Safety and efficacy of implantable defibrillator therapy with programmed shock energy at twice the augmented step-down defibrillation threshold: results of the prospective, randomized, multicenter Low-Energy Endotak Trial

Systematic Review of Defibrillation Threshold Testing at De Novo Implantation

Background—

Recent results from the largest multicenter randomized trial (Shockless IMPLant Evaluation [SIMPLE]) on defibrillation threshold (DFT) testing suggest that while shock testing seems safe, it does not reduce the risk of failed shocks or prolong survival. A contemporary systematic review of DFT versus no-DFT testing at the time of implantable cardioverter–defibrillator implantation was performed to evaluate the current evidence and to assess the impact of the SIMPLE study.

Methods and Results—

Electronic searches were performed using 6 databases from their inception to March 2014. Relevant studies investigating implant DFT were identified. Data were extracted and analyzed according to predefined clinical end points. Predefined outcomes for interrogation were all-cause mortality, composite end point of implantable cardioverter–defibrillator efficacy (arrhythmic deaths and ineffective shocks), and composite safety end point (the sum of complications recorded at 30 days). Meta-analysis was performed including 13 studies and 9740 patients. No significant differences between DFT versus no-DFT cohorts were found in terms of all-cause mortality (risk ratio, 0.90; 95% confidence interval, 0.71–1.15; P =0.41), composite efficacy outcome (risk ratio, 1.24; 95% confidence interval, 0.65–3.37; P =0.51), and 30-day postimplant complications (risk ratio, 1.18; 95% confidence interval, 0.87–1.60; P =0.29). No significant difference was found in the trends observed when the results of the SIMPLE study were excluded or included.

Conclusions—

This systematic review of contemporary data suggests a modest average effect of DFT, if any, in terms of mortality, shock efficacy, or safety. Therefore, DFT testing should no longer be compulsory during de novo implantation. However, DFT testing may still be clinically relevant in specific patient populations.

Frequency characteristics and associations with the defibrillation threshold of ventricular fibrillation in patients with implantable cardioverter defibrillators

OBJECTIVE

The dominant frequency (DF) in frequency analyses is considered to represent the objective cycle length and complexity of activation under conditions of ventricular fibrillation (VF). However, knowledge regarding the mechanisms determining the DF in human VF is limited. We studied the characteristics of the DF of human VF and relationship between DF and the defibrillation threshold.

METHODS

Seventy-two implantable cardioverter-defibrillator patients and 211 VF were studied. Using defibrillation tests, we performed a frequency analysis with fast Fourier transformation. The correlations between DF and clinical characteristics, including the defibrillation threshold, were assessed.

RESULTS

The mean DF of all induced VFs was 5.2±0.8 Hz. The patients were divided into two groups according to DF: the low-DF (DF <5.2 Hz, n=32) and high-DF (DF ≥5.2 Hz, n=40) groups. The frequency of structural heart disease was significantly higher in the low-DF group. In addition, the QRS duration, QT interval and effective refractory period of the right ventricle (RV-ERP) were significantly longer in the low-DF group. A multivariate analysis showed RV-ERP to be the only independent predictor of DF. Excluding patients receiving group III anti-arrhythmic drugs, which are known to have potent defibrillation threshold effects, the defibrillation threshold was significantly lower in the low-DF group (p=0.026).

CONCLUSION

We found that the DF of human VF is associated with underlying heart disease, the cardiac function, cardiac conduction, ventricular refractoriness and defibrillation threshold. Our findings may be useful for identifying and managing patients with a high defibrillation threshold.

