Cardiac Rhythm Management
Articles Articles 2012 February

ICD Implant without Defibrillation Threshold Testing: Patients with Chagas disease versus Patients with Ischemic Cardiomyopathy

DOI: 10.19102/icrm.2012.030206

1FRANCISCO FEMENÍA, MD, 1MAURICIO ARCE, MD, 1MARTÍN ARRIETA, Tc, 2WILLIAM F. MCINTYRE, MD, and 2ADRIAN BARANCHUK, MD, FACC

1Unidad de Arritmias, Departamento de Cardiología, Hospital Español de Mendoza, Argentina
2Heart Rhythm Service, Kingston General Hospital, Queen's University, Kingston, Ontario, Canada

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ABSTRACT.Defibrillation threshold testing (DFT) in patients undergoing implantable cardioverter-defibrillator (ICD) implantation is being revised. Little information is available on technical aspects of ICD implants in patients with Chagas disease. The aim of this study was to evaluate patients with Chagas cardiomyopathy (ChCM, group 1) versus ischemic cardiomyopathy (ICM, group 2) who did not undergo routine DFT at implant. Retrospective analysis included consecutive patients with an ICD implanted in a single center. Statistical comparisons were performed using the two-tailed Student's t-test and the Spearman test for correlation. p values <0.05 were considered to be statistically significant. A total of 179 patients were analyzed. Group 1 was younger, 53.29 versus 64.20 years (p=0.0001), and had better left ventricular ejection fraction, 41.13% versus 31.74 % (p=0.0001). Primary prevention ICD indication was more frequent in group 2, 48.6 versus 72.2% (p=0.006). The intraoperative measurements were sensing (mV): P wave, 3.4 versus 3.42, p=NS; R wave (RV), 13.63 versus 13.22, p=NS; R wave (LV), 12.57 versus 10.45, p=NS; pacing threshold (V): RA, 1.28 versus 1.18, p=NS; RV, 1.01 versus 0.69, p=0.0001; LV, 2.75 versus 2, p=0.006; lead impedance (Ω): RA, 638 versus 620, p=NS; RV, 817.80 versus 898.75, p=0.025; LV, 883 versus 527.98, p=NS. The subthreshold impedance test was similar in both groups (49.6 versus 51.18 Ω, p=0.001) and no differences in intraoperative complications were seen between groups. The procedure time (35.63 versus 32.38 min, p=NS) and radioscopic time (8.14 versus 7.93 min, p=NS) were similar in both groups. No undersensing events were detected during the follow-up and no need for lead repositioning was seen in this series. In 19 patients (26.4%) of group 1 and 27 patients (25%) of group 2, ventricular arrhythmias resulting in appropriate device therapies were seen (p=0.05). Overall mortality was 6.14% (4 patients in group 1 and 7 in group 2); none related to device failure. ICD implant without DFT in patients with Chagas disease appears as a safe option. This may result in reduction of implant time and cost-saving. Long-term follow-up is not different from patients with ischemic disease.

KEYWORDS.defibrillation threshold testing, implantable cardioverter-defibrillator.

The authors report no conflicts of interest for the published content.
Manuscript received November 30, 2011, final version accepted December 20, 2011.

Address correspondence to: Dr. Francisco Femenía, Av. San Martín 965. Godoy Cruz., Mendoza, Argentina, CP: 5501. E-mail: femeniafavier@hotmail.com

Introduction

Implantable cardioverter-defibrillators (ICD) is the most effective treatment for those patients who are at high risk of life-threatening ventricular arrhythmias.13

Historically, ICD implants included long and laborious defibrillation threshold testing (DFT) in order to prove the ability of the ICD to terminate ventricular fibrillation (VF).46 Subsequently, modified protocols reduced the number of VF inductions and shocks to a single induction delivering a shock with a safety margin of about 10 J.7,8

The rationale for this practice was based on the presumption that a successful defibrillation in the electrophysiology (EP) laboratory would warrant adequate ICD functioning during a spontaneous VF episode.

