Safety of Dobutamine Stress Echocardiography Supervised by Registered Nurse Sonographers

ORIGINAL ARTICLES

Safety of Dobutamine Stress Echocardiography Supervised by Registered Nurse Sonographers Merri L. Bremer, BSN, RN, RDCS, Kristi H. Monahan, RN, RDCS, Vicky L. Stussy, RN, Fletcher A. Miller, Jr., MD, James B. Seward, MD, and Patricia A. Pellikka, MD, Rochester, Minnesota

Dobutamine stress echocardiography (DSE) is widely used for the diagnosis and evaluation of coronary artery disease. Studies examining the safety of this technique typically have involved DSE supervised by physicians. At the Mayo Clinic, experienced registered nurse (RN) sonographers were trained to perform DSE under the direct supervision of a physician. To prove that the safety of DSE was not compromised with the change in supervision, we examined data from 1035 consecutive outpatient studies: 516 patients were monitored by

Dobutamine stress echocardiography (DSE) has become widely used for the diagnosis and evaluation of patients with coronary artery disease.1-3 The safety of DSE has been established in several studies. Mertes et al.4 studied 1118 patients who underwent DSE in a hospital setting; there were no serious complications in this group. Secknus and Marwick5 reviewed their experience in 3011 patients who underwent DSE; despite current use of more aggressive protocols, major complications were rare. DSE also has been reported to be safe when it is performed in an outpatient setting6 and in patients with left ventricular dysfunction.7 Major complications with DSE do occur; a multicenter study by Picano et al.8 described a series of 2949 DSE examinations. Nine major cardiac complications occurred: three cases of ventricular tachycardia, two cases of ventricular fibrillation, two cases of acute myocardial infarction, one case of prolonged myocardial ischemia, and one episode of severe, persistent hypotension. In 650 patients who underwent high-dose dobutamine stress testing, Poldermans et al.9 reported venFrom the Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic and Mayo Foundation. Presented in part at the Seventh Annual Scientific Sessions of the American Society of Echocardiography, Chicago, Ill., June 9 to 12, 1996. Reprint requests: Patricia A. Pellikka, MD, Mayo Clinic, 200 First St. SW, Rochester, MN 55905. Copyright © 1998 by the American Society of Echocardiography. 0894-7317/98 $5.00 1 0 27/1/89817

cardiologists or cardiology fellows (group 1) and 519 were monitored by trained RN sonographers (group 2). Risk factors, history of coronary artery disease, stress parameters, and complication rates were similar in both groups. In group 1, one patient experienced sustained ventricular tachycardia requiring treatment. In group 2, one patient experienced ventricular fibrillation during recovery and was successfully resuscitated. Outpatient DSE is safe when supervised by RN sonographers. (J Am Soc Echocardiogr 1998;11:601-5.)

tricular fibrillation in 1 patient, sustained ventricular tachycardia in 3 patients, paroxysmal atrial fibrillation in 8 patients, and nonsustained ventricular tachycardia in 12 patients. Lewis et al.10 recently reported 2 cases of acute myocardial infarction in a series of 650 patients who had DSE. In the initial Mayo Clinic experience in 1000 patients, as reported by Pellikka et al.,11 the complication rate was less than 1%. Complications included extension of a recent myocardial infarction in one patient, a transient ischemic attack in one patient, and sustained ventricular tachycardia in four patients. Most of the literature examining the safety of DSE has a common thread: The examinations were supervised by physicians. This approach is consistent with our previous practice. However, our utilization of DSE as a diagnostic method has grown rapidly in the past 5 years. DSE is relatively time consuming; the infusion and recovery periods must be supervised by qualified personnel. With time, it became clear that the physicians responsible for supervising DSE could be better utilized in other areas of the echocardiography laboratory. Thus the decision was made to train qualified registered nurse (RN) sonographers to fill the supervisory role. Several series in the literature, with a total of more than 100,000 patients, have examined paramedical supervision of exercise stress tests.12-17 The incidence of cardiac events appears to be no higher in these groups than with physician-supervised exercise stress tests. The literature examining the safety of pharmacologic stress testing when supervised by nurses is sparse. Recently, the feasibility of telemedicine inter601