Electroporation induced by internal defibrillation shock with and without recovery in intact rabbit hearts

Defibrillation shocks from implantable cardioverter defibrillators can be lifesaving but can also damage cardiac tissues via electroporation. This study characterizes the spatial distribution and extent of defibrillation shock-induced electroporation with and without a 45-min postshock period for cell membranes to recover. Langendorff-perfused rabbit hearts (n = 31) with and without a chronic left ventricular (LV) myocardial infarction (MI) were studied. Mean defibrillation threshold (DFT) was determined to be 161.4 ± 17.1 V and 1.65 ± 0.44 J in MI hearts for internally delivered 8-ms monophasic truncated exponential (MTE) shocks during sustained ventricular fibrillation (>20 s, SVF). A single 300-V MTE shock (twice determined DFT voltage) was used to terminate SVF. Shock-induced electroporation was assessed by propidium iodide (PI) uptake. Ventricular PI staining was quantified by fluorescent imaging. Histological analysis was performed using Masson's Trichrome staining. Results showed PI staining concentrated near the shock electrode in all hearts. Without recovery, PI staining was similar between normal and MI groups around the shock electrode and over the whole ventricles. However, MI hearts had greater total PI uptake in anterior (P < 0.01) and posterior (P < 0.01) LV epicardial regions. Postrecovery, PI staining was reduced substantially, but residual staining remained significant with similar spacial distributions. PI staining under SVF was similar to previously studied paced hearts. In conclusion, electroporation was spatially correlated with the active region of the shock electrode. Additional electroporation occurred in the LV epicardium of MI hearts, in the infarct border zone. Recovery of membrane integrity postelectroporation is likely a prolonged process. Short periods of SVF did not affect electroporation injury.

QRS prolongation is associated with high defibrillation thresholds during cardioverter-defibrillator implantations in patients with hypertrophic cardiomyopathy

BACKGROUND

Although high defibrillation threshold (DFT) is a major and unavoidable clinical problem after implantation of an implantable cardioverter defibrillator (ICD), little is known about the cause and management of a high DFT in patients with hypertrophic cardiomyopathy (HCM). The purpose of this study was to assess the predictors of a high DFT in patients with HCM.

METHODS AND RESULTS

Twenty-three patients with non-dilated HCM who underwent ICD implantation were included. The DFT at the time of the device implantation was measured in all patients. The patients were divided into 2 groups, a high DFT group (DFT >or=15J, n=13) and a low DFT group (DFT <15J, n=10); and their baseline characteristics were compared. The QRS duration was longer in the high than in the low DFT group (128 +/-31 vs 103 +/-12 ms, respectively; P=0.02). QRS duration, left ventricular (LV) end-systolic diameter, and LV ejection fraction were significant predictors of DFT in univariate analysis. However, in multivariate analysis, the only factor significantly associated with DFT was QRS duration (P=0.002).

CONCLUSIONS

QRS duration is the most consistent predictor of a high DFT in HCM patients undergoing ICD implantation.

[Single- and dual-chamber ICDs: Are there still significant differences compared to pacemakers with regard to implantation and follow-up?]

Due to bulky generator size, abdominal pocket preparation and epicardial defibrillator lead placement, cardioverter-defibrillator (ICD) implantation was initially an extensive surgical intervention, which had to be performed in the operating room by cardiac surgeons under general anesthesia. The development of transvenously applicable endocardial defibrillator leads rendered thoracotomy unnecessary. The decrease in generator size enabled pectoral implantation. As a consequence of the simplified surgical procedure, implantation by cardiologists or electrophysiologists in the catheterization laboratory under local anesthesia and brief deep sedation with preserved spontaneous respiration was made possible. As a result, the implantation techniques of ICDs and pacemakers are converging. The present article illustrates the still existing significant differences between ICD and pacemaker treatment with regard to implantation and follow-up.

Patient-tailored implantable cardioverter defibrillator testing using the upper limit of vulnerability: the TULIP protocol

AIMS

We evaluated the feasibility of the TULIP (Threshold test using Upper Limit during ImPlantation) protocol, which was designed to provide a confirmed, low defibrillation energy value during implantable cardioverter defibrillator (ICD) implantation with only two induced ventricular fibrillation (VF) episodes.

METHODS AND RESULTS

Ninety-eight patients (62 +/- 12 years, 86 male) from 13 clinical centres underwent an active can ICD implantation. A single coupling interval derived from electrocardiogram lead II during ventricular pacing was used for VF induction shocks at 13, 11, 9, and 6 J in a step-down manner until the upper limit of VF induction (ULVI) was determined. If ULVI >or=9 J, a defibrillation energy of ULVI + 4 J was tested. For ULVI <9 J, the defibrillation test energy was 9 J. In 79/98 patients (80.6%), two induced VF episodes were sufficient to obtain confirmed defibrillation energy of 11.1 +/- 3.3 J. The mean strength of the successful VF induction shock was 6.8 +/- 4.3 J, the coupling interval was 303 +/- 35 ms, and the number of delivered induction shocks until the first VF induction was 3.9 +/- 1.6.

