YEAR IN CARDIOLOGY SERIES
The year in echocardiography
Arthur E. Weyman, MD*
Massachusetts General Hospital, Cardiac Ultrasound Laboratory, Boston, Massachusetts
Manuscript received November 16, 2004;
accepted December 1, 2004.
* Reprint requests and correspondence: Dr. Arthur E. Weyman, Massachusetts General Hospital, Cardiac Ultrasound Laboratory, 55 Fruit Street, VBK-508, Boston, Massachusetts 02114.
(Email: Aweyman{at}partners.org).
As echocardiography passes its golden anniversary, the number and sophistication of the combined echocardiographic techniques continue to grow, as does the ability of these techniques to address complex clinical questions, elucidate mechanisms of disease, and define response to therapy. This growth occurs in both simplicity and complexity from small, hand-held devices that provide basic information simply and inexpensively to complex, dynamic three-dimensional (3D) imaging of regional myocardial function. As with other diagnostic techniques, echocardiography progresses through the: 1) introduction and validation of new techniques, 2) refinement or extension of existing methods, and 3) addition of new information in areas of particular clinical interest.
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The introduction and validation of new techniques
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The most important new technique to arrive in the last several years has been real-time three-dimensional echocardiography (RT3DE). This technique offers several advantages over previous 3D methods, because it does not require external registration of imaging planes, permits shorter scanning time, and can be recorded during a single breath hold. Because images are often assembled over four cardiac cycles, it is not technically a real-time method but still provides important dynamic 3D cardiac data. Studies are now appearing that validate the accuracy of RT3DE in assessing cardiac structure and function.
Left ventricular (LV) volumes, mass, and ejection fraction (EF).
In a study comparing two-dimensional (2D), 2D-derived M-mode, and RT3DE with magnetic resonance imaging (MRI) measurements of LV volume, mass, and EF, MRI end-diastolic LV volume (mean 172 ± 53 ml) was underestimated by 2D echocardiography (mean difference –54 ± 33 ml) but only slightly by RT3DE (–4 ± 29 ml). Similarly, end-systolic volume by MRI (mean 91 ± 53 ml) was underestimated by 2D echocardiography (mean difference –28 ± 28 ml) and by RT3DE (–3 ± 18 ml). The LV mass was overestimated by M-mode and 2D echocardiography but slightly underestimated by 3D, with M-mode showing the greatest difference from MRI. Correlation with MRI EF was similar for 2D and 3D (r = 0.76 and r = 0.74, respectively—values lower than typically reported for 2D correlations with angiography) (1). Importantly, test-retest variability, which involves repetition of the entire acquisition and analysis process, was superior for 3D than 2D for EF, supporting the role of 3D for serial evaluation. Unfortunately, 10 patients (18%) had to be excluded from analysis, 8 for inadequate echocardiography recordings. However, the major limitation of 3D echocardiography was the analysis time of 630 ± 60 s versus 90 ± 27 s for 2D echocardiography for volume calculations (1). For a laboratory performing 10,000 studies per year, this would equal 0.8 man-years just analyzing LV volumes, making it unlikely that this approach will be generally employed until rapid and accurate methods for automated analysis are developed. A feasibility study using such an automated approach in patients selected for good image quality and sinus rhythm showed excellent correlation between the semi-automated method with both manually defined volumes and MRI volumes, with a slight underestimation of both end-diastolic and -systolic volumes but comparable EFs. Surprisingly, the time for semi-automated 3D data analysis was 12 ± 5 min compared with 4 ± 1 min for manual tracing of the 3D contours (2). Because most patients do not have optimal images, a great deal more work needs to be done in the area of automated calculation of volumes and mass.
Valvular heart disease.
In patients with rheumatic mitral stenosis, it is often difficult to align the 2D scan plane parallel to the limiting orifice, particularly for inexperienced examiners. To help with this problem, RT3DE was compared with 2D planimetry, the Doppler pressure half-time (PHT), and the proximal acceleration method (PISA) for assessing mitral valve area in comparison with the Gorlin formula in 80 patients with rheumatic mitral stenosis. Mean mitral valve area was similar by all methods (PHT: 1.28 cm2; 2D: 1.39 cm2; PISA: 1.24 cm2; RT3DE: 1.26 cm2; and the Gorlin method: 1.30 cm2). However, the agreement of the mitral valve area by 3D echocardiography and the Gorlin formula was better by Bland-Altman analysis than with any of the other methods. A recording and analysis time for RT3DE of 23 ± 7 min was observed in a subgroup of 20 patients (3).
