Diagnostic Yield and Optimal Duration of Continuous-Loop Event Monitoring for the Diagnosis of Palpitations: A Cost-Effectiveness Analysis

Palpitations are one of the most common reasons why patients present to internists and cardiologists. Holter monitoring is routinely used to identify the cause of palpitations, but palpitations are often sporadic and may not occur during the 24 to 48 hours of conventional Holter monitoring [1, 2]. Patient-activated continuous-loop event recorders allow more prolonged surveillance and have proven to be more efficacious and cost-effective than Holter monitoring for the diagnosis of palpitations [1, 3], but the optimal duration of event recording for the indication of palpitations has yet to be defined. To address this issue, we prospectively evaluated the yield and timing of diagnoses made with continuous-loop event recorders in 105 consecutive patients referred for evaluation of palpitations. We also sought to determine the incremental cost-effectiveness of each week of event monitoring for palpitations. Methods Patients Between May and November 1996, 112 ambulatory patients were referred to the Arrhythmia Monitoring Laboratory of Beth Israel Hospital, Boston, Massachusetts, for placement of a continuous-loop event recorder to evaluate palpitations. Seventy percent of the patients were referred by general internists, and the rest were referred by cardiologists and electrophysiologists. We excluded 7 patients (6%) from analysis because of incomplete documentation of the timing of transmissions or because the patient could not confirm that the transmitted event represented his or her clinical palpitations. The remaining 105 patients made up the study sample. Monitoring Protocol All studies were done with a King of Hearts monitor (Instromedix, Hillsboro, Oregon). The duration of monitoring was determined by the referring physician. During each transmission, the technical staff of the Arrhythmia Monitoring Laboratory questioned the patient to ensure that the symptom provoking the transmission was identical to the palpitations for which the monitor had originally been ordered. Serious arrhythmias were defined as atrial fibrillation or atrial flutter of any duration, any sustained supraventricular tachycardia, symptomatic sustained or nonsustained ventricular tachycardia, junctional rhythm, sinus bradycardia (<50 beats/min), and complete or high-grade heart block. Patients were informed of the nature of their rhythm only if it was defined as a serious arrhythmia or if they asked. Referring physicians were immediately notified of all serious arrhythmias or repeated transmissions (>3) of the same nonserious arrhythmia. Costs The monitoring cost was determined on a weekly basis and included the costs of monitoring equipment, laboratory technical staff, and the interpreting physician. All costs were assessed from the perspective of the medical care system and were expressed in 1997 U.S. dollars [4]. Equipment cost included the cost of the continuous-loop event recorder ($8.00 per week) and the cost of the central monitoring station [including an annual maintenance fee] $6.54 per week). We assumed that a single central monitoring station would have an economic life of 5 years and would serve 20 monitors continuously during that time. Technical costs ($3.90 per transmission) for each patient were calculated on a weekly basis by using the number of transmissions per week, a mean duration of 15 minutes per transmission, and the average hourly technician's wage plus benefits. The cost of the interpreting physician was based on the 1997 Medicare fee schedule ($268.00 per standard 4-week monitoring period) and was pro-rated for actual duration of monitoring in each patient. Data Analysis For our purposes, any event (serious or not) that was transmitted by the patient and was confirmed to represent the patient's palpitations was considered diagnostic. For each patient, the initial transmission of a particular rhythm was counted as a diagnostic event. Further transmissions of the same rhythm were not counted as new diagnoses, but subsequent transmissions of a different arrhythmia were considered to represent additional diagnoses. Continuous data are expressed as the mean SD with median values and selected interquartile ranges. Weekly transmission rates were highly skewed and thus were compared by using the Wilcoxon rank-sum test. The diagnostic yield of the continuous-loop event recorder was calculated in two different ways: as the percentage of patients successfully diagnosed as a function of time (patient-based analysis) and as the absolute number of new diagnoses per patient per week (diagnosis-based analysis). For the patient-based analysis, the cumulative percentage of patients with one, two, or three diagnoses as a function of time was estimated by using the Kaplan-Meier technique [5]; 95% CIs were determined by using the Greenwood approximation. For the diagnosis-based analysis, the absolute number of new diagnoses made in a given week was divided by