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pretation of DSE in the emergency department was evaluated by Trippi et al.18 Patients being studied for chest pain and at low risk for ongoing myocardial infarction underwent DSE supervised by specially trained nurses. There were no major complications. To determine the safety of DSE when supervised by RN sonographers, we reviewed our initial experience of RN sonographer-supervised DSE and compared it with a retrospective group of examinations supervised by physicians. The objective was to determine whether outpatient DSE can be supervised safely by a trained RN sonographer with achievement of comparable end points.

METHODS All outpatient DSE studies performed before March 1, 1995, were supervised by cardiologists or advanced cardiology fellows (group 1). Beginning March 1, 1995, all outpatient DSE studies were supervised by RN sonographers (group 2). The study included 1035 consecutive outpatient studies from April 1, 1994, to February 1, 1996. In each case, dobutamine was administered according to a written protocol. Three experienced RN sonographers with stress testing or critical care background were trained to monitor and interpret electrocardiographic and echocardiographic stress data and to make decisions regarding test end points and administration of medication. A cardiologist was present in the immediate area to function as a resource and to respond if needed. RN Sonographer Training Three RN sonographers with stress echocardiography experience and either critical care or stress monitoring experience were chosen to fill the supervisory role. All had training in interpretation of 12-lead electrocardiograms and were certified in advanced cardiac life support (ACLS). The RN sonographers were trained to recognize test end points, symptoms, and complications. For each DSE, a written protocol was followed that included a stress protocol and guidelines for administration of medication. Each RN sonographer was required to monitor approximately 20 dobutamine examinations under the supervision of a physician before functioning independently. When training was completed, the RN sonographers supervised all DSE outpatient studies. A staff cardiologist was required to be present in the immediate area but not in the examination room when DSE was being performed. Dobutamine Infusion Protocol11 After peripheral intravenous access was obtained, dobutamine was infused intravenously beginning at a dose of 5 mg/kg per minute. At 3-minute intervals, the infusion rate was increased to 10, 20, 30, and 40 mg/kg per minute (maximal dose). When the target heart rate, defined as 85%

of the age-predicted maximum, was not achieved with the use of dobutamine alone, 0.5 to 1.0 mg of atropine was given at 1-minute intervals to a maximal total dose of 2.0 mg. The infusion was terminated when one of the following end points was reached: (1) achievement of target heart rate, (2) worsening regional wall motion abnormalities of moderate severity, (3) peak doses of dobutamine or atropine, (4) ventricular or supraventricular dysrhythmias, (5) echocardiographic changes ($1 mm ST elevation or $2 mm horizontal or downsloping ST depression), (6) angina of at least moderate severity, (7) intolerable symptoms, (8) hypotension (defined as a decrease in systolic blood pressure $20 mm Hg from the previous stage or systolic blood pressure ,90 mm Hg), or (9) hypertension (defined as systolic blood pressure .220 mm Hg or diastolic blood pressure .110 mm Hg). Blood pressure was measured with a sphygmomanometer at rest, in the last minute of each stage, and every 3 minutes during recovery. A 12-lead electrocardiogram was obtained at rest and every 1 minute during infusion. Monitoring was continued until the recovery heart rate was within 20 beats of the baseline heart rate. Echocardiographic images were recorded on videotape at rest, throughout the infusion, and 5 minutes into recovery and were digitized at rest, low-dose, prepeak (10 to 15 beats per minute below target heart rate), and peak infusion. Late recovery images also were obtained before dismissal of the patients. Statistical Methods Demographic data, medical history, risk factors, medications, cardiac history, electrocardiographic and echocardiographic data, hemodynamic data from the stress test, adverse effects, and complications were entered into a prospectively maintained database. Complications were defined as sustained ventricular tachycardia, cardiac arrest, stroke or transient ischemic attack, myocardial infarction, or death. Groups were compared by use of the chi square method. A value of p , 0.001 was considered statistically significant. Hemodynamic data were presented as mean 6 standard deviation.