CONCLUSION

TULIP is a safe and simple device testing procedure allowing the determination of confirmed, low defibrillation energy in most patients with two VF episodes induced at a single coupling interval.

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.

Inductionless or Limited Shock Testing Is Possible in Most Patients With Implantable Cardioverter- Defibrillators/Cardiac Resynchronization Therapy Defibrillators

Background— Implantable cardioverter-defibrillators and cardiac resynchronization therapy defibrillators have relied on multiple ventricular fibrillation (VF) induction/defibrillation tests at implantation to ensure that the device can reliably sense, detect, and convert VF. The ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation With Implantable Cardioverter-Defibrillator Implantations) is the first large, multicenter, prospective trial comparing vulnerability safety margin testing versus defibrillation safety margin testing with a single VF induction/defibrillation.

Methods and Results— A total of 426 patients receiving an implantable cardioverter-defibrillator or cardiac resynchronization therapy defibrillator underwent vulnerability safety margin or defibrillation safety margin screening at 14 J in a randomized order. After this, patients underwent confirmatory testing, which required 2 VF conversions without failure at ≤21 J. Patients who passed their first 14-J and confirmatory tests, irrespective of the results of their second 14-J test, had their devices programmed to a 21-J shock for ventricular tachycardia (VT) or VF ≥200 bpm and were followed up for 1 year. Of 420 patients who underwent 14-J vulnerability safety margin screening, 322 (76.7%) passed. Of these, 317 (98.4%) also passed 21-J confirmatory tests. Of 416 patients who underwent 14-J defibrillation safety margin screening, 343 (82.5%) passed, and 338 (98.5%) also passed 21-J confirmatory tests. Most clinical VT/VF episodes (32 of 37, or 86%) were terminated by the first shock, with no difference in first shock success. In all observed cases in which the first shock was unsuccessful, subsequent shocks terminated VT/VF without complication.

Conclusions— Although spontaneous episodes of fast VT/VF were limited, there was no difference in the odds of first shock efficacy between groups. Screening with vulnerability safety margin or defibrillation safety margin may allow for inductionless or limited shock testing in most patients.

Using the Upper Limit of Vulnerability to Assess Defibrillation Efficacy at Implantation of ICDs

The upper limit of vulnerability (ULV) is the weakest shock strength at or above which ventricular fibrillation (VF) is not induced when the shock is delivered during the vulnerable period. The ULV, a measurement made in regular rhythm, provides an estimate of the minimum shock strength required for reliable defibrillation that is as accurate or more accurate than the defibrillation threshold (DFT). The ULV hypothesis of defibrillation postulates a mechanistic relationship between the ULV-measured during regular rhythm-and the minimum shock strength that defibrillates reliably. Vulnerability testing can be applied at implantable cardioverter defibrillator (ICD) implant to confirm a clinically adequate defibrillation safety margin without inducing VF in 75%-95% of ICD recipients. Alternatively, the ULV provides an accurate patient-specific safety margin with a single fibrillation-defibrillation episode. Programming first ICD shocks based on patient-specific measurements of ULV rather than programming routinely to maximum output shortens charge time and may reduce the probability of syncope as ICDs age and charge times increase. Because the ULV is more reproducible than the DFT, it provides greater statistical power for clinical research with fewer episodes of VF. Limited evidence suggests that vulnerability testing is safer than conventional defibrillation testing.

Antitachycardia Pacing for Spontaneous Rapid Ventricular Tachycardia in Patients with Prophylactic Cardioverter-Defibrillator Therapy

AIMS

Antitachycardia pacing (ATP) has not routinely been used in patients who received implantable cardioverter defibrillators (ICDs) for primary prevention of sudden death. This study investigated the efficacy of empirical ATP to terminate rapid ventricular tachycardia (VT) in heart failure patients with prophylactic ICD therapy.

