(Circulation. 1996;94:1350-1356.)
© 1996 American Heart Association, Inc.
Articles |
Hospital Readmission in Patients Treated With Tiered-Therapy Implantable Defibrillators
the Department of Cardiology, the Cleveland (Ohio) Clinic Foundation.
Correspondence to Sergio L. Pinski, MD, The Cleveland Clinic Foundation, Desk F15, 9500 Euclid Ave, Cleveland, OH 44195. E-mail pinskis@cesmtp.ccf.org.
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Abstract |
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Background We wished to determine the incidence, reasons, costs, and predictors of cardiac-related hospital readmission in patients with tiered-therapy implantable defibrillators. Hospital readmission in patients with defibrillators reduces their quality of life and increases the cost associated with such therapy.
Methods and Results We retrospectively studied 65 consecutive local patients (median age, 67 years; median ejection fraction, 0.34) who underwent tiered-therapy defibrillator implantation at this institution. Patients were followed for a median of 19 months (interquartile range, 10 to 27 months). The cause, duration, costs, and predictors of cardiac-related rehospitalizations were analyzed. There were 76 cardiac admissions for 34 patients. The rate of cardiac-related hospital readmission was 0.72 per patient-year of follow-up. Arrhythmia-related admissions accounted for 43 of such admissions in 24 patients. Actuarial freedom from cardiac-related admissions was 0.57 and 0.40 at 1 and 2 years, respectively. The median length of stay for hospital readmissions was 5 days (interquartile range, 3 to 8 days). The median cost per admission was $5842 (interquartile range, $3549 to $12 170). The time to first readmission and the total rehospitalization time per year of follow-up were associated with a poor preimplant New York Heart Association functional class. Readmission for cardiac arrhythmias was not predicted by clinical parameters.
Conclusions Rehospitalization for cardiac reasons is common in patients receiving implantable defibrillators and is responsible for substantial resource consumption. The need for readmission for arrhythmia-related reasons cannot be predicted by clinical parameters at the time of device implantation.
Key Words: heart-assist device • cost-benefit analysis • tachyarrhythmias • death, sudden • defibrillation
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Introduction |
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Implantable cardioverter-defibrillators (ICDs) are remarkably effective in preventing sudden cardiac death in patients with life-threatening ventricular arrhythmias.1 2 3 However, their impact on overall survival, cardiac morbidity, quality of life, and healthcare expenditure remains ill-defined.4 The use of ICDs is increasing, partly as a result of recent technological advances that have refined their versatility5 6 7 and facilitated their implantation.8 9 These advances have also prompted proposals to implant ICDs in populations previously considered unsuitable for this therapy.10 11 12 However, recent changes in the socioeconomic climate mandate justification of the use of expensive medical interventions.13 Since the realization that overall survival is unlikely to be dramatically improved in most patients treated with ICDs,14 15 a greater emphasis has been placed on "softer" clinical end points such as morbidity and cost-effectiveness. Although the morbidity and costs associated with initial ICD implantation are well established,16 17 previous studies of the long-term cost-effectiveness of ICD therapy did not systematically examine the impact of hospital readmissions on cumulative medical costs.18 19 20 In this retrospective study, we analyze the incidence, causes, predictors, and resource consumption of cardiac-related hospital readmissions in a population of consecutive patients who underwent initial successful implantation of a tiered-therapy ICD and were prospectively followed in a single center. Our findings will help to put in perspective the significant contribution of hospital readmission to overall morbidity and costs associated with modern ICD therapy.
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Methods |
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Patients
The study population consisted of 65 consecutive patients who underwent successful initial implantation of a tiered-therapy ICD system at the Cleveland Clinic Foundation between January 1, 1991, and December 31, 1993, and lived in Cuyahoga County or one of five surrounding counties. We were the primary providers of arrhythmia- and device-related care for these patients, none of whom emigrated from the area during the study period. Clinical characteristics of the patients are depicted in Table 1
. Preoperative comorbid conditions were classified by the Charlson et al21 comorbidity index, a weighted score of the number and severity of comorbid diseases.
