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How Much Should a Ecg Continuous Monitoring Service Cost

Written By Wednesday 26 October 2022 Add Comment Edit

Atrial fibrillation (AF) is a common and treatable cause of ischemic stroke. AF causes approximately 15% of strokes,1 and treatment with anticoagulation reduces the annual risk of recurrent stroke in patients with AF by two thirds.2 Thus, it is important to determine whether patients who have had an ischemic stroke have underlying AF. However, AF is frequently paroxysmal and asymptomatic, making its diagnosis difficult.3 To address this, clinical guidelines recommend that patients with ischemic stroke undergo at least 24 hours of inpatient cardiac monitoring to detect underlying AF.4

More prolonged outpatient cardiac monitoring, however, is not widely accepted5 despite studies suggesting that it increases the chance of detecting paroxysmal AF.6–11 Anticoagulation has been proven to reduce the risk of recurrent stroke in patients with AF, and it follows that the detection and appropriate treatment of more cases of paroxysmal AF through the use of more prolonged cardiac monitoring will lead to better clinical outcomes.2 On the other hand, monitoring patients with stroke for >24 hours incurs additional cost and inconvenience, and its cost-effectiveness is unknown. We therefore examined the cost-effectiveness of outpatient cardiac monitoring to detect AF after ischemic stroke.

Materials and Methods

Design

We calculated the cost per quality-adjusted life-year (QALY) gained by outpatient cardiac monitoring after ischemic stroke. As detailed subsequently, we used meta-analysis to obtain key model inputs. We compared 2 strategies: (1) standard care, whereby aspirin is prescribed after ischemic stroke and no outpatient cardiac monitoring is performed; versus (2) an additional 7 days of outpatient cardiac monitoring, which could detect AF and trigger a change from aspirin to warfarin.

Analysis

Because the yield of outpatient cardiac monitoring after ischemic stroke was a key input in our model, we estimated this parameter using a systematic review of the English-language literature. We used broad, standardized criteria (Table 1) to search all studies published between 1966 and 2008 and listed in the MEDLINE database. One investigator (H.K.) reviewed all abstracts identified in this manner and excluded studies that were obviously irrelevant. Two investigators (M.H. and D.J.) blinded to the study author(s) and journal independently reviewed the remaining studies and selected those that fulfilled prespecified inclusion criteria. Data were extracted using standardized forms. Disagreements were resolved by a third investigator (H.K.). The searches were complemented by reviewing the reference lists of all included publications and by using the "Related Articles" function on PubMed. Study authors were contacted for necessary clarifications and to inquire about unpublished data or studies. Four studies of the yield of outpatient cardiac monitoring in patients without AF after 24 hours of monitoring fulfilled our inclusion criteria. Schuchert et al studied patients for an additional 2 days and found new AF in 4.9% of patients9; Barthelemy et al monitored for an additional 3 days and found new AF in 7.7% of patients8; and Jabaudon et al monitored for an additional 7 days and found new AF in 5.7% of patients.7 Tayal et al monitored for an additional 21 days and found new AF in 23% of patients, but only 5.4% had episodes long enough to meet the standard definition of paroxysmal AF (ie, lasting >30 seconds).10,12 Using a random-effects model based on the method of DerSimonian and Laird,13 we performed a meta-analysis of these studies to estimate the yield of outpatient monitoring. All analyses were performed on the logit of the reported data to avoid compression of the standard error that can occur when the observed proportions are near zero.14 We tested for significant heterogeneity between studies using the Cochran Q test as well as the I2 method of Higgins and Thompson.15,16 Based on this analysis, we estimated that the yield of outpatient monitoring would be 5.9% (95% CI, 3.6% to 9.3%). There was no evidence of significant heterogeneity among these 4 studies (Q test P=0.78; I2=0).