Thus, although data are beginning to appear supporting the value of RT3DE in a variety of clinical settings, the analysis time to this point is prohibitive beyond the research environment.
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Refinement or extension of existing methods
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Tissue Doppler, strain rate, and strain imaging.
Tissue Doppler myocardial velocities have been suggested to be an objective quantitative method for assessing myocardial function. However, both systolic (Sm) and early diastolic (Em) tissue velocities have been shown to be load-dependent. Conversely, myocardial acceleration during isovolumic contraction has been shown to be an accurate measure of both right and left ventricular contractile function that is unaffected by changes in preload and afterload (4,5). In a follow-up experimental study, peak acceleration during isovolumic relaxation was examined as a load-independent measure of diastolic function. Peak septal acceleration during isovolumic relaxation correlated with both pressure-derived peak negative dP/dt (r = –0.80) and tau (r = –0.87) but not with left atrial (LA) pressure. However, peak acceleration during the diastolic filling period did correlate (r = –0.81) with mean LA pressure. Peak lateral wall acceleration also correlated with –dP/dtmin and tau but less closely than septal acceleration (6).
Although the ability to measure regional function is a potentially powerful tool, these measurements are not simple, and the results can be complex to interpret. For example, in a study to determine normal, age-adjusted values for longitudinal strain for individual walls (anterior, posterior, medial, and lateral) and segments (apical, mid, and basal), there was a general velocity gradient from base to apex for both the systolic (S) wave and the diastolic E and A waves. Both the S- and E-wave velocities (cm/s) decreased with age, whereas the A-wave velocity increased. Strain rate was not age- or gender-dependent. However, strain data showed inconsistencies with a base-to-apex gradient for the septum and an apex-to-base gradient for the anterior wall. This is in contrast to MRI data that show that longitudinal strain increases from 15% at the base to 19% at the apex. The difference in the echocardiography results was explained by the high sensitivity of strain measurements to misalignment of the insonation angle relative to the true wall orientation; however, when such findings occur in selected normals, they highlight the care that must be taken in acquisition and interpretation of strain data (7).
The mitral E/E' ratio has been suggested as an estimate of LV filling pressure in selected subsets of patients. In a study comparing the accuracy of this ratio in predicting LV end-diastolic pressure in primary mitral regurgitation (prolapse and flail leaflets) and secondary mitral regurgitation (dilated and ischemic cardiomyopathy), it was demonstrated that while the E/E' ratio showed a reasonable correlation with LV end-diastolic pressure in patients with secondary mitral regurgitation (r = 0.61), there was no relationship in patients with primary mitral regurgitation and preserved LV function (8).
Several small studies have reported that tissue Doppler recording of mitral annular velocity can distinguish between constrictive pericarditis and restrictive myopathies. These observations were confirmed in two larger studies (9,10) of patients with constrictive pericarditis and various control groups. In one study, an E' velocity of  8 cm/s differentiated patients with constriction from those with amyloid or restrictive cardiomyopathy with a sensitivity of 95% and a specificity of 96% (9). In the second study, annular velocities from the septal and lateral regions were normal (8 cm/s) in 45 patients (88.9%) with constrictive pericarditis and decreased in one or both regions in five patients (three patients with reduced LV function and two patients with extensive mitral annular calcification). In patients with restrictive myopathy, 8 of 11 (72.7%) had reduced E' velocities, whereas 3 patients had normal E' velocities at one or both corners of the mitral annulus (10).
Myocardial contrast echocardiography (MCE).
Basic science
Changes in myocardial perfusion after therapeutic interventions have been difficult to assess because of the small size of the vessels of interest, which generally cannot be resolved by angiography, and the difficulty of performing biopsies of the target areas in clinical studies. As a result, MCE is increasingly used to assess myocardial perfusion in the experimental assessment of therapies designed to limit infarct size and restore function after infarction.
