RESUMEN

To compare the long-term prognosis of a group of patients treated by an early invasive approach after a non-Q-wave anterior wall acute myocardial infarction (AMI) with a similar group treated conservatively, data from 110 consecutive patients with non-Q-wave AMI were retrospectively obtained from 3 different hospitals: (1) a hospital with coronary angioplasty and coronary bypass facilities favoring on early invasive approach, (2) a hospital with a catheterization laboratory and no coronary angioplasty or coronary bypass facilities, and (3) a community hospital without a catheterization laboratory. Patients were divided according to the presence or absence of an early invasive approach: those who had undergone in-hospital catheterization and revascularization (n = 55) and those with a conservative approach (n = 55). The early invasive approach resulted in a significant decrease in major events. The rate of recurrent myocardial infarction was 29% in the conservative group versus 7.2% in the invasive group (p = 0.025). Survival rate curves at 3-year follow-up showed significant differences in mortality (p = 0.001), recurrent myocardial infarction (p = 0.002), recurrent angina pectoris (p = 0.001), and development of congestive heart failure (p = 0.05). Multivariate analysis disclosed the early invasive approach to be an independent predictor for decreasing the likelihood of recurrent infarction by 86% (odds ratio 0.14, confidence intervals 0.04 to 0.48, p = 0.0006), and for decreasing the likelihood of recurrent angina by 66% (odds ratio 0.34, confidence intervals 0.18 to 0.63, p < 0.005). The early invasive strategy may result in an improved outcome in the treatment of patients with non-Q-wave anterior wall AMI compared with patients treated conservatively.

Asunto(s)

RESUMEN

Isolated, perfused rat hearts (30 degrees C, n = 13) were paced from 218 +/- 4 beats/min to 433 +/- 4 beats/min while systolic and diastolic pressure were recorded and intracellular Na+ concentration ([Na+]i) was monitored by 23Na nuclear magnetic resonance (NMR) spectroscopy. [Na+]i increased progressively with increasing stimulation frequency. In seven hearts (group I) an initial, progressive increase in systolic pressure was observed followed by a decrease in pressure with further increase in frequency. From the onset, a progressive decrease in systolic pressure was observed in group II (n = 6) in response to increased frequency. In group I an [Na+]i increase of up to 134 +/- 7% of control (P < 0.001) was observed, whereas in group II the gain in [Na+]i with increasing pacing rate was attenuated, reaching a maximum of 120 +/- 3% of control (P < 0.02). The differential pressure response between group I and group II hearts may reflect an enhanced sensitivity of rat hearts to the shortening of the restitution period of the sarcoplasmic reticulum, outweighing the positive inotropic effect induced by an increased [Na+]i. Only in rat hearts whose [Na+]i-induced increase in pressure outweights the restitution deficit would a complete positive inotropic effect be anticipated.

Asunto(s)

RESUMEN

In patients with aortic regurgitation (AR), knowledge of the severity of AR, and the degree of left ventricular (LV) dysfunction are important for optimal management. Previous nuclear magnetic resonance (NMR) studies to assess these parameters used multiple tomographic planes that are time-consuming to obtain and analyze, and thus not cost-effective. In addition, these studies assessed the severity of AR by looking simply at the size of the regurgitant jet, a parameter that relates only poorly to regurgitant volume. The present study evaluates a rapid, single-plane, cine NMR approach (scan time < 10 minutes), and a new grading system for AR that is based on the presence, size and persistence of not only the regurgitant jet, but also the zone of proximal signal loss. Compared with color Doppler echocardiography (n = 42), the NMR approach detected AR with a specificity of 100% and a sensitivity of 95%. NMR regurgitant jet area correlated well with color Doppler regurgitant jet area (n = 20; r = 0.81; p < 0.01), but did not discriminate well between all grades of AR as compared with x-ray contrast aortography (n = 14). Using the new NMR grading criteria, AR grade by NMR was in accordance with aortographic grade in 12 patients, differing by only 1 grade in the remaining 2 patients. NMR grade was in accordance within 1 grade of Doppler in all patients compared (n = 20). LV volumes and ejection fraction using this single-plane approach correlated well with a previously validated, NMR biplane approach (r > 0.87; n = 18).(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

