Europace Advance Access originally published online on March 3, 2008
Europace 2008 10(4):453-457; doi:10.1093/europace/eun042
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ICD FOR PRIMARY PREVENTION: MORE IMPLANTS ARE NEEDED
Estimation of the requirement for implantable cardioverter defibrillators for the primary prevention of sudden cardiac death post-myocardial infarction based on UK national guidelines (2006)
1 Wessex Cardiothoracic Unit, Southampton University Hospital, Tremona Road, Southampton SO16 6YD, UK; 2 Department of Cardiology, Portsmouth Hospitals NHS Trust, Queen Alexandra Hospital, Portsmouth PO6 3LY, UK
Manuscript submitted 4 December 2007. Accepted after revision 2 February 2008.
* Corresponding author. Tel: +44 2380 798693; fax: +44 2380 794036.E-mail address: paul.andrew.scott{at}btinternet.com
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Abstract |
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Aims: To assess the impact of the new UK National Institute for Health and Clinical Excellence (NICE) guidelines on the incidence of implantable cardioverter defibrillator (ICD) indications for the primary prevention of sudden cardiac death following myocardial infarction (MI).
Methods and results: We performed a retrospective single centre study in a District General Hospital. The transthoracic echocardiogram reports of all patients with a discharge diagnosis of MI during a 6-month period were studied. We reviewed the notes of all patients with an estimated left ventricular ejection fraction (LVEF) of <35% and used UK national guidance to assess the incidence of potential ICD indications. Five hundred and forty-six patients had a discharge diagnosis of MI. Fifty had estimated LVEF <35% and 8–11 of these met the NICE post-MI primary prevention criteria for ICD implantation. This gives an estimated incidence based upon our local population of 29–39 patients/million/year. Most of these patients (64–88%) were identified purely by ECG criteria (QRS > 120 ms) and LVEF.
Conclusion: The latest published UK ICD data give a new implantation rate of 
40/million/year. Combining our results with published data for NICE secondary prevention indications gives a combined ICD indication incidence of 105–115/million/year. This suggests there is currently significant under-provision of ICD therapy in the UK.
Key Words: Implantable cardioverter defibrillators, Guidelines, National Institute for Health and Clinical Excellence, Sudden cardiac death
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Introduction |
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Since their introduction in the 1980s, the evidence supporting the use of implantable cardioverter defibrillators (ICDs) has steadily increased. Implantable cardioverter defibrillators are now the primary treatment modality for the prevention of sudden cardiac death (SCD) in high-risk patients. The National Institute for Health and Clinical Excellence (NICE) is an independent organization responsible for providing national guidance on clinical practice in the UK. National Institute for Health and Clinical Excellence initially published guidance on the indications for ICD insertion in 2000. Since then the evidence base for their use in the primary prevention of SCD following myocardial infarction (MI) has extended,1
,2 and this guidance was recently updated in 2006 to take account of these expanded indications (Table 1).3
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It remains uncertain as to what impact NICE guidance will have on absolute ICD implantation rates and the associated health resources. Previous audits assessed the incidence of ICD requirements based on the initial NICE guidelines.4
–6 However, the revised indications are likely to increase this rate and the true need for ICD implantation for primary prevention post-MI in the UK is not known. We therefore performed a retrospective single centre study in a UK District General Hospital to provide greater insight. |
Methods |
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Portsmouth Hospitals NHS Trust is a large District General Hospital Trust serving a population of
560 000 people. All patients with acute MI are admitted via a single site. Using ICD-10 clinical coding, we identified all patients during a 6-month period from February to July 2006 with any discharge diagnosis of MI. All transthoracic echocardiograms (TTE) reports in our institution are stored on a database (Tomcat Systems Ltd, Belfast, Northern Ireland), which we searched to obtain TTE reports during or early after hospital admission. If there were multiple reports, we took the most recent. We reviewed hospital notes for patients whose left ventricular (LV) systolic function was reported as ‘severely impaired’ (or ‘severe dysfunction’) or ‘moderate-severely impaired’ (or ‘moderate–severe dysfunction’). Age, sex, and type of infarct (ST-elevation or non-ST-elevation) were recorded. The most recent electrocardiogram (ECG) prior to discharge (or death) was evaluated and QRS width noted. Documented contraindications to an ICD and evidence of ventricular arrhythmias which might meet secondary prevention guidelines for an ICD were also noted.
