By Elizabeth H. Charuvastra, RN, and Dorothy D. Dance, RN
The correct diagnosis of electrocardiogram (ECG) abnormalities is the first step in treatment of patients with cardiac rhythm disturbances. But for patients with intermittent symptoms it is difficult to record an ECG when symptoms are occurring.
A 12-lead ECG recording provides the most complete information, but such a recording is rarely practical for patients with intermittent symptoms. To solve the problem, several systems have been developed that record the ECG over longer periods but use fewer leads.
Holter monitoring and transtelephonic cardiac event recording are diagnostic tools designed to document a patient's ECG in an ambulatory setting. Although lacking the depth of information of the 12-lead ECG, these systems using one to three leads provide the advantage of monitoring a patient over relatively long periods, thus increasing the likelihood of capturing the patient's ECG during the intermittent symptoms.
For many years the Holter monitor, a portable device small enough for a patient to wear during daily activities, has been the accepted method of recording a patient's ECG over a relatively long period. Holter monitors record two or three channels of ECG data on a cassette tape over 24 to 48 hours. The information is later analyzed by a technician using a computer with specialized diagnostic hardware and software. The Holter monitor is a valuable diagnostic tool in the treatment of patients with certain sets of symptoms, but its efficacy is limited by the fact that a patient's symptoms may not occur during monitoring. The use of serial Holter procedures is often too costly.
In recent years, transtelephonic cardiac event recording has made it possible for patients with intermittent symptoms to record an ECG when symptoms occur. A patient activates the cardiac event recorder, or monitor, when he or she notices symptoms. The monitor records the ECG, which remains in the monitor's memory until it is transmitted by telephone to an ECG receiving center. The receiving center, often a specialty laboratory or part of a hospital, is staffed by nurses and technicians who are trained to evaluate complex ECGs.
Transtelephonic ECG monitoring was developed in the 1960s to monitor patients who had implanted pacemakers. The technology now provides the standard tool for diagnosing transient cardiac events in many institutions and physician practices.
Two main types of cardiac event monitors are available for use in transtelephonic cardiac event recording: the looping memory (presymptom) monitor and the post-symptom event monitor.
The looping memory monitor is a small device attached to the patient's chest via two electrodes. It continuously monitors the heart's rhythm. The smallest looping memory monitor is the size and shape of a pager. The available memory is five minutes, and the memory may be programmed to suit the patient's symptoms. For example, a patient with palpitations would receive a monitor programmed to record five one-minute episodes of ECG tracing. A special feature of the looping memory monitor is that it can record a section of the ECG that occurred before the patient activated the monitor. For the patient with palpitations, this means that 45 seconds of memory can be allocated to record the ECG tracing before the patient activated the monitor and 15 seconds after activation. With this method of monitoring, even the most transitory symptoms may be documented.
A patient with symptoms of intermittent syncope would be given a monitor programmed to record several minutes before activation. If the patient has an episode of syncope, on regaining consciousness, he or she presses the record button on the monitor and locks the previous five minutes of ECG into the monitor's memory. The recording includes the ECG at the onset and throughout the syncopal episode.
In patients with tachyarrthymias, the onset of the arrhythmia may contain diagnostic information, and documentation of this portion of the ECG can be important in determining the type and the origin of the arrhythmia. Only the looping memory monitors are capable of recording the ECG before the patient has activated the monitor. These monitors have an LED visual display screen that tells patients how many events have been recorded and the status of the battery life. Long-term cardiac monitoring is typically 30 days, although some patients with extremely intermittent symptoms are monitored for up to several months.
The looping memory monitor can capture transient symptoms, including intermittent palpitations, episodes of dizziness or lightheadedness, and syncope or near syncope. In addition, looping memory monitors are well-suited to tracking symptoms suggestive of myocardial ischemia that require a monitor that has a low frequency response (rather like the bass frequency on a stereo system) to detect ST segment and T wave changes. The ST segment and the T wave are the terminal portion of the electrical cardiac cycle and represent the recovery phase of the cycle, or diastole. The looping memory monitors are also well-suited for patients who have had myocardial infarctions and for other patients with chest pain.
The postsymptom event monitor is simpler than the looping memory monitor and may be handheld or have a wristwatch design. The patient uses the handheld monitor by pressing the electrode feet to the chest and activating the monitor's record button. The electrode feet are small metal buttons on the back of the monitor. The metal allows conduction of the electrical signal from the heart into the monitor's memory.