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Hardware
Devices implanted included the PCD 7217B (Medtronic Inc) in 34 patients, the Cadence V100 (Ventritex) in 17 patients, the Ventak PRx 1700/1705 (Cardiac Pacemakers Inc) in 7 patients, the Res-Q 101-01 (Intermedics) in 5 patients, and the Guardian ATP 4210 (Telectronics) in 2 patients. Characteristics of the devices have been described previously.22 Defibrillator systems were implanted via a nonthoracotomy or thoracotomy approach according to the availability of investigational systems and the need to perform concomitant cardiac surgery. The 31 thoracotomy lead systems, including epicardial patches and sutureless epimyocardial rate-counting/pacing leads, were supplied by the following manufacturers: Cardiac Pacemakers, DAIG Corp, Intermedics, Medtronic, Telectronics, and Ventritex. Of the 34 nonthoracotomy lead systems, the Transvene lead (Medtronic) was used in 22 patients and incorporated a subcutaneous or submuscular patch in all but 1 patient. The Endotak lead system (Cardiac Pacemakers) was used in 8 patients; it was used in combination with the Ventak PRx defibrillator in 3 patients, 1 of whom needed a patch, and with the Cadence V100 in 5 patients, none of whom required a patch. The model 497-05 lead system (Intermedics) was used in 4 patients, all of whom required a patch. The characteristics of these lead systems have been described previously.17 Implant techniques and postoperative follow-up are described elsewhere.8 17 23
Antitachycardia pacing was allowed at discharge exclusively in patients with clinical sustained monomorphic ventricular tachycardia who exhibited reliable termination without any episode of acceleration at predischarge testing.24 Programmable features designed to enhance diagnostic specificity of the device were activated in only 1 patient before hospital discharge.
Follow-up
The follow-up period in all patients started on the day of hospital discharge after ICD implantation and ended on the date of death or June 30, 1994. No patients were lost during follow-up. In one patient, follow-up was censored at the time of elective hospital admission for a successful cardiac transplantation. At the time of each outpatient visit, patients were specifically questioned regarding hospitalizations outside of this institution. Pertinent information was obtained by reviewing patients' hospital records and by telephone contact with patients, their families, or their private physicians.
Classification of Hospital Readmissions
For each patient, all readmissions were classified as cardiac or noncardiac by consensus between two investigators (G.J.F., S.L.P.). For the purposes of this study, only cardiac readmissions were further scrutinized. Cardiac readmissions were subcategorized as arrhythmia-related or non–arrhythmia-related readmissions. Arrhythmia-related admissions were subdivided into those caused by ventricular arrhythmias (including readmissions for multiple appropriate defibrillator discharges), supraventricular arrhythmias, bradyarrhythmias (including pacemaker implant), antiarrhythmic drug side effects, device-related, and miscellaneous. Nonarrhythmic cardiac admissions were divided into those resulting from congestive heart failure or ischemic heart disease (eg, unstable angina, acute myocardial infarction). When patients were admitted for a combination of the above reasons, the dominant problem was considered to be the reason for readmission.
Cost Analysis
For hospital readmissions occurring entirely at this institution, cost data were retrieved from a commercially available data management system (Transition Systems, Inc), which consists of a detailed activity-based accounting system linked to a computerized database. A "bottom-up" approach25 was used to estimate all costs incurred during a hospital admission. Costs were measured by a combination of "microcosting" techniques and categorized as technical or professional, and each category was further divided into direct or indirect costs. Direct costs included those directly linked to the production of a given service (defibrillator hardware, disposable supplies, pharmaceuticals). Indirect (overhead) costs included those that cannot be directly traced to a given output such as electricity, laundry, and maintenance.
