Ambulatory Monitoring: Technical Aspects and Prospects

The purpose of this article is to explain technical aspects of ambulatory monitoring in order to achieve accurate reporting and minimize the potentials for repeating the requested testing. This article will also enlighten readers as to the importance of human factor in such vital practice. We need to remember that ambulatory monitoring is vital in both adult and pediatric settings. Ambulatory monitoring in cardiology includes Holter monitoring, event monitoring, and ambulatory blood pressure monitoring.

Holter Monitor

The Holter monitor is a small — and now getting much smaller — device that records the ECG as frontal plane/view (Leads I, II, and III) application. Usually Holter recorders are applied to collect 2 and 3 channels of ECG or full 12-lead ECGs. Holter recorders are very delicate devices that should be handled with extra care. Most manufacturers provide 24- to 48-hour Holter recorders, which can record 2-3 channels of ECG, although some Holter recorders can record up to 7 days. On some occasions, the Holter application may warrant modifying the landmarks of electrodes in a different configuration such as the horizontal plane (V1 to V6, and right-sided chest leads) in order to enhance the ECG signal for better visualization of arrhythmias and pacemaker spikes. Should this be the case, then a copy of the new lead application should be attached to the report for medical records and future reference in order to avoid misdiagnosis (e.g., polymorphic ventricular ectopy). In patients with dextrocardia, the medical director can assist in modifying the application of leads. Digital Holter recorders are proven to be superior in accurate measuring of ECG intervals, especially in cases of long QT syndrome and bundle branch block. However, without exception we have all encountered tape drag artifact when using analog Holter recorders, which may make the ECG intervals unreliable. Holters are mainly applied during outpatient visits; however, they can also be applied during inpatient procedures, especially after cardiac surgeries, pacemaker implantation, and during inpatient management of arrhythmias.

The Holter process according to the current CPT codes: The first code is 93225: This code is dedicated for hook up. I cannot emphasis enough how crucial this step is. If it fails, then the study must be repeated, which will impact proper patient care (especially if monitoring antiarrhythmic medications) as well as patient frustration and time, since patients will have to return to the clinic to reapply the Holter. The ultimate goal of Holter monitoring is to minimize repeats via proper application and patient education. This step should take about 15 minutes. Medical staff, from the ordering cardiologist, schedulers, nurses, and Holter technologist, should respect the importance of this step. Some primary practitioners order Holters and bypass referring patients to cardiology; however, this is not recommended since patients should be referred to cardiology for proper evaluation, starting from resting ECG, echo, stress testing, Holter, and event monitor, etc. Electrode size and type is also very important. Apply adult size electrodes whenever possible. If the Holter is to be applied on a newborn or infant, then smaller electrodes may be applied, but pay extra attention to those small electrodes, which may peel off easily and increase the risk of failure. You may apply tape on top of the wires for extra stability. Solid gel electrodes are superior since they provide better conduction and the gel will not escape under the adhesive as you apply the electrodes. Rubbing the skin with alcohol is sufficient for a good signal. There is no need for skin abrasion, especially on the younger population. The patient should be instructed to perform the regular daily activity and postpone physical activity toward the end of the study; this will ensure continuous uninterrupted recording. The patient should also be instructed to document on a paper diary their symptoms and any medication they may take, including the name of the medicine and time it was administered, and any unusual events as fever, vomiting, etc. Unfortunately, the event button on the Holter recorder is not of much value, since it does not tell us exactly what the symptoms (e.g., chest pain, dizziness, fast heart beat at rest, etc.) were during recording. The patient should be provided with extra electrodes and an application map in order to fix any fallen electrodes; this will ensure better quality of the study, especially when the study is being downloaded to the computer for analysis by the technologist. Electrodes should be applied on areas with minimal motion, such as on the upper part of the sternum and the horizontal line extending between V4 (left side of the chest) and V4R (right side of the chest). Again, please instruct your staff and patients to cooperate and respect this step, since the next two steps greatly depend upon the success of this Holter hook up. Please instruct the patient not to engage in vigorous or contact sports during Holter monitoring, because this may defeat the purpose of the study — contact sports could break the recorder or lead to excessive perspiration, during which the electrodes could fall off and lose their signal. In addition, patients should not wear the Holter on their belt, since the electrodes may fall off when the patient uses the restroom, or put it in their pocket because it may drop on the floor and break. The second code is 93226: It takes between 40-120 minutes for the technologist to generate an accurate and honest report. It is recommended that the analyzed report be available if certain segments of the study require revision. Current steps used in accurate reporting include the viewing of accurate template recognition by the computer algorithm; the Holter analyst should be able to control the software (and not vice versa), since this will allow proper overriding of errors created by the algorithm. The analyst should be able to document minimum and maximum heart rates on a rhythm strip and 3-6 minutes of ECG signal in order to reflect slow onset and offset of sinus bradycardia and sinus tachycardia, maximum and minimum R-R intervals, longest and fastest runs of supraventricular tachycardia (SVT), ventricular tachycardia (VT), junctional ectopic tachycardia (JET), ectopic atrial tachycardia (EAT), intermittent atrial fibrillation or atrial flutter, and intermittent Wolff-Parkinson-White (WPW), in addition to any unusual events and intermittent BBB, etc. This cannot be achieved without the most crucial step in the whole analysis, which is manual revision and editing of the raw data by utilizing the full disclosure function. The evolution of full disclosure function should eliminate the wrong description of the current CPT code of 93226, which states “superimposition.” Superimposition is an outdated process that should be corrected in the CPT book to “manual editing of fully disclosed ECG.” Most computer algorithms analyze the raw data according to R waves, including determining how premature or how wide. If premature and narrow, then the computer will assume it is a supraventricular ectopy; if premature and wide, then the computer will assume it is a ventricular ectopy. This is a problem since aberrantly conducted PACs may be seen by the computer as PVCs, and fusion PVCs may be seen as normal beats. This may explain the importance of human factor in Holter analysis versus the computerized automated and auto strip process, which may impact the proper clinical evaluation. Medication side effects are also a crucial factor in the Holter application, since some medications may have intermittent side effects that should be evaluated by the full disclosure function. Patients undergoing ablation should wear a Holter before and after the procedure and every few months afterwards in order to evaluate for recurrence of the arrhythmia and possible side effects. Some patients may develop second-degree heart block, especially at higher heart rates after ablations. Patients with a pacemaker may develop unusual pacemaker behavior such as pacemaker-mediated tachycardia or Wenckebach upper rate response, oversensing, undersensing, non-capture, etc., which may not be visible during regular pacemaker interrogation. I cannot emphasis enough the importance of this step for patient safety and proper management. The points I addressed are not intended to be a full explanation of this step in analysis, but are intended to enlighten the importance of the human factor in Holter analysis. Some Holter reports may be generated in 40 minutes, while others may take longer depending on the quality of the hook up and how loaded the study is with arrhythmias. One more item I need to add for accurate reporting is that heart rate parameters should be adjusted according to the patient’s age, since this varies between premature baby, newborn, infant, toddler, and adults. Automated Holter reports that rely solely on the computer and bypass the human factor should be rejected and eliminated from the practice, since they are rarely accurate. The third code is 93227: This is dedicated to cardiologist interpretation. This step should be reserved only for cardiologists/electrophysiologists and not for family practitioners, internists, physician assistants, or advanced practice nurses. Only cardiologists and electrophysiologists are qualified to evaluate the Holter report, especially when evaluating pacemakers. This step depends on successful completion of the previous two steps of 93225 and 93226. Lastly, I also need to add the importance of the clinical correlation of bradycardia and heart block that may occur only during sleep, especially asystole and heart block in patients with suspected sleep apnea.

