Outpatient Rhythm Monitoring: Available Options and Diagnostic Yield

March 29, 2016

Holter_monitor_NIHBy Iulia Giuroiu, MD

Peer Reviewed

A 70-year-old woman with hypertension, early dementia, and non-specific chest pain of unclear etiology presents with recurrent left-sided chest pain. Unfortunately, she is a poor historian; it appears that her chest pain is similar to past episodes. Prior workups, which included an echocardiogram, had been unremarkable. To confound matters further, the patient’s current pain appears to be reproducible when pressure is applied to her chest. She is admitted overnight for close observation. No electrocardiogram (ECG) changes are found and serial troponin levels remain undetectable. She is discharged with a follow-up appointment in the cardiology clinic; however, while waiting in the discharge pharmacy she slumps over and appears to briefly lose consciousness, leading to readmission to the hospital. Subsequent telemetry monitoring only reveals occasional short bouts of sinus tachycardia and the patient remains asymptomatic. 

This case raises the following question: In an elderly patient with recurrent, intermittent symptoms concerning for a cardiac abnormality and a subsequent new episode of syncope, what is the best approach to correlate symptoms with objective findings in the outpatient setting?

Outpatient telemetry monitoring became available in 1957, when Dr. Norman Holter introduced the first ambulatory ECG (AECG) device [1]. Up until 2009, when the Federal Drug Administration (FDA) approved the Zio Patch (an ECG patch monitor), only two main classes of outpatient cardiac monitoring devices had been available, the Holter monitor and the loop recorder [2]. These older devices have undergone extensive evaluation in clinical trials, which have validated their accuracy in diagnosing a range of cardiac conditions, from arrhythmias to ischemia.

Holter monitors are external devices that continuously record and save up to 24 or 48 hours of ECG tracings, which are then analyzed for the presence of arrhythmias. External loop recorders (ELRs) also continuously record ECG tracings, but save only a few minutes of data before replacing it with new recordings, allowing for prolonged monitoring. Moreover, ELRs also allow patients to trigger the devices upon experiencing symptoms in order to permanently save the recordings occurring before and after the trigger. A hybrid of these two devices, the ECG patch monitor, continuously records up to 14 days of data and also allows patients to record symptoms through a built-in trigger.

The Holter monitor offers either 3-lead or 12-lead ambulatory ECG recordings [3]. In their review of ECG monitoring in syncope, Ruwald and Zareba conclude that Holter monitors prove most useful in diagnosing underlying cardiac etiologies of syncope among patients who experience frequent symptoms and frequent episodes of arrhythmia, which are more likely to occur in the short period of time a patient wears the monitor [3].

ELRs constantly record and subsequently delete 1 or 2-lead ECGs every 5-15 minutes until the patient experiences symptoms and activates the device’s recording feature [3]. Patients who experience an episode of syncope and trigger recording upon regaining consciousness save ECGs that represent activity 1-15 minutes prior to and 1-5 minutes after the episode [3]. In the COLAPS study that randomized 100 patients with syncope or pre-syncope to Holter monitoring versus ELR monitoring, up to 90% of patients experienced their first recurrence of symptoms after a total of 33 days, which could only be captured by ELR monitoring [3,4]. A diagnosis was defined as a correlation, or lack thereof, between symptoms and recorded arrhythmia, and thus 90% of patients in this study carried a diagnosis by 33 days. Most importantly, this study proved useful in ruling out arrhythmias as the cause of syncope among patients with frequent episodes of syncope and no known underlying structural heart disease [5]. Holter monitoring, conversely, revealed significant ECG abnormalities in up to 40% of patients [3,6]. By extending the duration of monitoring up to 8 consecutive weeks, ELRs were shown to increase the negative diagnostic yield of unexplained syncope from 14-22% (with Holter monitoring) to 17-56% [3,5-10].

As expected, external monitoring devices are often cumbersome to patients due to their bulkiness and because these devices must be kept dry. Moreover, patients are responsible for changing leads and electrodes when monitoring exceeds 1-2 days [11,12].

Thus, implanted patient-triggered event recorders (implantable loop recorders, ILRs) were developed in an attempt to improve ease of use and compliance with outpatient ECG monitoring. ILR devices are placed subcutaneously in the left upper chest, much like pacemakers or implantable cardioverter defibrillators (ICDs) [3]. ILRs not only extend the duration of monitoring to months and even years, but also extend the length of the recorded period to 40 minutes prior to symptom-triggered activation and 1-5 minutes after the trigger [3]. Among the 570 patients with unexplained pre-syncope and syncope who were analyzed in the PICTURE observational registry, syncope recurred in up to 38% of patients by 15 months, with the ILR contributing to a diagnosis in over 78% of these patients [13].

