Norbert P. de Bruijn

The utility of transesophageal echocardiography and Doppler color flow imaging in patients undergoing cardiac valve surgery

To assess the value of intraoperative transesophageal echocardiography during cardiac valve surgery, 154 consecutive patients who had a valve operation in conjunction with pre- and postcardiopulmonary bypass transesophageal imaging were studied. Prebypass imaging yielded unsuspected findings that either assisted or changed the planned operation in 29 (19%) of the 154 patients. Imaging immediately after bypass revealed unsatisfactory operative results that necessitated immediate further surgery in 10 (6%) of the 154 patients. Postbypass left ventricular dysfunction, prompting administration of inotropic agents, was identified in 13 patients (8%). Transesophageal echocardiography proved most useful when both two-dimensional and Doppler color flow imaging were employed in patients undergoing a mitral valve operation, where surgical decisions based on echocardiographic results were made in 26 (41%) of 64 cases. Postbypass echocardiographic findings identified patients at risk for an adverse postoperative outcome. Of 123 patients whose postbypass valve function was judged to be satisfactory, 18 (15%) had a major postoperative complication and 6 (5%) died, whereas of 7 patients with moderate residual valve dysfunction, 6 (86%) had a postoperative complication and 3 (43%) died (p less than 0.05 for both). Likewise, of 131 patients with preserved postbypass left ventricular function, 12 (9%) had a major complication and 7 (5%) died, whereas of 23 patients with reduced ventricular function, 17 (73%) had a postoperative complication and 6 (26%) died (p less than 0.05 for both). These data indicate that intraoperative transesophageal echocardiography is useful in formulating the surgical plan, assessing immediate operative results and identifying patients with unsatisfactory results who are at increased risk for postoperative complications.

Perioperative evaluation of regional wall motion by transesophageal two-dimensional echocardiography.

With the introduction of transesophageal two-dimensional echocardiography into the operating room the subject of regional left ventricular (LV) wall motion presents itself to the clinical anesthesiologist. Overwhelming evidence of the sensitivity of regional wall motion as a marker of regional myocardial perfusion suggests that it will find a place for the monitoring of patients at risk for ischemia. In this review, we define regional wall motion, normal and abnormal, and examine its relationship to regional myocardial perfusion. The practical aspects of recognizing, describing, and treating regional wall motion abnormalities will be addressed, with emphasis on transesophageal two-dimensional echocardiographic techniques. The development of transesophageal imaging techniques has taken place only during the past 10 yr. Frazin and co-workers in 1976 reported the use of an M-mode esophageal transducer for patients in whom conventional imaging techniques failed (1). Generally, transthoracic images are technically poor when excessive adipose or lung tissue lies between the external transducer and the heart. Thus, the esophagus provided better access to the heart. Matsumoto and co-workers employed esophageal transducers in subjects performing supine bicycle exercise and also in anesthetized patients (2,3). The incorporation of the transducer into a flexible gastroscope from which the fiber optics had been removed permitted the operator to direct the ultrasound beam in multiple planes from any position within the esophagus. With the development of miniature phased array transducers, excellent two-dimensional imaging became feasible from the esophagus. Schluter and co-workers reported their use of such a transducer in 1982 (4), and it is this type of esophageal transducer that has been used by most investigators and that has produced the images presented in this review.

Heparin-free cardiopulmonary bypass : first reported use of heparinoid (org 10172) to provide anticoagulation for cardiopulmonary bypass

Org 10172 provided adequate anticoagulation for this patient. An excellent correlation between anti-factor Xa activity and ACT was observed at the doses used for CPB. If high-dose Org 10172 is used, these data suggest that it may be possible to circumvent the measurement of anti-factor Xa activity by using the ACT as an index of this heparinoids anticoagulant effect. Because postoperative bleeding may be excessive, however, development of a method of reversal of Org 10172 is desirable. Although the optimal ACT, dose, plasma concentration, and means of reversal (e.g., protamine vs. heparinase) remains to be determined, heparinoids provide an alternate means of anticoagulation for CPB in patients unable to receive standard heparin.