Statistical Methods
Continuous variables are presented as median and interquartile ranges. Rates of readmission were determined by dividing the number of hospitalizations by the total number of person-years of follow-up time both for individual patients and for groups. The probabilities of survival and freedom from cardiac-related and arrhythmia-related readmissions were estimated by the method of Kaplan and Meier. Associations between clinical variables and time to first cardiac-related or arrhythmia-related readmission were estimated by Cox proportional-hazards model. The total burden of cardiac-related admissions was assessed by computing the total hospital days for cardiac-related readmissions per month of follow-up. The Mann-Whitney test was used to compare the total hospitalization time for cardiac-related readmissions per year of follow-up for patients with and without the clinical variables of interest. For this purpose, continuous variables were dichotomized at the median value, except for age and left ventricular ejection fraction, which were dichotomized at 65 years and 0.30, respectively.26 A similar analysis was performed that considered only hospital days for arrhythmia- or device-related readmissions. Costs for arrhythmia-related readmissions versus those for readmissions for other cardiac causes were compared by the Mann-Whitney test. A two-tailed value of P
.05 was considered statistically significant for all comparisons. Statistical analyses were performed with Egret (Statistics and Epidemiology Research Corp) and Statistica 4.5 (StatSoft) software.
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Results |
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After a median follow-up of 19 months (interquartile range, 10 to 27 months), there were 76 cardiac-related readmissions in 34 patients (55%). There were seven cardiac-related hospital readmissions in 1 patient, six in 1, five in 1, four in 2, three in 6, two in 9, one in 14, and 0 in 31 patients. The rate of cardiac-related hospital readmission was 0.72 per patient-year of follow-up. The probability of freedom from cardiac-related readmission was 0.57 (95% CI, 0.43 to 0.68) and 0.39 (95% CI, 0.25 to 0.53) at 1 and 2 years, respectively (Fig 1
). The median duration of hospitalization for cardiac-related readmissions per patient-year of follow-up was 1.36 days (interquartile range, 0 to 6.77 days).
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The distribution of cardiac-related readmission according to categories is depicted in Fig 2.
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There were a total of 43 arrhythmia- or device-related readmissions in 24 patients (37%). The rate of cardiac-related hospital readmission was 0.40 per patient-year of follow-up. The probability of freedom from arrhythmia-related readmission was 0.71 (95% CI, 0.58 to 0.81) and 0.60 (95% CI, 0.45 to 0.73) at 1 and 2 years, respectively (Fig 1
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Ventricular Arrhythmias
Ventricular arrhythmias were responsible for 18 admissions for 14 patients. On 15 occasions, patients were admitted after the delivery of appropriate shocks for sustained ventricular tachyarrhythmias. One of these was precipitated by myocardial ischemia and was treated by percutaneous transluminal coronary angioplasty. Treatment included ICD reprogramming in 2 readmissions; in 1 patient, the pacing rate was increased because of bradycardia-induced arrhythmias, and in another, antitachycardia pacing was activated after its efficacy was confirmed during electrophysiological testing. Changes in the antiarrhythmic drug regimen were required during 7 readmissions in 6 patients, necessitating device retesting during 3 of these readmissions. Treatment with sotalol was started on 2 occasions; mexiletine in 2 (in 1, antitachycardia pacing was also enabled); and amiodarone, quinidine, and moricizine were each started on 1 occasion. One patient with hypokalemia received intravenous potassium replacement. Four patients were admitted for observation and to rule out reversible triggers for their ventricular arrhythmias. One patient died of intractable ventricular electrical storm. One patient was admitted for treatment of symptomatic ventricular bigeminy and, on another occasion, for frequent runs of nonsustained ventricular tachycardia triggering aborted ICD shocks. Treatment on both occasions consisted of increasing the ventricular pacing rate as well as initiating antiarrhythmic drugs (mexiletine and sotalol, respectively). Another admission occurred in 1 patient with hemodynamically compromising sustained ventricular tachycardia below the programmed rate cutoff. The rate cutoff was decreased and the new detection algorithm tested during induced ventricular arrhythmias.
Atrial Fibrillation
Atrial fibrillation was responsible for 11 admissions in 7 patients, 3 of whom suffered inappropriate shocks. Treatment in these cases consisted of external cardioversion, a change in antiarrhythmic drug regimen, and in 2 patients, radiofrequency catheter ablation of the AV node and insertion of a dual-chamber pacemaker with mode-switching capability.
