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J Am Coll Cardiol, 2003; 42:502-504, doi:10.1016/S0735-1097(03)00660-0
© 2003 by the American College of Cardiology Foundation
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EDITORIAL COMMENT

Implantable looprecorders

dollars and sense*

Cheryl C. Kürer, MD, FACC{dagger},*

{dagger} Pediatric Center for Heart Disease, Hackensack University Medical Center, Hackensack, New Jersey, USA

* Reprint requests and correspondence: Dr. Cheryl C. Kürer, Pediatric Center for Heart Disease, 30 Prospect Avenue, Hackensack, New Jersey 07601, USA.
cckmd{at}aol.com

Syncope is a common, often perplexing clinical problem causing emotional stress to patients, their families, and often, the physicians caring for them. In a large, 26-year prospective study of men and women ages 30 to 62 years, 3% of men and 3.5% of women experienced at least one syncopal episode (1). That study excluded adolescent and elderly populations. Syncope has been reported in up to 47% of healthy college men (2) and has been shown to have a 6% one-year incidence in elderly institutionalized patients 75 years and older (3). Although many who experience syncope do not seek medical advice, syncope accounts for approximately 3% of emergency room visits and 1% to 6% of hospital admissions in the U.S. (4,5).

"Syncope" is defined as a sudden, brief loss of consciousness associated with a loss of postural tone that recovers spontaneously (6). The differential diagnosis of this symptom is extensive. Syncope may be divided into cardiac, neurally mediated, and noncardiac causes. Cardiac causes include organic heart disease such as aortic stenosis, hypertrophic cardiomyopathy, dilated cardiomyopathy, pulmonary stenosis, pulmonary hypertension, atrial myxoma, myocardial infarction, coronary disease, postoperative congenital heart disease, cardiac tamponade, and aortic dissection. Also included in this group are arrhythmias from sinus node disease, advanced degrees of heart block, pacemaker malfunction, supraventricular tachycardia, ventricular tachycardia, and torsade de pointes. Neurally mediated causes include vasovagal syncope, situational syncope, carotid sinus hypersensitivity, orthostatic hypotension, and postural orthostatic tachycardia syndrome. Noncardiac causes encompass neurologic conditions such as migraines, transient ischemic attacks, seizures, and subclavian steal syndrome. Other noncardiac causes include metabolic derangements, hyperventilation, anxiety disorders, major depression, and hysteria reactions (6–9).

Based on a review of published data between 1984 and 1990, Linzer et al. (8) estimated the cause of syncope to be neurally mediated in 24%, cardiac in 18%, neurologic in 10%, and psychiatric in 2%. Approximately 34% of cases remained unexplained. In a more recent review that in-cluded tilt testing, Alboni et al. (10) found that 58% of patients had neurocardiogenic syncope, 23% had cardiac syncope, and 18% of patients remained undiagnosed after conventional testing.

The prognosis in patients with syncope is variable and based on the patient’s age, overall health, and cause of syncope. In healthy persons, neurocardiogenic syncope is considered a benign entity (1,9). Morbidity, however, may have a significant impact, especially in the elderly. Mortality rates in patients with underlying cardiac disease and a cardiac cause of syncope have been reported at around 30% (4,11).


   The diagnostic dilemma
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 The diagnostic dilemma
Implantable loop recorders
 Cents and sensibility
 References
 
The diagnosis of syncope is hampered by its multiple etiologies, sporadic events, difficulty correlating symptoms with clinical data, and lack of a diagnostic gold standard. The cornerstone evaluation is a thorough history and physical examination in conjunction with a baseline electrocardiogram and postural blood pressure measurements. This basic evaluation may be diagnostic in 26% to 50% of patients (8,10,11). Further testing is guided by the initial evaluation and may include echocardiography to assess structural or functional pathology, despite its low diagnostic yield (3%) (10,12).

When arrhythmia is suspected, electrocardiographic monitoring during a clinical event unambiguously establishes the diagnosis. Because of sporadic events, Holter monitoring has only a 5% to 19% diagnostic yield (10,13). Loop recorders worn for several weeks or months have been shown to increase diagnostic yield to 35%; however, human error limits diagnostic efficacy in 32% of patients (14,15). Patients with known or suspected cardiac disease are at greatest risk for life-threatening events. Electrophysiologic (EP) studies in high-risk patients have a 50% diagnostic yield, including 21% with inducible ventricular tachycardia and 34% with bradycardia (13). Unfortunately, EP testing has low sensitivity (37%) in diagnosing transient bradyarrhythmias and may reveal clinically irrelevant disturbances in rhythm (16). In patients with structurally normal hearts, the diagnostic yield of EP testing is low (13).

