Clinical Practice
Zimetbaum et al14 provides an overview and evaluation for care with patients that present with palpitations. There are many factors to be considered in the etiology of palpitations. Cardiac disorders are the most common cause of palpitations and include arrhythmias, structural heart disease, conduction system abnormalities, valvular disease, pacemaker syndrome, atrial myoma, sympathetic stimulation and catecholamine release during exercise and high output cardiac states. Other etiology of palpitations may include psychiatric disorders, medication effects, substance abuse, endocrine disorders, and metabolic disorders.
The workup for a patient who presents with palpitations typically includes an extensive medical history along with a 12-lead ECG, physical exam and limited laboratory testing.14(p3)
When an arrhythmia is not identified on the 12-lead ECG, the patient’s medical history can be helpful to note the age of symptom onset, duration of palpitations, heart rate and rhythm regularity, additional symptoms that are associated with the palpitations (pre-syncope or syncope), the onset and resolution of the palpitations, effects of positional changes and if the patient is able to alleviate the palpitations on their own. In addition, the cardiac exam should include the patient’s family cardiac history and co-existing medical conditions such as pregnancy, metabolic and endocrine issues, chronic obstructive pulmonary disease, and psychiatric disorders.14(p2)
Following an extensive cardiac exam, if the etiology of the palpitations remains unclear limited laboratory testing for anemia, hyperthyroidism, and toxicology testing may be indicated, as well as echocardiography for patients with possible structural heart disease.
Holter vs. Continuous Long-Term Electrocardiographic (LT-ECG) Monitors
Barrett et al15 conducted a prospective analysis of cardiac arrhythmias using the Holter monitor and the Zio patch between April 2012 and July 2012. The goal was to compare arrhythmia detections over the course of 14 days to the arrhythmia events detected in the first 24 hours of monitoring.
One hundred and forty-six patients between the ages of 22 and 94 participated in the study. The average wear time of the AECG monitors ranged between one day for the Holter monitor and eleven days for the patch monitor. Both devices were activated simultaneously and monitored for 24 hours for the Holter monitor and up to 14 days for the patch monitor. All arrhythmias were evaluated by the Scripps Translational Science Institute and the McNemar’s test was implemented to compare if arrhythmias were clinically significant and what type of arrhythmias were detected by each monitor.
Arrhythmia detection was placed into six categories: supraventricular tachycardia (SVT) (>4 beats, not including A-Fib or A-Flutter), A-Fib/A-Flutter (>4 beats), pause >3 seconds, atrioventricular block (Mobitz type II or third-degree atrioventricular [AV] block), ventricular tachycardia (VT) (>4 beats), or polymorphic ventricular tachycardia/ventricular fibrillation.15(p14)
The results demonstrated that the “patch monitor detected 96 arrhythmia events compared with 61 arrhythmia events by the Holter monitor (P< .001)."15(p12) The patch monitor and Holter monitor detected the same number of events, but “14 clinically significant arrhythmia events were detected by the adhesive patch monitor that went undetected by the Holter monitor."15(p12)
The secondary effect was to determine the arrhythmias that were detected in the first 24 hours. It was noted that the Holter monitor detected 61 arrhythmias compared to 52 arrhythmias detected by the patch monitor (P=.013). In review of the arrhythmia types three events were considered ‘clinically significant’ and were ultimately detected by the patch monitor beyond the first 24 hours.
In conclusion, the first seven days of AECG monitoring has the greatest detection of arrhythmias. Typically monitoring greater than seven days may only provide an additional 3.9% chance of identifying a different diagnosis as noted by the Zimetbaum (1998) article.
Rosenberg et al16 conducted a single-center pilot study to compare the use of a continuous LT-ECG recorder, with a 24-hour Holter monitor in 74 patients with paroxysmal A-Fib (AF), between April 2011 and May 2012. During the initial 24-hour monitoring period, both the Holter monitor, and the continuous LT-ECG recorder detected 25 AF occurrences. Patients continued to wear the continuous LT-ECG recorder for an additional two weeks, during which 43 more patients were diagnosed with AF. This indicates that AF episodes were detected in significantly more patients wearing a continuous LT-ECG recorder due to the longer duration of detection, compared with the Holter monitor. Furthermore, in this study, the LT-ECG recorder also detected cardiac pauses after the initial 24-hour monitoring, thus prompting physicians to review medications and initiate pacemaker referrals for this patient group.
Holter Monitor
Paudel et al17 conducted a prospective, single center study that included 335 patients who had symptoms of recurrent chronic palpitations or a single episode of palpitations. These patients were older than 18 years of age and the study was conducted from January 2010 to May 2012.