Table 1. Search Strategy and Inclusion Criteria of Literature Search for Yield of Outpatient Cardiac Monitoring to Detect AF After Ischemic Stroke

Search Strategy Inclusion Criteria
("Electrocardiography, Ambulatory" [Mesh] OR ambulatory ECG OR EKG OR Holter OR "cardiac monitoring" OR telemetry OR "loop recorder") Consecutive patients with ischemic stroke
AND ("Atrial Fibrillation" [Mesh] OR "Atrial Flutter" [Mesh] OR "atrial fibrillation" OR flutter) More than 24 hours of continuous cardiac monitoring Specifically report AF as an outcome
AND Either exclude or state proportion of patients with known history of AF, AF on baseline electrocardiogram, and AF on <24 hours of monitoring
("Stroke" [Mesh] OR stroke OR CVA OR "transient ischemic attack" OR "cerebral infarction" OR "cerebrovascular accident")

Based on preliminary data from a study of new diagnoses of AF after ischemic stroke,17 we estimated that 25% of cases of asymptomatic paroxysmal AF not detected by standard inpatient cardiac telemetry would be diagnosed before a recurrent stroke even without outpatient cardiac monitoring. Therefore, AF would be diagnosed in 5.9% of the monitoring group and 5.9%×25%=1.45% of the standard care group. These numbers were then used to assign the cost and utility of warfarin therapy to each group as calculated subsequently.

As previously detailed,18 we used a semi-Markov model19 to compare the cost and utility of warfarin and aspirin therapies to prevent stroke in patients with AF. In the interaction between AF and cerebrovascular disease, the probability of moving from 1 health state to another depends on the previous state (ie, a patient with AF with prior stroke is more likely to have a stroke in the future than 1 with uncomplicated AF). Thus, we modeled multiple health states (eg, uncomplicated AF, AF and prior stroke, AF and prior intracerebral hemorrhage, etc). Our base case was a hypothetical cohort of 70-year-old patients with nonvalvular AF and prior ischemic stroke. We reviewed relevant clinical trials of warfarin therapy for stroke prevention in patients with AF to obtain the following key model inputs: a 4.5% annual rate of ischemic stroke despite the fact that the patient was on aspirin, a 0.48 relative risk of stroke with warfarin compared with aspirin, a 0.4% annual rate of hemorrhagic stroke with warfarin, and a 0.59 relative risk of hemorrhage with aspirin compared with warfarin (Table 2).18 In our model, detection of AF by cardiac monitoring would change treatment to warfarin in all cases; in other words, those with existing indications for or contraindications to warfarin would not undergo monitoring. All patients without AF would be treated with aspirin.20

Table 2. Value and Source of Key Model Inputs Used in the Base Case and Ranges Used in Sensitivity Analysis *

Variable Value Range References
*Further details about the variables used to calculate the cost and utility of warfarin versus aspirin in this model have been published previously.18
Age, years 70 65–90 Assumed
Male, % 50 50 Assumed
Rate of ischemic stroke on aspirin, % per year 4.5 2–12 18
Relative risk of stroke, warfarin versus aspirin 0.48 0.37–0.63 18
Rate of hemorrhagic stroke on warfarin, % per year 0.4 0.4–1.2 18
Rate of major hemorrhage on warfarin, % per year 2.5 2.0–4.0 18
Relative risk of hemorrhage, aspirin versus warfarin 0.59 0.5–0.7 18
Utility of each life-year on warfarin 0.987 0.953–1.0 18
Utility of each life-year on aspirin 0.998 0.994–1.0 18
Utility of each life-year given major residual symptoms 0.39 0–1.0 18
Utility of each life-year given minor residual symptoms 0.75 0–1.0 18
Yield of outpatient cardiac telemetry to detect AF, % 5.9 0–20 7–10
Rate of diagnosis of AF without outpatient monitoring 25 0–95 17
Rate of incidental arrhythmias requiring evaluation, % 5 0–20 10, 24, 25
Cost of outpatient monitoring, $ 168 50–2500 23, 52, 53
Rate of β-blocker use, % 100 0–100 12, 21, 33
Rate of cardioversion or ablation, % 0 0–50 12, 21, 33
Rate of pacemaker placement, % 0 0–5 10, 24, 25, 34
Rate of electrophysiological study, % 0 0–3 34–38
Rate of depression, % 0 0–2.5 39–41
Utility of remaining life-years with arrhythmia 1.0 0.99–1.0 39–41

