiographic estimations of the fraction of myocardium showing abnormal wall motion are often used as an index of infarct size even though they rely on image plane positioning and geometric assumptions that may not be valid. Three-dimensional echocardiographic reconstruction of the endocardial surface eliminates the need for these assumptions and may improve echocardiographic estimates of infarct size.

Methods. Coronary ligation was performed in 14 open chest dogs, and echocardiographic imaging of the ventricle was performed 6 h later. Three-dimensional echocardiography used seven or eight spatially registered short-axis images to measure percent of endocardial surface and mass showing abnormal wall motion. Three two-dimensional echocardiographic methods using multiple, nonspatially registered images were evaluated. One method used seven or eight short-axis slices and a summation of discs algorithm for computing surface area. The second method used the same images and a conical model for the left ventricle. The third used basal, middle and apical short-axis plus apical four- and two-chamber views comparing summed endocardial lengths showing abnormal wall motion with the total of the endocardial dimensions, expressed as percent. The percent of left ventricular mass and surface area infarcted was determined by staining with triphenyltetrazolium chloride.

Results. Three-dimensional echocardiographic measurements of endocardial surface area correlated more closely with infarct mass (r = 0.94, SEE ±3.6%) than did the two-dimensional method using the summation of discs algorithm (r = 0.85, SEE ±6.6%), the summation of conical sections algorithm (r = 0.82, SEE ±5.4%) or the method using summed endocardial lengths (r = 0.79, SEE ±7.4%). Limits of agreement analysis comparing mass showing abnormal wall motion with anatomic infarct mass and surface area showing abnormal wall motion with anatomic infarct surface area showed the smallest limits for three-dimensional echocardiography.

Conclusions. Three-dimensional echocardiography is a more accurate means of noninvasively estimating myocardial infarct size in this canine model than two-dimensional echocardiography.     

Myocardial contrast echocardiography in the perfusion imaging in coronary occlusion and reperfusion

The availability of myocardial contrast echocardiography (MCE) has potential for several applications in coronary diseases. Experimental studies have demonstrated a good correlation between measurements of myocardial blood flow and regional contrast intensity, and therefore capabilities of MCE in detecting myocardial ischemia during stress. Clinical studies must then demonstrate the value of such approaches in comparison with existing techniques such as stress echo and radionuclide imaging.     

Augmentation of regional function in nonischemic myocardium during coronary occlusion measured with two-dimensional echocardiography

Increased regional left ventricular function frequently occurs in the nonischemic myocardium after acute coronary occlusion. To further define the regional and global effects of this increased remote function in the ischemic left ventricle, 22 dogs were studied with two-dimensional echocardiography before and 1 h after left circumflex coronary artery occlusion. Two groups of dogs were identified with and without compensatory increased regional left ventricular function, defined as regional wall thickening in the nonischemic zone greater than 2 SD above baseline. After coronary occlusion, nonischemic wall thickening was 76 +/- 15% in the hyperfunction group (n = 11) and 45 +/- 14% in the nonhyperfunction group (n = 11) (p less than 0.001). Despite similar left ventricular end-diastolic cavity areas and equivalent degrees of ischemic wall thinning, dogs with increased left ventricular function in the nonischemic myocardium had a smaller extent of circumferential left ventricular dysfunction (136 +/- 33 versus 170 +/- 43 degrees, p less than 0.001) and a higher area ejection fraction (38 +/- 9% versus 27 +/- 6%, p less than 0.001). These functional differences occurred despite similar myocardial areas at risk by autoradiography (41 +/- 6% versus 37 +/- 12%, p = NS). The data suggest that increased left ventricular function in the nonischemic myocardium determines the global functional impact of acute coronary occlusion and, through interaction with adjacent myocardium, modifies the extent of circumferential left ventricular dysfunction.     