We used NICE criteria (Table 1) to estimate the incidence of potential post-MI primary prevention ICD indications in our cohort. With reference to TTE assessment of LV systolic function, based on our departmental reporting criteria, we made a pragmatic assumption that ‘severely impaired’ reflected LV ejection fraction (LVEF) <30% and ‘moderate-severely impaired’ 30–35%. As there was no systematic screening for post-MI primary prevention ICD indications in our hospital at the time of the study, anticipated results from Holter monitoring and electrophysiological studies (EPS) were extrapolated from published data (Table 2).7–12 Patients who died within 4 weeks of their MI (as they would not meet NICE guidance), had a ‘secondary prevention’ indication for an ICD, or had a documented contraindication to an ICD were excluded.
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Results |
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We identified 546 patients admitted to hospital during the 6-month study period with an ICD-10 diagnosis of MI. Four hundred and four (74%) had reported TTEs, of which 50 had estimated LVEF <35%. Of these 50 patients, one set of notes was unavailable and therefore 49 were evaluated in more detail—27 with ‘severely impaired’ and 22 with ‘moderate-severely impaired’ LV systolic function (Table 3). Under NICE guidance, all post-MI patients with LVEF <35% should be considered for an ICD. However, the need for further testing prior to device implantation depends on the severity of LV impairment. Patients with LVEF <30% require only a QRS width of >120 ms, whereas patients with LVEF 30–35% require both non-sustained ventricular tachycardia (NSVT) on Holter monitoring and inducible ventricular tachycardia (VT) at EPS. Consistent with NICE guidelines, we considered these two patient groups separately (Figure 1).
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Of the 27 patients with ‘severely impaired’ LV systolic function (assumed equivalent to LVEF <30%), six died within 4 week of their MI, four had a ‘secondary prevention’ indication for an ICD, and one had limited life expectancy due to non-cardiac co-morbidity. Of the remaining 16, seven patients had a QRS width greater than 120 ms and would have met the guidance for consideration of ICD implantation without need for further testing assuming LVEF remained <30% after 4 weeks. The remaining nine with a narrow QRS would need to meet the same requirements as those with LVEF 30–35% (NSVT on Holter monitoring and inducible VT at EPS) and are discussed below (Figure 1).
Of the 22 patients with ‘moderate-severely impaired’ LV systolic function (assumed equivalent to LVEF 30–35%), two died before 4 weeks and two had a ‘secondary prevention’ indication for an ICD (Figure 1). To meet NICE criteria, the remaining 18, in addition to the nine with LVEF <30% but narrow QRS, would need to demonstrate NSVT on Holter monitoring and inducible VT at EPS. Making the assumptions outlined in Table 2 gives an estimate of between one and four patients over the 6-month study period requiring an ICD for this indication.
Therefore, out of 546 post-MI patients identified over a 6-month period, between eight and 11 met the NICE post-MI primary prevention criteria for potential ICD indication. Extrapolating this for our population (560 000 people) for the whole year gives an incidence of 29–39 patients/million/year.
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Discussion |
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The most recent published UK ICD data give a new implantation rate of just over 40/million/year (2005).13
Our estimate of 29–39/million/year relates only to post-MI primary prevention. A recent estimate of the incidence of ICD secondary prevention indications based on current NICE guidance was 76/million/year.5 Taken together, these imply a combined ICD indication incidence of 105–115/million/year. This suggests there is currently considerable under-provision of ICD therapy in the UK, although requirements may not be as high as some studies have proposed.5,6
An increase in device use to achieve the estimated implantation rate based on our findings would have significant cost implications. Using the published NICE costing of £20 102,14 which includes follow-up appointments and replacement/repair costs (though based on 2004 costings) but not the potential cost saving of a reduction in cardiac events, would mean an extra cost of approximately £74–86 million ($152–177 million, 103–120 million euro) per year to the NHS.