Because monitoring would detect asymptomatic cases of AF, and because a rhythm control strategy does not reduce the risk of thromboembolism,21 patients found to have AF would not undergo cardioversion or ablation and would instead be prescribed lifelong generic β-blockers to control their heart rate.12 The estimated cost of therapy for heart-rate control, based on the average annual wholesale cost of generic metoprolol at a dose of 50 mg twice daily, would be $403 per year.22 We estimated that 1 week of outpatient monitoring (with an event-triggered loop recorder) would cost $168, including the cost of equipment, technician services, and physician interpretation.23 We assumed that monitoring would incidentally reveal potentially serious cardiac arrhythmias other than AF in 5% of patients10,24,25 necessitating a cardiological evaluation. The estimated cost of this evaluation, based on the Medicare payment for a moderate-complexity outpatient consultation (Current Procedural Terminology code 99244), would be $150.26,27 We did not include the cost of echocardiography because it is routinely included in the evaluation of patients with stroke.4

We calculated costs from the perspective of a health maintenance organization or insurance company paying for medical care and prescription drugs. Lost wages are small in this population28 and were captured in the utilities used for the various health states. Our analysis was identical to 1 taking a societal perspective, except for the exclusion of costs borne by caretakers. We did not calculate the direct effect of outpatient cardiac monitoring on patients' quality of life because it is well tolerated and the duration of monitoring is relatively short29; however, the potential long-term effects on quality of life of a diagnosis of AF or an incidentally discovered arrhythmia were explored in sensitivity analyses. Costs and life-years were discounted at 3%.30 Costs and utilities were projected over a maximum of 20 years; median expected survival was 13.3 years. Costs were converted to 2010 dollars using the medical care component of the consumer price index.31 We defined cost-effective as a cost-utility ratio of ≤$50 000 per QALY.30 To examine the effects of our assumptions and model inputs on the cost-utility ratio, we performed univariate sensitivity analyses by changing each input at the same time as holding other variables constant, as described in detail subsequently.

Sensitivity Analysis

We performed sensitivity analyses to examine our assumptions about the natural history of undiagnosed AF. Monitoring may (1) reveal AF that would never have been diagnosed; (2) reveal AF that would eventually have been diagnosed by other means; (3) truly rule out AF; (4) fail to reveal AF that then remains undiagnosed; and (5) fail to reveal AF that is eventually diagnosed by other means. Our base case assumed a mix of scenarios 1, 2, and 3, and we examined the effects of our chosen inputs by varying the relative proportions of these scenarios (ie, by varying the yield of outpatient monitoring and the proportion of patients whose AF would be diagnosed by other means before a recurrent stroke). Scenarios 4 and 5 had no effect on quality-adjusted survival in our model, because in these cases, the natural history of AF would be unaffected by outpatient monitoring; the effect on cost was addressed by varying the yield of outpatient monitoring.

To examine the effect of inputs used to calculate the cost and utility of warfarin therapy for stroke prevention, we varied the key parameters in our model across a wide range. We examined the cost implications of differing strategies for managing AF by varying the proportion of patients who would receive a trial of cardioversion in addition to rate-control agents. Guidelines recommend against cardioversion for patients in our study population,12 but it continues to be used in the community, albeit at a decreasing rate.32 In addition, we varied the proportion of patients who would undergo catheter ablation for AF, although this procedure is indicated in patients with symptomatic AF.33

To test our assumption that patients with incidentally discovered arrhythmias would require only cardiological consultation, we varied the proportion of patients for whom outpatient monitoring would lead to further interventions such as pacemaker placement or invasive electrophysiological testing. Based on studies of cardiac monitoring after stroke,10,24,25 we estimated a priori that monitoring might directly lead to pacemaker placement in at most 5% of patients.34 Furthermore, outpatient monitoring might directly lead to placement of an automatic implantable cardioverter–defibrillator (AICD) if it were to reveal nonsustained ventricular tachycardia in an asymptomatic patient with prior myocardial infarction and a left ventricular ejection fraction of 30% to 40%.34 For these patients to qualify for an AICD, invasive electrophysiological study must show inducible ventricular fibrillation or sustained ventricular tachycardia,34 which might be found in approximately one third of these patients.35 In our base case, we assumed that a negligible proportion of patients would fit this narrow and specific profile, but we varied the proportion in our sensitivity analyses.36 Using studies of cardiac monitoring after stroke,10,24,25 the prevalence of congestive heart failure in patients with stroke,20 and studies of echocardiography after stroke,37,38 we estimated a priori that at most 3% of patients might undergo an invasive electrophysiological study to evaluate the need for an AICD. We also performed a separate sensitivity analysis taking into account the QALYs gained from AICD placement.36

