Asian Cardiovasc Thorac Ann 2003;11:139-142
© 2003 Asia Publishing EXchange Ltd
Transesophageal Echocardiography in Hypotensive Post-Coronary Bypass Patients
Harpreet Wasir, MCh,
Yatin Mehta, FRCA1,
Yugal K Mishra, MCh,
Sameer Shrivastava, DM2,
Sanjay Mittal, DM2,
Naresh Trehan, MD
Department of Cardiovascular Surgery
1 Department of Anaesthesia
2 Department of Cardiology, Escorts Heart Institute and Research Centre, New Delhi, India
For reprint information contact: Yatin Mehta, FRCA Tel: 91 11 6825000/6825001 Fax: 91 11 6825013 email: yatinmehta{at}hotmail.com Department of Anaesthesia, Escorts Heart Institute and Research Centre, Okhla Road, New Delhi 110 025, India.
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ABSTRACT
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The utility of transesophageal echocardiography in the evaluation of hypotension in the postoperative period after coronary artery bypass was assessed in 126 patients in the intensive care unit. There were 86 men and 40 women, with a mean age of 58.3 years. The indication for transesophageal echocardiography was hypotension refractory to conventional treatment. Valuable diagnostic information was obtained in 103 patients (82%). Based on the echocardiographic findings, 24 patients (19%) underwent urgent surgical intervention. The mean time required to obtain a diagnosis was 9.6 ± 2.8 min. No significant complications were noted. Our experience suggests that transesophageal echocardiography is highly specific in diagnosing the cause of postoperative hypotension, thus preventing unnecessary surgical intervention and facilitating decision making in cardiac surgical emergencies.
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INTRODUCTION
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Hypotension after a cardiac operation is a clinical emergency that necessitates immediate action.1 Evaluation of the electrocardiogram (ECG), chest radiograph, and hemodynamic data often fails to provide sufficient information to establish and treat the cause. Conventional transthoracic echocardiography (TTE) has limitations in such patients.2,3 Reflection of the ultrasound beam by the air-blood interface in the mediastinum, hyperinflation of the lungs due to mechanical ventilation, and chest bandages prevent adequate precordial imaging. Transesophageal echocardiography (TEE) circumvents these problems, allowing evaluation of the heart and its structures, and it has emerged as an important diagnostic technique in this subgroup of patients.4,5 We assessed the utility and safety of TEE in patients who had hypotension after coronary artery bypass grafting (CABG).
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PATIENTS AND METHODS
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From October 2001 to June 2002, 3,240 patients underwent CABG at our institution; off-pump CABG was performed in 2,122 (65%) of them. Any patient in the intensive care unit who met the following criteria was subjected to TEE: hypotension unresponsive to conventional treatment (infusion of fluids, administration of inotropics); hypotension associated with ECG changes suggestive of ischemia, infarction, or tamponade; persistent hypotension after adequate volume replacement, associated with significant chest tube drainage (bleeding) or controlled bleeding with a positive or doubtful finding on chest radiography; hemodynamic instability and inconclusive or negative TTE findings. All patients were monitored by an arterial catheter, a central venous line, and a pulmonary artery catheter, for continuous cardiac output and hemodynamic assessment. The first 24 patients in whom TEE was performed had initially undergone TTE using a Sonos 5500 ultrasound system (Hewlett Packard, Inc., Andover, MA, USA) with 2.5–3.5-MHz imaging probes. In each case, TTE was inadequate or partially diagnostic, thereby leading us to set a departmental protocol for obtaining a TEE examination in all patients with hemodynamic instability. The TEE studies were carried out in patients who were intubated.
All TEE investigations were performed by a senior consultant cardiologist with substantial knowledge and experience of the procedure. None of the patients had any ongoing arrhythmias or esophageal pathology contraindicating TEE. Studies were performed with a Sonos 5500 using a 5-MHz omniplane probe. Unless the patient was already sedated, intravenous midazolam (2–4 mg) was used for adequate sedation in the intubated patient. All studies were recorded on videotape for subsequent review and analysis. Specific causes looked for were collection, clot, tamponade, evidence of hypovolemia, new regional wall motion abnormalities (RWMA), reduction in ejection fraction (EF), and new valvular pathology. Findings were compared with the routine detailed preoperative echocardiographic findings.
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RESULTS
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Transesophageal echocardiography was carried out in 126 patients: 86 men and 40 women, with a mean age of 58.3 years. The probe was inserted by blind intubation in 96 patients (76%), and under direct vision using a laryngoscope in 30 (24%). No clinically significant complication was noted. Minor complications were seen in 17 patients (13%), benign rhythm disturbances in 7 (6%), a transient increase in heart rate and blood pressure in 8 (6%), and minor pharyngeal bleeding in 2 (2%). There was no mortality in this series. The mean time from probe insertion to diagnosis was 9.6 ± 2.8 min. There were 46 patients who underwent TEE after inconclusive or incomplete TTE results.
Normal TEE findings were observed in 23 patients (18%). Eight patients (6%) had echocardiographic evidence of hypovolemia (reduced end-diastolic volumes in both left and right ventricles) despite volume replacement that was considered adequate. These patients had normal cardiac indices (2.5–4.2 L•min-1•m-2), central venous pressures (10–12 mm Hg), pulmonary artery wedge pressures (10–12 mm Hg), and mean pulmonary artery pressures (18–24 mm Hg); all responded to volume replacement.
