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Sally Richards is a lecturer at Yale University School of Nursing.
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In 1998, an estimated 553 000 coronary artery bypass graft procedures and 89 000 valve procedures were performed in the United States.3 The length of stay in the hospital after surgery has become shorter as cost constraints dictate earlier discharge from healthcare facilities. With the declining length of stay, cardiac monitoring may need to expand from the hospital to the home. We just completed a study in which we used intermittent loop recorders, a type of ambulatory electrocardiographic (ECG) device, to examine the incidence, timing, and symptoms of and risk factors for postoperative atrial fibrillation. In this article, we describe ambulatory ECG, discuss how we used this technique to monitor for atrial fibrillation after cardiac surgery, and present examples of 2 patients whose atrial fibrillation was detected by using ambulatory ECG.
AMBULATORY ECG MONITORING
Ambulatory ECG monitoring is used primarily to determine the association between a patient’s transient symptoms and cardiac arrhythmias.4 In 1957, Norman Holter introduced the first portable device to record ECGs. Since then, technological advances have greatly expanded the applicability of these devices. Ambulatory ECG devices can be classified into 2 broad categories: continuous and intermittent.5 Continuous recorders, also known as Holter monitors, are typically used for 24 to 48 hours to investigate ECG events likely to occur within that time frame. Intermittent recorders may be used for longer periods (weeks to months) to provide briefer, intermittent recordings to investigate events that occur infrequently.
Two types of intermittent recorders are available: loop and event. Loop recorders, so called because of their loop memory, are worn continuously and are activated by patients in the event of symptoms such as palpitations. Recently, an autoloop function has been added to some loop recorders. This mechanism allows the recorder to store the ECG tracing to memory automatically when the heart rate is outside the preprogrammed ranges. Event recorders, which lack a memory function, are held to the chest by patients and activated immediately after the onset of symptoms. The advantage of loop recorders is their ability to capture the rhythm that occurs before the patient activates the record function; the advantage of event recorders is that they are smaller and do not have to be worn continuously. For both types of intermittent recorders, the recorded ECG is transmitted over the telephone to a receiving center and is analyzed by a healthcare provider.
Newer loop recorders can be implanted just under the skin in the upper part of the chest for longer-term monitoring.6 The Reveal Insertable Loop Recorder manufactured by Medtronic (Minneapolis, Minn) is inserted in about 15 minutes by using local anesthesia and can remain in place for up to 14 months. It is smaller than a package of chewing gum and has electrodes on its surface that detect the cardiac rhythm. If symptoms suggestive of atrial fibrillation occur, a hand-held activator is placed over the loop recorder to store the ECG. The patient then must go to a healthcare provider who has a device that will retrieve the ECG for analysis. Once a diagnosis is made, the device can be removed as easily as it was inserted.
The American College of Cardiology and the American Heart Association, in collaboration with the North American Society for Pacing and Electrophysiology, recently published guidelines for ambulatory ECG.5,7 Traditional use of ambulatory ECG for detection of arrhythmias has expanded as a result of technological advances.
Ambulatory ECG is used in adults (Table 1
) to detect arrhythmias in symptomatic patients, determine prognosis on the basis of detected arrhythmias or heart rate variability in asymptomatic patients, assess the efficacy of antiarrhythmic therapy, assess the function of pacemakers and implantable cardioverter-defibrillators, and detect myocardial ischemia. Use of ambulatory ECG in children is presented in the guidelines5,7 but is beyond the scope of this article.
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Although routine use of ambulatory ECG is not recommended for patients recovering from cardiac surgery, we thought that ambulatory ECG could be useful in our examination of the incidence, timing, and symptoms of and the risk factors for atrial fibrillation in patients discharged from the hospital after cardiac surgery. In our study, patients wore the King of Hearts Express recorder, manufactured by Instromedix (San Diego, Calif), continuously for 2 weeks after discharge from the hospital after cardiac (coronary artery bypass graft or valve) surgery.
Recorder
The King of Hearts Express recorder (Figure 1) is a small pager-size loop recorder that attaches with 2 paste-on electrodes and can be clipped to a belt, put into a shirt pocket, or worn around the neck like a pendant. It is designed for long-term ambulatory ECG monitoring and is especially useful for documenting rhythms associated with elusive symptoms, such as dizziness, palpitations, and syncope. Worn day and night, it continuously scans ECG activity to capture information both before and after an event occurs. When patients experience symptoms, they press the record button, and the ECG information is recorded and stored in a solid-state memory that has a capacity of 300 seconds (5 minutes). The time frame during which the ECG activity is captured and stored in memory can be programmed.
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Receiving Center
In our study, we used the LifeSigns Receiving Center 2000 Model 3 with the CardioMagic Arrhythmia Manager Software manufactured by Instromedix. This receiving center is capable of receiving, processing, and printing waveforms and other vital information from the King of Hearts Express recorder. The receiving center is used with Arrhythmia Manager software, which was created to be used with ambulatory ECG monitors. When a patient transmits a stored ECG strip, the incoming ECG and other digital information are displayed on the screen as they are received. The Arrhythmia Manager software allows on-screen editing of ECG rhythm strips. This editing includes measuring heart rate and PR and QT intervals and adding information about rhythm interpretation, the patient’s symptoms and activity, and any follow-up care.