METHODS AND RESULTS

Ninety-three patients with a mean left ventricular ejection fraction of 22 +/- 7% (range: 9-35%) due to nonischemic or ischemic cardiomyopathy received prophylactic ICDs with empiric ATP. At least 2 ATP sequences with 6-pulse burst pacing trains at 81% of VT cycle length (CL) were programmed in one or two VT zones for CL below 335 +/- 23 ms and above 253 +/- 18 ms. Ventricular flutter and fibrillation (VF) with CL below 253 +/- 18 ms were treated in a separate VF zone with ICD shocks without preceding ATP attempts. During 38 +/- 27 months follow-up, 339 spontaneous ventricular tachyarrhythmias occurred in 36 of 93 study patients (39%). A total of 232 VT episodes, mean CL 293 +/- 22 ms, triggered ATP in 25 of 36 patients with ICD interventions (69%). ATP terminated 199 of 232 VT episodes (86%) with a mean CL of 294 +/- 23 ms in 23 of 25 patients (88%) who received ATP therapy. ATP failed to terminate or accelerated 33 of 232 VT episodes (14%) with a mean CL of 287 +/- 19 ms in 12 of 25 patients (48%) who received ATP therapy.

CONCLUSIONS

Painfree termination of rapid VT with empirical ATP is common in heart failure patients with prophylactic ICD therapy. The occasional inability of empiric ATP to terminate rapid VT in almost 50% of patients who receive ATP for rapid VT warrants restrictive ICD programming with regard to the number of ATP attempts in order to avoid syncope before VT termination occurs.

Defibrillation threshold testing: is it really necessary at the time of implantable cardioverter-defibrillator insertion?

OBJECTIVES

The purpose of this study was to (1) determine how often implantable cardioverter-defibrillator (ICD) system modifications were needed to obtain an adequate safety margin for defibrillation, (2) identify how often and for what indications defibrillation threshold (DFT) testing was not performed, and (3) identify factors predicting the need for modification.

BACKGROUND

Ventricular fibrillation (VF) typically is induced at the time of ICD insertion. Although DFT testing often is minimized, a safety margin of 10 J has been utilized as a standard of care. However, current devices offer technology such as biphasic waveforms and high outputs, and the need for testing has been questioned.

METHODS

We reviewed the records of the last 1,139 patients undergoing initial ICD placement, generator replacement, or revision.

RESULTS

Seventy-one patients (6.2%) were identified as having an unacceptably high DFT (<10 J safety margin) requiring intervention, and some required >1 modification. Use of a high-output device alone was not enough to obtain an adequate DFT in 48% (34/71) of patients who required modifications (3% of the total population). No arrhythmia inductions were performed in 54 patients (4.7%) because of well-defined clinical conditions. Patients who required system modification had a lower ejection fraction, were younger, were less likely to have coronary artery disease, were more likely to be undergoing upgrade/generator replacement, and were more likely to be taking amiodarone. Long-term mortality was not different between the group of patients who required modification compared with those who did not (17% vs 20%, P = NS).

CONCLUSIONS

Routine VF induction and documentation of effective defibrillation still remains a reasonable part of ICD placement because an inadequate safety margin may occur in >6% of patients. The incidence of patients who were inappropriate for testing based on well-defined clinical conditions is small (<5%) in this unselected large series. Although some clinical features may predict the need for system modification, additional studies are needed to better define "acceptable efficacy" of ICDs in preventing sudden death prior to altering these standards in selected patients.

One conversion of ventricular fibrillation is adequate for implantable cardioverter-defibrillator implant: An analysis from the Low Energy Safety Study (LESS)

OBJECTIVES

The purpose of this study was to analyze defibrillation conversion data from the Low Energy Safety Study (LESS) to determine how implant criteria that use fewer inductions of ventricular fibrillation (VF) correlate with outcome and, in particular, to assess the reliability of using a single VF induction and test shock at 14 J.

BACKGROUND

A safety margin of 10 J has become standard for implantation of an implantable cardioverter-defibrillator (ICD), but the specifics and rigor of the implant test sequence are not standardized.