Infarct size limitation
P-selectin immunoneutralization: it is recognized that leukocytes can induce microvascular damage in the reperfused myocardium. P-selectin is the key molecule responsible for the recruitment of neutrophils in areas of inflammation and adhesion of platelets to neutrophils. In an ischemia reperfusion model, it was demonstrated that after 120 min of reperfusion, the replenishment parameters A (capillary volume), ß (myocardial blood velocity), and A x ß (myocardial blood flow) were higher in the risk area and that the infarct size was smaller in animals after immunoneutralization of P-selectin than in controls, with an associated reduction in the extent of neutrophil-mediated inflammation (11).
Glycoprotein inhibition
Platelets play a major role in the dissociation of epicardial artery recanalization and tissue level perfusion, the "no reflow phenomenon." In a canine model of acute infarction, glycoprotein IIb/IIIa inhibition by tirofiban was directly demonstrated to improve myocardial perfusion in the infarct zone by both quantitative MCE and fluorescent microspheres, early after reperfusion independent of epicardial patency. Infarct size was also significantly reduced in glycoprotein IIb/IIIa inhibition-treated dogs versus control animals (12).
Bone marrow cell transplantation
Bone marrow cell transplantation into the heart has been shown to induce angiogenesis. Bone marrow cell transplantation at one month after left anterior descending coronary artery ligation was shown to increase capillary density in the transplant area. Wall thickening in the transplant area was also increased. Myocardial contrast intensity measured as acoustic units correlated linearly with capillary density (r = 0.92) (13).
Gene therapy
Enhanced gene transfection has previously been demonstrated using ultrasound bubble destruction. This is presumed to be due to cavitation of microbubbles that transiently perforate cell membranes or disrupt the capillary wall to allow delivery of bioactive agents into cells or interstitial space. Whereas transfection of an adenovirus-mediated reporter gene has previously been observed after transthoracic insonation, the transfection of a functional gene with a naked plasmid in combination with ultrasound microbubble insonation has not been demonstrated. Hepatocyte growth factor (HGF) prevents myocyte death resulting from oxidative stress and myocyte apoptosis during reperfusion injury. The HGF transfection before myocardial ischemia attenuates reperfusion injury, whereas transfection by direct intramyocardial injection immediately after coronary ligation induces angiogenesis in infarcted myocardium. In a rat model of myocardial infarction (MI), ultrasound microbubble insonation was combined with naked HGF plasmid injected into the LV chamber, and HGF was successfully transferred into the myocardium as evidenced by significant expression of HGF protein at seven days. In treated animals, infarct size was decreased by 60% versus control animals. Subsequent remodeling was also decreased. Scarring was much smaller, capillaries in the myocardium adjacent to the infracted areas were increased, and inotrophic reserve for sympathetic stimulation by isuprel was preserved (14).
Transplant rejection
The detection of acute transplant rejection currently requires endomyocardial biopsy, which is invasive and can yield false positives in patients with focal or patchy rejection. The microbubbles used for MCE are adhesive to and phagocytosed by leukocytes including macrophages. In an experimental study of isograft and allograft rejection, myocardial signal intensity (in gray levels) obtained after a 10-min period to allow microbubble contrast interaction demonstrated a clear gradient between untreated allografts (12 ± 2), allografts treated with low-dose cyclosporine (9 ± 5), allografts treated with high-dose cyclosporine (6 ± 3), and isografts (2 ± 1). These changes corresponded to similar changes in macrophage and T-lymphocyte counts (15).
Clinical studies.
Determination of LV function
Intravenous echocardiographic contrast agents have been shown to enhance visualization of the LV blood pool and thereby improve endocardial definition and the assessment of regional and global LV function. In a study of 110 consecutive patients, echocardiography assessment of LV volume and EF with and without contrast were compared with MRI values. Contrast increased the feasibility for single-plane and biplane volume analysis from 87% to 100% and 79% to 95%, respectively. Echocardiography volumes underestimated MRI values, but the underestimation was less using contrast (16). In a second study, use of contrast agents in intensive care unit patients was demonstrated to salvage 51% of previously non-diagnostic transthoracic echocardiograms, a significant proportion of which were in postoperative patients (17).