Current guidelines offer a Class I recommendation for the use of ILRs in two groups of patients. The first group includes those with recurrent syncope, but without high-risk features such as severe structural or coronary artery disease, clinical or ECG features suggesting an arrhythmic syncope, or co-morbidities like severe anemia and electrolyte abnormalities [14]. The latter patients should be monitored on inpatient telemetry for 24-72 hours [3,14]. The second group includes those at high risk according to the above criteria who remain undiagnosed and untreated even after extensive workup [14]. In spite of the diagnostic advantages of ILRs, the discomfort and risks associated with these invasive devices make them less attractive options for patients, undoubtedly paving the way for the invention of a less invasive device with long term monitoring capabilities. Enter the ECG patch monitor. The ECG patch monitor is a hybrid of its two predecessors—it is an external continuous monitoring device capable of more prolonged patient-initiated recordings before and after symptomatic episodes. A waterproof device, this patch provides up to 14 days of analyzable data. At the end of that period, the device is mailed to a centralized interpreting center. In a prospective trial, Rosenberg et al compared the ECG patch monitor to a 24-hour Holter monitor for the diagnosis of paroxysmal atrial fibrillation [11]. This study of 74 patients revealed a strong correlation between the periods of atrial fibrillation in the first 24 hours recorded by the patch monitor compared to the Holter monitor [11]. Patients continued to wear the ECG patch monitor for a mean of 10.8 days, when the majority (50%) of patients’ triggers correlated to sinus rhythm and 38% correlated to episodes of atrial fibrillation [11]. Most recurrent episodes of atrial fibrillation occurred within 7 days of monitoring on the patch monitor, with a small number of additional episodes occurring by 12 days [11]. More notably, longer monitoring using the patch monitor resulted in a change in management for 28% of the patients enrolled in this study [11]. Of note, the ECG patch monitor proved useful in identifying episodes of atrial fibrillation even in patients who had undergone ablation for atrial fibrillation and frequently remained asymptomatic during these recurrent episodes [11]. A retrospective study by Turakhia et al analyzed data from almost 27,000 distinct uses of the ECG patch monitor in patients aged 60.2 ± 18.7 years who wore it for 7.6 ± 3.6 days for workup of palpitations, atrial fibrillation, and syncope or pre-syncope [12]. First instances of arrhythmia occurred after 48 hours for 29.9% of the patients. Among patients whose arrhythmias correlated to symptoms, 51.1% of recorded arrhythmias occurred after 48 hours, underscoring the importance and usefulness of monitoring patients continuously beyond the 48 hours covered by the Holter monitor [12]. The patch monitor also diagnosed pauses, Mobitz II (or complete atrioventricular block), supraventricular tachycardia (SVT), and ventricular tachycardia (VT) more frequently than the Holter monitor. Time to first arrhythmia was 1.7 ± 2.2 days and time to first symptom-triggered arrhythmia was 3.0 ± 2.9 days [12].

Practice guidelines have not yet been updated to formally include the ECG patch monitor as a diagnostic option for patients with syncope; however, we can offer some early conclusions based on current and past trials comparing ELRs to ILRs, even though the number of enrolled patients in each of these trials was notably small. ELRs have achieved a successful diagnosis (combined positive and negative diagnostic yield) at a rate of up to 50%, but difficulty with data transmission, specifically in patients who are more technologically averse or even those living alone, limits their usefulness [4,5,10,16]. Data from crossover Holter to ELR study arms has provided diagnostic information in up to 45% of patients, suggesting value in extending study duration beyond 24 to 48 hours [5,10]. At its current lifespan, the ECG patch monitor may achieve an intermediate diagnostic yield between Holter monitors and ELRs, with gains in ease of use but losses in duration of coverage. A prospective trial comparing Holter monitoring and the patch monitor activated simultaneously in the same patients showed that the patch monitor conferred a statistically significant improvement in capture of an arrhythmic event [17].

Of note, another external device known as a mobile cardiac outpatient telemetry (MCOT) system also became available in the mid-2000s. It consists of a pager-sized device with 3 external monitoring leads that are applied to the chest for as long as monitoring is desired [18]. The MCOT continuously monitors ECG recordings for arrhythmias and sends ECGs to a technician via a landline or wireless network upon recognition of an event [18]. In a randomized, prospective study of 266 patients, the MCOT established a diagnosis for pre-syncope and syncope in 89% of patients, compared to 69% of patients monitored via ELR [19]. However, studies have not yet compared this device to an ECG patch monitor. Previous concerns regarding a relative lack of user friendliness and expense still hold true [18, 19].

Ultimately, trials directly comparing the ECG patch monitor to loop recorders are expected to offer more direct answers about the potential effects of monitoring duration on diagnostic yield. In our increasingly cost-conscious healthcare economy, we might also benefit from comparing the suggested cost-effectiveness of direct ILR implantation to patch monitor use [15]. Currently, the patch monitor’s overall diagnostic advantage over ELRs lies in its extended duration of ECG recordings. While the ability to correlate arrhythmia to symptoms is lost if patients fail to record symptomatic episodes, the finding of life-threatening arrhythmias irrespective of symptom correlation may prove useful. More trials on the ECG patch monitor’s effectiveness and further technological advances are needed to extend its lifespan.

 Dr. Iulia Giuroiu, is a 3rd year resident, Internal Medicine at NYU Langone Medical Center

Peer reviewed by Scott Bernstein, Medicine, at NYU Langone Medical Center

Image courtesy of Wikimedia Commons


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