Lastly, the discovery of AF and other arrhythmias may affect the cost-effectiveness of outpatient monitoring by decreasing patients' quality of life. We explored this in our sensitivity analyses by examining the effects of major depression (with a reduction of 0.2 in the utility of patients' remaining life-years39) in a plausible proportion of patients discovered to have AF or another arrhythmia. We also examined this from a slightly different perspective by assuming a small decrease in the value of the remaining life-years of all patients with AF or another arrhythmia. Given the relatively small increases in symptoms of depression and anxiety40 or absenteeism from work41 found in studies of screening for asymptomatic conditions, we estimated a priori that at most 2.5% of patients diagnosed with AF or another arrhythmia might develop depression because of the new diagnosis, or that the utility of the remaining life-years of all patients with AF or another arrhythmia might be reduced by at most 1%.

Results

Cost-Utility

In a 70-year-old patient with nonvalvular AF and prior ischemic stroke, lifelong warfarin therapy would result in a gain of 0.782 QALYs and would cost $1627 more than aspirin (this includes the higher cost of warfarin therapy minus the cost savings from fewer strokes compared with aspirin). Outpatient cardiac monitoring would detect 59 new cases of AF for every 1000 patients monitored compared with 15 new cases that would be diagnosed per 1000 patients without monitoring and by triggering warfarin therapy would result in a comparative gain of 34 QALYs. The cost of monitoring 1000 patients would be $168 000; the cost of β-blocker therapy and the comparative cost of warfarin in those identified to have AF would be $264 000; and the cost of cardiological consultation in those with an incidentally discovered arrhythmia other than AF would be $7500, resulting in a net cost of approximately $440 000. Therefore, the cost-utility ratio of outpatient cardiac monitoring would be approximately $13 000 per QALY gained (Table 3).

Table 3. Costs and Quality-Adjusted Survival Associated With Outpatient Cardiac Monitoring in the Base Case, Which is a Hypothetical Cohort of 70-Year-Old Patients With AF, Prior Stroke, and No Contraindication to Warfarin Therapy

Outpatient Monitoring Standard Care Difference
*This is the net cost of warfarin therapy compared to aspirin therapy, which reflects the higher cost of warfarin as well as the cost savings from prevention of strokes compared with aspirin.
No. of hypothetical patients 1000 1000
Yield (no. of cases of AF detected) 59 15 44
Lifetime cost associated with warfarin,* $ 95 000 24 000 71 000
Lifetime cost of β-blockers, $ 257 000 64 000 193 000
Cost of cardiological evaluation, $ 7500 0 7500
Cost of monitoring, $ 168 000 0 168 000
Net cost, $ 528 000 88 000 440 000
Increase in QALYs 46 12 34
Cost-utility ratio ($/QALY) 13 000

Sensitivity Analysis

The cost-utility ratio of outpatient monitoring was plotted for a range of values of key model inputs (Figure). Monitoring was cost-effective at any yield >0.8% and any cost <$2000 per patient. In addition, outpatient monitoring remained cost-effective even if up to 85% of patients with underlying AF were to be diagnosed without outpatient monitoring and started on warfarin before a recurrent stroke; in other words, even if only 15% of those with underlying AF were to remain undiagnosed until presenting with another stroke, the QALYs that would have been saved by expeditiously diagnosing that small group of patients would justify the expense of routine outpatient monitoring. Lastly, outpatient monitoring after stroke remained cost-effective even if it were to lead to the maximum reasonable proportion of patients undergoing additional interventions such as electrophysiological study or pacemaker or AICD placement.

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Figure. Univariate sensitivity analyses of the cost-utility ratio of outpatient cardiac monitoring as a function of key variables. Base case values of model inputs are shown in Table 2.