RESULTS Patient Population Of the 1035 consecutive studies, 516 were in group 1 and 519 were in group 2. Eighty-eight percent of patients had a physical limitation that precluded exercise testing. Each group had similar numbers of patients by sex (group 1: 278 men, 238 women; group 2: 283 men, 236 women; p 5 0.833). The patients in group 1 were slightly older (mean age, 70 6 10 years vs 69 6 10 years) (p 5 0.2882). There were no significant differences between groups 1 and 2 in regard to indications for DSE (Table 1) or reason for use of pharmacologic stress (Table 2). Risk factors were similar in both groups, as was the incidence of previous myocardial infarction (Table 3).

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Table 1

Bremer et al. 603

Indication for DSE in 1035 patients

Table 3

Group 1 (n 5 516)*

Group 2 (n 5 519)†

Indication

No.

%

No.

%

p Value

Evaluation of known coronary artery disease Diagnosis of chest pain or dyspnea Preoperative assessment for noncardiac operation Other

147

28

191

37

0.004

156

30

145

28

0.416

186

36

160

31

0.075

27

5

23

4

0.548

*DSE supervised by cardiologist or cardiology fellow. †DSE supervised by RN sonographer.

Table 2 Reason for use of pharmacologic stress in 1035 patients who had DSE

Risk factors in 1035 patients who had DSE Group 1 (n 5 516)*

Group 2 (n 5 519)†

Factor

No.

%

No.

%

p Value

Hypertension Diabetes Current or past smoking Family history of CAD Hypercholesterolemia Previous MI Previous PTCA Previous CABG

322 97 334

62 19 65

333 112 311

64 22 60

0.361 0.455 0.169

199 273 139 64 81

39 53 27 12 16

218 301 128 74 97

42 58 25 14 19

0.249 0.100 0.403 0.380 0.202

CABG, Coronary artery bypass grafting; CAD, coronary artery disease; DSE, dobutamine stress echocardiography; MI, myocardial infarction; PTCA, percutaneous transluminal coronary angioplasty. *DSE supervised by cardiologist or cardiology fellow. †DSE supervised by RN sonographer.

Table 4 Stress parameters in 1035 patients who had DSE

Group 1 (n 5 516)*

Group 2 (n 5 519)†

Reason

No.

%

No.

%

p Value

Orthopedic limitation Peripheral vascular disease Lung disease Debility Other Clinical preference

213 129

41 25

194 123

37 24

0.199 0.626

53 35 32 54

10 7 6 10

39 40 43 80

8 8 8 15

0.119 0.566 0.196 0.018

Group 1 (n 5 516)*

Group 2 (n 5 519)†

Parameter

No.

%

No.

%

p Value

164

32

187

36

0.149

*DSE supervised by cardiologist or cardiology fellow. †DSE supervised by RN sonographer.

Administration of atropine Positive DSE Peak dose dobutamine, mg/kg per minute Mean peak heart rate, bpm

Test Parameters and End Points

*DSE supervised by cardiologist or cardiology fellow. †DSE supervised by RN sonographer.