Acute reduction in functional infarct expansion with late coronary reperfusion: assessment with quantitative two-dimensional echocardiography

Reperfusion performed too late to salvage myocardium decreases chronic infarct expansion in experimental animals. However, the acute effects of delayed reperfusion are not known. Twenty-two dogs underwent 3 (n = 8), 4 (n = 8) or 6 h (n = 6) of circumflex artery occlusion followed by 3 h of reperfusion. Effects of reperfusion on diastolic expansion were assessed in two ways: 1) change in mean radius of curvature of the infarct segment, and 2) change in the ratio of the length of the diameter from the center of the infarct zone to the opposite wall (septal-lateral diameter) to the length of the diameter perpendicular to this (anteroposterior diameter). Effects on systolic expansion were examined with quantitative two-dimensional echocardiographic systolic thickening analysis. Delayed reperfusion produced an immediate decrease in diastolic infarct expansion. The ratio of septal-lateral/anteroposterior diameters, which had increased with occlusion from a preocclusion baseline of 0.98 +/- 0.06 to 1.13 +/- 0.08 (p less than 0.001), decreased with reperfusion to 1.02 +/- 0.07 at 15 min and 1.03 +/- 0.08 at 3 h of reperfusion (p = 0.001). This was due solely to a decrease in the septal-lateral diameter. The radius of curvature of the infarcted segment increased from 2.1 +/- 0.5 cm before reperfusion to 2.74 +/- 0.8 cm at 15 min and 2.6 +/- 0.85 cm at 3 h of reperfusion (p = 0.009). This occurred despite a significant (13.6%) decline in end-diastolic cavity area and is compatible with flattening of the reperfused infarct region. Systolic infarct expansion also improved slightly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diltiazem and progression of myocardial ischemic damage during coronary artery occlusion and reperfusion in porcine hearts

This study was designed to investigate whether a cardioprotective intervention could delay the completion of necrosis so that subsequent reperfusion would be more useful. Thirty-six pigs were randomly allocated to treatment with diltiazem (15 micrograms/kg per min) or saline solution and to a 60 or 120 minute coronary occlusion period followed by reperfusion. The treatment was begun 15 minutes before coronary occlusion and terminated 75 minutes after reperfusion. Twenty-four hours after the procedure, the heart was sliced and incubated in triphenyltetrazolium chloride. The infarct area and the maximal transmural area of extension of the infarct were calculated by planimetry. The total number of red blood cells in a transmural section was also counted. In the pigs with a 60 minute coronary occlusion, diltiazem (compared with saline solution) significantly reduced infarct size from 9.7 +/- 1.5% of left ventricular mass to 5.9 +/- 0.6% (p less than 0.05) and the percent transmural extension from 0.72 +/- 0.05 to 0.61 +/- 0.05% (p less than 0.05). Red blood cell extravasation in the infarcted area was reduced from 161,934 +/- 59,905 to 78,525 +/- 46,484 cells/mm3 (p less than 0.05) with diltiazem and the percent transmural extension of the hemorrhagic necrosis from 70 +/- 10 to 36 +/- 15% (p less than 0.05). No such differences were observed in the 120 minute coronary occlusion groups. Mean red blood cell counts and the extent of hemorrhagic necrosis did not correlate with either infarct size or transmural extension.(ABSTRACT TRUNCATED AT 250 WORDS)     

Real-time intracardiac two-dimensional echocardiography: an experimental study of in vivo feasibility, imaging planes, and echocardiographic anatomy

The traditional transthoracic and transesophageal echocardiographic examination have proven to be useful imaging tools for studying cardiac morphology, pathology, and function. Recently, catheter-based ultrasound transducers have been available for intravascular ultrasonic imaging. We supposed that echocardiographic examination performed from within the heart itself can provide useful information about cardiac structure and function, especially in settings where transthoracic or transesophageal echocardiography may be technically difficult to perform or poorly tolerated by the patient. To explore this concept, we performed intracardiac echocardiography in vivo in 22 dogs using both 5-MHz and 20-MHz transducers. High-quality images were obtained in all animals. Using the higher frequency transducer, detailed images with only a limited depth of field were obtained. With the 5-MHz transducer, a comprehensive cardiac examination was feasible from within the right atrium and inferior vena cava. We were able to visualize the great vessels, all cardiac valves, and cardiac chambers in a multitude of imaging planes. Alterations in ventricular function were instantly recognized. Color Doppler capabilities allowed visualization of flow abnormalities as well. We conclude that intracardiac echocardiography is feasible and could be potentially useful in certain clinical situations. With further research and development, this technique may have an important clinical impact in cardiac therapy and diagnosis.     