Discussion

In this cost-utility analysis based on a systematic review of the literature, 1 week of continuous outpatient cardiac monitoring after ischemic stroke appears cost-effective through identification of patients with underlying paroxysmal AF who would benefit from warfarin therapy. Outpatient monitoring would be expected to establish a new diagnosis of AF in 4.4% of patients at an approximate cost of $13 000 per QALY gained, well below a standard $50 000 per QALY threshold generally considered cost-effective.30

When determining the utility of warfarin versus antiplatelet therapy in patients with AF and stroke, we chose aspirin as the standard antiplatelet agent for several reasons. First, we could not find any randomized trials comparing warfarin with clopidogrel or low-dose aspirin plus extended-release dipyridamole for the prevention of recurrent stroke in patients with AF. A recent trial compared warfarin with the combination of aspirin and clopidogrel,42 but in our base case, patients with undiagnosed AF would be treated with a single antiplatelet agent per the standard of care.20 Second, although clopidogrel and low-dose aspirin plus extended-release dipyridamole may be slightly superior to aspirin for secondary stroke prevention, a recent analysis showed this difference to be slight43 and probably not of significance to our model. In estimating the annual risk of stroke with aspirin in our patient population, we initially looked to 2 randomized trials comparing warfarin with aspirin for the prevention of recurrent stroke in patients with AF.44,45 However, in this era of aggressive statin use46 and blood pressure control,47 the annual rate of recurrent stroke on aspirin in patients with AF is probably lower than the 9% to 10% rate seen in these 2 studies.44,45 In a recent trial, patients with AF and a history of stroke or transient ischemic attack who were not eligible for warfarin had a 6.3% annual rate of recurrent stroke while taking aspirin.48 To be conservative, we estimated a 4.5% annual risk of recurrent stroke with aspirin. It is notable that even as aggressive lipid and blood pressure control has led to lower overall rates of recurrent stroke in patients with AF, warfarin remains superior to antiplatelet therapy for the prevention of recurrent stroke,42 and therefore our assumptions about the efficacy of warfarin remain applicable. Furthermore, although there are many promising new treatments for stroke prevention in AF such as the direct thrombin inhibitor dabigatran49 and devices for percutaneous closure of the left atrial appendage,50 these treatments have not been widely proven and adopted in clinical practice, and for now, warfarin remains the gold standard for the prevention of thromboembolism in patients with AF.51

To examine the effect of age on the cost-effectiveness of outpatient cardiac monitoring, we varied the age of patients in our model from 65 to 90 years. Assuming a constant rate of stroke throughout this age range, outpatient cardiac monitoring was more cost-effective in younger patients, probably because of the greater cumulative risk of stroke in younger patients with AF and the higher long-term costs of caring for younger stroke survivors. However, this analysis did not account for the fact that younger patients with AF face a lower yearly risk of stroke than older patients. Furthermore, it is important to emphasize that our sensitivity analyses did not extend to patients <65 years of age, and so our results cannot be extrapolated to young patients with stroke for whom many of the parameters we assumed in our model may not be applicable.

In selecting cost inputs for our base case, we used the cost of 1 week of monitoring, because there are few data on the yield of longer periods of monitoring. However, outpatient cardiac event monitors are commonly reimbursed on a 30-day basis.52 The cost of 30 days of outpatient cardiac monitoring ranges from $284 to $783 with an average of $532.23,53 As seen in our sensitivity analyses, outpatient monitoring remained cost-effective throughout this range, even without assuming an increased yield from a longer period of monitoring. We based our model on the use of autotriggered, nonattended, surface loop recorders as the most economical and rational choice for monitoring. A wide variety of devices and services are available to provide outpatient ambulatory electrocardiography; choices include implantable versus surface electrodes, the real-time availability of a technician or physician to review recordings, patient- versus autotriggered recording, and automatic versus manual data transmission. Patient-triggered event monitors are unlikely to detect asymptomatic AF. Furthermore, although the detection of AF in a patient with a recent stroke should lead to prompt consideration of anticoagulation therapy, it is not a medical emergency requiring 24-hour technician or physician review. The study that we used to estimate the cost of cardiac monitoring did not specify whether the monitors used were patient- or event-triggered,23 but these types of monitors have similar costs and reimbursement.52