A single-channel lead II tracing is recorded for approximately 30 seconds. The lead II ECG tracing records a slice of the electrical activity of the heart, as if a line were drawn from the right shoulder to the left leg. Other leads record other slices of the heart, but lead II is the most commonly used in cardiac event recording.
The patient typically keeps the handheld style recorder in a convenient place, such as a pocket or purse, for use when symptoms occur. The wristwatch style monitor is worn constantly on the left arm; it creates a bipolar lead I ECG tracing.
Both of these postsymptom monitors record one or more events that are stored in the monitors' memory for later transmission to the receiving center. Unlike looping memory monitors, postsymptom monitors are not able to record the ECG before activation. The recording starts when the patient activates the monitor, so post-symptom monitors are useful in documenting the ECG during symptoms that last for more than a few seconds, or when the onset of the arrhythmia is not diagnostically important. Arrhythmias such as atrial fibrillation, atrial flutter, and supraventricular tachycardias that last more than a few seconds can be documented using a post-symptom monitor.
For patients undergoing pharmacological therapy for arrhythmias, the cardiac event monitor is an excellent method for monitoring drug efficacy on an outpatient basis. The looping memory monitor should be used with chest leads in a consistent configuration to monitor atrial and ventricular conduction intervals in addition to rate and rhythm changes. Some cardiac monitors have an automatic trigger that is activated when the monitor detects bradycardia or tachycardia. Other monitors automatically detect and record the high voltage discharge of an implanted cardioverter-defibrillator.
For long term cardiac monitoring, a single-channel hookup appears to be well tolerated by most patients. Electrodes should be repositioned on the chest every 24 to 48 hours to prevent chafing but in the same lead configuration for consistency whenever possible. Some monitors record two channels of ECG data; they require additional electrodes for the second recording channel, and patients may be less likely to comply with a more involved monitoring procedure.
Although cardiac event recorders are relatively simple to use, patients need education in the correct operation of these devices. When looping memory monitors are used, the skin preparation and application of the electrodes determine the quality of the ECG tracing that will be recorded. The skin should be free of oils and creams. The site of the electrodes should be thoroughly cleansed with alcohol on a gauze square and the skin rubbed until it is slightly pink. This method ensures that the top layer of dead skin cells is removed. (This layer impedes the electrical signal from the heart.)
The patient is likely to be wearing the monitor for a long period of time, so the care of the skin is an important part of the monitoring process. The electrodes can be worn in the shower or bath and can be moved around as long as they are placed in the general area that will provide an adequate and consistent signal.
Patients also need to be taught how to transmit an ECG over the telephone. On most monitors, the send button is easy to operate. The monitors typically have two buttons, one to start the recording process and the other to activate sending the ECG to the receiving center.
To transmit the ECG the patient is instructed by the receiving center staff to place the telephone mouthpiece over the microphone on the front of the monitor. The receiving center staff can help patients solve problems related to telephone equipment. Many cardiac event recording centers contact patients at home soon after the start of the monitoring period so that patients can practice making transmissions from their own telephone before the need arises.
Once a patient's ECG is recorded and saved in the monitor's memory, the patient calls the ECG receiving center and sends the ECG over a standard telephone to the center. The staff at a center evaluate the ECG, correlate it with the patient's symptoms, and generate a report for the referring physician. Reports on nonurgent ECGs are usually sent to the physician during normal business hours. However, sometimes a patient transmits an ECG that contains a life-threatening arrhythmia or an arrhythmia requiring medical attention or drug titration. In these cases, the physician is notified immediately and action is taken to provide the patient with emergency care.
Arrhythmia monitoring is essentially a specialty branch of nursing telephone triage. In this new and growing field, nurses apply their skills in patient care and history-taking over the telephone. Nursing telephone triage has become widely used in managed care settings; it is cost-effective because it provides a service to patients who may not need to visit a hospital or clinic. With the use of specially developed protocols, patients who transmit their ECGs over the telephone can receive reassurance, advice, and care from a nurse on the telephone.
The most important essentials for providing transtelephonic patient assessment and triage of cardiac events are:
Although making a clinical diagnosis is the role of the patient's physician, the nonphysician staff in an ECG receiving center are responsible for a rapid assessment of the patient's ECG. This assessment of the ECG is combined with assessment of the patient's symptoms.