Intraoperative Transesophageal Color Flow Mapping: Initial Experience

Transesophageal Doppler color flow mapping (TEDCFM) is a new ultrasound modality now being developed. It provides a convenient, noninvasive way to image cardiac anatomy and intracardiac blood flow that is applicable to intraoperative use. We describe its use in one normal subject and seven cardiac surgical patients. Blood flow characteristics as visualized by TEDCFM are described for these patients. Transesophageal Doppler color flow mapping provided specific information about the presence, site, and severity of mitral regurgitation, aortic regurgitation, and interatrial shunting. Paravalvular leak was detected in one patient after mitral valve replacement. The intimal tear of a type 1 aortic dissection was located with positive identification of the true and false lumina. A high incidence of mild asymptomatic mitral regurgitation was found in patients undergoing coronary artery bypass grafting (CABG).

Hemodynamic effects of esmolol in chronically β-blocked patients undergoing aortocoronary bypass surgery

The hemodynamic effects of esmolol were studied in 40 patients scheduled for elective coronary artery surgery to determine whether the administration of esmolol in chronically beta-blocked patients would result in additional attenuation of sympathetically mediated hemodynamic stress responses to noxious stimuli. Patients were randomly assigned to receive IV infusions of esmolol or 5% dextrose in water (D5W). All received their regular dose of beta-adrenergic blocker within 6 hr of surgery and were anesthetized with diazepam, pancuronium, and enflurane. Increases (greater than 25% above baseline) in systolic blood pressure were treated with sodium nitroprusside (SNP). Esmolol was started before induction of anesthesia and continued until 5 min after maximal sternal spread. There were no statistically significant differences between the esmolol and control groups in any hemodynamic parameter during induction, intubation, skin incision, and sternotomy. Only at 5 min after maximal sternal spread was there a statistically significant lower systolic blood pressure in the esmolol-treated group. However the incidence and magnitude of SNP use in the control group was significantly (P less than 0.05) greater. Thus, the lower blood pressure, in the absence of changes in systemic vascular resistance, cardiac index, heart rate, and pulmonary capillary wedge pressure points toward a decrease in myocardial contractility, suggesting that the addition of esmolol to chronically used beta-blockers resulted in an additional negative inotropic effect. We conclude that in patients with coronary artery disease in whom chronic beta-blocker therapy is continued until the time of surgery, esmolol does not further attenuate the heart rate response but does attenuate the increase in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hypothermia on median nerve somatosensory evoked potentials

Median nerve somatosensory evoked potentials (SEP) were monitored in ten patients undergoing cardiac surgery with hypothermic cardiopulmonary bypass (CPB). Anesthesia was induced and maintained with sufentanil, oxygen, and pancuronium. Esophageal, nasopharyngeal, rectal, and blood temperatures were continuously monitored. SEPs were recorded before induction of anesthesia, after induction, and during cooling and rewarming on CPB. There was a strong negative correlation between SEP latencies and temperature (except rectal) (r = -.91, P < .001). for cortical latency and esophageal temperature. A decrease in esophageal temperature of 1 degrees C resulted in an increase in SEP latency of 1 ms. There was also a weak positive correlation between evoked potential amplitude and temperature (r = .19) for cortical amplitude and esophageal temperature.

Alterations in somatosensory evoked potentials associated with inadequate venous return during cardiopulmonary bypass

N EUROLOGIC COMPLICATIONS following cardiopulmonary bypass (CPB) have long been recognized and continue to contribute to morbidity following heart surgeryJ Central nervous system compromise might be detected earlier by appropriate neurophysiologic monitoring. Evoked potential monitoring has been successfully used to predict the incidence of and to prevent neurologic deficits after various noncardiac surgical procedures, including scoliosis correction and intracranial procedures) A case is reported of reversible cerebral dysfunction detected by somatosensory evoked potential (SEP) monitoring in a patient undergoing coronary revascularization.