Patients were provided a Cardio Blue® 24-hour Holter monitor that recorded in either three or five channels and allowed for recording of arrhythmias, as defined by the American College of Cardiology (ACC)/American Heart Association (AHA), with or without corresponding documented symptoms.
The arrhythmias that were identified via the Holter monitor were: less than 10% ventricular ectopy, 36.7% bigeminy, less than 10% supraventricular episodes, 5.7% non-sustained VT and 12.5% sustained VT.
The study groups were noted to be statistically significant for patients that were younger than 50 years of age and those who were 50 years of age or older. The highest categories of arrhythmias were related to patients that were older than 50 years of age. This study group had a 72% rate with premature ventricular contactions (PVCs) and 44% with bigeminy as compared to 38.7% having PVCs and 23.1% with bigeminy that were younger than 50 years of age.
The authors reviewed literature provided by Mayet (1995) and Stein (2010). The conclusion of those two articles determined that Holter monitors detect arrhythmias such as ventricular bigeminy, VT, SVT, AV blocks, and silent ischemia in older patients who are more at risk of sudden cardiac death.
Event Recorders/Intermittent Monitors
Fredriksson et al18 studied intermittent AECG recordings versus continuous event recording in detecting A-Fib for patients 75-76 years of age. Two-hundred and sixty-nine patients that were included in this analysis were from the STROKESTOP II study from Europe. This study was conducted over a two-week period with 55 days on average for the intermittent recorders and 13 days on average for the continuous recorders. The devices were R-test 4® and Novocaor® (for continuous recording) and a 30 second handheld device Zenicor II® (for intermittent recording). All devices had activation buttons for symptomatic arrhythmias, and patients were given a symptom diary as well. Within the study, A-Fib was defined by the European Society of Cardiology (ESC) as “absolute irregular rate-to-rate intervals, no discernable distinct p-waves, and duration of at least 30 seconds” and recordings were manually inspected and validated on computerized algorithms.18(p360)
After the review of data, it was determined that continuous event recordings identified three times more cases of A-Fib (6%; n=15/269) than the intermittent AECG recordings (2%; n=5/269) (p=.002). On average, continuous recordings identified a 1-8 interquartile range (IQR) on day four and a 4-14 IQR on day eight for intermittent monitoring (P=.135). These IQR’s were analyzed using the Mann-Whitney U test and Chi-square tests in relation to proportions. While comparisons between the two monitoring methods were performed, the use of the McNemar’s test resulted in P< .05, which was considered significant when testing for dichotomous variables and paired sample t-test for continuous variables.18(p356)
Surprisingly, only six percent of the patients reported symptoms within their diaries when having verified A-Fib and none of the patients had reported palpitations. Limitations of the study include: patients that were part of a larger study (STROKESTOP II) and were thus highly motivated and possibly healthier than peers, use of one-lead AECGs that potentially complicate the analysis of the p-waves, possible bias by misclassification case, and conflicts of interest for those study team members receiving grants from companies such as Bayer, Pfizer, Sanofi, AstraZeneca, and Medtronic.
External Loop Recorders/Mobile Cardiovascular Outpatient Telemetry
Favilla et al19 provides a retrospective cohort study of 227 patients with cryptogenic stroke (179 patients) or transient ischemic stroke (48 patients). These patients underwent a 28-day mobile cardiac outpatient telemetry (MCOT), post cryptogenic or transient ischemic stroke. Of the 277 patients, 14% had A-Fib detected on MCOT, 58% of which was ≥ 30 seconds in duration. It was determined that age and prior cortical or cerebellar infarctions were independent predictors of A-Fib.
Rothman et al20 provided a prospective clinical trial of randomized patients that were evaluated with the CardioNet® system in 17 multicenter facilities. Two-hundred and sixty-six patients who had palpitations, presyncope, and/or syncope were included. The goal was to confirm or exclude the etiology of arrhythmias that caused patient symptoms. All patients had previously undergone 24 hours of monitoring with a Holter monitor, which failed to provide diagnostic information. These patients were placed in two groups for 30 days of monitoring with either the MCOT or with an external looping event monitor (ELM).
During monitoring, clinically significant arrhythmias were detected in 55 (41%) patients with the MCOT versus 19 (15%) patients with the ELM (P< 0.001). For patients who had prior syncope or presyncope, clinically significant arrhythmias were detected in 52% of patients with MCOT and in 16% of patients with loop recorders (P< 0.001). In most cases, the arrhythmias detected were A-Fib, atrial flutter, or ventricular tachycardia. There were two subgroups noted in the study. For one subgroup of patients presenting with “syncope or presyncope, a diagnosis was made in 89% of MCOT subjects versus 69% of LOOP subjects (P=0.008).”20(p243) A second subgroup analysis was performed at the centers that used auto-triggered loop monitoring rather than patient-activated monitoring. For this subgroup, a definitive diagnosis was obtained for 88% of MCOT patients and only 46% (P=0.002) of the ELM patients; however, this subgroup analysis involved only 50 of the 266 patients.
