Alternative Rhythm Recording Options
While the traditional Holter concept has been slow to advance, other rhythm recording options are available. The alternatives and various features are summarized in Table 1. This includes the event recorder, a Holter-like device with electrodes that provides continuous 'loop' recording for a limited time; however, recordings are erased and replaced with more up-to-date rhythms unless the patient activates the device to permanently store the rhythm concurrent with symptoms. Variants of event recorders allow for patient application and activation of a device to record a symptomatic arrhythmia after it has initiated.[4] Typically, the stored rhythm for an event recorder is just 30 s, although multiple episodes (typically up to 10 min) can often be saved. A major advance is that the device may be utilized for up to 30 days, valuable for patients with infrequent symptoms.
Table 1.
Comparison of the major heart rhythm monitoring options.
Concern has been raised regarding signal quality and the number of channels recorded in various rhythm monitoring options. Traditional Holter monitors utilize a minimum of three leads that produce multichannel recordings, typically two channels simultaneously. The newer monitors, including most event monitors, the cell phone monitor and the Zio Patch, record a single-channel ECG with digital filtering (Figure 3). These utilize newer signal component algorithms based on the single dipole model of the heart related to body surface potentials which account for the temporal movements and rotations of the cardiac dipole, together with advances in digital noise suppression.[5] A head-to-head comparison of multichannel Holter recordings with the single-channel Zio Patch found a highly significant correlation between the two recording modalities for atrial fibrillation with r = 0.96 and p < 0.0001.[6] The signal quality of Zio Patch recordings is further improved by consistent placement and a skin preparation kit (including an abrading tool and razor) provided with the patch (Figures 2 & 3).[102]
Figure 3.
Sample Zio® Patch rhythm strips.
AF: Atrial fibrillation; avg: Average; HR: Heart rate; No: Number; SVT: Supraventricular tachycardia.
The real-time mobile outpatient cardiac telemetry (MCOT) was first popularized over a decade ago.[7] Analogous to inpatient hospital telemetry systems, it permits real-time cardiac rhythm transmission to a monitoring center with subsequent physician notification of a suspected abnormality. Similar to a Holter, both event recorders and MCOT devices typically require electrodes and wires for monitoring. The MCOT device uses cellular technology to provide real-time surface electrogram transmission analogous to cardiac telemetry provided in inpatient hospital cardiology units. This concept provides the advantage of real-time monitoring transmitted to a vendor site supervised by a telemetry technician, who has the ability to notify the prescribing physician of a rhythm abnormality. Of course, there is no capability for emergent therapy delivery should a life-threatening rhythm, such as ventricular fibrillation or asystole, be uncovered. As a result of its cost, MCOT has been slowly accepted by physicians and insurers.[7,103]
In addition to clinical utility, reimbursement has driven the technology advances. Typically, physician practices purchase a Holter monitor recording and analysis system, yet commonly find the labor involved in placement and analysis may be cost–prohibitive. Recent reductions in reimbursement for MCOT also have limited its acceptance.[103] Unfortunately, insurance carriers have recognized that physicians will prescribe event recording systems even if cost–prohibitive. This 'loss-leader' concept is tolerated by physicians both in the interest of patient care as well as in the hope of uncovering an abnormality that could result in compensation for a subsequently better reimbursed procedure such as catheter ablation or device implant.
Recently, a smart-phone ECG reader has become available (AliveCor, CA, USA). The current product is limited for sale to licensed physicians in the USA and is only compatible with older generation Apple (CA, USA) iPhone® 4 and 4S models, with an iPhone 5-compatible device planned for the second quarter of 2013. It has the capability to store and save a 30-s single-channel rhythm recording. A similar concept is directly available to consumers as a standalone device (HeartCheck, BC, Canada) that also records a single-channel ECG for storage and later physician interpretation. Each of these devices only have a 30-s recording time per episode and are designed for recording symptomatic events after they have started. There is no public information as to why the Heart Check device was approved by the US FDA for direct sale to individuals, yet the AliveCor and Zio Patch products require prescription by a US licensed physician.
Invasive options for rhythm evaluation are also available. The implanted loop recorder is a variant of the event recorder, with improved sensitivity and functions without the need for the patient to use electrodes or wires.[8] However, it is invasive, implanted surgically, and does not provide therapy. It is estimated that less than 4000 implanted loop recorders are implanted annually worldwide.[104]
Even more invasive options include cardiac electrophysiologic study, which utilizes intracardiac temporary pacing and recording catheters in an attempt to initiate arrhythmias that may correlate with clinical rhythm abnormalities. Cardiac implanted electrical devices are pacemakers or implanted defibrillators, which not only store intracardiac rhythms, but also provide potentially life-saving therapy.[9] Of course, invasive options, such as electrophysiologic study or cardiac implanted electrical devices, are indicated only for selected patients.[10]
While it is beyond the scope of this publication to provide an algorithm for the proper diagnostic tool, generalizations can be made. Life-threatening symptoms such as cardiac arrest and recurrent syncope with associated trauma typically warrant hospitalization for real-time monitoring and consideration for invasive testing. Real-time monitoring is also available with MCOT devices, although emergency care is typically not promptly available. The most common indication for heart rhythm monitoring relates to less critical symptoms such as palpitations, heart racing, dizziness and irregular pulse, among others. If it is only desired to determine the rhythm during a symptomatic event, a leadless event monitor or the smart-phone ECG reader may be appropriate. For recording asymptomatic as well as symptomatic arrhythmias, a continuous recording device such as a Holter monitor or Zio Patch is preferable. The implanted loop recorder or diagnostic electrophysiologic study is generally reserved for patients with recurrent severe symptomatic events undiagnosed after use of less-invasive alternatives.
Future Cardiol. 2013;9(3):325-333. © 2013 Future Medicine Ltd.