Event Recorders

Event recorders include looping (pre symptoms), non-looping (post symptoms), and implantable. The type of event recorder should be selected according to the patient’s symptoms. Looping event recorder: This is also called a pre-symptom memory loop recorder, since it can be programmed to capture 30 seconds or longer of ECG prior to being triggered by the patient. Again, please instruct the patient not to wear the recorder on their belt as a pager or put the recorder in their pocket; instead the patient should be provided a few disposable pouches so they can wear the monitor as a necklace under their clothing. This will make the recorder totally hidden but also still accessible. Plenty of electrodes, an extra battery, and cable should also be provided for the patient. I estimate teaching time to take no more that 20-30 minutes. Like Holters, the looping event recorder is not appropriate for patients who engage in sports, since they are likely to break the recorder or sweat the electrodes off. Ideally this recorder is prescribed for patients with very brief symptoms and who are presyncopal. Looping recorders are now available as auto trigger for asymptomatic bradycardia, tachycardia, and atrial fibrillation. Non-looping event recorder: When using the non-looping event recorder, patients hold and trigger the recorder against bare skin on their chest as their symptoms occur (although this can be cumbersome for female patients). The moment the patient develops symptoms, the non-looping event recorder should be positioned on the left side of the chest where the metal sensors on the back of the recorder are in direct contact against bare skin. The patient should be instructed to stay still during the entire recording time in order to minimize motion artifact. Ideally it is prescribed for patients with long episodes of symptoms (though of course not applicable for syncopal patients). Again, the patient is provided with a few disposable pouches to wear the recorder as a necklace. Wrist non-looping event recorder: This recorder is widely used for patients who are symptomatic during exercise or in females who are not comfortable using the traditional non-looping recorder. Patients who develop SVT during exercise will benefit from these recorders, especially if the SVT was non-inducible via traditional stress testing. Implantable looping event recorder: This type of recorder is implanted during a minimally invasive outpatient procedure. The device can be triggered by a small remote control. The patient is instructed to report to the cardiology clinic once the device has triggered, in order to download the ECG via special equipment.

Ambulatory Blood Pressure Monitoring

Many might think that ambulatory blood pressure monitors are prescribed only by the nephrology clinic. This may be true, but it is also of great use in both adult and pediatric cardiology patients for evaluation of elevated blood pressure, management of hypertension, and evaluation of white coat syndrome. Traditionally the patient will spend about 20-30 minutes in the clinic to be educated about and fitted with the proper size cuff on the non-dominant arm. The right arm may be used in cases of coarctation of the aorta, and if the patient is having a surgical AV shunt for dialysis, then also use the other arm. The recorder will be programmed to obtain automated readings at certain intervals; during that time the patient should remain still — the device should be used during a time that the patient will not be extremely active. Finally, one needs to decide whether to order a 24- or 48-hour study. We encourage the 48-hour application, especially since the cuff may shift off during sleep. It is very important to monitor during sleep, since one needs to evaluate for proper nocturnal dipping of the blood pressure. The patient can remove the recorder between any two cycles, but only once every day for a quick shower. Also, the patient should again not be engaged in any kind of sport since this may break the recorder or result in a false positive result, due to normal response of systolic blood pressure to exercise.