Insertable Cardiac Monitor/Subcutaneous Cardiac Rhythm Monitors
Nadkarni21 provides an overview of subcutaneous cardiac rhythm monitors (SCRMs) with the high diagnostic yield for “cryptogenic stroke, syncope, palpitation and AF [A-Fib] Monitoring."21(p588) It has long been noted that there is no established guideline for the use of SCRMs and the rate of false-positive transmissions has been the ‘Achilles heel’ of AECG. The author determines that the indications for use, techniques used in implantation, programming, and connectivity determine the clinical benefits for patients. Within this overview the author cites the ABACUS prospective randomized control trial by Kapa et al. This trial noted that SCRMs “led to more actionable events and higher rates of antiarrhythmic discontinuation when compared with other forms of rhythm monitoring in a post AFib ablation population."21(p588)
The versatility of the SCRM allows for adjustments in tachycardia and bradycardia thresholds, minimum episode durations, and the detection of atrial tachycardia and atrial fibrillation. Along with the versatility is the ability to transmit data in two ways: alert notifications and manual downloads by the patient via their home or cell phone application. With that noted and continual advancements, SCRMs have proven to be beneficial for patients.
SCRMs remain a valuable tool in the diagnosis of cardiac events.
Professional Societies and Associations
American College of Cardiology (ACC)/American Heart Association (AHA) Task Force on Clinical Practice Guidelines
Kusumoto8 provides a consensus statement on behalf of the ACC/AHA and the task force for clinical practices. The statement provides an overview and recommendations regarding appropriate use of AECG monitoring, particularly in the context of diagnosing bradyarrhythmia, and patients with bradycardia and cardiac conduction delays, patients can be managed with a 24-to-48-hour continuous AECG. For patients that present with symptoms that are greater than 30 days between symptoms, the use of a broad array of modalities, such as long-term monitors, implantable cardiac monitors, etc., would be appropriate if the initial non-invasive evaluation was not diagnostically conclusive. The guideline indicates that the “Choice of device is predicated on frequency of symptoms and the degree to which symptoms incapacitate the patient” and that regardless of the monitoring system, it is important for the system to notify health care providers in a timely fashion, especially in regard to identifying potentially dangerous arrhythmias.8(p399)
American Heart Association /American College of Cardiology/ Heart Rhythm Society Clinical Practice Guidelines
Al-khatib9 provides clinical guidelines for the use of AECG monitoring indicating that suspected arrhythmias, the frequency of arrhythmias, and the associated symptoms dictate monitor type. For example, event or ‘Looping’ monitors are more appropriate and have greater diagnostic yields for sporadic symptoms. It further explains that when ventricular arrhythmias are identified and potentially harmful, AECG may not be appropriate. Further information upon the use of AECG monitoring is indicated when assessing medical therapy response.
International Society for Holter and Noninvasive Electrocardiology (ISHNE), and the Heart Rhythm Society (HRS) expert consensus statement
Steinberg7 provides a consensus statement that outlined the limitations, clinical indications, pharmacological treatment of arrhythmias, and the use of external monitoring for pacemaker malfunctioning/placement. It is noted that for the selection of specific AECG monitors, one must consider the diagnostic power, the monitoring capability and the accuracy, local availability, symptom frequency, patient compliance and the condition of the patient. Within the article there are descriptions of advantages and limitations associated with each AECG monitor. The clinical indications for use of the various types of monitors can include the following: syncope, bradyarrhythmia, tachyarrhythmia, palpitations, chest pain and coronary ischemia, ischemic heart diseases and postinfarction, hypertrophic cardiomyopathy, arrhythmic right ventricular dysplasia/cardiomyopathy, Wolff-Parkinson-White syndrome, inherited primary arrhythmic diseases, Short or Long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardias, early repolarization syndromes, idiopathic ventricular fibrillation with nonischemic dilated cardiomyopathy, dialysis and chronic kidney disease associated arrhythmias. It is noted that the use of monitoring with AECG for neurological and muscular disease is controversial. The article further indicates an appropriate clinical assessment may include a continuous AECG, and if unsuccessful, additional monitoring should include an intermittent external loop recording. If patients remain undiagnosed after prolonged noninvasive monitoring, an internal loop recorder (ILR) may be necessary.