Myocardial perfusion-rest studies
Assessment of the severity of coronary stenosis: Although contrast echocardiography is widely reported to be a reliable method to assess myocardial perfusion, a consistent protocol has yet to emerge. In a study comparing intermittent high mechanical index and real-time low mechanical index imaging, it was shown that low mechanical index imaging has a lower sensitivity for single-photon emission computed tomography (SPECT)-defined perfusion defects than high mechanical index imaging for a variety of technical reasons (18). However, in other studies, low mechanical index contrast imaging was reported to differentiate degrees of left anterior descending coronary artery obstruction (none, mild to moderate, moderate to severe, and total occlusion) in a group of 35 patients undergoing coronary angiography (19). In another study of patients with acute MI, qualitative MCE was sensitive but not specific for the detection of perfusion defects, whereas quantitative MCE showed a significant difference between blood flow values (ß x A) for Thrombolysis In Myocardial Infarction (TIMI) flow grade 0 to 2 versus TIMI flow grade 3. Although these reports and others (20,21) show roughly similar results, the absolute values for ß and ß x A were quite different (Table 1).
Assessment of collateral flow
Collateral blood flow after acute MI can sustain myocardial viability despite persistent occlusion of the infarct-related artery. Low power intravenous MCE at baseline and with dipyridamole stress was used to assess collateral flow in 20 patients with akinetic segments after acute MI who underwent thrombolysis, had a persistent occluded infarct-related artery, and subsequently underwent revascularization. Thirty-two percent of segments in the territory of the infarct-related artery were akinetic. Of the akinetic segments, 36% showed contractile reserve with low-dose dobutamine after revascularization. Contractile reserve was present in 24 of 29 segments with homogeneous contrast opacification and absent in 60 of 73 segments (82%) with reduced or absent opacification. All three quantitative myocardial contrast parameters (peak contrast intensity [A], bubble velocity [ß], and myocardial blood flow [A x ß]) were significantly higher in segments with contractile reserve. These results are similar to those previously reported for patients with chronically occluded arteries beyond the acute phase of acute MI (22).
Variability in quantitative assessment of flow
Although quantitative MCE has been used to assess perfusion, absolute values for A, ß, and A x ß differ between studies and with method of data acquisition, even in patients with normal flow. Table 1 compares the values reported for A, ß, and A x ß from several of the studies discussed earlier for control flow in normal vessels. Although the reason for all of these differences is unclear, in general, absolute values for ß are significantly lower during low compared with high MI imaging. Several reasons have been suggested for this difference, including: 1) alteration of the input function as a result of excessive destruction of bubbles in the LV cavity as a result of multiple flash frames; 2) microbubble destruction that may also occur because of high frame rates despite low MI; or 3) errors that may occur from differences in dynamic range, incorrect curve fitting, and noise (23). Despite these differences, values for ß and A x ß reserve appear almost identical. This suggests that the baseline quantitative values may not be comparable between studies and that patients and some form of stress may be required to determine changes in flow reserve.
Exercise echocardiography.
Outcome in patients referred for dyspnea
The results of exercise echocardiography in patients referred for dyspnea were examined in a group of 443 patients. Compared with patients referred for chest pain, patients with dyspnea alone were older, predominantly men, and had a lower workload, lower EF, more previous infarcts, and abnormal electrocardiograms. Patients with both symptoms were similar to those with dyspnea but had more previous revascularizations. Exercise echocardiography showed ischemia in 42% of patients with dyspnea, 19% with chest pain, and 58% with both symptoms. During a mean of 3.1 ± 1.8 years of follow-up, cardiac death (5.2% vs. 0.9%) and non-fatal MI (4.7% vs. 2.0%) occurred more often in patients with dyspnea. In patients with dyspnea, independent predictors of events were previous MI, male gender, EF, and increased wall motion score with exercise but not chest pain. Patients with lung disease precluding satisfactory echocardiographic images or with recognized noncardiac causes for dyspnea were excluded, and thus most patients in the study had a cardiac cause for dyspnea (24).
Prediction of preoperative risk in patients with submaximal exercise tests
Dobutamine stress echocardiography (DSE) is widely used in the preoperative evaluation of ischemic risk in patients with known or suspected coronary disease. The absence of ischemia on maximal stress tests is associated with excellent outcomes. However, despite the use of high-dose dobutamine and atropine, it is not always possible to reach the goal of 85% age-adjusted heart rate. Perioperative MI was reported to occur more frequently (9.4%) in patients with positive tests (either maximal or submaximal), but with equal frequency in patients with maximal or submaximal tests (submaximal = 74% of maximum despite completing the entire dobutamine atropine protocol), 6 of 335 (1.8%) versus 1 of 62 (1.6%), respectively. The negative predictive value was 98%, with events occurring exclusively in patients with resting wall motion abnormalities (25).