METHODS

In LESS, 611 ICD recipients completed a rigorous VF induction test scheme that began at 14 J and continued until the energy that succeeded three times without a failure was determined (DFT++). The data were analyzed to determine how well the outcome of the first 14-J shock and various other combinations of first and/or second shocks predicted a rigorous gold standard of DFT++ < or =21 J (i.e., three successes at < or =21 J).

RESULTS

The positive predictive accuracy for the 91% of patients in whom the first 14-J shock succeeded was virtually identical to the positive predictive accuracy for the commonly used criteria of two successes at < or =17 J (99.1% vs 99.0%, P = .69), and slightly higher than the positive predictive accuracy for two successes at < or =21 J (98.8%, P = .51). A single success at 17 J or 21 J had a somewhat lower positive predictive accuracy of 98.2% (P = .17). Eliminating VF induction testing would have resulted in a significantly lower positive predictive accuracy of 97.1% (P = .01).

CONCLUSIONS

A single conversion success at 14 J on the first VF induction provides similar positive predictive accuracy as two successes at 17 J or 21 J. Using this criterion, 91% of patients meet implant criteria with a single induction of ventricular fibrillation.

Prospective randomized comparison of two defibrillation safety margins in unipolar, active pectoral defibrillator therapy

Various techniques are used to establish defibrillation efficacy and to evaluate defibrillation safety margins in patients with an ICD. In daily practice a safety margin of 10 J is generally accepted. However, this is based on old clinical data and there are no data on safety margins using current ICD technology with unipolar, active pectoral defibrillators. Therefore, a randomized study was performed to test if the likelihood of successful defibrillation at defibrillation energy requirement (DER) + 5 J and + 10 J is equivalent. Ninety-six patients (86 men; age 61.0 +/- 10.3 years; ejection fraction 0.341 +/- 0.132; coronary artery disease [n = 65], dilated cardiomyopathy [n = 18], other [n = 13]) underwent implantation of an active pectoral ICD system with unidirectional current pathway and a truncated, fixed tilt biphasic shock waveform. The defibrillation energy requirement (DER) was determined with the use of a step-down protocol (delivered energy 15, 10, 8, 6, 4, 3, 2 J). The patients were then randomized to three inductions of ventricular fibrillation at implantation and three at predischarge testing with shock strengths programmed to DER + 5 J at implantation and + 10 J at predischarge testing or vice versa. The mean DER in the total study population was 7.88 +/- 2.96 J. The number of defibrillation attempts was 288 for + 5 J and 288 for + 10 J. The rate of successful defibrillation was 94.1% (DER + 5 J) and 98.9% (DER + 10 J; P < 0.01 for equivalence). Charge times for DER + 5 J were significantly shorter than for DER + 10 J (3.65 +/- 1.14 vs 5.45 +/- 1.47 s; P < 0.001). A defibrillation safety margin of DER + 5 J is associated with a defibrillation probability equal to the standard DER + 10 J. In patients in whom short charge times are critical for avoidance of syncope, a safety margin of DER + 5 J seems clinically safe for programming of the first shock energy.

Safety of a single successful conversion of ventricular fibrillation before the implantation of cardioverter defibrillators

Multiple successful conversions of ventricular fibrillation (VF) at 10 J below the maximum output of implantable cardioverter defibrillator (ICD) have been recommended as a minimum device implantation criterion. This recommendation is based on the probabilistic properties of defibrillation that necessitates multiple shocks to establish an adequate safety margin for the conversion of subsequent spontaneous arrhythmias. We hypothesized that a single successful shock at a 14 J may suffice.

METHODS AND RESULTS

The Low Energy Safety Study (LESS) enrolled 720 patients undergoing initial ICD implantation with a dual-coil transvenous lead and active pulse generator. At implant, an enhanced defibrillation threshold (DFT++) was determined by a rigorous protocol beginning at 14 J, and requiring at least 4 shocks. Fifty percent of all patients were then randomized to full output shock energy and the conversion rates for spontaneous ventricular tachyarrhythmias at rates > 200 beats/min were measured. There were 318 patients randomized to 31 J, of whom 254 were successfully defibrillated by an initial 14 J shock. During a mean follow-up of 24 +/- 12 months, 112 spontaneous VF episodes occurred in 31 patients. The combined conversion success of the first and second shock (when needed) did not differ between the subgroup of patients who were successfully defibrillated by an initial 14 J shock, regardless of the results of additional testing, and the whole cohort who underwent more systematic testing (97% vs 97%). All spontaneous episodes of VF were successfully treated during long-term follow-up.

