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

Transesophageal echocardiography and noncardiac surgery

The use of transesophageal echocardiography (TEE) for monitoring during cardiac and noncardiac surgery has increased exponentially over the past few decades. TEE has evolved from a diagnostic tool to a monitoring device and a procedural adjunct. The close proximity of the TEE transducer to the heart generates high-quality images of the intracardiac structures and their spatial orientation. The use of TEE in noncardiac and critical care settings is not well studied, and the evidence of the benefits of its use in these settings is lacking. Despite the widespread availability of TEE equipment in US hospitals, less than 30% of anesthesiologists are formally trained in the use of perioperative TEE. In this review, the safety and indications of TEE are reviewed and detailed analysis of the best available evidence in this regard is presented. Landmark trials evaluating the use of TEE and its therapeutic impact in noncardiac surgical setting are critically reviewed. This article details recommendations to familiarize anesthesiologists with TEE technology to exploit it to its fullest potential to achieve better patient monitoring standards and eventually improve outcome. Training of greater numbers of anesthesiologists in TEE is needed to increase awareness of the indications and contraindications. Until relatively inexpensive TEE equipment is available, the initial cost of equipment acquisition remains a significant prohibitive factor limiting its widespread use.

Effects of tachycardia on regional wall motion in acute ischemic canine heart

Tachycardia accompanies the preload reduction. Our aim is to assess the effect of the heart rate change on wall motion in ischemic heart. In 8 dogs with occlusion of left anterior descending artery, we changed the heart rate (heart rate 90, 120, and 150 beats/minute) after using UL-FS49, a selective bradycardic agent, with atrial pacing. Preload was changed by inferior vena caval occlusion at a heart rate of 90 beats/minute. With either an increase in heart rate or an inferior vena caval occlusion, the end-diastolic length was decreased, but the end-diastolic length relationships between the non-ischemic and the ischemic region made different lines from those of the heart rate change and inferior vena caval occlusion. When increasing the heart rate, isovolumetric shortening was unchanged in the non-ischemic region with more expansion in the ischemic region. While inferior vena caval occlusion at a heart rate of 90 beats/minute, isovolumetric shortening was increased in the non-ischemic region, with more expansion in the ischemic region. Both in tachycardia and by the inferior vena caval occlusion, ejectional shortenings decreased in the non-ischemic and ischemic regions. Our results suggest that, in ischemic heart, tachycardia changes both in the end-diastolic length relationship between the non-ischemic and the ischemic region and at the isovolumetric contraction phase. The changes seem to be not only due to the inferior vena caval occlusion, but also due to tachycardia itself.

Effects of afterload increase on systolic and diastolic functions of the myocardium after myocardial infarction

The evaluation of noninfarcted zone function after myocardial infarction by the use of noninvasive methods is very important. The authors speculated that phenylephrine, which increases systemic vascular resistance and blood pressure and has no effect on central ischemic and border-zone myocardium but does have an effect on remote myocardium, could be used as a stress agent as information is gathered about the functional capacity of the left ventricle and the status of coronary arteries in patients with recent myocardial infarction. Forty-six patients with recent myocardial infarction (5 women, 41 men; mean age: 53.6 +/-9.3 years) and 15 individuals with normal findings from coronary angiography and ventriculography (9 women and 6 men; mean age: 39.0 +/-11.2 years) were included in the study. The study was performed on the 4th or 5th day of the myocardial infarction. Preejection period/left ventricular ejection time (PEP/LVET), diastolic mitral flow velocity, isovolumic relaxation time (IVRT), and deceleration time (DT), were measured before and after the phenylephrine infusion, with M-mode, pulse wave, and continuous-wave echocardiography. After pressor stress with phenylephrine infusion, all the parameters were measured again. Coronary angiography and ventriculography were performed on all the patients on the 7th to 10th day of the myocardial infarction. All the patients were grouped according to their ejection fraction and the number of involved coronary arteries. The increase in the PEP/LVET ratio in Group 1 (left ventricle ejection fraction [EF] below 40%) and multivessel coronary artery lesion group was significant (p<0.01). PEP/LVET ratio decreased significantly in both Group C (patients with normal-appearing coronary arteries and ventriculographies) and the single-vessel coronary disease group. Although the early diastole flow/atrial systole flow (E/A) ratio increased significantly in the 3 groups, the 0.5 and more increase in E/A ratio had high sensitivity (86%) and specificity (80%) in differentiating the low EF group. The 0.5 and more increase in E/A ratio had 65% sensitivity and 69% specificity in differentiating the multivessel coronary stenosis group. A deceleration time of 130 msec and below in basal conditions had a high sensitivity (86%) and specificity (92%) for detecting the group in which EF was below 40%. After phenylephrine infusion, the shortening of IVRT was significant in Group 1 (p<0.01). Phenylephrine, which has been shown to be an alpha-1 receptor agonist in low doses and effective only on remote myocardial function, may be given with low complication rates in the early postinfarction period. The increase in PEP/LVET ratio, 0.5 and more increase in E/A ratio, and shortening of DT and IVRT after phenylephrine infusion may be indicators of low LV functional capacity and widespread coronary artery disease. This test may suggest performance of early invasive detection of coronary artery disease and early revascularization. This study may also be interesting from a pathophysiological point of view.