Use of stress testing to predict perioperative events
Despite the data suggesting that preoperative stress testing is a potent indicator of postoperative cardiac events, this has not been proven in randomized trials. A small prospective, randomized study designed to test the validity of American Heart Association/American College of Cardiology guidelines for preoperative stress testing before noncardiac (vascular) surgery showed that preoperative stress testing (DSE) offers no incremental value for determining postoperative adverse cardiac outcomes. As the authors note, larger randomized trials are needed to confirm this finding (26).
Relationship of test performance to transmural extent of scar
Dobutamine stress echocardiography and thallium SPECT remain the most widely available tests for the detection of myocardial viability. Thallium SPECT has been shown in a number of studies to be more sensitive, whereas DSE is more specific. In a complex study of patients with previous MI, the relationship of the transmural extent of scar by contrast-enhanced MRI was correlated with resting wall motion and estimates of viability by thallium SPECT and DSE. Over 50% of segments showed some residual contraction despite the presence of the transmural extent of scar from 25% to 75% of wall thickness. Disagreements in the assessment of viability were related to greater extent of the transmural extent of scar in the segments viable by thallium but not by DSE. These data in chronic ischemia differ significantly from early dog studies of acute infarction that demonstrated loss of transmural thickening, with a transmural extent of infarction of 20% (27). Unfortunately, because contrast-enhanced MRI defines necrosis and not viability and because recovery of function was not demonstrated, viability can only be inferred (28).
Exercise testing in mitral stenosis
In patients with mitral stenosis, there is frequently a discrepancy between mitral valve area and New York Heart Association functional class, particularly after mitral commisurotomy. Previous studies have used DSE to identify patients with mitral stenosis who have an important increase in pulmonary artery pressure with exercise; these studies have shown that reduced atrial (net) compliance is responsible for pulmonary hypertension in patients with apparently mild mitral stenosis by the pressure half time method. In a study of 53 patients with mitral stenosis, 29 (55%) presented with clinical events (16 hospitalizations, 7 cases of acute pulmonary edema, and 6 symptomatic supraventricular arrhythmias) during a mean 60.5 ± 11 months of follow-up. Thirty-one patients had a previous commisurotomy. Multivariate analysis showed both mitral valve area and a mean mitral gradient at peak exercise of 18 mm Hg to be significant predictors of future events. However, in patients with a mitral valve area >1.0 cm2, peak gradient >18 mm Hg best predicted outcome (sensitivity 90%, specificity 87%, and accuracy 90%). Patients with any other significant valvular disease or more than mild mitral regurgitation or tricuspid regurgitation were excluded, restricting the application of these findings. In addition no follow-up echocardiographic or clinical data (change in New York Heart Association functional class) are reported so that it is unclear whether or not simple progression of clinical or echocardiography-Doppler areas or gradients might also have predicted future events. Despite these limitations, the study confirms the potential of DSE to identify selected patients with moderate mitral stenosis who are at increased risk for complications (29).
Intracardiac echocardiography.
The use of intracardiac echocardiography to monitor transcardiac interventions continues to expand. In many institutions, intracardiac echocardiography has replaced transesophageal monitoring of device closure of atrial septal defects, patent foramen ovale, and a variety other procedures including balloon valvuloplasty, ventricular tachycardia ablation (30), and coil ablation of pulmonary A-V fistulae (31,32). Intracardiac echocardiography has several advantages over transesophageal echocardiography: it eliminates the need for general anesthesia, thus allowing greater flexibility in procedure scheduling. It provides direct access to intracardiac structures by the interventionalist and thus allows him to answer his own questions and eliminates the need for an echocardiographer. The technique provides accurate measurement of the fossa ovalis, obviating the need for balloon sizing that can itself affect the size of the defect (33). Procedure time is no different than that using transesophageal echocardiography (33). Although the catheters are expensive, the overall cost is similar to that of transesophageal echocardiography when anesthesia and echocardiographic time are considered.