Transesophageal Doppler color flow mapping: initial experience

As has been explained elsewhere in this book (Chapter 4.1), esophageal transducers were developed by echocardiographers who were frustrated in their efforts to obtain images through the chest wall in obese and emphysematous patients. The avoidance of adipose tissue, lung and ribs, intervening between the transducer and the heart by positioning the transducer in the esophagus immediately behind the heart results in much better definition of cardiac structures (Fig. 1). The left atrium and left ventricle, are particularly well imaged from an esophageal approach with conventional Doppler echocardiography or Doppler color flow mapping (DCFM). A further advantage of the esophageal approach becomes apparent with Doppler studies when the esophageal transducer is positioned behind the left atrium and directed towards the cardiac apex. This provides a four chamber long axis view in which the ultrasound beam is aligned almost parallel with the majority of normal intracardiac blood flow and provides excellent conditions for the detection of abnormal flow across the mitral valve. Esophageal approaches are also useful for evaluation of flow across the aortic valve. Although transesophageal M-mode and 2D transducers have been available for a number of years [1, 2, 3], the use of Doppler techniques with the esophageal approach is a relatively new development. In 1982, Schluter and coworkers first reported the use of 2-dimensional imaging with a phased array transducer in 26 awake patients, leading several other investigators to explore the clinical value of transesophageal imaging [4]. Later Schluter et al. [5] demonstrated, using conventional pulsed Doppler echocardiography, that the sensitivity and specificity of transesophageal imaging for the detection of mitral regurgitation is far superior to that of the transthoracic approach. They evaluated six patients with competent mitral valves and 12 patients with angiographically proven mild-to-moderate mitral regurgitation. The transesophageal approach detected regurgitation in 100% of cases whereas the transthoracic approach was successful in only 58%.

Quantitative Analysis of 2D Echocardiography Images

Two-dimensional cardiac imaging provides an enormous amount of information that can be used to derive quantitative information about cardiac function. A videotape recording is made at a rate of 30 frames per second, so that, for a heart beating at a rate of 60 times per minute, one cardiac cycle amounts to 30 frames of video information. On each video stop-frame, the myocardium is defined by two lines: the epicardium and the endocardium. Therefore, at each stage of the cardiac cycle, two things can be identified: the size of the cavity contained by the endocardium and the thickness of the myocardial wall. We can compare the differences between diastole and systole, and thus estimate how much blood has been ejected or measure how much wall thickening has occurred, but this is information about regional function, derived from a single two-dimensional view of the heart. Global function can be assessed only by considering several views of the left ventricle with echocardiography, unless one can select a view that is fairly representative of global function. It is the echocardiographer who can make the first mistake, therefore, by his selection of an inappropriate 2D view, but having decided upon which part of the left ventricle should be examined, a videotape recording is then made, spanning several cardiac cycles.

Development of Transesophageal Echocardiography

Technology using reflected sound waves to localize objects was initially developed for naval sonar but expanded in many directions. The use of ultrasound for imaging dynamic cardiac structures was first introduced in 1954 by Edler and Hertz [1] and has since revolutionized diagnostic approaches to cardiac disease. Ultrasound waves reflected from cardiac surfaces can be presented as dots or moving lines (M-mode echocardiography), but a more understandable representation of the heart is provided when the reflected ultrasound waves are oriented in two dimensions to produce an image resembling a cross section of the heart (2D echocardiography). Transmission of ultrasound into living tissue has proved to be safe, and comfortable for patients; thus since 1954 many refinements have taken place to explore its full potential in clinical and research use. A variety of hand-held transducers capable of emitting and receiving ultrasound have been used by cardiologists. The standard technique requires that the transducer is placed on the skin surface overlying the heart. Since ultrasound frequencies are not transmitted well through air, contact between the skin and the transducer is maintained by the use of a coupling gel applied liberally to the skin. The heart lies at a variable depth within the thorax and thus cardiac imaging is often facilitated by positioning the patient on his left side so that the heart falls against the left anterior chest wall. With all the various improvements in equipment, successful cardiac imaging still requires first of all that the heart lie within the field of view of the ultrasound transducer, and it is essentially this particular aspect of imaging that led to the development of esophageal transducers.