Utility of predischarge and one-month transvenous implantable defibrillator tests

Device therapies in the post-myocardial infarction patient with left ventricular dysfunction

The post-myocardial infarction (MI) patient with left ventricular dysfunction (LVD) is at risk for ventricular arrhythmias resulting in sudden cardiac death. In high-risk post-MI patients with a depressed left ventricular ejection fraction, prophylactic implantable cardioverter defibrillators (ICDs) may significantly improve survival. These benefits are in addition to those of optimal pharmacologic therapy, and ICD therapy should be considered the standard of care in these patients. Recent device trials have demonstrated the benefits of prophylactic ICD placement in patients who have been selected based on post-MI left ventricular systolic dysfunction alone. In addition, cardiac resynchronization therapy can improve the quality of life beyond that achievable with drug therapy alone and should be considered in patients with symptomatic heart failure with QRS prolongation. Further risk stratification studies of post-MI LVD patients will allow ICD therapy to be applied in a more cost-effective manner.

Testing the Implantable Cardioverter-Defibrillator After Implantation?Is It Necessary?

The results of intraoperative and postoperative predischarge implantable cardioverter-defibrillator (ICD) testing of 211 consecutive patients, starting at 15 J and requiring two successful terminations of induced VT/VF with a relative defibrillation safety margin (DSM) of >10 J, were reviewed. The aim was to define the type of intraoperative response that would make postoperative predischarge testing unnecessary. The intraoperative responses were divided into three types: A, a DSM > or =10 J and an absolute energy level of < or =20 J; B, a DSM of > or =10 J and an absolute energy level of >20 J; and C, a DSM <10 J and an absolute energy level of >20 J. At operation, the responses to defibrillation were A, 88.6%; B, 7.1%; and C, 4.3%. Accepting an A response only would leave 11.4% of the patients for postoperative testing. The positive and negative predictive values for diagnosing a postoperative C response were 0.78 and 0.97, respectively. Similarly, the predictive values for diagnosing a postoperative B or C response were 0.71 and 0.97, respectively. The postoperative testing responses were A, 89.1%; B, 4.3%; and C, 6.6%. In summary, an intraoperative A response was sufficient to make a postoperative defibrillation testing unnecessary, while it was found that intraoperative B and C responders should undergo postoperative testing. Applying these criteria, approximately 90% of the patients could be discharged without any postoperative induction test.

The dilemma of ICD implant testing

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients. This review reappraises ICD implant testing. At implant, defibrillation success is influenced by both predictable and unpredictable factors, including those related to the patient, ICD system, drugs, and complications. For left pectoral implants of high-output ICDs, the probability of passing a 10 J safety margin is approximately 95%, the probability that a maximum output shock will defibrillate is approximately 99%, and the incidence of system revision based on testing is < or = 5%. Bayes' Theorem predicts that implant testing identifies < or = 50% of patients at high risk for unsuccessful defibrillation. Most patients who fail implant criteria have false negative tests and may undergo unnecessary revision of their ICD systems. The first-shock success rate for spontaneous VT/VF ranges from 83% to 93%, lower than that for induced VF. Thus, shocks for spontaneous VT/VF fail for reasons that are not evaluated at implant. Whether system revision based on implant testing improves this success rate is unknown. The risks of implant testing include those related to VF and those related to shocks alone. The former may be due to circulatory arrest alone or the combination of circulatory arrest and shocks. Vulnerability testing reduces risks related to VF, but not those related to shocks. Mortality from implant testing probably is 0.1-0.2%. Overall, VF should be induced to assess sensing in approximately 5% of ICD recipients. Defibrillation or vulnerability testing is indicated in 20-40% of recipients who can be identified as having a higher-than-usual probability of an inadequate defibrillation safety margin based on patient-specific factors. However, implant testing is too risky in approximately 5% of recipients and may not be worth the risks in 10-30%. In 25-50% of ICD recipients, testing cannot be identified as either critical or contraindicated.