Often the patient is called back an hour after transmitting a significant arrhythmia, and a follow-up ECG is taken. The patient's condition is assessed and a determination of current cardiac rhythm status is made.
Nurses with critical care experience are particularly valued staff members at ECG receiving centers. Their critical care training and ability to adapt these skills to patient care and assessment over the telephone provide patients high-quality care.
The clinical expertise of the monitoring center staff is critical during the assessment of the patient's ECG and during the subsequent patient interview. Once the transtelephonic ECG has been transmitted, the patient is asked about specific symptoms. If the patient denies any symptoms in the presence of an arrhythmia, it may be necessary for the staff to ask questions such as: Were you dizzy or lightheaded when you pressed the record button on the monitor? What specifically did you feel that caused you to record this event? How do you feel now?
The clinician must listen carefully to the patient, assess any auditory signals from the patient (such as shortness of breath causing difficulty in speaking), and combine this information with the patient's perceptions of the episode when annotating ECGs and notifying the referring physician.
Protocols for physician notification vary slightly, but primarily include new-onset arrhythmias, arrhythmias in combination with chest pain or pressure, and clinically significant or symptomatic changes in heart rate, rhythm, or pacemaker function.
The ECG in Tracing 2 was called into the receiving center by a 19-year-old man who reported a slightly faster heart rate than usual after playing hockey for 15 minutes. After transmission of the ECG to the receiving center, a nurse interviewed the patient to determine what symptoms had prompted him to activate the cardiac event monitor. The nurse asked him about any current symptoms, and a follow-up ECG was taken to verify his cardiac rhythm status.
The referring physician was notified of the patient's arrhythmia and of the cardiac rhythm status of the follow-up ECG. The patient ultimately underwent radiofrequency catheter ablation.
During this procedure a fine wire catheter is inserted through the femoral vein; it is placed at the site of the abnormal heart tissue that causes the arrhythmia. Radiofrequency waves are then passed through the wire catheter to destroy the abnormal issue. The procedure eliminates the arrhythmias permanently.
In another case, a 61-year-old woman was referred for cardiac event monitoring after reporting intermittent symptoms she described as "pounding in the chest." Examination by a physician revealed an active woman in good general health with a normal resting 12-lead ECG. A stress test and laboratory findings proved negative. The patient used a looping memory monitor while she traveled to several cities as part of a business trip. The ECG strip in Tracing 3 was recorded during an episode of mild palpitations while the patient was in Dallas. When sustained ventricular tachycardia was identified by the staff at the receiving center, the referring physician in Los Angeles was notified immediately. Therapy with a beta-blocking agent was initiated and sinus rhythm was re-established. This patient, who has no underlying heart disease, has been symptom-free for many months. She continues to use a low dosage beta-blocker.
Although the technology is not new, cardiac event monitoring is still evolving as a diagnostic tool for the assessment of patients with transient arrhythmias. By offering monitoring over a longer time, transtelephonic cardiac event monitoring has proved itself more useful than Holter monitoring in the diagnosis of intermittent rhythm abnormalities.
Cardiac event monitoring is now offered through many home health agencies. The home health staff often can provide hookup for patients in their homes and provide patient support in addition to the support offered by the receiving center staff.
As a diagnostic tool, event monitors are beginning to be used when patients are discharged from the emergency room after visits prompted by symptomatic cardiac events that do not require hospitalization.
Cardiac event monitoring may also be a valid tool in clinical research trials on new antiarrhythmic medications and drug titration in patients with refractory arrhythmias. Event monitoring is also being used in some settings for out-of-hospital monitoring of patients taking vasoactive medications for cardiac support before heart transplants. With future advances in event monitoring and telecommunications, home-based cardiac rehabilitation may be an additional application.
As the cost of health care continues to be a concern for our rapidly aging society, effective technologies such as cardiac event recording will provide diagnostic information for patients and physicians at a relatively low cost compared with traditional cardiac diagnostic testing.
Elizabeth H. Charuvastra, RN, is the clinical director of Beverly Glen Medical Systems Inc., an ambulatory monitoring service in Los Angeles. She is a consultant specializing in the development of computer software for electrocardiographic monitoring. Nurses seeking more information may call Charuvastra at (800) 834-8858.
Dorothy D. Dance, RN, is the clinical director of Arrhythmia Monitoring Inc. in Olney, Md. Her experience includes 14 years as a cardiac nurse and five years as the owner and director of an ambulatory monitoring center and mobile pacemaker clinic.
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