Antiarrhythmic Drug Side Effects
In 3 patients, there were 5 admissions for evaluation and treatment of antiarrhythmic drug side effects and initiation of alternative drugs under ECG monitoring. Sotalol-induced fatigue and quinidine-related diarrhea each accounted for 1 admission in 1 patient, who was then treated with amiodarone. These changes necessitated device retesting on 2 occasions. Another patient was admitted for mexiletine-induced nausea and amiodarone-induced hypothyroidism on 1 occasion, and he was then treated with moricizine, which caused cholestasis, requiring readmission. Device retesting was performed after each drug change. Procainamide-induced lupus accounted for the other admission in another patient. Disopyramide was substituted for procainamide, and the device was not retested.
Hardware Problems
Readmission was required on 4 occasions in 4 patients for problems directly related to the implanted hardware. Infection of a nonthoracotomy ICD system occurred in 1 patient and required explantation, antibiotic therapy, and implantation of a new system. Migration of an epicardial patch that required surgical revision occurred in 1 patient, and premature battery depletion necessitating generator replacement occurred in another. In addition, 1 patient admitted for ventricular arrhythmias required surgical revision of an incidentally discovered folded subcutaneous defibrillation patch to prevent impending erosion. Undersensing during sinus rhythm occurred in 1 patient and was corrected by reprogramming of the sensitivity of the device with induction of ventricular fibrillation to ensure its reliable detection.
Need for Pacemaker Insertion
One patient with symptomatic sinus bradycardia despite ventricular demand pacing was admitted electively for the implantation of a dual-chamber, rate-responsive pacemaker. Permanent pacemaker implantation was required during 4 other admissions: in 2 after AV nodal ablation for treatment of paroxysmal atrial fibrillation and in another 2 because of antiarrhythmic drug-induced symptomatic sinus bradycardia.
Other Arrhythmic Reasons
Syncope or near syncope of undetermined cause despite extensive assessment accounted for 3 admissions for 3 patients. In another patient, readmission was required because of imagined ICD shocks necessitating psychiatric intervention.
Nonarrhythmic Reasons for Readmission
There were 25 admissions for 15 patients for treatment of heart failure and 8 admissions in 6 patients because of unstable angina.
Predictors of Cardiac- or Arrhythmia-Related Readmissions
Of the variables listed in Table 1, New York Heart Association (NYHA) functional class III to IV for congestive heart failure was the only one associated with a significantly shorter time to first cardiac-related readmission (1-year freedom from cardiac readmission, 0.29 [95% CI, 0.04 to 0.61] versus 0.6 [95% CI, 0.58 to 0.72]; hazard ratio, 3.08; P=.01, Cox proportional-hazards model; Table 2 and Fig 3). Similarly, NYHA functional class III to IV for congestive heart failure was the only variable with a significant association with total hospitalization time for cardiac-related readmission per patient-year of follow-up (median, 6.85 days; interquartile range, 1.29 to 36.51 days versus median, 0.73 days; interquartile range, 0 to 6.18 days; P=.038, Mann-Whitney test; Fig 4). No variable was significantly associated with time to first arrhythmia-related readmission or rehospitalization time for arrhythmia-related readmission. It should be noted that only 4 patients died during follow-up: 1 among the 7 patients in functional class III to IV at implantation and 3 among those in functional class I to II at implantation. The 1-year survival probabilities were 0.76±0.17 versus 0.96±.03, respectively (P=.26, log-rank test).
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Hospital Costs
The median length of stay for hospital readmissions was 5 days (interquartile range, 3 to 8 days). Patients were admitted to an intensive care unit during 20 of the 76 admissions (26%). For these 20 admissions, the median length of stay in an intensive care unit was 2 days (interquartile range, 1 to 3 days). Fifty-two (68%) of the admissions occurred entirely at our institution. Median hospital cost per admission was $5842 (interquartile range, $3549 to $12 170). There were no significant differences in the costs for arrhythmia-related readmissions compared with readmissions for other cardiac causes (median, $5525; interquartile range, $1620 to $5810 versus median, $7570; interquartile range, $3807 to $21 266; P=.14, Mann-Whitney test).