Patients with suspected neurocardiogenic syncope and those with unexplained syncope have undergone head-up tilt testing. Sensitivity of tilt testing with and without pharmacologic provocation in patients with suspected vasovagal syncope has ranged from 67% to 83%, and positive tests have been reported in 26% to 90% of patients with unexplained syncope (13). Using head-up tilt and EP testing, 26% of patients remain undiagnosed (17). Additional metabolic or neurologic testing adds little except expense to the diagnostic yield of syncope unless underlying medical conditions or focal neurologic signs are present (4,11).


   Implantable loop recorders
Top
 The diagnostic dilemma
 Implantable loop recorders
Cents and sensibility
 References
 
In 1995, a novel approach to the diagnoses of unexplained syncope was reported in 16 patients using an implantable subcutaneous monitoring device capable of storing electrograms after patient activation for up to two years. Using this technique, an etiology for syncope was established in 94% of patients, with bradyarrhythmias predominating (18). In a multicenter series, implantable loop recorders established a symptom-rhythm correlation in 86% of patients with syncope during follow-up (19). However, 16% of patients were unable to properly activate the device, and 4% developed postoperative wound complications. Of 21 patients with documented arrhythmias, 18 had bradyarrhythmias and 3 had tachyarrhythmias. Potential problems with this technique include an inability to distinguish bradycardia by mechanism, the need for an invasive procedure with associated operative risks, and the possibility of placement in a high-risk patient who develops a fatal arrhythmia during monitoring (20).

A randomized assessment of the implantable loop recorder was recently reported (21). Sixty patients with unexplained syncope, left ventricular ejection fraction >35%, and history not typical for neurally mediated syncope were randomized into conventional testing (external loop recorder followed by tilt and EP study) or one-year prolonged monitoring strategies and given the option of crossover if the initial evaluation was negative. In this highly selected study group, prolonged monitoring was more likely to result in a diagnosis than was conventional testing (55% vs. 19%). In this issue of the Journal, the cost implications of this randomized trial were evaluated by Krahn et al. (22). Using regionalized Canadian cost estimates, this study concluded that the cost per diagnosis using the prolonged monitoring strategy was significantly less than the cost of conventional testing ($5,852 vs. $8,414) despite a higher initial cost investigation ($2,731 vs. $1,683). A greater incremental cost effectiveness ratio was reported after combining crossover data. Whether these data can be extrapolated to global investigations of syncope remains unclear; however, trends derived from this work may promote more cost-effective diagnostic strategies in selected patients.


   Cents and sensibility
Top
 The diagnostic dilemma
 Implantable loop recorders
 Cents and sensibility
References
 
The need for cost containment in the evaluation of syncope has been long recognized. In 1982, the average cost per patient undergoing syncope evaluation in the U.S. was $2,600, with an estimated cost of $24,000 per diagnosis (23). Annual per-patient cost has doubled in recent analysis (24). Estimated costs per diagnostic yield for commonly performed tests have been reported to range from $529 for the external loop recorder to $73,260 for EP testing in patients without structural heart disease (25). Nontargeted evaluations produce unnecessary expense, as demonstrated by patients with typical histories for vasodepressor syncope, in whom baseline testing resulted in elevated diagnostic costs (up to $16,000) above the cost of a confirmatory tilt study ($453) (26). In the Canadian study reported in this issue, 60% of patients underwent nondiagnostic neurologic testing before randomization into the clinical trial at an average cost of $1,327 (22).

Accurate and cost-effective diagnostic strategies must be employed in the evaluation of syncope. Funding for medical services is limited, and fiscal waste cannot be tolerated. Low-yield and unnecessary tests should be avoided. The use of implantable loop recorders in selected patients helps further the combination of cost containment and diagnostic accuracy in unexplained syncope. Targeted, judicious use of diagnostic testing is imperative in reducing costs and easing the economic burden of this perplexing and common medical problem.


   Footnotes
 
* Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. Back


   References
Top
 The diagnostic dilemma
 Implantable loop recorders
 Cents and sensibility
 References
 

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