Stress parameters (Table 4) and test end points (Table 5) were similar in both groups. Target heart rate, sometimes concurrent with another end point, was achieved in similar numbers of patients in both groups (422 [82%] patients of group 1 and 413 [80%] patients of group 2, p 5 0.369). Ischemia occurred in similar numbers of patients: 232 (45%) patients of group 1 and 243 (47%) of group 2 (p 5 0.548). Atrial fibrillation occurred in 13 (2.5%) patients of group 1 and 7 (1.4%) patients of group 2 (p 5 0.17). In group 1, the atrial fibrillation was transient in seven patients and sustained in six. In group 2, the atrial fibrillation was transient in three patients and sustained in four. Two patients in group 1 and one patient in group 2 were hospitalized for treatment of sustained dobutamine-induced atrial fibrillation. Nonsustained ventricular tachycardia occurred in 41 (8%) patients in group 1 and 34 (7%) patients in group 2 (p 5 0.387). There were no patients with myocardial infarction, stroke, transient ischemic attack, or death. In group

232 45 36 6 11

243 47 34 6 9

0.548 0.0005

132 6 15

127 6 16

,0.0001

1, one patient experienced sustained ventricular tachycardia, which was successfully treated with administration of esmolol. In group 2, one patient experienced ventricular fibrillation during early recovery; this patient was successfully resuscitated and hospitalized. DSE in this case was markedly positive, and subsequent cardiac catheterization revealed severe triplevessel coronary artery disease. In summary, the complication rates between the two groups were similar (group 1 5 0.2%, group 2 5 0.2%; p 5 0.997).

DISCUSSION DSE is widely used for the assessment and evaluation of patients with known or suspected coronary artery disease.1-3 The safety of DSE has been described in multiple studies.4-11 However, no previously published studies specifically address the safety of DSE when supervised by nonphysicians. The supervision

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Table 5 Test end points in 1035 patients who had DSE Group 1 (n 5 516)*

Group 2 (n 5 519)†

End point

No.

%

No.

%

p Value

Achievement of THR RWMA Peak dose Ventricular dysrhythmia Supraventricular dysrhythmia ECG changes Angina Intolerable symptoms Hypotension Hypertension

391 21 33 11

76 4 6 2

378 44 19 12

73 8 4 2

0.279 0.003 0.044 0.844

12

2

3

0.6

0.019

6 13 23 3 3

1 3 4 1 1

2 12 30 13 6

0.4 2 6 3 1

0.153 0.828 0.334 0.012 0.319

DSE, Dobutamine stress echocardiography; ECG, electrocardiogram; RWMA, regional wall motion abnormalities; THR, target heart rate. *DSE supervised by cardiologist or cardiology fellow. †DSE supervised by RN sonographer.

of stress tests by paramedical personnel is not a new practice. In 1979, the American Heart Association (AHA) revised its exercise testing guidelines to allow for supervision of stress tests by experienced health care personnel.19 The 1990 ACP/ACC/AHA Task Force Statement on Clinical Competence in Exercise Testing agreed that stress testing in selected patients (excluding those with severe angina pectoris, possible unstable angina pectoris, exertional left ventricular dysfunction, or arrhythmia) could be safely performed by properly trained paramedical staff working under the direct supervision of a physician.20 The 1997 ACC/AHA Guidelines for Exercise Testing again recommended that selected patients may be safely monitored by properly trained paramedical professionals.21 In our study, two groups of patients undergoing DSE were compared. The patient population in the group of patients supervised by nurses (group 2) had risk factors and cardiac history similar to those in a group of patients supervised by physicians (group 1). Test end points and the percentage of patients achieving target heart rate also were comparable. The mean peak heart rate in group 1 (132 6 15 bpm) was slightly higher than that in group 2 (127 6 16 bpm). The peak dose of dobutamine in group 1 (36 6 11 mg/kg per minute) was also slightly higher than that in group 2 (34 6 9 mg/kg per minute). Although both of these differences were statistically significant (p , 0.0001 and 0.0005, respectively), the actual numbers differ only slightly; therefore the differences are of doubtful clinical significance. The percentages of DSE examinations in each