In estimating the utility of outpatient cardiac monitoring, we assumed that underlying paroxysmal AF not diagnosed at the time of stroke would eventually be diagnosed before a recurrent stroke in one fourth of cases. This assumption was based on preliminary findings from a study examining the rate of new diagnoses of AF after ischemic stroke17; regardless, our cost-utility ratio was relatively insensitive to changes in this proportion. Furthermore, our model assumed a flat rate of stroke recurrence, but the risk of recurrent stroke in patients with AF is probably higher in the short term; a recent meta-analysis of randomized trials of anticoagulation for acute cardioembolic stroke showed a 4.9% rate of recurrent stroke within 2 weeks.54 Although outpatient monitoring would not lead to treatment of AF within the first few weeks, both for practical reasons (ie, the time required to arrange and obtain results from monitoring and then achieve therapeutic levels of anticoagulation) and safety reasons (ie, the increased risk of hemorrhage seen with acute anticoagulation for stroke from AF55), the asymptotic nature of the rate of recurrent stroke may increase the importance of rapidly diagnosing AF. This would partially offset the fact that patients with underlying AF may eventually be diagnosed in the long term without monitoring. In addition, in our base case, we assumed that all patients with ischemic stroke would be monitored, but monitoring only patients with unexplained or suspected cardioembolic stroke may increase the yield of monitoring. In a recent study, 30 days of outpatient monitoring revealed previously undiagnosed AF in 20% of selected patients with cryptogenic stroke.11 When including the study by Tayal et al in our meta-analysis, we conservatively included only episodes of AF lasting >30 seconds, but these investigators found briefer episodes of AF in 23% of patients with cryptogenic stroke.10

Monitoring in this population aims to detect cases of asymptomatic AF, and so we did not include in our base case the costs of cardioversion or ablation, because these procedures are indicated in selected patients with symptomatic AF,33 which would come to light even without monitoring. We further assumed that all patients with a potentially serious arrhythmia other than AF would simply be referred to a cardiologist for evaluation. However, it is possible that some patients would undergo cardioversion or ablation or receive more extensive investigation of incidental arrhythmias, thereby decreasing the cost-effectiveness of outpatient cardiac monitoring. Regardless, in our sensitivity analyses, outpatient cardiac monitoring remained cost-effective if the maximum reasonable proportion of patients underwent cardioversion, ablation, electrophysiological testing, or pacemaker or AICD placement, even without considering any QALYs gained from these procedures.

In addition to the cost implications of incidental findings as discussed, we also examined their effect on patients' quality of life. Studies have suggested that the incidental discovery of medical conditions may increase anxiety, depressive symptoms, and absenteeism from work39,40; the discovery of AF or other asymptomatic arrhythmias by outpatient monitoring may have similar adverse effects. However, the effect on quality of life in these studies was clinically small. Furthermore, it may not be appropriate to directly compare the reduction in disability and the years of life saved by detection of AF with a reduction in patients' quality of life from incidentally discovered asymptomatic conditions that do not affect patients' lifespans.56 In any case, varying the utility of the remaining life-years of patients with incidentally discovered arrhythmias throughout a reasonable range did not significantly change our final cost-utility ratio.

Lastly, cost-effectiveness analyses should preferably take a societal perspective30 and, strictly speaking, ours did not because we excluded the costs of caretakers. However, because monitoring would be expected to reduce the rate of recurrent stroke and therefore the need for caretakers, including these costs would probably have increased the cost-effectiveness of outpatient cardiac monitoring.

Summary

Our analysis suggests that 1 week of outpatient cardiac monitoring after ischemic stroke is cost-effective. Guidelines published by the American Heart Association and the American Stroke Association in 2006 recommend that patients with acute ischemic stroke undergo cardiac monitoring to detect important cardiac arrhythmias, including AF.20 They note the absence of clinical trials addressing the optimal length of monitoring and report a general consensus that monitoring should extend for at least 24 hours. Multiple studies have shown that monitoring beyond 24 hours detects more cases of AF,6–11 but objections to outpatient cardiac monitoring have been raised because of a perceived lack of cost-effectiveness.5,57 Therefore, our study may justify changing the guidelines so that routine outpatient cardiac monitoring is recommended. Our analysis would be made more robust by more data on the yield of outpatient cardiac monitoring, but even with existing data, we recommend at least 1 week of outpatient cardiac monitoring to detect underlying AF in patients with unexplained stroke.

B.F.G. thanks the American Heart Association for salary support.

Disclosures

None.

Footnotes

Correspondence to Hooman Kamel, MD, 505 Parnassus Avenue, Box 0114, San Francisco, CA 94143. E-mail [email protected]

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Source: https://www.ahajournals.org/doi/10.1161/strokeaha.110.582437

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