Intercardiac echocardiography is used increasingly to monitor ablation procedures for atrial fibrillation (AF). It is recognized that thrombus formation is a risk associated with these procedures. In a study of 232 patients with AF undergoing ablation procedures, LA thrombus (n = 30) was observed in 24 patients (10.3%). Thrombi measured 12.9 ± 11.1 mm (length) and 2.2 ± 1.3 mm (width) and in each case were attached to the sheath or mapping catheter. Most thrombi were eliminated from the LA by withdrawing the sheath and catheter into the right atrium (RA); however, two became stuck in the interatrial septum. Patients who developed thrombi had an increased LA diameter, spontaneous echocardiography contrast, and a history of chronic AF. Multivariate analysis showed spontaneous echocardiography contrast to be the most important determinant of LA thrombus formation. No patient with LA thrombus developed clinical thromboembolic complications (34).
Doppler studies.
Effects of LA pressure on the age-related change in transmitral flow
Age-related changes in the pattern of LV filling (prolongation of the isovolumic relaxation time, reduction in the early diastolic [E] wave, a more gradual deceleration of early filling [deceleration time], and an augmentation of the atrial component of the filling wave [A]) have been repeatedly documented. It has been suggested that these age-associated changes in filling dynamics result primarily from a slowing of the rate of LV pressure decline manifest by a prolongation of the time constant of isovolumic pressure decay ( ). However, a recent combined echo-Doppler and MRI study of normals of varying age failed to show a decline in LV pressure decay during isovolumic relaxation and suggested that age may exert its effect on E-wave velocity and isovolumic relaxation time through a reduction in early LA pressure. Thus, the alteration in LV filling patterns with age may be more complex than currently appreciated and may be due in part to a reduced atrial contribution to the early diastolic pressure gradient (35).
Several recent studies reported that the time interval between the onset of mitral inflow and mitral annulus velocity (TE'-E) correlated well with the time constant of LV pressure decay () and was proposed as a new index of LV relaxation (36,37). In a surprising study of 40 patients undergoing cardiac catheterization, initially designed to validate this ratio, TE'-E showed no correlation with tau (range 31 to 70 ms). In the patient with the highest tau value there was simultaneous onset of mitral inflow and mitral annulus velocity (38). This is obviously an area that needs further study.
Several confirmatory Doppler studies were also reported, including: 1) the demonstration that color M-mode E-wave velocity propagation (Vp), an essentially preload-independent measure, was a better predictor of LV end-diastolic pressure and pulmonary congestion based on the E/Vp ratio than the E/A ratio (39); 2) color M-mode accurately reported ejection interventricular pressure gradients (40); 3) a restrictive LV filling pattern (E-wave deceleration time  130 ms) in patients with acute MI was associated with a lower EF, greater LV dilation, and a smaller decrease in percent wall motion abnormality during follow-up than patients without a restrictive pattern. Patients in whom the restrictive pattern was reversible before discharge had better outcome (four-year survival) than those who did not (93% vs. 79%) (41); and 4) the value of the peak pulmonary regurgitant velocity was validated as a measure of mean pulmonary artery pressure, with improved correlation when the right atrial pressure was added to the Bernoulli-derived value (42).
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Addition of new information in areas of particular clinical interest
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Cardiac resynchronization therapy (CRT).
The duration of the QRS complex, an indication of an abnormal pattern of ventricular electrical activation (left bundle-branch block and a QRS duration >120 ms), has been the standard method for identifying patients likely to benefit from CRT. Unfortunately between 20% and 30% of patients so identified fail to respond to CRT, and patients with a normal QRS duration may have important dyssynchrony. Recent data have confirmed that mechanical dyssynchrony is not necessarily related to electrical dyssynchrony and that the presence of important mechanical dyssynchrony is a major predictor of a response to CRT (43). A number of echocardiographic methods have been used to assess asynchrony, including M-mode recording of the time delay between septal and posterior wall motion; 2D analysis of the phase of LV contraction and regional area change; and tissue Doppler, strain, and strain rate imaging which permit the timing of peak systolic velocity in different regions to be compared (43). To further define this question, the onset of regional contraction by tissue Doppler imaging was examined in 49 consecutive patients undergoing CRT (27 responders and 22 nonresponders). There was a large overlap in individual values of QRS duration between responders and nonresponders. However, tissue Doppler imaging-derived indices of intraventricular and interventricular asynchrony accurately predicted positive LV remodeling, and the sum of these variables predicted responders with sensitivity, specificity, and accuracy of 96%, 77%, and 88%, respectively (44). In another study comparing electrocardiographic and tissue Doppler imaging estimates of dyssynchrony, severe dyssynchrony was observed in 27% of patients with a narrow QRS complex (120 ms), in 60% of patients with moderate electrocardiographic dyssynchrony (QRS 120 to 150 ms), and in 70% of patients with wide QRS complexes (45). These and other studies (46,47) continue to show the lack of reliability of electrocardiographic criteria for the detection of dyssynchrony relative to the direct measurement of mechanical activity.