BACKGROUND: Intramyocardial hemorrhage occurs frequently after reperfusion of acute myocardial infarction. However, its significance has not yet been established, mainly because of the lack of methods for detecting such hemorrhage. The following ex vivo study was carried out to assess the potential of nuclear magnetic resonance (NMR) imaging to detect and quantitate postreperfusion intramyocardial hemorrhage. METHODS AND RESULTS: Sixteen adult mongrel dogs underwent 3 hours of coronary occlusion followed by 1 hour of reperfusion, and three dogs underwent 4 hours of occlusion without reperfusion. Radiolabeled microspheres and 51Cr-labeled red blood cells were used to assess flow and evaluate the extent of hemorrhage. These results were later compared with both NMR and histology. Spin-echo NMR imaging was performed on the excised hearts using a 1.5-T system. Macroscopic assessment of the sliced myocardium revealed the existence of hemorrhage in 14 of the 16 dogs that underwent reperfusion but in none of those with occlusion only. In all 16 dogs with reperfusion, zones of increased signal intensity (SI) ratio (1.68 +/- 0.41 compared with control, p less than 0.05) were seen in regions relating to the distribution of the occluded coronary artery, whereas in 13 of the 16 dogs, areas of decreased SI within the zone of increased SI ratio (0.81 +/- 0.16 compared with control, p less than 0.05) were also seen, corresponding to regions with macroscopic hemorrhage. In contrast, in the three dogs without reperfusion, no macroscopic hemorrhage was observed, and likewise, no NMR zones of reduced SI were detected. Hemorrhage size by NMR (decreased SI zones), correlated well with hemorrhage size calculated from tissue slices (r = 0.96, SEE = 0.92%, p less than 0.01), or by 51Cr labeling (r = 0.78, SEE = 1.5, p = 0.1). In the reperfusion group, T2 relaxation times in the infarcted hemorrhagic zone (58 +/- 9 msec) were significantly lower than the infarcted zones without hemorrhage (98 +/- 13 msec, p less than 0.001). In contrast, when compared with control (964 +/- 72 msec), T1 relaxation times were significantly increased in both infarct zones, either with (1,284 +/- 176 msec) or without (1,266 +/- 103 msec) hemorrhage. The selective shortening of T2 relaxation times in the hemorrhagic regions is consistent with the paramagnetic effects of deoxyhemoglobin. CONCLUSIONS: NMR imaging may provide a noninvasive approach for the detection and quantitation of intramyocardial hemorrhage. This observation may provide a means to further characterize pathological processes associated with acute myocardial infarction and assess the role of myocardial hemorrhage after reperfusion therapy.

Asunto(s)

RESUMEN

The increase in intracellular sodium (Nai), resulting from inhibition of the Na/K ATPase by cardiac glycosides, is known to increase calcium influx via Na(+)-Ca2+ exchange, and thereby increase contractility. This increase in intracellular Ca2+ has been related to the development of intracellular acidification and enhanced activity of the Na(+)-H+ exchanger as a measure by the cell to prevent further acidification. Thus, the efflux of the H+ ions results in an additional increase in Nai. This may subsequently lead to an increased rate of Ca2+ influx and therefore to the potentiation of the effects of cardiac glycosides. To assess the role of Na(+)-H+ exchange in the mechanism of ouabain action in the beating heart we used amiloride, a known inhibitor of Na(+)-H+ exchange. Isolated rat hearts were perfused with either ouabain (50 microM) alone (n = 8, Group I), amiloride (1.0 mM) + ouabain (50 microM) (n = 8, Group II), or amiloride (1.0 mM) alone as a control group (n = 4, Group III). 23Na and 31P NMR spectroscopy were used to assess the changes in Nai and intracellular pH (pHi), respectively, while simultaneous and continuous monitoring of left ventricular pressure was carried out. Perfusion with both ouabain alone (Group I) or ouabain + amiloride (Group II), resulted in a time dependent increase in Nai levels, reaching (within 25 mins) a maximum of 200 +/- 7% of control in Group I, and 170 +/- 10% of control in Group II. Concurrently, a mild but significant decrease in pHi was observed in both groups. This decrease, however, was significantly higher in Group II compared to Group I (0.34 pH units vs. 0.19 pH units, respectively; P less than 0.05), suggesting that inhibition of Na(+)-H+ exchange by amiloride limits the recovery from ouabain-induced intracellular acidification. While developed pressure gradually increased in Group I to a maximum of 268 +/- 52% of control, the addition of amiloride in Group II substantially reduced the positive inotropic effect. Ventricular fibrillation (VF) developed in three of the eight hearts in Group I within 10-13 mins after the addition of ouabain. Interestingly, the rate of Nai increase in hearts that sustained VF was significantly higher compared to those without VF (mean slope 10.1 +/- 2.11 vs. 3.9 +/- 1.0, respectively; P less than 0.0001). Ventricular fibrillation did not develop in Group II or III.(ABSTRACT TRUNCATED AT 400 WORDS)