group that were positive for ischemia also were similar. The complication rate was low in both groups (0.2%) and consistent with the rate in previous reports.3-11 Only one patient in each group experienced a life-threatening complication. There were no relevant differences between the groups in regard to either safety or effectiveness of DSE as a diagnostic method. Examination of our data supports our decision to allow trained RN sonographers to supervise dobutamine stress tests. Dedicated personnel can offer more timely and consistent supervision of DSE. However, the current era of cost containment makes it challenging for a high-volume echocardiography laboratory to dedicate physician time solely to the supervision of DSE. Using the physician for only the infusion period was also problematic; in our laboratory, physicians typically are assigned to full-time interpretive and oversight duties. Requiring personal supervision of all DSE examinations in addition to these duties had a negative impact on both patient and staff waiting time. It became clear that the physicians responsible for supervising DSE must be better utilized. Therefore, RN sonographers were trained to perform DSE under the direct supervision of a physician. The RN sonographers were first trained to supervise DSE in the outpatient population, under the assumption that outpatients would be less prone to complications. Subsequently, RN sonographers assumed supervision of both outpatient and inpatient DSE examinations. The continued effectiveness of DSE and the low incidence of complications reflect the safety of the procedure itself and the conscientious supervision of DSE by carefully trained RN sonographers. Conclusions In this large population undergoing DSE, two similar groups of patients supervised by RN sonographers and physicians were compared. The overall complication rate was low, with one serious complication in each group. Stress testing end points and induction of ischemia were similar in both groups. Outpatient DSE can be performed safely when supervised by a trained RN sonographer. REFERENCES 1. Sawada SG, Segar DS, Ryan T, et al. Echocardiographic detection of coronary artery disease during dobutamine infusion. Circulation 1991;83:1605-14. 2. Segar DS, Brown SE, Sawada SG, Ryan T, Feigenbaum H. Dobutamine stress echocardiography: correlation with coronary lesion severity as determined by quantitative angiography. J Am Coll Cardiol 1992;19:1197-202.

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3. Geleijnse ML, Fioretti PM, Roelandt JR. Methodology, feasibility, safety and diagnostic accuracy of dobutamine stress echocardiography. J Am Coll Cardiol 1997;30:595-606. 4. Mertes H, Sawada SG, Ryan T, et al. Symptoms, adverse effects, and complications associated with dobutamine stress echocardiography: experience in 1118 patients. Circulation 1993;88:15-9. 5. Secknus MA, Marwick TH. Evolution of dobutamine echocardiography protocols and indications: safety and side effects in 3,011 studies over 5 years. J Am Coll Cardiol 1997;29:1234-40. 6. Gordon BM, Mohan V, Chapekis AT, et al. An analysis of the safety of performing dobutamine stress echocardiography in an ambulatory setting. J Am Soc Echocardiogr 1995;8:15-20. 7. Cornel JH, Balk AH, Boersma E, et al. Safety and feasibility of dobutamine-atropine stress echocardiography in patients with ischemic left ventricular dysfunction. J Am Soc Echocardiogr 1996;9:27-32. 8. Picano E, Mathias W Jr, Pingitore A, Bigi R, Previtali M, on behalf of the Echo Dobutamine International Cooperative Study Group. Safety and tolerability of dobutamine-atropine stress echocardiography: a prospective, multicentre study. Lancet 1994;344:1190-2. 9. Poldermans D, Fioretti PM, Boersma E, et al. Safety of dobutamineatropine stress echocardiography in patients with suspected or proven coronary artery disease. Am J Cardiol 1994;73:456-9. 10. Lewis WR, Arena FJ, Galloway MT, Bommer WJ. Acute myocardial infarction associated with dobutamine stress echocardiography. J Am Soc Echocardiogr 1997;10:576-8. 11. Pellikka PA, Roger VL, Oh JK, Miller FA, Seward JB, Tajik AJ. Stress echocardiography, II: dobutamine stress echocardiography: techniques, implementation, clinical applications, and correlations. Mayo Clin Proc 1995;70:16-27. 12. Lem V, Krivokapich J, Child JS. A nurse-supervised exercise stress testing laboratory. Heart Lung 1985;14:280-4.

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