Transesophageal Echocardiography and Transcranial Doppler Monitoring in Coronary Surgery without Cardiopulmonary Bypass: Preliminary Results

Neurologic and neuropsychologic dysfunctions remain important complications of coronary artery bypass grafting (CABG) [1]and have largely been attributed to adverse effects of cardiopulmonary bypass (CPB); nonetheless, patients undergoing CABG are intrinsically at a higher risk of developing neurologic injuries.Microemboli are thought to be one of the major causes of neurologic and neuropsychologic complications after CABG. Transcranial Doppler (TCD) and transesophageal echocardiography (TEE) monitoring became useful tools to detect and quantify emboli [2], and their occurrence has been particularly related to CPB techniques (bubble oxygenators and nonfiltered bypass) [3, 4, 5, 6]and also to specific operative events mainly attributable to aortic atheroma, such as insertion of aortic cannula, bypass onset and discontinuation, aortic cross-clamping and declamping [2, 7, 8]. Embolic signals (ES) have previously been described, by both methods, in most patients undergoing CABG [2, 3, 4, 5, 6, 7, 8]. The use of TEE has also been recommended to assess the severity of aortic atheroma during surgery [2].CABG without CPB may be safe, effective and can be an alternative technique, sometimes advantageous, for myocardial revascularization in certain conditions [9]. To our knowledge, TCD and TEE monitoring have never been described in CABG without CPB. Our aim is to determine the presence of microemboli by TEE and TCD monitoring during CABG without CPB.The protocol was approved by our institutional review board. Patient selection to CABG without CPB was based exclusively on technical aspects: patients with diagonal, left anterior descending and right coronary artery lesions were eligible for CABG without CPB, according to previously described criteria [9].After induction with midazolam, etomidate, fentanyl and pancuronium, anesthesia was maintained with fentanyl and isoflurane. Ascending, transverse and descending aortic examination was performed using multiplanar TEE with a 5-MHz probe immediately after the induction of anesthesia to assess the severity of the aortic atheroma.We then continuously monitored 6 patients (median age = 61 years; range 44–77; 3 males) undergoing routine CABG without CPB with TEE. The last 2 patients had also concomitant continuous middle cerebral artery TCD monitoring with a 2-MHz probe (EME-Companion) placed on the patient’s temple, adjusted to a depth of 4.5–6.0 cm, with an angle that gives the strongest Doppler signals, from the induction of general anesthesia to the end of the surgical procedure.TEE ES were defined as echogenic intraluminal signals not present in the same position on consecutive cross-sectional frames, whereas TCD ES were defined as high-amplitude (greater than flow velocity), unidirectional transient signals lasting less than 0.1 s, associated with a characteristic chirping sound, as described before [2]. The data were stored on disks and subsequently reviewed. We recorded all major intraoperative events, such as lateral aortic clamping and declamping, heart manipulation, hemodynamic changes and arrhythmias.All patients had at least one of the following potential risk factors for vascular diseases: hypertension (4 patients), cigarette smoking (3 patients), dyslipidemia (3 patients), diabetes mellitus (3 patients), alcohol consumption (3 patients), prior myocardial infarction (3 patients) and peripheral vascular disease (1 patient). None had a history of stroke or transient ischemic attack.Ascending, transverse and descending aortic examination after the induction of anesthesia showed aortic atheroma of grade I–III in all patients, i.e. mild to extensive intimal thickness with atheroma protruding less than 5 mm into the aortic lumen [10].We detetcted no ES during surgery by either method in the first 6 patients monitored; however, flow velocity and pulsatility index changes, mainly related to arrhythmias and heart manipulation, were frequently observed during TCD monitoring (fig. 1a).This is a pilot study with the first report of TCD or TEE monitoring in patients subjected to CABG without CPB.Embolus detection by TCD or TEE has been described in virtually all patients subjected to CABG with CPB [2, 3, 4, 5, 6, 7, 8, 11]and the number of ES has been related to neurologic [7, 8]and neuropsychologic [6, 8]outcome. We hypothesized that during CABG without CPB most of the embolic sources would not exist, despite the fact that heart manipulation and lateral aortic clamping [8]still remain as possible risk factors.We were not able to find ES in the first 6 patients monitored during CABG without CPB. One could argue that our patients had only grade I–III [10]aortic atheroma as detected by TEE, a fact that could explain the absence of emboli we found. Nonetheless, Barbut et al. [7, 12]could not confirm a clear relationship between the number of ES and the severity of the aortic atheroma, suggesting that they might be predominantly nonatheromatous. In addition, Jacobs et al. [11]also found ES related to CPB rather than to aortic manipulation. Furthermore TCD monitoring has some well-known technical limitations and pitfalls [13]that could account for the absence of ES in our patients; however, we have been able to detect ES in patients operated with CPB with the same technique (fig. 1b).CPB may not be the single cause of neurologic morbidity in patients after CABG: neurologic and neuropsychologic deficits may also be related to general and hemodynamic aspects of surgery [14]. We found changes in flow velocity and pulsatility index by TCD sonography in our patients related to arrhythmias and systemic hypotension. The role of TCD monitoring to evaluate cerebral blood flow during CPB remains controversial [15, 16]; nevertheless, TCD may be useful to monitor cerebral perfusion in patients subjected to CABG without CPB. The changes in flow velocity and pulsatility index observed in our patients during hemodynamic changes may contribute to define the complex and probably multifactorial genesis of neurologic morbidity after cardiac surgery.Although no firm conclusions can be drawn, our preliminary data suggest that CABG without CPB may reduce the frequency of emboli related to surgery. The impact of this finding and its relation to neurologic outcome deserve further studies.