Cardiac complications in noncardiac surgery: value of dobutamine stress echocardiography versus dipyridamole thallium imaging.

OBJECTIVES: The objective of this study was to determine the relative value of dobutamine stress echocardiography (DSE) and dipyridamole thallium imaging (DT) in the preoperative assessment of cardiovascular risk before noncardiac surgery. DESIGN: Prospectively DSE was performed in patients who had undergone DT as a part of their preoperative evaluation. SETTING: A large urban veterans' affairs medical center. PARTICIPANTS: Thirty-seven patients undergoing major noncardiac surgery were assessed for complications during a 1-month follow-up period. INTERVENTIONS: Both DSE and DT were performed before surgery. The medium interval between the two tests were 15.5 days. MEASUREMENTS: Left ventricular wall motion was assessed at baseline and peak dobutamine dose in a standard fashion. Wall motion was scored and indexed using a 16-segment model. A positive DSE was defined as failure of augmentation, new or worsening of baseline wall motion abnormalities in two or more contiguous segments. Myocardial perfusion studies after DT were performed according to conventional method. A positive DT was defined as a reversible perfusion defect, increased lung uptake, and/or transient left ventricular dilatation. Complications were defined as myocardial infarction or cardiac death occurring as a result of the operation, or need for revascularization before surgery. RESULTS: DSE was positive in 19 patients, whereas DT was positive in 25 patients. Fourteen patients had both an abnormal DSE and DT. Five patients had major postoperative cardiac complications: fetal myocardial infarction (1); fatal cardiac arrest (1); and severe coronary artery disease necessitating coronary artery bypass surgery (2) or percutaneous transluminal coronary angioplasty (1). DSE was positive in all 5 (100%), whereas DT was positive in 4 of 5 (80%) patients with complications. The sensitivity for each test was comparable: for DSE it was 100% (95% C.I. 56% to 100%) and for DT 80% (37% to 96%). Specificity for DSE (60%, 43%-74%) was somewhat higher than DT (38%, 24% to 54%), although this did not reach statistical significance (p = 0.06). CONCLUSIONS: The ability of DSE to predict major cardiac complications related to noncardiac surgery appears to be similar to DT and may be used as an alternative to DT imaging in the preoperative risk assessment of patients undergoing noncardiac surgery.

Left atrial appendage contractile function in atrial fibrillation. Influence of heart rate and cardioversion to sinus rhythm.

BACKGROUND: A high incidence of embolic phenomena is associated with atrial fibrillation (AF) and the left atrial appendage (LAA) is frequently the source of the emboli. Thrombus formation may be due to stasis within the fibrillating and inadequately emptying LAA. Because LAA emptying in AF may be the result of mechanical compression by the adjacent left ventricle, it is possible that left ventricular diastolic filling duration will importantly influence passive emptying of the LAA. We hypothesized that the magnitude of emptying of the LAA in AF is related to the duration of left ventricular diastolic filling which is determined by the ventricular response rate in AF. OBJECTIVE: The objective of our study was to determine the relationship of ventricular response rate in AF to LAA emptying and to assess the influence of sinus rhythm and heart rate on LAA emptying immediately after direct current cardioversion to sinus rhythm. METHODS: To study this, we used transesophageal echocardiography to measure LAA ejection fraction ([LAAmax-LAAmin]/LAAmax x 100%) and evaluated its relationship to left ventricular response rate (VRR) in 26 patients with AF (mean age, 65 +/- 7 [1 SD] years). RESULTS: There was a strong inverse relationship between LAA ejection fraction and VRR in AF (r = -0.73; p < 0.001). LAA ejection fraction during AF was 26 +/- 10%, and immediately after successful cardioversion, it increased to 46 +/- 12% (p < 0.001). However, during sinus rhythm there was no relationship between LAA ejection fraction and VRR (r = 0.06; p = NS) in the subgroup of patients who were successfully converted to sinus rhythm. There were poor relationships between LAA ejection fraction and peak transmitral flow velocity (r = -0.41; p = NS) or pulmonary venous flow velocity (r = -0.03; p = NS) in AF. CONCLUSION: These results indicate that the magnitude of LAA emptying in AF is strongly and inversely influenced by ventricular rate. Direct current cardioversion to sinus rhythm is associated with an increase in the magnitude of LAA emptying that is not influenced by heart rate. The magnitude of LAA emptying may be an important factor in the formation of thromboemboli in AF. The extent to which controlling the VRR in chronic AF will prevent stasis and LAA thrombus formation remains to be determined.