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Discussion |
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Since their clinical introduction in 1980,27 ICDs have become increasingly sophisticated, and they remain an expensive therapeutic modality. In this study encompassing a population of unselected consecutive patients receiving tiered-therapy ICDs, we show that the incidence of cardiac-related hospital readmissions and their resource consumption are substantial. We also demonstrate that subsequent readmissions for cardiac- but not arrhythmia-related reasons can be predicted by a poor functional class.
Previous Studies
The CASCADE study28 reported a rehospitalization rate of 0.79 per patient-year of follow-up for the entire population and of 0.75 for a subgroup of patients with first-generation ICDs (74% of the readmissions in these patients were for cardiac reasons). Kuppermann et al18 analyzed costs over a lifetime of care for patients with ICDs. In their model, they incorporated an estimate of a panel of seven academic cardiac electrophysiologists of 0.5 to 0.7 arrhythmia- or device-related hospitalizations per year for the first year after implant and 0.5 to 0.6 per year for subsequent years. This is similar to the incidence found in the present study of 0.40 arrhythmia- or device-related readmissions per patient-year of follow-up. The charges (not costs) for each readmission were based on data obtained from the Health Care Financing Administration of 65 patients who were readmitted for either lead or generator replacement. This charge, including physician fee, was 21 810 1986 US dollars per rehospitalization. This is substantially greater than the median cost of $5842 per admission in the present study. Larsen et al,19 using a Markov decision model, concluded that the cost-effectiveness of ICD therapy was comparable to that of amiodarone and highly dependent on generator battery life. Data for their model were derived from the literature and a relatively small group of survivors of cardiac arrest who were treated in a single center. Costs of hospital readmission were incorporated into their model, but these data were derived from only 21 patients, and the frequency and reason for each readmission were not published. Anderson and Camm20 examined the relative cost of the ICD per life-year saved in populations with various risks of sudden cardiac death. However, their model did not allow for costs of hospital readmission.
Reasons for Readmission
The significant risk of hospital readmission for nonarrhythmic cardiac reasons is not unexpected, because most of these patients are prone to recurrent episodes of myocardial ischemia and failure, which should not be prevented by ICD therapy.
Complications associated with first-generation ICDs have been well described.29 30 Despite increased sophistication in diagnostic and therapeutic algorithms of tiered-therapy ICDs,5 6 7 31 recurrent arrhythmias were a significant source of morbidity in our patients, confirming the findings of a recent study by O'Nunain et al.32 Inaccurate discrimination between supraventricular and ventricular tachyarrhythmias continues to be a shortcoming of ICD therapy. The greater versatility of tiered-therapy ICDs has allowed their use in patients with relatively slow and well-tolerated ventricular tachycardias, whose rates are more likely to overlap with those of supraventricular origin.33 After a follow-up of 15 months, O'Nunain et al found that 28% of their patients with tiered-therapy ICDs received inappropriate device shocks, mostly for supraventricular tachyarrhythmias. Grimm et al34 reported that after a mean follow-up of 14 months, 20 of 54 patients (35%) with ICDs with electrogram storage capabilities received spurious shocks. Aside from the physical discomfort of each discharge, multiple shocks delivered inappropriately for supraventricular rhythms constitute a particularly undesirable event; they may trigger a long-lasting state of extreme anxiety and belligerence directed at the ICD,35 36 as well as potentially life-threatening proarrhythmic responses.37
The impact of the relatively frequent use of antiarrhythmic drugs in our patients on the incidence of hospital readmission is difficult to discern. This practice may have protected patients from readmission triggered by recurrent arrhythmias, as reflected by the relatively low number of readmissions due to atrial fibrillation in our series. However, drug side effects were responsible for five readmissions, and their negative inotropic effects may also have contributed to some episodes of cardiac decompensation.