Simultaneous assessment of myocardial perfusion and left ventricular function during transient coronary occlusion

Objectives. We used technetium-99m sestamibi imaging to evaluate the magnitude of changes in left ventricular function and perfusion and to investigate their interdependence during transient coronary occlusion.

Background. Transient coronary occlusion during coronary angioplasty provides a unique opportunity for examining the effects of acute myocardial ischemia on left ventricular function and perfusion.

Methods. Thirty-five patients with normal left ventricular function underwent first-pass radionuclide angiography with technetium-99m sestamibi using a multicrystal gamma camera during balloon occlusion of a coronary artery. Single-photon tomography was performed 2.1 ± 1.7 h later. Subsequently, all scans were repeated at rest.

Results. The mean size ± SD of the perfusion defect during coronary occlusion was 23 ± 18%, with significantly larger defects observed for occlusions of the left anterior descending coronary artery (39 ± 20%) than for occlusions of the left circumflex (15 ± 11%) or right (15 ± 9%) coronary artery (p < 0.05). The mean change in ejection fraction from recovery to occlusion was −17 ± 17% and was significantly larger for left anterior descending (−26 ± 21%) and left circumflex (−15 ± 11%) than for right (−8 ± 10%) coronary artery occlusions (p < 0.05). For the entire group, ejection fraction during occlusion correlated significantly with perfusion defect size ( r= 0.63, p = 0.0004), whereas the extent of ischemic myocardium correlated with the decrease in ejection fraction (r = 0.69, p = 0.0001). The defects present during occlusion reversed within a few hours.

Conclusions. Changes in left ventricular function and perfusion develop pari passu during coronary occlusion and are more severe when the left anterior descending artery is occluded. Although a significant correlation exists between the extent of the perfusion defect and the severity of the decrease in ejection fraction, there is a substantial individual variation with respect to changes in both myocardial perfusion and ventricular function during acute coronary occlusion.     

Effect of afterload alterations on the functional border zone measured with two-dimensional echocardiography during acute coronary occlusion

In the setting of acute myocardial infarction, pharmacologic intervention resulting in afterload changes are common but the effect of these changes on regional left ventricular function, and specifically the functional border zone, has not been fully investigated. Accordingly, we studied the effects of afterload manipulation on circumferential flow-function relationships and the functional border zone in 16 open-chest, anesthetized dogs. During left circumflex coronary artery occlusion, eight animals were infused with phenylephrine to increase afterload; eight others received nitroprusside for afterload reduction. Following coronary artery occlusion, subendocardial blood flow and wall thickening decreased in the ischemic zone (p less than 0.001). The circumferential extent of hypoperfusion did not differ when coronary artery occlusion alone was compared to occlusion in combination with phenylephrine or nitroprusside, but in both groups the circumferential extent of the wall thickening abnormality was consistently greater than the extent of hypoperfusion. When blood pressure was decreased by 33%, the extent of the functional border zone did not change relative to that during coronary artery occlusion (22 +/- 11 degrees vs 36 +/- 16 degrees, p = ns). Similarly, when blood pressure was increased by 47%, the extent of the functional border zone did not change (32 +/- 10 degrees vs 37 +/- 10 degrees). Therefore circumferential flow-function relations and the spatial extent of the functional border zone are not altered by changing afterload during acute left circumflex coronary artery occlusion in this model.     

Regional myocardial dysfunction during coronary angioplasty: evaluation by two-dimensional echocardiography and 12 lead electrocardiography