the number of patients who continued to wear the monitor during that week. For this approach, standard errors at each time point were calculated on the basis of the Poisson distribution. Because we thought that patients could have more than one correct diagnosis for their palpitations, we chose cost per new diagnosis as the relevant measure of cost-effectiveness for the loop recorder. The incremental cost-effectiveness of each week of monitoring was calculated as the incremental cost for each week of monitoring divided by the number of new diagnoses per monitored patient for each week of monitoring. A 95% CI for each cost-effectiveness ratio was estimated by substituting the upper and lower confidence bounds for the number of diagnoses per monitored patient in the denominator of the ratio. Because previous studies have shown loop recording to be less costly and more effective than Holter monitoring for the diagnosis of palpitations [1], we did not consider Holter monitoring as an alternative strategy in the cost-effectiveness analysis. Results The study sample consisted of 78 women and 27 men with a mean age of 52 21 years (median age, 52 years [range, 19 to 78 years]). The mean duration of monitoring was 18 6 days (median duration, 16 days [range, 2 to 51 days]). All patients wore the continuous-loop event recorder for at least 2 days; 101 patients (97%) wore the device into week 2, and 71 (68%) wore it into week 3 or beyond. During week 1, the mean number of transmissions per patient wearing the monitor was 5.3 5.2 (median, 4 [interquartile range, 1 to 8]). During week 2, this number decreased to 3.7 4.9 transmissions per monitored patient (median, 2 [interquartile range, 0 to 6]; P < 0.001). During week 3 and beyond, it further decreased to 1.2 2.9 (median, 0 [interquartile range, 0 to 0]; P < 0.001). The decreasing number of transmissions was primarily due to less frequent transmissions among patients who had already received a diagnosis in week 1. Among patients who had at least one diagnostic transmission during week 1, the number of transmissions decreased from 6.6 5.1 (median, 6 [interquartile range, 3 to 10]) to 4.4 5.1 (median, 3 [interquartile range, 0 to 7]) during week 2 and 1.5 3.1 (median, 0 [interquartile range, 0 to 1]) during week 3 (P < 0.001 for both comparisons). Patients without a diagnosis in the first week of monitoring had 1.0 2.3 transmissions (median, 0 [interquartile range, 0 to 0]) during week 2 and no transmissions in week 3 and beyond. During week 1, 109 diagnostic rhythm strips were transmitted for an average of 1.04 diagnoses per patient (95% CI, 0.84 to 1.28 diagnoses per patient) (Table 1). Of these transmissions, only 30 (28%) were considered clinically important or potentially serious (Table 2). The remaining 79 diagnostic transmissions included transmissions of normal sinus rhythm (21%), atrial premature beats (22%), isolated ventricular premature beats (23%), and sinus tachycardia (6%). During week 2, the diagnostic yield decreased to 0.17 diagnoses per patient (CI, 0.03 to 0.25 diagnoses per patient). An additional 17 diagnoses were made in 17 patients; 8 were considered potentially serious (3 diagnoses of atrial fibrillation and 5 diagnoses of paroxysmal supraventricular tachycardia). Only one new diagnosis (isolated ventricular premature depolarization) was made in week 3; this occurred in a patient who had his first diagnosis established in week 1. Thus, the yield in week 3 was only 0.01 diagnoses per monitored patient (CI, 0 to 0.04 diagnoses per monitored patient). Because we considered any new rhythm transmitted during an episode of confirmed palpitations to be diagnostic, one patient could receive one or more diagnoses for his or her palpitations. In fact, multiple diagnoses were made in 38 patients (2 diagnoses in 35 patients and 3 diagnoses in 3 patients). Table 1. Number of New Patients Receiving a Diagnosis and New Diagnoses by Week of Monitoring among 105 Patients Referred for Evaluation of Palpitations Table 2. Serious Diagnoses by Week of Monitoring Figure 1 and Figure 2 show the cumulative diagnostic yield of the continuous-loop event recorder as a function of monitoring duration. When any transmission that was confirmed to represent the patient's symptom of palpitations was considered diagnostic, the per-patient yield was 80% (CI, 72.2% to 87.8%) after week 1, was 83.9% (CI, 76.7% to 91.1%) after week 2, and was unchanged after week 3 (Figure 1, top). Second diagnoses were made in 23.2% (CI, 14.4% to 32.0%) of patients during week 1, and the cumulative incidence of second diagnoses increased to 31.2% (CI, 22.0% to 40.4%) after week 2 and to 32.7% (CI, 23.3% to 42.1%) after weeks 3 and 4 (Figure 1, bottom). A third diagnosis was made in three patients during the monitoring period, for a cumulative incidence of 3.1% (CI, 1.4% to 4.8%) after week 2 that was unchanged thereafter. When only serious arrhythmias were considered diagnostic, the diagnostic yield was significantly lower at each time point (Figure 2) and did not in