Value of Pre-Hospital Discharge Defibrillation Testing in Recipients of Implanted Cardioverter Defibrillators

Opinions vary regarding the need to perform defibrillation testing prior to hospital discharge in recipients of state-of-the-art cardioverter defibrillators (ICDs). Our protocol is to perform predischarge ICD testing 1 day after implant. This report includes 682 consecutive implants. Adverse observations at testing were grouped into (1) risk of defibrillation failure, (2) surgical complications, (3) sensing/pacing issues or narrow defibrillation margin warranting closer follow-up, or (4) findings correctable by device reprogramming. Among the 682 patients, 63% had single-chamber and 37% dual-chamber or biventricular ICDs. In 48 patients (7%) there were 69 concerns and/or interventions, with overlaps among the four categories, including one failure to defibrillate (0.15%), and six other patients at risk. Surgical complications included 11 hematomas (1.6%), and six lead dysfunctions. Closer follow-up was indicated in 19 patients (2.7%), for high pacing thresholds in seven, sensing issues in seven, and <10 J defibrillation margin in five. Device reprogramming was needed in 31 patients (4.5%), for tachycardia detection and therapy settings in 12, and for pacing/sensing functions in 22 patients. In eight patients ventricular fibrillation could not be induced. There was no morbidity or mortality due to testing. The state-of-the-art ICDs delivering biphasic shocks are remarkably reliable. The routine pre-hospital discharge defibrillation testing of such ICDs may be optional and left to the physicians' discretion.

Implantable Cardioverter Defibrillator Events in Patients with Asymptomatic Nonsustained Ventricular Tachycardia:

Primary prevention trials have demonstrated that patients with coronary disease, reduced left ventricular function, and nonsustained ventricular tachycardia (NSVT) have improved survival with implantable cardioverter defibrillator (ICD) therapy, presumably secondary to effective termination of life-threatening arrhythmias. However, stored intracardiac electrograms were not always available and specific arrhythmias leading to ICD therapy were not always known. We examined the occurrence of ICD events in 51 consecutive patients who match the described patient profile to determine the frequency of appropriate and inappropriate ICD therapy. ICD detections were noted in 18 (35%) patients during a median follow-up period of 13.1 months. Appropriate therapy for sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) occurred in 11 (22%) patients, with appropriate shocks in 8 (16%) patients and appropriate antitachycardia pacing (ATP) in 4 (8%) patients. The time to first appropriate therapy occurred at a mean of 17 +/- 12 months (median 18 months, range 3-36 months). Inappropriate therapy occurred in 5 (10%) patients with inappropriate shocks in 4 patients and inappropriate ATP in 2 patients. Inappropriate therapy was delivered for supraventricular arrhythmias (SVAs) in 4 patients and for T wave oversensing in 1 patient. The reason for shock therapy was unknown in 1 patient (2%) due to ICD malfunction. The mean arrhythmia rate leading to appropriate therapy for VT/VF was 232 +/- 72 beats/min (range 181-400 beats/min), and the mean rate leading to inappropriate therapy for SVT was 168 +/- 10 beats/min (range 160-180 beats/min). Patients with coronary disease and asymptomatic NSVT commonly receive appropriate defibrillator therapy. These results support the need for ICD implantation for primary prevention, with attention to careful programming of the detection rate to prevent inappropriate therapy.

The value of predischarge ICD tests in patients with a successful peroperative test

An internal cardioverter defibrillator (ICD) is normally extensively tested during implantation. The necessity of retesting prior to discharge of the patient is a matter of debate. In our material of 30 patients undergoing first-time implantation of a transvenous internal defibrillator system, we retrospectively compare the predischarge defibrillation test with the peroperative test. A successful peroperative defibrillation test with no failed shocks at 10 J below maximal energy level was followed by a successful predischarge test with the same safety margin in 18/19 patients, while one patient required a maximal energy ICD shock for conversion at the predischarge test. We conclude that the predischarge defibrillation test can be omitted if the peroperative test was successful, with no failed shocks at 10 J below maximal energy level and if the shock therapy is set to maximal energy level.

Implantable Cardioverter Defibrillator: Current Progress and Management

With greater technologic advances during the past decade, use of the implantable cardioverter defibrillator (ICD) has increased to more than 200,000 implants worldwide to date. Indications for ICD implant have expanded to include both patients who have survived sudden cardiac death (secondary prevention of cardiac arrest) and those who are at high risk for experiencing lethal arrhythmias (primary prevention of cardiac ar rest). Thus, it is likely that physicians will encounter defibrillators in their clinical practice and must be familiar with their indications for implant, basic opera tion, and long-term management of devices. Several prospective clinical trials have recently shown the long- term efficacy of ICD therapy at aborting sudden death in the high-risk patient population. Although still evolving, general guidelines and indications for ICD implant have been put forth and are discussed in this review. From the first defibrillation in humans during surgery in 1947 to the sophisticated dual-chamber pacing and memory functions of the modern device, ICD development has led to ever smaller devices with more complex technol ogy. The implant procedure of current ICDs parallels that used to place pacemakers. However, the anesthe sia team plays a vital role in initial ICD implantation by monitoring cardiopulmonary status during defibrilla tion threshold (DFT) testing. Additionally, long-term management of ICDs often requires repeat DFT testing with anesthesia involvement. Finally, possible electro magnetic (environmental) interactions with the ICD of which physicians should be aware are described in this article.