The incidence of hardware-related readmissions was low in this study. With nonthoracotomy defibrillator systems, lead complications tend to occur soon after implant, allowing their detection and resolution during the initial admission.38 The long-term incidence of lead failure for current nonthoracotomy lead systems is unknown. We found no instance of lead failure after a median follow-up time of 19 months, but if the durabilities of defibrillator and endocardial pacing lead systems prove comparable, a longer follow-up time will be required to allow manifestation of most lead failures.39
Predictors of Readmission
It is not surprising that the presence of NYHA functional class III to IV for congestive cardiac failure predicted subsequent cardiac readmission. Levine et al40 have reported poor long-term survival after ICD shocks in such patients. Our sample size was underpowered to detect differences in survival, but interestingly, most patients in functional class III to IV survived the follow-up period. These findings suggest that crude survival may be an inadequate outcome measure to judge the potential benefits of defibrillator therapy and that an alternative measure (eg, quality-of-life–adjusted survival) may be more relevant in clinical trials or cost-effectiveness studies. A high incidence of hospital admissions should be expected when ICD therapy is contemplated as a "bridge" to cardiac transplantation or for prophylactic use in patients with severe left ventricular systolic dysfunction.41
Strategies to Prevent Arrhythmia-Related Readmission in Implantable Defibrillator Recipients
The more frequent use of diagnostic-enhancing features in the devices may decrease the incidence of inappropriate defibrillator interventions for supraventricular tachycardias.42 However, despite studies demonstrating that these features do not significantly compromise device sensitivity,43 there has been reluctance to activate them routinely. In future devices, advances in detection algorithms44 may improve diagnostic specificity. The judicious use of adjunctive therapies such as radiofrequency ablation of monomorphic ventricular tachycardia and the AV node may also contribute to minimization of the incidence of device interventions.45 46 47 48
Ventricular demand pacing incorporated in tiered-therapy ICDs does not suffice in many patients treated with this modality, and it is associated with potentially serious technical problems.49 50 The incorporation of dual-chamber, rate-responsive pacing capabilities in future ICDs may decrease the incidence and costs of readmission in patients who require chronic pacing during follow-up.
The optimal use of antiarrhythmic drugs in patients with ICDs is undefined. Although the current trend is to avoid their use,51 this may result in an increase in the incidence of readmission for recurrent arrhythmias.52 In the present study, the use of antiarrhythmic drugs at initial hospital discharge is higher than that usually reported. This reflects a high commitment to the suppression of supraventricular tachyarrhythmias and minimization of the frequency of appropriate ICD therapies.
Study Limitations
The length of follow-up is relatively short. However, there were enough events to characterize the short- to medium-term readmission patterns, rates, and costs. It is possible that other clinical variables could be significantly associated with readmissions in a larger population with a longer follow-up time. Costs were analyzed from a single center only. Therefore, the results of costs from this study need careful consideration before extrapolation to other institutions and healthcare systems. The use of ß-blockers in 31% of our patients reflects the current pattern of underuse in this country.53 It is possible that more extensive use of ß-blocking agents could result in decreased hospital readmission rates. The relatively small proportion of patients treated with antitachycardia pacing reflects our strict selection criteria for activating this form of treatment. The effects of a more empirical approach to activation of antitachycardia pacing are currently under investigation. In addition, our patients were older than those in most series and the use of antiarrhythmic drugs was more frequent than that usually reported. Epicardial lead systems were used in fewer than half of our patients. However, the vast majority of present-day implants use nonthoracotomy systems, the long-term performance of which is uncertain. These factors should be considered in the interpretation of the results of this study. The exclusive examination of local patients is not a limitation of this study, because it tends to protect from selection biases, ensures a high level of consistency in the pattern of care and the threshold for hospital admission, and minimizes the number of patients lost to follow-up. Finally, we made no attempt to compare costs of ICD therapy with those of alternatives; thus, the study is not a formal cost-benefit analysis but rather an effort to identify sources of increased resource consumption that should be specifically targeted.
Conclusions
Despite greater physician experience and recent technological advances, readmission for cardiac reasons in ICD recipients remains frequent, can be predicted by an advanced NYHA functional class, and is responsible for substantial resource consumption. Therefore, the costs of ICD therapy are not exclusively "front-loaded," and those incurred during follow-up should be incorporated in any meaningful analysis of the cost-effectiveness of this therapy.
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Acknowledgments |
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We wish to thank Susan M. Daunch, RN, for her expert help in retrieving cost data and Siobhan Dorrian for her excellent secretarial work.
Received November 28, 1995; revision received February 5, 1996; accepted April 7, 1996.
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