Intraoperative testing of the implantable cardioverter-defibrillator: how much is enough?

Canadian Registry of ICD Implant Testing procedures (CREDIT): current practice, risks, and costs of intraoperative defibrillation testing

BACKGROUND

There is uncertainty about the proper role of defibrillation testing (DT) at the time of implantable cardioverter defibrillator (ICD) insertion.

METHODS

A prospective registry was conducted at 13 sites in Canada between January 2006 and October 2007.

OBJECTIVES

To document the details of DT, the reasons for not conducting DT, and the costs and complications associated with DT.

RESULTS

DT was conducted at implantation in 230 of 361 patients (64%). DT was more likely to be conducted for new implants compared with impulse generator replacements (71% vs 32%, P = 0.0001), but was similar for primary and secondary prevention indications (64% vs 63%, P = NS). Among patients not having DT, the reason(s) given were: considered unnecessary (44%); considered unsafe, mainly due to persistent atrial fibrillation (37%); lack of an anesthetist (20%); and, patient or physician preference (6%). When performed, DT consisted of a single successful shock > or = 10J below maximum device output in 65% of cases. A 10J safety-margin was met by 97% of patients, requiring system modification in 2.3%. Major perioperative complications occurred in 4.4% of patients having DT versus 6.6% of patients not having DT (P = NS). ICD insertion was $844 more expensive for patients having DT (P = 0.16), largely due to increased costs ($28,017 vs $24,545) among patients having impulse generator replacement (P = 0.02).

CONCLUSIONS

DT was not performed in a third of ICD implants, usually due to a perceived lack of need or relative contraindication.

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.

Habitual Cocaine Use Is Associated with High Defibrillation Threshold During ICD Implantation

BACKGROUND

Habitual cocaine use can lead to dilated cardiomyopathy (DCM) and sudden cardiac death. Based on prior clinical observations, we hypothesized that prior habitual cocaine use is a strong predictor of high defibrillation threshold (DFT) during implantable cardioverter-defibrillator (ICD) implant.

METHODS

We reviewed the medical records of 130 consecutive patients undergoing initial ICD implantation or revision at Parkland Hospital and the Dallas VA Hospital, Dallas, TX, from January 2002 to November 2005. Patient characteristics and DFT data were collected retrospectively.

RESULTS

The study group includes 11 patients (8.46%) who were identified as having a history of prior habitual cocaine use as demonstrated by history and urine toxicology; the rest (119 patients) form the control group. Cocaine-using patients tended to be younger (48.2 +/- 10 vs 60.1 +/- 12.3 years; P = 0.0026), were less likely to have coronary disease (36.3% vs 72.2%; P = 0.032), and had less comorbidity. The average DFT was 27.9 +/- 7.8 J for all cocaine-using patients and 14.5 +/- 4.1 J for noncocaine-using patients (P = 0.00018). In the cocaine-using group, three out of 11 patients required a subcutaneous array compared to none in the control group.

CONCLUSIONS

Our results suggest that patients with a history of habitual cocaine use may be at increased risk to have a high DFT during ICD implantation. This is the first study to demonstrate such association. ICD implantation in patients with this history should be planned with these findings in mind, as larger output generators or subcutaneous arrays might be required.

Defibrillation testing at the time of implantation of cardioverter defibrillator in the clinical practice: a nation-wide survey

AIMS

Despite an effective defibrillation testing (DT) is considered mandatory to be consistent with the rules of good clinical practice, some physicians are concerned about the risk of complications related to the induction test, and in real world clinical practice, several implant procedures are performed without any induction test. We conducted a systematic nation-wide retrospective survey in order to determine the DT rate and its complications.

METHODS AND RESULTS

An ad hoc questionnaire was sent to all 343 Italian implanting centres and the data from the 229 (67%) centres that answered were analysed. During the year 2005, a total of 7857 patients underwent a first implantation of cardioverter defibrillator (ICD), 38% of which with cardiac resynchronization therapy (CRT). Of these, 2356 (30%) were implanted without any induction test. In 35 (15%) centres, the induction test was performed in < 25% of the patients, whereas in 136 (59%) centres, it was performed in > 75% of the patients. At multivariable analysis, performed in a subset of 1206 patients from 107 centres, CRT device (OR = 1.82) and primary prevention (OR = 1.47) were independent predictors of the decision to not perform DT. However, altogether, the clinical variables accounted only for 35% of the total variance, whereas the remaining 65% was probably unrelated to clinical factors. There was a total of 22 (0.4%) life-threatening complications as a consequence of the induction test: 4 deaths (0.07%), 8 cardiopulmonary arrests requiring resuscitation manoeuvres (0.15%), 6 cardiogenic shocks (0.11%), 3 strokes (0.05%), and 1 pulmonary embolism (0.02%).

CONCLUSION

In real world practice, DT is not performed in a substantial number of patients, most of these in the absence of legitimate reasons. The clinical impact of DT vs. no DT remains unclear until the not negligible complication rate is compared against the long-term potential benefit.

Stepped defibrillation waveform is substantially more efficient than the 50/50% tilt biphasic

BACKGROUND

Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series.

OBJECTIVES

The purpose of this study was to assess the clinical utility of improved defibrillation waveforms.

METHODS

We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel).

RESULTS

The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance.

CONCLUSION

The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.