Are routine arrhythmia inductions necessary in patients with pectoral implantable cardioverter defibrillators?

INTRODUCTION

The value of ventricular arrhythmia inductions as part of routine implantable cardioverter defibrillator (ICD) follow-up in new-generation pectoral ICDs is unknown.

METHODS AND RESULTS

We performed a retrospective analysis of a prospectively collected database analyzing data from 153 patients with pectoral ICDs who had routine arrhythmia inductions at predismissal, and 3 months and 1 year after implantation. Routine predismissal ventricular fibrillation (VF) induction yielded important findings in 8.8% of patients, all in patients with implantation defibrillation threshold (DFT) > or = 15 J or with concomitant pacemaker systems. At 3 months and 1 year, routine VF induction yielded important findings in 5.9% and 3.8% of tested patients, respectively, all in patients who had high DFT on prior testing. Ventricular tachycardia (VT) induction at predismissal, and 3 months and 1 year after implantation resulted in programming change in 37.4%, 28.1%, and 13.8% of tested patients, almost all in patients with inducible VT on baseline electrophysiologic study and clinical episodes since implantation.

CONCLUSION

Although helpful in identifying potentially important ICD malfunctions, routine arrhythmia inductions during the first year after ICD implantation may not be necessary in all cases. VF inductions have a low yield in patients with previously low DFTs who lack concomitant pacemakers. VT inductions have a low yield in patients without baseline inducible VT and in the absence of clinical events. Definite recommendations regarding patient selection must await larger prospective studies as well as consensus in the medical community about what comprises an acceptable risk justifying avoidance of the costs and inconveniences of routine arrhythmia inductions.

Multicenter evaluation of implantable cardioverter defibrillator testing after implant: the Post Implant Testing Study (PITS)

To reassess the function of the implantable cardioverter defibrillator (ICD) many electrophysiology centers perform a second test after the initial test at implant. A prospective multicenter study evaluated the necessity and yield of routine postimplant defibrillator testing. The results of 843 postimplant defibrillator tests were collected from 31 centers. The 764 routine tests in which ventricular fibrillation was successfully induced were analyzed. Variables examined included patient age, presenting arrhythmia, underlying heart disease, left ventricular ejection fraction, defibrillator age, make and model of ICD, electrode system, defibrillation threshold, polarity, and waveform. The overall failure rate was 3.1% (24/764). Units tested later than 365 days after implant tended to have a higher failure rate than those tested within the first month or the next eleven months (6.5%, 3.0%, 2.3%, respectively, P = 0.374). The failure rate was higher in patients with left ventricular ejection fraction < 40% than those with higher ejection fractions (3.8% vs 2.0%, P = 0.167). These trends did not reach statistical significance. No other baseline characteristic was associated with higher failure rates. Routine testing of ICDs reveals an overall failure rate of 3.1%. While the rate was low, defibrillator failure places the patient at high risk for sudden cardiac death. As any failure in this population is associated with a high risk of sudden cardiac death, routine defibrillator testing may be justified.

Inappropriate implantable cardioverter-defibrillator therapy due to the detection of premature ventricular complexes

Inappropriate shocks delivered by implantable cardioverter-defibrillators may occur in 15%-40% of patients treated with these devices. This article describes a rare cause for inappropriate shocks. Two patients received inappropriate shocks due to the presence of premature ventricular complexes during attempted reconfirmation of ventricular fibrillation. Knowledge of device algorithms for detection and reconfirmation of ventricular fibrillation, designed to have a high degree of sensitivity and therefore lower specificity, allows for reprogramming to avoid further inappropriate shocks.

Prehospital discharge defibrillation testing in ICD recipients: a prospective study based on cost analysis

Prehospital discharge defibrillation testing is often performed to verify the function of newly implanted cardioverter defibrillators (ICDs). To determine whether elimination of predischarge testing could reduce costs without placing patients at additional risk, 31 patients were randomized in this prospective clinical evaluation to either receive or not receive a predischarge ICD defibrillation test. Expenses associated with postimplant care was the primary endpoint. All patients underwent induction of ventricular fibrillation after 6 months to evaluate ICD function. The groups were well matched in terms of patient characteristics, initial lead implant parameters, and defibrillation thresholds. Elimination of prehospital discharge testing resulted in a savings of $1,800/patient after 6 months, with no difference between groups in terms of ICD complication rates or unanticipated hospital admissions. Further studies are needed to better define the most appropriate time to assess defibrillation thresholds in the first year after implantation.