CONCLUSIONS

A first successful shock of 14 J may be a sufficient endpoint to allow the implantation of ICDs with the Triad lead configuration, when programming all shocks to 31 J.

Efficacy and temporal stability of reduced safety margins for ventricular defibrillation: primary results from the Low Energy Safety Study (LESS)

BACKGROUND

Traditionally, a safety margin of at least 10 J between the maximum output of the pulse generator and the energy needed for ventricular defibrillation has been used because lower safety margins were associated with unacceptably high rates of failed defibrillation and sudden cardiac death. The Low Energy Safety Study (LESS) was a prospective, randomized assessment of the safety margin requirements for modern implantable cardioverter-defibrillator (ICD) systems.

METHODS AND RESULTS

A total of 636 patients undergoing initial ICD implantation with a dual-coil lead and active pulse generator were evaluated. The defibrillation threshold (DFT) and enhanced DFT (DFT+ and DFT++) were measured using a modified step-down protocol. Conversion testing of induced ventricular fibrillation before discharge, at 3 months, and at 12 months was performed, as was randomization to chronic programming at either 2 steps above DFT++ or maximal output. The induced ventricular fibrillation data had conversion success rates of 91.4%, 97.9%, 99.1%, 99.6%, and 99.8% for safety margins of 0, 1, 2, 3, and 4 steps above the DFT++, respectively. A margin of 4 to 6 J was adequate to maintain high conversion success over time (98.9% before discharge versus 99.2% at 12 months; P=NS). Over a mean follow-up of 24+/-13 months, conversion of spontaneously occurring ventricular tachyarrhythmias >200 bpm was identical (97.3%), despite a safety margin difference of 5.2+/-1.1 J for the 2-step group versus 20.8+/-4.2 J for maximal output.

CONCLUSIONS

With a rigorous implantation algorithm, a safety margin of about 5 J is adequate for safe implantation of modern ICD systems.

Implantation of cardioverter defibrillators without induction of ventricular fibrillation

BACKGROUND

The upper limit of vulnerability (ULV) is the weakest shock at which ventricular fibrillation (VF) is not induced by a T-wave shock. This study tested the hypothesis that a vulnerability safety margin based on the ULV can be used as an implantable cardioverter-defibrillator implantation criterion.

METHODS AND RESULTS

Implantable cardioverter-defibrillators were implanted in 80 patients if T-wave shocks did not induce VF and the baseline-rhythm R wave was >/=7 mV. The T-wave shock was 10 J in the first 45 patients (group A) and 15 J in the last 35 patients (group B). After inductionless implantations, the first VF shock was programmed to the T-wave shock plus 5 J. If T-wave shocks induced VF, the ULV was measured and the first shock was programmed to the ULV+5 J. Inductionless implantations were performed in 58 patients (72%), 28 in group A (62%) and 30 in group B (86%; P=0.04). If T-wave scanning had been done at 15 J in group A patients, inductionless implantations could have been performed in 84% of them. At 3 months, VF was induced twice during electrophysiological study in 75 patients (94%). All VFs were detected in </=4.7 s and were terminated by the first shock. During follow-up, 197 of 198 appropriate first shocks for rapid ventricular tachycardia or VF (99%) were successful in patients who had inductionless implantations (95% confidence intervals, 97% to 100%).

CONCLUSION

Inductionless implantations can be performed in >80% of implantable cardioverter-defibrillator recipients using a vulnerability safety margin based on a T-wave scan at 15.

The implantable cardioverter defibrillator

Implantable cardioverter defibrillators (ICDs) have evolved from the treatment of last resort to the gold standard therapy for patients at high risk for ventricular tachyarrhythmias. High-risk patients include those who have survived life-threatening arrhythmias, and individuals with cardiac diseases who are at risk for such arrhythmias, but are symptomless. Use of an ICD will affect the patient's quality of life. Some drugs can substantially affect defibrillator function and efficacy, and possible drug-device interactions should be considered. Patients with ICDs may encounter cell phones, antitheft detectors, and many other sources of potential electromagnetic Interference. In addition to treating ventricular tachyarrhythmias, new defibrillators provide full featured dual chamber pacing, and could treat atrial arrhythmias, and congestive heart failure by means of biventricular pacing.