Asunto(s)

RESUMEN

1H NMR imaging has been used to define zones of myocardial infarction (MI), which appear as areas of relatively increased signal intensity (SI). However, zones of decreased SI have been observed within or around the areas of infarction in NMR images acquired at high magnetic fields. To determine the cause of these areas of reduced SI, ex vivo spin-echo 1H NMR imaging at 1.5 T was performed in eight dogs following 72 h of coronary artery occlusion. In all dogs, a zone of increased SI (122 +/- 7% compared to control myocardium; P less than 0.01) was observed in the territory of the occluded coronary artery. In seven of the dogs, additional zones were also seen, within or around the central zone of increased SI, which displayed SI that was reduced in comparison with the local enhanced intensity, but was similar to the intensity of normal myocardium (97 +/- 7% compared to control; P = NS). Gross inspection and histological assessment of sliced myocardium disclosed hemorrhage in these regions characterized by locally decreased NMR SI. Image-derived calculation of T2 in the various infarct regions revealed a significant shortening of T2 in the hemorrhagic infarct zones characterized by decreased SI, in comparison with the nonhemorrhagic infarct zones characterized by increased SI (59 +/- 7 ms vs 73 +/- 10 ms, P less than 0.05). No difference was found, however, between the observed T2's of hemorrhagic infarct and of control tissue (57 +/- 4 ms). Using a biexponential analysis of T2 from the hemorrhagic infarct zones, the intrinsic T2 of water protons affected by hemorrhage was determined to be 43 +/- 9 ms, significantly reduced in comparison with the values obtained with the standard monoexponential fit. The reduction in T2 in the hemorrhagic zone is consistent with the paramagnetic effects of deoxyhemoglobin associated with intramyocardial hemorrhage. Thus the apparent T2, measured in hemorrhagic infarct tissue, represents the result of an averaging effect of infarct and hemorrhage on T2 relaxation times. These observations improve our understanding of the changes in NMR SI within the infarcted regions, and may provide a noninvasive method for the detection and quantitative assessment of intramyocardial hemorrhage.

Asunto(s)

RESUMEN

Nuclear magnetic resonance (NMR) imaging now offers a powerful means of assessing a variety of clinically important parameters in patients with valvular heart disease. NMR approaches will probably be most useful in patients with chronic valvular regurgitation, in which there continues to be uncertainty regarding the optimum timing for surgical intervention. In these patients it is possible to simultaneously assess both the valvular regurgitation and the resulting changes in myocardial structure and function. In patients with aortic stenosis, NMR can be applied to the assessment of left ventricular mass, both before and after valvuloplasty or valve replacement. In mitral stenosis, NMR may be applied to the assessment of right ventricular volumes and function. NMR may be used for the detection of prosthetic valve regurgitation when Doppler studies are equivocal. Finally, NMR imaging may be applied in patients with congenital or aortic root disease to evaluate valvular function in addition to diagnostic assessment of such patients. The future development of isotropic three-dimensional acquisition approaches, ultrafast imaging strategies, automated surface detection techniques, and more rapid function and flow analysis could considerably enhance the use of the current NMR approaches. The application of spectroscopic techniques could provide a means of monitoring myocardial metabolic abnormalities in ventricles exposed to chronic overload. Meanwhile, in patients with valvular regurgitation and stenosis, it would seem timely to initiate long-term serial NMR studies to further define natural history and the effects of various medical regimens and to ultimately help determine optimum medical and interventional regimens.