Reports summarizing all transmissions can be stored, printed, and transferred to a database system (eg, Microsoft Access, Redmond, Wash). Reports include the date and time, ECG interval measurements, rhythm interpretation, the patient’s symptoms and activity, and any follow-up care. We used this information to document the incidence and timing of postoperative atrial fibrillation and to ascertain the nature of symptoms and their relationship to occurrences of atrial fibrillation. The software system is also used to keep an inventory of all cardiac event recorders in use.
Procedure
On the day of a patient’s discharge from the hospital, a member of the research team cleaned and prepared the patient’s skin and applied the lead pads in a lead II configuration. We told patients to change lead pads whenever the pads appeared loose or if contact with the skin appeared to be incomplete. We then attached the King of Hearts Express recorder to the patient and showed him or her how to record and transmit an ECG rhythm strip over a telephone to the receiving center. We asked patients to demonstrate proper lead placement and operation of the recorder and to verbalize appropriate times for recording a rhythm strip. Patients recorded their first rhythm strip, called the receiving center, and transmitted the rhythm strip under the supervision of the researcher just before discharge from the hospital.
Patients wore the recorder for the 14 days immediately after discharge from the hospital. This interval was chosen in an attempt to capture most episodes of postoperative atrial fibrillation.1,8 The patients recorded a rhythm strip whenever they had symptoms suggestive of atrial fibrillation, such as palpitations, a feeling of an irregular heart beat, fatigue, shortness of breath, dizziness, or syncope. As soon as possible, the patients called a member of the research team at the receiving center and transmitted the stored recording. In addition, patients recorded and transmitted an ECG daily at an agreed-upon time. The patient’s physician was notified and was faxed a copy of the ECG rhythm strip whenever relevant arrhythmias (eg, atrial fibrillation) were detected. Table 2 is an example of instructions given to the patients.
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CASE EXAMPLES
Mr P., a 59-year-old man, was admitted to the hospital for elective coronary artery bypass graft surgery. He had a history of hyper-lipidemia, an inferior wall myocardial infarction, and a percutaneous transluminal coronary angioplasty complicated by an acute dissection. Mr P. had double-vessel coronary artery bypass graft surgery. Postoperatively, he was extubated without complications, and his hemodynamic condition was stable. He remained in a sinus rhythm, except for a single brief episode of nonsustained supraventricular tachycardia. Wearing a King of Hearts Express monitor, Mr P. was discharged to home on postoperative day 5. His daily ECG transmissions revealed a normal sinus rhythm without ectopy.
On postoperative day 16, Mr P. was eating breakfast when he started to experience palpitations and some shortness of breath. He pressed the record button on the monitor and then called the researcher at the receiving center. His cardiac rhythm was atrial fibrillation with a heart rate of about 120/min (Figure 2). His cardiologist was informed, and Mr P. was admitted to the hospital.
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Ms C., a 68-year-old woman, was admitted to the hospital for an elective mitral valve repair. Her medical history included hypertension, hyperlipidemia, and mitral regurgitation. Ms C. had a 12-beat run of ventricular tachycardia in the immediate postoperative period, and treatment with lidocaine was started. She was atrially paced, but no other arrhythmias were noted. The remainder of her hospitalization was uneventful, and she was discharged on postoperative day 4 with a King of Hearts Express recorder in place.
On postoperative day 5, the routine daily ECG transmission indicated that Ms C. was in atrial fibrillation with a heart rate of about 90/min (Figure 3). Other than feeling tired, she was asymptomatic at this time. Her cardiologist was informed, her medications were adjusted, and she converted back to sinus rhythm.
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Mr P. and Ms C. are 2 examples of patients who benefitted from ambulatory ECG after cardiac surgery. Atrial fibrillation was detected in Mr P. when he recorded his heart rhythm in response to an episode of symptoms. Atrial fibrillation was detected in Ms C. upon routine daily recording and transmission at a time when she was asymptomatic.
Without ambulatory ECG, these 2 patients might not have sought timely advice from a healthcare provider. Most likely, Mr P. would have called his cardiologist or cardiac surgeon if the symptoms he was experiencing continued or worsened. However, it would be unlikely for Ms C. to see her cardiologist before her follow-up appointment after discharge from the hospital, especially if she remained asymptomatic.
CONCLUSIONS
Consequences of atrial fibrillation include hemodynamic instability and thromboembolic phenomena, such as stroke. The rapid heart rate can result in syncope and heart failure, and the irregular rhythm can promote the formation of thrombi in the atria, especially when the atrial fibrillation persists for a long time before converting to sinus rhythm.
Currently, ambulatory ECG is not recommended for routine use in patients discharged from the hospital after cardiac surgery. We hope that the results of our study will help support the value of ambulatory ECG during the initial recovery period after cardiac surgery.
References
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