Balloon inflation performed during percutaneous transluminal coronary angioplasty causes transient total occlusion of the coronary artery and thus provides a model for evaluation of the regional myocardial responses to transient ischemia. Twenty patients with normal left ventricular function undergoing angioplasty of isolated stenosis of the proximal left anterior descending coronary artery were studied. In group A (14 patients) analysis of one inflation-deflation sequence per patient was performed. Group B (six patients) had multiple (greater than 5) inflations; the first and last sequences were analyzed. Assessment included continuous two-dimensional echocardiography with computerized quantitative analysis of regional left ventricular wall motion, and continuous 12 lead electrocardiographic recordings. The mean duration of inflation in group A was 62 +/- 6 seconds (mean +/- SD). The onset of regional left ventricular dysfunction was 12 +/- 5 seconds after inflation. Profound dysfunction was noted in all patients. After 60 seconds of balloon occlusion of the coronary artery, 29% of patients had severe hypokinesia of the ischemic region and 71% had akinesia or dyskinesia. With deflation there was prompt recovery of regional function, with full recovery at 43 +/- 17 seconds. Comparison of data from first and last inflations in group B revealed no significant differences in time to onset of dysfunction, magnitude of dysfunction or time to complete recovery of function. The onset of ischemic electrocardiographic changes lagged behind the onset of wall motion abnormalities, with only 64% of patients showing evidence of ischemia on 12 lead electrocardiograms at 20 seconds of inflation. After 60 seconds, 86% had ischemia detectable by electrocardiography. Thus, balloon inflation during coronary angioplasty leads to profound but reversible regional left ventricular dysfunction. Repeated occlusions of the coronary artery during angioplasty do not have a cumulative ischemic effect. It may be hazardous to apply these findings to patients who have underlying major left ventricular dysfunction and in whom the reversibility of dysfunction and lack of cumulative ischemic effect may not be assured.     

Quantitative assessment of myocardial perfusion during graded coronary artery stenoses by intravenous myocardial contrast echocardiography

OBJECTIVES: The purpose of this study was to examine whether coronary stenoses of variable severity could be quantitatively assessed by analysis of myocardial perfusion as determined by intravenous (IV) myocardial contrast echocardiography. BACKGROUND: Recently, new contrast agents and imaging technology have been developed that may enable improved assessment of myocardial perfusion by IV contrast injection. METHODS: Variable obstruction of the left anterior descending (LAD) coronary artery in dogs was produced by a screw occluder. Coronary artery flow was measured with a transit time flowmeter during baseline, pharmacological vasodilation, a non-flow-limiting stenosis at rest in conjunction with vasodilation, a flow-limiting stenosis, and total occlusion. Myocardial contrast echocardiography was performed after IV injection of the contrast agent NC 100100. Time-intensity curves were obtained off-line for the LAD risk area and the adjacent left circumflex (LCx) territory, and peak background-subtracted video intensity was determined. Fluorescent microspheres were injected at each intervention for determination of regional myocardial blood flow. RESULTS: During non-flow-limiting stenosis, flow limiting stenosis and total occlusion, LAD/LCx ratios of peak myocardial videointensity and blood flow decreased proportionately. Both LAD/LCx ratios of video intensity and blood flow identified the non-flow-limiting and the flow-limiting stenoses as well as total occlusion of the LAD artery. A significant correlation between LAD/LCx video intensity and blood flow ratios was observed (r = 0.83, p < 0.0001). CONCLUSIONS: The degree of blood flow mismatch between ischemic and normal myocardial regions during graded coronary stenoses can be estimated in the dog by quantitative assessment of myocardial perfusion produced by IV myocardial contrast echocardiography.     

Utility of intracardiac echocardiography in left heart ablation for tachyarrhythmias

Catheter-based radiofrequency ablation in the left heart can provide effective therapy for tachyarrhythmias. The recent development of the real time intracardiac echocardiography (ICE) with 2D and Doppler color flow imaging can facilitate left heart ablation procedures. This report reviews the use of ICE during radiofrequency catheter ablation procedures for atrial fibrillation (AF) and ventricular tachycardia and is based on our own experience in 955 patients. ICE has a critical role for guiding transseptal catheterization, assisting placement of mapping/ablation catheters and monitoring lesion morphologic changes, especially in the pulmonary vein ostia, Marshall ligament region, thickened interatrial septum, left atrial posterior wall contiguous to esophagus, aortic valve cusps, and the epicardial regions. One of the more powerful utilities of ICE lies in its ability to identify and potentially reduce procedural complications including damage to intracardiac structures, residual atrial septal defect, left atrial thrombus formation, pulmonary vein stenosis, esophageal injury, myocardial air-embolization and pericardial effusion during left heart ablation.