In a study examining the regional distribution of strain in the LV immediately before and a day after the onset of CRT, it was demonstrated that CRT patients at baseline had a 106 ± 74 ms delay between contraction at the papillary muscle insertion sites which shortened to 39 ± 43 ms after CRT and was significantly correlated with reduction in mitral regurgitant fraction (48). This suggests that improved coordination of mechanical activation of the papillary muscle insertion sites may reduce abnormal tethering and be responsible for the immediate decrease in mitral regurgitation. This does not exclude the effect of increasing dP/dt and closure forces as previously described and underscores the complex forces effecting mitral valve closure (49).
Relationship of aortic atherosclerosis and stroke.
A number of studies have reported an association between aortic atherosclerosis recorded by transesophageal echocardiography and increased cardiovascular and stroke morbidity and mortality. However, these studies were generally based on highly selected transesophageal echocardiography patients, most with previous strokes, and variable adjustment for the effects of age and other comorbid conditions. In a prospective study of a group of 579 patients (mean age 66.9 ± 13.3 years) from the Stroke Prevention: Assessment of Risk in a Community (SPARC) study, the relationship between simple and complex (>4 mm thick or mobile debris) atherosclerotic plaque and vascular events during follow-up (mean 5.0 years) was studied. Simple plaques were identified in 253 (43.7%) and complex plaques in 44 (7.6%) persons. By univariate analysis, atherosclerosis grade was associated with cardiac and cerebrovascular events; however, after adjustment for age, gender, and other risk factors, there was no significant relationship between either type of atherosclerosis and cardiac or cerebrovascular events. Several atherosclerotic risk factors (age, male gender, higher pulse pressure, and diabetes) were significant independent predictors of cardiac events. Predictors of cerebrovascular events included age, previous MI, and AF (50). Although a limited number of patients with complex atherosclerosis were studied and the mortality in this group was only one-half that of the local population, the data prompt a reevaluation of the association between aortic atherosclerosis and cardiovascular morbidity and mortality.
LA.
The LA remains an area of considerable investigation because of the continuing interest in ablation therapy for AF and the recognized role of atrial size as a marker of diastolic function in patients without primary mitral valve disease. In patients with acute MI, LA volume >32 ml/m2 determined within the first 48 h after infarction was confirmed to be an independent predictor of five-year mortality and to provide incremental prognostic information to clinical (age, diabetes) and echocardiographic data (LV EF) (51,52).
The LA is the source of cardiac emboli in  90% of patients with nonrheumatic AF in whom an intracardiac thrombus has been visualized. Although warfarin anticoagulation is the standard method of prevention, many patients with AF are unable to take warfarin. To treat these patients, a percutaneous LA appendage transcatheter occlusion device (PLAATO) has recently been introduced to exclude the LA appendage from the rest of the circulation. However, the impact of long-term deployment of the device on adjacent structures is unknown. In 11 patients who completed six months of follow-up, the device appeared stable with minimal residual flow around PLAATO similar to that seen at baseline. The PLAATO caused no change in the size of the left pulmonary vein, transmitral flow velocities, LA size, or mitral regurgitation compared with baseline (53).
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Summary
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In summary, the number and complexity of echocardiographic techniques continue to grow, with the result that many methods are proposed to answer similar questions each with positive but generally imperfect results. Because time and expense preclude the application of multiple methods to the same question, further efforts must be made to standardize approaches and identify situations in which a particular method is most appropriate.
Given that MRI is the gold standard to which echocardiography is compared in many of these studies, it is often questioned whether MRI will eventually replace echocardiography for most applications. The answer is in the wheels. When the first MRI machine is seen being wheeled down the hall and into the patient's room, echocardiographers should be concerned, but until then the flexibility, portability, and requisite clinical accuracy will cause echocardiography to continue to grow for the foreseeable future.
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