Systolic time intervals after phenylephrine administration for early stratification of patients after acute myocardial infarction

This study was designed to assess the usefulness of the changes in left ventricular (LV) systolic time intervals after phenylephrine administration for detecting high-risk patients soon after acute myocardial infarction by correlation with the angiographic and ventriculographic findings. The procedure was performed in 76 consecutive patients (group I) on the fourth postinfarction day and in 12 normal subjects (group II) free of coronary artery disease. In 20 patients with LV ejection fraction < or = 40% (subgroup IA) the preejection period (PEP)/LV ejection time (ET) ratio increased from 0.410 +/- 0.107 to 0.535 +/- 0.102 (p = 0.01) after phenylephrine, whereas in the remaining 56 patients (subgroup IB) with LV ejection fraction > 40% and in the 12 normal subjects the PEP/LVET increased nonsignificantly. Of patients with LV ejection fraction > 40% a subset of 20 patients was distinguished with proximal stenosis in both left anterior descending and either a dominant right or left circumflex coronary artery (subset IB-a). In these the PEP/LVET increased from 0.347 +/- 0.056 to 0.445 +/- 0.019 (p = 0.0001) after phenylephrine, whereas in the remaining 36 patients (subset IB-b) without proximal lesions in 2 main arteries the PEP/LVET increased nonsignificantly. In conclusion, the PEP/LVET response to phenylephrine administration early after acute myocardial infarction is a precise, safe, noninvasive bedside method for early stratification of these patients.

Ischemic expansion during acute myocardial infarction and reversal by coronary reperfusion

Previous studies have shown that infarct expansion occurs at least 1 day after a large transmural infarction. To assess whether regional left ventricular expansion is evident within hours of an acute myocardial infarction, 25 adult mongrel dogs underwent left circumflex coronary artery occlusion for 2 hours and 22 of these were subsequently reperfused. Two-dimensional echocardiography was used to record left ventricular topography and function at baseline, at 2 hours of occlusion, and following reperfusion. Short-axis midpapillary echocardiograms were analyzed using a microcomputer digitizing routine by establishing a 360-degree circumferential map of the left ventricle. The central ischemic zone was defined as that region with the most depressed contractility after 2 hours of occlusion, and the normal zone was set at 180 degree away from the central ischemic zone. Endocardial and epicardial segment lengths and wall thickness were measured for both the normal zone and the central ischemic zone at end diastole. After 2 hours of occlusion, diastolic central ischemic endocardial (1.3 +/- 0.05 to 1.42 +/- 0.04 cm, p less than 0.01) and central ischemic epicardial (1.84 +/- 0.06 to 1.93 +/- 0.06 cm, p less than 0.05) segment lengths were significantly increased. There were no significant changes in segment lengths or wall thickness in the normal zone. After 2 hours of occlusion, there was significant diastolic left ventricular (LV) dilatation (LV area increased from 18.2 +/- 1.3 to 21.0 +/- 1.3 cm2, p less than 0.01). Furthermore, central ischemic endocardial and epicardial segment length changes from baseline to occlusion correlated significantly with LV dilatation (r = 0.56, p less than 0.003; r = 0.55, p less than 0.004 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

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.