Optimal method to achieve consistently low defibrillation energy requirements

Reduction of the defibrillation energy requirement offers the opportunity to decrease implantable cardioverter defibrillator (ICD) size and to increase device longevity. Therefore, the purpose of this prospective study was to obtain confirmed defibrillation thresholds (DFTs) of < or = 15 J in each patient with an endocardial dual-coil lead system incorporating an active pectoral pulse generator (TRIAD lead system: RV- --> SVC+ + CAN+). According to our previous clinical and experimental studies, we tried to lower DFTs that were > 15 J by repositioning the distal coil of the endocardial lead system in the right ventricle. A total of 190 consecutive patients requiring ICDs for ventricular fibrillation and/or recurrent ventricular tachycardia were investigated at the time of ICD implantation (42 women, 148 men; mean age 61.9 +/- 12.0 years; mean left ventricular ejection fraction 42.7 +/- 16.6%). Coronary artery disease was present in 139 patients; nonischemic dilated cardiomyopathy in 34 patients; and other etiologies in 17 patients; 47 patients had undergone previous cardiac surgery. Regardless of optimal pacing and sensing parameters, for patients having DFTs > 15, we repositioned the distal coil of the endocardial lead system toward the intraventricular septum to include this part of both ventricles within the electrical defibrillating field. In 177 of 190 patients, induced ventricular fibrillation was successfully terminated with < or = 15 J (group I) using the initial lead position. Repositioning of the endocardial lead was necessary in 13 patients whose DFT(plus) (DFT(plus) = second additional success at lowest energy level) were > 15 J (group II). In all patients, repositioning was successful within a 15 J energy level (100% success). The mean DFT(plus) was 7.3 +/- 3.5 J (group I) and 11.0 +/- 4.5 J (group II; p<0.005). The mean DFT(plus) of all patients enrolled in the study was 7.6 +/- 3.7 J (range: 2 to 15 J). In 87% of all patients, DFT(plus) of < or = 10 J was achieved. Repositioning of the endocardial lead in the right ventricle is a simple and effective method to reduce intraoperative high DFTs. As a result of this procedure, ICDs with a 20 J output should be sufficient for the vast majority (87%) of our patients. Furthermore, we were able to avoid additional subcutaneous or epicardial electrodes in all patients.

Emergencies related to implantable cardioverter-defibrillators

Implantable cardioverter-defibrillators (ICDs) have become the dominant therapeutic modality for patients with life-threatening ventricular arrhythmias. ICDs are implanted using techniques similar to standard pacemaker implantation. They not only provide high-energy shocks for ventricular fibrillation and rapid ventricular tachycardia, but also provide antitachycardia pacing for monomorphic ventricular tachycardia and antibradycardia pacing. Devices incorporating an atrial lead allow dual-chamber pacing and better discrimination between ventricular and supraventricular tachyarrhythmias. Intensivists are increasingly likely to encounter patients with ICDs. Electrosurgery can be safely performed in ICD patients as long as the device is deactivated before the procedure and reactivated and reassessed immediately afterward. Prompt and skilled intervention can prove to be life-saving in patients presenting with ICD-related emergencies, including lack of response to ventricular tachyarrhythmias, pacing failure, and multiple shocks. Recognition and treatment of tachyarrhythmia can be temporarily disabled by placing a magnet on top of an ICD. The presence of an ICD should not deter standard resuscitation techniques. Multiple ICD discharges in a short period of time constitute a serious situation. Causes include ventricular electrical storm, inefficient defibrillation, nonsustained ventricular tachycardia, and inappropriate shocks caused by supraventricular tachyarrhythmias or oversensing of signals. ICD system infection requires hardware removal and intravenous antibiotic therapy. Deactivation of an ICD with the consent of the patient or relatives is reasonable and ethical in terminally ill patients.