Noninvasive detection of transplant coronary artery disease by dobutamine stress echocardiography.

Coronary artery disease has emerged as the leading cause of late morbidity and mortality in heart transplant recipients. The incidence of allograft coronary artery disease has been reported to be as high as 40% to 50% by 5 years. Coronary angiography remains the standard approach for surveillance of coronary artery disease in this patient population. However, the detection and surveillance of allograft coronary disease by noninvasive methods remains a challenge. The purpose of this study was to determine the value of dobutamine stress echocardiography as a noninvasive screening test to rule out the presence of anatomically significant allograft coronary artery disease and to assess its prognostic power. Dobutamine stress echocardiography was carried out according to a standard protocol in which dobutamine was infused at 5, 10, 20, 30, and 40 micrograms/kg/min intravenously at 5-minute stages with 12-lead electrocardiogram and blood pressure monitoring. Left ventricular wall motion was analyzed at baseline and at peak dobutamine dose. Mean age (+/- standard error of the mean) of the study population was 50.5 +/- 1.5 years, and mean duration (+/- standard error of the mean) since transplantation was 57 +/- 5 months. The sensitivity, specificity, and positive and negative predictive accuracy of dobutamine stress echocardiography were 95%, 55%, 69%, and 92%, respectively. In the 12-month follow-up study 12 patients with abnormal dobutamine stress echocardiographic findings had 15 major cardiac events whereas no event occurred in patients with normal dobutamine stress echocardiograms.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressure generation in a contracting myocyte.

The central hypothesis of this investigation is that a shortening myocyte generates a time-varying transmural pressure, or intracellular pressure. A mathematical model was formulated for a single myocyte, consisting of a fluid-filled cylindrical shell with axially arranged contractile filaments, to quantitate the fiber-fluid interaction. In this model, the intracellular pressure mediates the interaction between myofilament force, cell shortening, and the mechanical properties of the sarcolemma. Shortening of myofibrils, which are embedded in the fluid-filled myocytes, deforms the myocyte, thereby altering its transmural fluid pressure. This increase in transmural pressure counteracts fiber shortening, hence constituting an internal load to shortening. The shortening of the myocyte is accompanied by thickening, due to the incompressible nature of its contents. Consequently, the overall contractile performance of the cell is integrally linked to the generation of intracellular pressure. The model manifests a positive transmural pressure during shortening, but not without shortening. The pressure in the myocyte, therefore, is not a direct function of the force generated, but rather of shortening. Intracellular pressure was measured through a fluid-filled glass micropipette (5 mu ID) employing a servo-nulling pressure transducer in a standard micropuncture technique. Measured intracellular pressure in a contracting isolated skeletal myocyte of the giant barnacle is observed to be dynamically related to shortening, but not to tension without shortening. The relation between the force of contraction, cell shortening, and intracellular pressure was assessed during both isotonic and isometric contractions. The results support the prediction that isometric, or nondeforming, contractions will not develop intracellular pressure and identify a reason for relengthening of the myocytes during relaxation.

Ischemia-induced regional wall motion abnormality is improved after coronary angioplasty: demonstration by dobutamine stress echocardiography.