Forty-seven patients (37%) showed TEE evidence of pericardial collection without tamponade. Cardiac output and cardiac index were borderline, and hypotension was partially corrected by optimizing the inotropics and volume replacement. Of these 47 patients, 15 had no significant postoperative chest tube drainage but the cardiothoracic ratio was increased by a mean of 0.35; none required reexploration on the basis of TEE findings. Five of these 47 patients were found to have small clots abutting the right atrium and anterior to the right ventricle, which were not detected by routine TTE; they were also managed conservatively. All of these patients had an uneventful postoperative course.
In 24 patients (19%), TEE was carried out because of hypotension associated with ECG changes suggestive of ischemia, infarction, or tamponade, which were observed on the monitor; a 12-lead ECG was subsequently obtained. There was a mean ST-segment elevation of 1.8 mm in the lateral chest leads in 13 patients, and 11 had a mean ST-segment elevation of 1.96 mm in the inferior leads; TEE did not reveal any new RWMA compared to the detailed preoperative echocardiography, and there was no change in EF. They were stabilized by optimizing their inotropics and vasodilators. We strictly followed a departmental protocol that considered any new RWMA or decrease in EF as a significant finding needing urgent surgical intervention, especially as 90% of CABG operations in our institution are performed off pump and we have a high index of suspicion for graft occlusion. Creatine kinase-MB levels were normal in 21 (88%) of the 24 patients with ECG changes, and elevated in 3. Retrospectively, it was observed that they had diffuse coronary artery disease with poor-quality target vessels correlating to a change in the respective ECG lead. None of these patients underwent a surgical intervention.
The ECG was positive and new RWMA were observed on TEE in 6 patients (5%). The dosage of inotropics was increased, but they continued to show evidence of low cardiac output. All underwent immediate surgical reexploration. In 3 patients with TEE evidence of a severely hypokinetic anterior region, the mid and basal septa were found to have inadequate flow from a left internal mammary artery graft, on intraoperative Doppler flow studies, thus requiring an additional distal vein graft to the left anterior descending artery. In 2 patients, there was severe hypokinesia of the lateral wall, with decreased EF. Reexploration showed kinking of the vein graft to the second obtuse marginal in one case, and a blocked radial artery graft in the other. The vein graft was revised in the first patient, and the second patient had a separate vein graft anastomosed. In one patient, the right coronary artery graft was blocked, which was indicated by significant ST-segment changes in the inferior leads; TEE showed an akinetic inferior wall with new onset of moderate mitral regurgitation. The patient was reexplored immediately and the right graft was revised. All 6 patients did well after reexploration and had an uneventful postoperative period.
Eighteen patients (14%) showed TEE evidence of pericardial collection with tamponade. Chest radiography was not diagnostic for significant pericardial effusion, nor was there any evidence of a paradox on the arterial pressure trace. All 18 patients had borderline cardiac indices and initially responded to volume infusion and inotropics. They underwent reexploration that yielded positive findings. All did well postoperatively. In 7 of these patients, TTE had not revealed any tamponade; the other 11 underwent TEE only.
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DISCUSSION
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A prompt diagnosis is required for any hemodynamic instability in cardiac surgical patients in the postoperative period. The utility and superiority of TEE for this assessment has been well demonstrated.6–10 It has been shown to be superior to TTE in the evaluation of an unstable patient.5,11 In this series, TEE clearly identified the cause of hemodynamic compromise in 103 of 126 patients (82%). In the majority (79/103; 77%), it prevented undue reexploration on the basis of inconclusive TTE findings. In our practice, TEE is the first-line diagnostic technique when there is any suspicion of graft compromise (as indicated by ECG changes in particular leads), pericardial collection, or any other etiology not responding to basic resuscitation measures. On the TEE findings, patients underwent reexploration without delay, which saved further myocardial insult due to ischemic changes.
Without TEE, the 6 patients with positive ECG changes would have suffered perioperative myocardial infarction which might have resulted in some mortality. There have been concerns about graft patency in off-pump CABG, and unless the surgical team has an open mind assisted by TEE findings of new RWMA, these concerns may prove well-founded.12 In this series, the incidence of perioperative myocardial infarction was only 3/126 (2.4%).
The 8 patients with hypovolemia detected by TEE would not have been diagnosed on the basis of hemodynamic parameters, as they had adequate filling pressures. Fortunately, reexploration and other unnecessary interventions such as increased inotropics and intraaortic balloon pumping were avoided because of the TEE findings. Reichert and colleagues7 showed the importance of TEE in determining the cause of hypotension in 91% of cases in which hypovolemia, tamponade, or wall motion abnormality was responsible. In 10% of their patients, left ventricular filling pressures were raised although TEE revealed evidence of hypovolemia. The correlation between left ventricular filling pressures and volumes is often impaired after CABG.13,14 Atrial pressures are affected by the compliance of the ventricles and can be high in a noncompliant system despite the fact that the patient would benefit from volume infusion. A TEE study reveals the immediate status of left ventricular preload and contractility, which might not be apparent from pulmonary artery pressure tracing.
Many studies now reflect the inconsistency of TTE compared to TEE, especially in the period immediately after cardiac surgery.3,10,15 In general, TEE is a safe procedure in experienced hands, with few complications. No major complication was encountered in our series, and most probe insertions were technically easy to perform. However, a lot depends on operator skill and experience, and it is most important never to force the probe during insertion. Two-dimensional TEE is of unequivocal importance in determining a definite diagnosis when other diagnostic methods prove inadequate, and it facilitates timely surgical intervention when necessary. As its importance becomes established, TEE will be used more liberally and become an indispensable diagnostic tool in cardiac intensive care units.
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ABSTRACT
INTRODUCTION