During the last 5 years, cumulative evidence has suggested that DFT may not be necessary to evaluate ICD functioning during the implant.9,10 There is little published data that describes the clinical outcomes in patients who do not undergo routine DFT at the time of ICD implantation.11,12

Data on technical aspects of ICD implant and testing on Chagas cardiomyopathy (ChCM), the most common form of non-ischemic dilated cardiomyopathy in Latin America, is scarce and has not been presented in a systematic manner yet.13

The aim of this retrospective study was to evaluate ICD implants without DFT in patients with ChCM versus ischemic cardiomyopathy (ICM).

Methods

Retrospective study included consecutive patients with ChCM (group 1) and ICM (group 2) implanted with an ICD in a single center at Mendoza, Argentina. Written informed consent was obtained from all patients prior to implant.

ICD and defibrillation lead systems

Patients were implanted with standard single, dual, or triple (cardiac resynchronization therapy defibrillator (CRT-D)) devices (manufactured by Medtronic, Minneapolis, MN; St Jude Medical, St Paul, MN; Guidant, St Paul, MN; Biotronik, Berlin, Germany). All devices had the ability to perform a painless lead integrity test, which measures defibrillation lead impedance using subthreshold (0.1–0.4 µJ) test pulses. All patients were implanted with a bipolar dual-coil lead.

Implant procedures and testing

All ICDs were implanted under local anesthesia in a left pectoral position. The ICD pulse generator and the transvenous lead system were inserted through a subclavian vein puncture (single, double, or triple) and a single pectoral incision. The defibrillation lead was connected to the defibrillator and the usual intraoperative device-based measurements of the pacing thresholds and R and P wave amplitudes were recorded to ensure an optimal stable lead position.

A subthreshold impedance test was performed in each patient. Successful implantation was defined as demonstration of adequate sensing (R wave amplitude ≥5 mV), adequate ventricular pacing threshold (≤1.5 V/0.5 ms) and adequate system integrity (45±15 Ω).

ICD programming

Bardycardia pacing was set at 40–60 bpm depending on the case; in those cases with CRT-D, the lower rate limit was programmed, intending 100% biventricular pacing. Two tachycardia detection zones (zone 1, cut off between 180 and 210 bpm; and zone 2, cut off ≥210 bpm) were programmed. Following antitachycardia pacing, maximal energy shocks (≥30 J) were programmed in all cases.

Follow-up

Patients were evaluated at 7-, 15-, and 30-day intervals. After the first month, ICDs were interrogated every 3 months, including pacing threshold and impedance, sensing parameters and therapies that had been delivered. Patients and their relatives were instructed to immediately report to our clinic in case of presyncope, syncope, palpitations, or ICD shocks.

Statistical analysis

Continuous variables are expressed as mean±SD. Statistical comparisons were performed using the two-tailed Student's t-test and the Spearman test for correlation. p values <0.05 were considered to be statistically significant.

Results

Patient population

Table 1 depicts the clinical characteristics and demographics of the patients. The current study included 179 consecutive patients (72 in group 1 and 107 in group 2) with ICD/CRT-D implantation or device upgrade. Primary prevention ICD implantation was less frequent in group 1 (48.6 versus 72.2%, p = 0.006). Patients of group 1 were younger (53.29±7.06 versus 64.20±7.37 years, p = 0.0001) and with better left ventricular ejection fraction (LVEF) (41.13±8% versus 31.74±4.7%, p = 0.0001). For groups 1 and 2 respectively New York Heart Association classes were class I, 49.3% versus 9.8%; class II, 30.6% versus 48.6%; class III, 20.8% versus 22.2%; class IV, 8.3% versus 19.4%.

Table 1: Patients clinical characteristic

crm-03-02-662-t1.jpg

Implant testing

Group 1 received fewer CRT-D devices and showed higher pacing thresholds at implant. The subthreshold impedance test was similar in both groups. No differences in intraoperative complications were seen between groups.