OBJECTIVES: The purpose of this study was to examine whether dobutamine stress echocardiography can detect reversal of ischemia-induced left ventricular regional wall motion abnormality immediately after percutaneous transluminal coronary angioplasty. BACKGROUND: Although angioplasty is routinely performed as a means of coronary revascularization, at present there is a question whether this results in an immediate improvement in ischemia-induced left ventricular regional function. METHODS: Thirty-five patients underwent dobutamine stress echocardiography 24 h before and 24 to 48 h after angiographically successful coronary angioplasty. Only patients with normal wall motion at rest were included. Dobutamine infusion was begun at 5 micrograms/kg per min and increased at 5-min intervals (10, 20, 30, 40 micrograms/kg per min). Echocardiographic images were stored into cine loops and analyzed off line with simultaneous comparison of images acquired at baseline, 5 micrograms/kg per min, peak infusion and recovery. Echocardiographic images were interpreted independently, without knowledge of other data, by two experienced cardiologists using the 16-myocardial segment model. RESULTS: Before angioplasty, dobutamine stress echocardiography induced wall motion abnormalities in 31 patients (88%). Wall motion score at peak dobutamine infusion improved in 28 (90%) of the 31 patients after angioplasty. Wall motion score at peak dobutamine infusion for the group improved from 20 +/- 3 before angioplasty to 17 +/- 2 after angioplasty (p < 0.001). There was no change in the rate-pressure product achieved for the group before and after angioplasty (20,038 +/- 6,415 beats/min x mm Hg before versus 20,775 +/- 5,435 after angioplasty, p = NS). Before angioplasty, dobutamine stress echocardiography induced angina in 13 patients (37%), whereas angina occurred only once after angioplasty. Electrocardiographic changes diagnostic of ischemia occurred seven times, all before angioplasty. CONCLUSIONS: We conclude that dobutamine stress echocardiography is an excellent method to demonstrate an immediate improvement in stress-induced regional left ventricular dysfunction in the distribution of the vessel undergoing successful angioplasty.

Isochronal behavior in left ventricular systolic pressure-wall thickness relations.

Regional left ventricular systolic pressure-thickness relations have been used to assess regional load-insensitive contractility with the assumption that they possess linear isochrones that are fundamental to the time-varying elastance model of global pressure-volume relations. We examined the shape and time-varying behavior of pressure-thickness isochrones in six open-chest canine preparations. Transmural wall thickening (sonomicrometry) and ventricular pressure were altered by abrupt preload alterations during control, dobutamine, and propranolol. In all dogs and interventions, linear isochrones (r2 mean +/- SE = 0.91 +/- 0.11) were found at 5-ms intervals. During control, linear isochrone slope rose monotonically from onset to end of systole. Thickness-axis intercepts also varied continuously in time, but peak intercept and maximal slope were asynchronous. Dobutamine caused a steeper earlier maximum slope and increased slope-intercept asynchrony. Propranolol reduced maximum slope and slope-intercept asynchrony. Isochronal data during early systole were better fitted to a parabolic than to the linear model; however, fits to linear and parabolic models were equally good near end of systole. Linear isochronal behavior exists in systolic pressure-thickness relations especially near end systole and is maintained during modest inotropic alterations.

Factors contributing to perforations resulting from laser coronary angioplasty: observations in an intact human postmortem preparation of intraoperative laser coronary angioplasty.

This investigation was designed to assess the potential use of laser coronary angioplasty as an intraoperative adjunct in the surgical treatment of ischemic heart disease. Among 17 postmortem hearts, simulated laser coronary angioplasty was performed at 53 sites with a No. 4F guiding catheter and 240 micron (200 micron core) quartz optical fiber. Perforation complicated laser coronary angioplasty in 33 (62%) of the 53 attempts. Most (n = 29) perforations were thermal; four were purely mechanical. Perforation sites were characterized by extensive calcific deposits (21 of 33 cases [64%] ) and the origin of a side branch (13 of 33 [39%] ). Excessive tortuosity of the extramural coronary artery contributed to arterial perforation in four cases, and precluded attempts to perform laser coronary angioplasty in two other cases. In 19 of the 53 attempts to perform laser coronary angioplasty, a high-frequency two-dimensional echocardiographic probe was used to image the coronary artery during antegrade manipulation of the optical fiber/guiding catheter and laser irradiation of the target arterial stenosis. Although perforation nevertheless occurred in 11 (58%) of 19 sites, only one mechanical perforation resulted; the remaining 10 were thermal. Characteristics of the perforation sites in this group were similar to those noted for the group as a whole. Experience with this model of laser coronary angioplasty indicates that even when access problems associated with percutaneous laser coronary angioplasty are obviated by a simulated intraoperative approach, perforation of the underlying coronary arterial wall continues to represent the "rate-limiting" complication of laser coronary angioplasty. Most perforations occurred in relation to calcific deposits, branch points, and tortuous coronary segments.(ABSTRACT TRUNCATED AT 250 WORDS)