Asunto(s)

RESUMEN

Cine nuclear magnetic resonance (NMR) imaging, as a noninvasive and high-resolution imaging modality, has been shown to be reliable for determining absolute left ventricular (LV) volumes and ejection fraction. A relatively new gradient echo cine NMR approach using 2 orthogonal long-axis planes (2- and 4-chamber) aligned with the true axes of the left ventricle has been previously developed and validated against radiographic biplane LV cineangiography. The aim of the present investigation was to determine the reproducibility of this more rapid cine NMR approach for the measurement of LV volumes and ejection fraction. Eighteen normal subjects underwent 2 cine NMR studies, on different days, using a 1.5-tesla clinical imaging system. Studies were analyzed on-line and blindly by 2 independent observers. Intraobserver error was also determined in a blinded manner. Mean values of measurements determined by this method in this group of normal subjects were end-diastolic volume (120 +/- 20 ml), end-systolic volume (39 +/- 9 ml) and ejection fraction (67 +/- 4%). Paired analysis of data revealed no significant bias between interstudy, interobserver or intraobserver measurements, except for interobserver end-diastolic volume, where the first observer measurements were slightly elevated (5.6 +/- 7.8 ml) compared with the second. This resulted in a small difference in ejection fraction (1.7 +/- 2.3%) between observers. The absolute variation between measurements (square root of variance components) was low for all interstudy, interobserver and intraobserver comparisons: end-diastolic volume was less than +/- 6.7 ml, end-systolic volume less than +/- 3.5 ml and ejection fraction less than +/- 2.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

Proton (1H) nuclear magnetic resonance (NMR) imaging has been used to define zones of myocardial infarction (MI), which appear as areas of relatively increased signal intensity (SI). However, zones of decreased SI have been observed within the areas of infarction and have been postulated to result from intramyocardial hemorrhage. To explore this phenomenon further, ex vivo spin-echo 1H NMR imaging at 1.5 Tesla was performed in 17 dogs after 24 hr (n = 9) and after 72 hr (n = 8) of coronary artery occlusion. In all dogs, a zone of increased SI (118 +/- 9% compared with normal myocardium) was observed in the distribution of the occluded coronary artery. In 12 of the 17 dogs, zones of decreased SI (92 +/- 8% compared with normal) were seen within or around the central zone of increased SI. Gross inspection and histological assessment of sliced myocardium usually disclosed hemorrhage in the regions of decreased SI. In three of the five dogs with no apparent zones of decreased SI on NMR, the infarct was small, and only minor hemorrhage was observed by gross inspection, whereas in the remaining two dogs no hemorrhage was seen. Myocardial flow in the hemorrhagic regions was significantly higher than in the necrotic core (59 +/- 29% vs. 31 +/- 24% compared with control, P less than 0.05). Image-derived calculation of T2 relaxation times in the different infarcted regions revealed a significant shortening of T2 in the infarcted hemorrhagic zones with decreased SI compared with the infarct zones with increased SI (49 +/- 8 msec vs. 66 +/- 8 msec, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