During the follow-up, group 1 presented with a higher percentage of atrial and ventricular pacing. Table 2 and Table 3 show device measurements at implant and follow-up, respectively.

Table 2: Device measurements at implan

crm-03-02-662-t2.jpg

Table 3: Device measurements during the follow-up

crm-03-02-662-t3.jpg

Follow-up

During the follow-up, 19 patients (26.4%) of group 1 and 27 patients (25%) of group 2 had ventricular arrhythmias resulting in appropriate device therapies (p = 0.05).

The time to first appropriate therapy was shorter in group 1 (13.53±6.8 versus 19.17±6.7 months, p = 0.01) (Table 4).

Table 4: Arrhythmic events and device therapies during the follow-up

crm-03-02-662-t4.jpg

No undersensing events were detected during the follow-up. No need for lead repositioning was seen in this series. Overall mortality was 6.14% (4 patients in group 1 and 7 in group 2; p = NS).

Discussion

To the best of our knowledge, this is the first study to evaluate ICD implant without DFT in patients with Chagas disease.

Major findings

The major finding of this study is that in this consecutive series of patients undergoing ICD or CRT-D implantation or device upgrade without DFT, a similar efficacy to prior strategies (performing DFT in every case) has been seen.

This longitudinal cohort of patients with a mean follow-up of 46.5 months represent real-life experience with ICD or CRT-D device implant without performing DFT.

In the last few years, the utility of DFT during ICD implantation has been questioned.7,14 DFT is usually performed in clinically stable patients, under deep sedation, so that the “primary success rate of defibrillation” may differ from that observed with spontaneous ventricular tachyarrhytmias, where several factors (ischemia, electrolyte disturbances, acidosis, and changes in medication) can affect the effectiveness of the shock.15,16

Several studies conducted in the ICD patient population have failed to show a relationship between first-shock efficacy or survival and the results of DFT.12,14,17

Prior studies of patients undergoing ICD implantation have found worse outcomes in patients whose DFT was not tested.7,8,18

Pires and Johnson8 found in their retrospective analysis that patients who did not undergo intraoperative defibrillation testing had significantly higher overall mortality rates than those who underwent either DFT or defibrillation safety margin testing. Hall et al18 recently corroborated these findings, and this results favors DFT or at least safety margin testing. However, patients were often not tested because of more significant comorbidities, and this selection bias may explain the difference in outcomes. Indeed, a study that compared outcomes in centers that either tested or did not test DFT routinely, which minimized selection bias, found no mortality difference between the two strategies.12

Other studies in patients with CRT-D found a higher incidence of elevated DFT in this population.17,19 Mainigi et al19 reported that elevated DFT was not associated with higher mortality.

Current clinical practice during ICD implantation, even in well-experienced implanting centers, varies considerably; indeed, there are, as yet, no international guidelines mandating DFT. Indeed, this procedure increases mean procedure duration, probably raises costs, and may cause higher morbidity.20 Inducing cardiac arrest may result in serious clinical consequences: several studies have shown that DFT testing may cause hemodynamic impairment and complications such as cerebrovascular stroke. Furthermore, there is evidence of myocardial cell damage after repeated ICD shocks.2124 Simplifying the testing procedure during ICD implantation undeniably allows greater hemodynamic stability and safety to be achieved, which, given the low ventricular function of ICD recipients, is highly desirable.

It is well known that problems leading to ICD malfunction are markedly attenuated by modern lead systems and biphasic shock waveform.25

Accurate and effective ICD function depends on a correct sensing of intracardiac electrical activity, appropriate interpretation by the device, and effective shock delivery.14

The Canadian Registry of ICD Implant Testing Procedures (CREDIT),9 which assessed the reasons for not conducting DFT, and the costs and complications associated with DFT, observed that 66% of all ICDs were implanted without DFT.

