Speaking at a debate about the value of defibrillator threshold testing in patients with implantable cardioverter defibrillators (ICDs), Klaus Witte (Leeds, UK) told delegates at the Heart Rhythm Congress (4–7 October, Birmingham, UK) that such testing was a “pointless” intervention because it does not provide benefit and may be associated with adverse events. Nick Linker (Middlesbrough, UK), who argued against Witte, said that there is still a significant proportion of patients-who were not included in the major trials of defibrillation testing-for whom defibrillation testing may be necessary.
Witte reported that, following the early studies of ICDs, defibrillation threshold testing became a mandatory part of ICD randomised controlled trials. He added that early investigators suggested that failure to successfully terminate life threatening arrhythmias might be the cause of 25% of sudden cardiac deaths in patients with ICDs and that “this figure might be higher if defibrillator threshold testing was not done”. However, Witte argues that all patients will eventually die, some with a refractory arrhythmia resistant to defibrillation. He also said that later studies of more effective ICDs, have suggested that defibrillator threshold testing provides limited benefit. For example, he noted that Roman-Gonzalez et al reported in 2001 that defibrillator testing-although “safe”-had “limited value”. Furthermore, Witte said that in 2006, results from SCDHeft (Sudden cardiac death in heart failure trial) indicated that there was no impact with “high defibrillator threshold testing on outcomes”.
He noted that the recent randomised controlled trials-SIMPLE (Shockless implant evaluation) and the NORDIC ICD (No regular defibrillation testing in cardioverter defibrillator implantation)-have also cast doubt on the value of the defibrillator testing. In SIMPLE, in a randomised trial of 2,500 patients, a non-testing strategy was non-inferior to a testing strategy in terms of the primary outcome of arrhythmic death or failed appropriate shock: 7% (of 1,247 patients assigned to no testing) vs. 8% (of 1,253 assigned to testing; pet al) concluded (in their report in the European Heart Journal) that: “Defibrillator testing during first-time ICD implantation should no longer be recommended for routine left-sided ICD implantation.”
Witte commented that, as well as data indicating that testing was “a pointless intervention”, there were some suggestions that testing was harmful, stating that a single-centre study from the University of California, Los Angeles found evidence of heart failure exacerbation in four patients who had undergone defibrillator testing but found no such events in patients who had not undergone testing. He added that an Ontario registry indicated that although defibrillator testing was “not associated with a risk of events but was associated with higher costs” and that an Italian registry showed that testing was associated with a 0.4% rate of life-threatening events-including four deaths “that we should not ignore.”
Summarising the available evidence, Witte stated: “Defibrillator threshold testing in any format, leads to higher costs, is not associated with improvement of outcomes (even in older, less effective devices), is-albeit rarely-associated with adverse events, and has been done to millions of people without evidence of benefit.”
Nick Linker (James Cook University Hospital, Middlesbrough, UK), who was arguing against Witte in the debate, said that the current evidence-base only suggested that defibrillator threshold testing was not necessary for certain patients-such as those receiving an ICD for primary prevention (eg. the patients in the NORDIC ICD study). He explained: “There were a significant proportion of patients who were not included in SIMPLE and NORDIC ICD [for example, only a small proportion of patients were undergoing ICD implantation for secondary prevention] and we need to do testing in these patients.” Furthermore, Linker commented that the hardware (ie. the ICD itself and its leads) may be an important consideration as to whether or not defibrillator threshold testing was needed, noting: “One size does not fit all. We do need to pause for thought and consider the hardware that we are implanting into the patient. We do tend to take an ICD and a lead and just stick them in. It may not be as simple as that-we do need to think about what we are putting in and how that affects the need for testing.” Different manufacturer’s devices do not deliver shocks in the same way and this needs to be taken into consideration when implanting and setting up a device.