Proton nuclear magnetic resonance (NMR) imaging has the potential to serially assess left ventricular (LV) volumes with optimal accuracy because it is a high-resolution, three-dimensional, noninvasive modality. Previous NMR studies to assess LV volumes have been suboptimal, as they have used either planes aligned with the axes of the body, which are compromised by partial volume effects, or spin-echo techniques that have been time-consuming to acquire and analyze. Accordingly, for LV volume measurement, we developed a gradient-echo (cine) NMR strategy that uses two orthogonal planes intersecting along the intrinsic long axis of the heart (two-chamber and four-chamber). This approach was validated against calibrated contrast biplane LV cineangiography (CATH) and also compared with a previously reported short-axis spin-echo NMR method. Twenty-one patients underwent CATH and NMR (long-axis, n = 21; short-axis, n = 14) within a 3-day interval. Although both long- and short-axis NMR LV volumes and ejection fractions correlated well with CATH (r greater than 0.90, p less than 0.001 in all), end-diastolic volumes by both long-axis (161 +/- 85 ml) and short-axis (151 +/- 81 ml) NMR were systematically less than those by CATH (182 +/- 85 ml) (p less than 0.05). Consequently, ejection fractions by long-axis (48 +/- 17%) and short-axis (49 +/- 17%) NMR consistently underestimated those by CATH (54 +/- 16%, p less than 0.05). End-systolic volumes by long-axis (94 +/- 71 ml) and short-axis (87 +/- 72 ml) NMR were not significantly different from those by CATH (92 +/- 69 ml). Both NMR techniques had low intraobserver and interobserver variation (less than 11%); however, short-axis spin-echo NMR involved longer acquisition/reconstruction (35 versus 18 minutes) and analysis (25 versus 10 minutes) times. We conclude that both short-axis spin-echo and long-axis gradient-echo NMR approaches reliably estimate LV volumes. Currently, the long-axis strategy appears more practical for clinical use because the scan and analysis times are relatively short.

Asunto(s)

Asunto(s)

RESUMEN

Previous nuclear magnetic resonance (NMR) imaging studies to assess left ventricular function have used multiple axial planes, which are compromised by partial volume effects and are time consuming to acquire and analyze. Accordingly, an imaging approach using cine NMR and planes aligned with the true cardiac axes of the left ventricle was developed in views comparable with left ventricular cineangiography. Cine NMR imaging was used to assess regional wall motion and was validated by comparison with biplane left ventricular cineangiography. Fifty-nine patients underwent cineangiographic and NMR studies within 72 h. A poor quality NMR study precluded analysis in 4. leaving a study group of 55 patients (mean age 58 +/- 12: 17 women). Cine NMR movie loops were acquired in two long-axis planes: 1) right anterior oblique plane, parallel to the septum, and 2) four chamber orthogonal plane, perpendicular to the septum (this view is comparable to the angiographic left anterior oblique view). To assess regional wall motion, the left ventricle in both cine NMR and cineangiographic images was divided into five segments and graded on a five point grading scale from 3 for normal through 0 for akinesia and -1 for dyskinesia. Regional wall thickening was used qualitatively to aid in the analysis of wall motion. For the 275 segments compared in the right anterior oblique view, agreement was within one grade in 263 (95.6%) of 275 segments, whereas absolute agreement was observed in 171 (62%) of 275 segments. In the left anterior oblique view, of 200 segments evaluated, agreement within one grade was achieved in 184 segments (92%) and agreement was complete in 132 (66%).(ABSTRACT TRUNCATED AT 250 WORDS)

Asunto(s)

RESUMEN

Application of NMR technology to the evaluation of the cardiovascular system is still in its infancy. NMR can frequently yield information equivalent to echocardiography or angiography but cost, long imaging times, and lack of portability have discouraged widespread use. To date, NMR has not replaced standard imaging modalities in the evaluation of most cardiovascular disease states, although it appears to have a unique role in the delineation of great vessel pathology, the evaluation of congenital heart disease, and the delineation of cardiac and paracardiac masses. Appearance of tissue and flowing blood and contrast between structures are highly dependent on magnetic field strength and the imaging pulse sequence used. Published comparisons between NMR and other imaging modalities have to be interpreted and extrapolated with caution, and sensitivity and specificity of NMR imaging in different disease entities should be further validated. With technological improvements, shortening of examination times and data processing times and true three-dimensional imaging may be possible in the near future. Ultimately, however, the clinical importance of NMR will depend on the development of unique applications such as examination of regional cardiac metabolism, noninvasive coronary and peripheral angiography, myocardial perfusion imaging, and improved tissue characterization.

Asunto(s)

Asunto(s)

RESUMEN

A 6-year-old girl with signs of a space occupying lesion had a CT scan compatible with a brain tumor. A preoperative hemogram revealed thrombocytopenia which was later proved to be due to ITP. Intracranial bleeding can rarely be the first manifestation of ITP. Early recognition of this situation aided by serial CT follow-up may lead to an improvement in the handling of these patients.

Asunto(s)