DFT was not performed most commonly due to a perceived lack of need to test patients having an ICD implanted for primary prevention or those having pulse generator replacement. A potential safety concern was cited as the reason for not testing in 37% of cases, most frequently the presence of atrial fibrillation. These data suggest not only a significant shift away from routine DFT, but also in the justification for not testing. The Canadian Registry, which assessed DFT-associated risks10 reported that DFT was performed in only 66% of new implants and in 24% of pulse generator upgrade. Physicians appeared to favor DFT in patients who were at lower risk of DFT-related complications and in those perceived to be at high risk of failed defibrillation testing due to concomitant use of amiodarone. Practice differed substantially between participating centers, and may be influenced by local resource limitations and physician bias.

Unlike other reports that have excluded specific patients for DFT at higher risk of presenting DTF associated complications,8,18,26 our series was consecutive and did not subselect patients.

We found adequate intraoperative parameters (pacing thresholds and R and P wave amplitudes). These parameters remained stable during the follow-up, without significant changes. No intraoperative complications were seen. No undersensing events or lead repositioning were detected during the follow-up.

During the follow-up, around one-third of the patients in both groups had ventricular arrhythmias resulting in appropriate device therapies, and we found no deaths related to device failure.

ICD without DFT in Chagas disease

Chagas disease is an endemic disease in Latin America caused by a unicellular parasite Trypanosome cruzi. Almost 18 million people are infected, and ≈25% of them will develop chronic myocardial disease after 20–30 years.13,27,28

Chagas disease has become a worldwide problem given the new patterns of immigration. Physicians around the world should become aware of its existence and how to recognize and treat it.27,28

In group 1 the indication for ICD implant for primary prevention was less common. A possible explanation would be the lack of guidelines on primary prevention of sudden cardiac death in patients with Chagas disease. Another reason would be economical. The usual perception is that patients referred for secondary prevention are sicker and at a higher risk of sudden death, and the limited sources are allocated to this group of patients. The Chagas disease group was younger and with better ventricular function, resulting in a smaller number of CRT-D implants.

During the follow-up, 19 (26.4%) patients of group 1 and 18 (17%) patients of group 2 had ventricular arrhythmias resulting in appropriate ICD therapies. No undersensing or failed shocks were seen.

Inappropriate therapy was significantly higher in group 1 (p = 0.001), probably related to an increased prevalence of atrial fibrillation (p = 0.001).

The global mortality rate during the follow-up in both groups was 6.14% and no significant differences were found between groups, in concordance with a study by Muratore et al (6.7%).13 There was no sudden cardiac death or death due to device malfunction or failure during the follow-up.

Unlike other reports where mortality during follow-up of Chagas disease patients with ICD implantation was significantly higher,29 Di Toro et al30 recently reported a large series of patients with ChCM and ICD analyzing mortality predictors. They found that age over 65 years and LVEF less than 30% were the only predictors associated with higher mortality within the first year. In agreement with these findings, in our study group 1 patients were younger and with a relatively preserved LVEF, which could account for the relatively low mortality.

Finally, despite major differences in underlying pathophysiology between both diseases, this study found no differences in detection or treatment of ventricular tachycardia (VT)/VF events between both groups of patients. ATP was the primary treatment for most of VT episodes. Shocks were effective to terminate VF in all cases.

Study limitations

This study has limitations inherent to its retrospective nature and the small sample size. We cannot be absolutely conclusive on the real impact of not performing DFT on the efficacy of ICD therapy. However, by selecting a consecutive sample that was uniform in terms of clinical characteristics, lead system, and waveform, we tried to eliminate some of the possible confounding factors. Randomized trials on ChCM are extremely difficult to pursue, and most of the valuable data come from registries.13,31

The relative small number of arrhythmias registered during follow-up should also be highlighted as a limitation.

We believe that given the scarce data available, our retrospective data set may help to simplify ICD implantation (by not performing DFT) in patients with Chagas disease without affecting its efficacy.

Conclusion

ICD implant without DFT in patients with Chagas disease appears to be a safe option. This may result in reduction of implant time and cost-saving. Long-term follow-up is not different from patients with ischemic disease.

References

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