The only other studies to assess the incidence of ICD indications based on NICE guidance used different methodology,5,6 and as they were published prior to the new guidance used the MADIT II study criteria for reference.2 Both studies produced significantly higher estimates of the overall incidence of patients requiring consideration for ICD implantation (453/million/year and 504/million/year), and there are a number of potential reasons for this disparity. The more inclusive MADIT II criteria did not use QRS width as a determinant—in our study, only 37% of patients with LVEF <30% had a broad QRS. The new NICE guidance also states that patients must be at least 4 weeks after their infarct to be considered for device therapy—in our study, only 78% of patients with LVEF <30% survived to this point. Furthermore, in 2005, 2 years after the publication of the MADIT II trial, the highest total (not new) ICD implantation rate in Europe in 2005 was 170/million/year (Germany), which is more in keeping with our estimate.13
In our cohort, 9% of post-MI patients had an LVEF <35%, which is lower than in other studies (11–16%).9,15 The diagnosis of MI in our study was based on the modern, more inclusive diagnostic criteria using troponin. In contrast, other published studies primarily enrolled patients with ST-elevation MIs, who are likely to have suffered larger infarcts with more myocardial damage. Contemporary treatment of acute MI may also contribute to better preservation of LV function. The number of patients with potential ‘secondary prevention’ ICD indications in our cohort was six, giving an incidence of 21/million/year, which is significantly lower than other studies.5 This is likely to be related to our study methodology where only those patients with LVEF <35% were included; a ‘secondary prevention’ indication but LVEF >35% will have been missed. In addition, patients who presented with VF/VT without a significant troponin rise would also have been excluded.
Our study estimated the incidence rather than prevalence of ICD requirements. In order to screen for the prevalence in our population, we would need to assess the records of all patients with heart failure and coronary artery disease in both outpatient and inpatient settings. In view of the potential logistical difficulties, we felt that estimation of incidence would still provide meaningful data. However, our estimate will be considerably lower than the equivalent prevalence.
To improve the uptake of primary prevention device therapy, the implementation of clinical pathways enabling the systematic identification and early assessment of potential candidates are needed. The 2006 NICE guidance advocates further testing for patients with LVEF 30–35% (Holter monitoring and EPS). It has been suggested that this guidance has not been widely followed because EPS, which is only available in larger cardiac departments, is perceived as a block.16 In our cohort, the vast majority of patients requiring consideration for ICD implantation (64–88%) were identified purely by ECG criteria (QRS > 120 ms). Therefore, the incremental benefit of further testing in addition to TTE and ECG in identifying high-risk patients is relatively small. These data suggest that merely evaluating LVEF and QRS width should be an initial priority when setting up a robust assessment programme.
Our study has potential limitations. Some of our data were incomplete. Approximately three-quarters of patients with a discharge diagnosis of MI had a TTE. Although this may have led to an underestimation of the ICD indication incidence, it is highly likely that those patients who did not have a TTE are less likely to have had an ICD indication. For example, in some instances the primary reason for admission will not have been an MI and these patients may be less likely to have an inpatient TTE. Patients with a clinically small infarct and no evidence of heart failure may also be less likely to receive an echo. However, even if it is assumed that the group of patients for whom full data were unavailable were identical in terms of spread of clinical features to those for whom data were complete, our adjusted rate would be 39–52/million/year and as such unlikely to dramatically alter our conclusions.
At the time of the study, there was no screening programme for post-MI primary prevention ICD implantation in our hospital and most TTEs were performed in the week after admission. Following MI, early LV remodelling may occur and according to NICE guidance, assessment of ICD need should be made with evaluation of LVEF at least 4 weeks after an MI. As such, our study truly estimates the number of patients requiring further assessment for contemplation of ICD implantation as opposed to an absolute indication for device therapy. Both beneficial and adverse LV remodelling can occur and we consider that our estimate of ICD requirement represents a realistic approximation. Furthermore, we believe it provides valuable insights into the services that need to be introduced to make a timely assessment of such patients.
TTE, although the most widely used tool to assess LVEF, suffers from intra- and inter-observer variability and some patients have limited echo windows. However, TTE remains the investigation of first choice when assessing cardiac structure and function in clinical practice and was the method used in the majority of ICD trials.1,2,17 In our department, LV systolic function is described qualitatively and in converting this into an approximate ejection fraction we have had to make some assumptions. However, this study reflects ‘real world’ practice in a busy District General Hospital where the majority of acute infarcts will present. It is likely that by taking this approach, we have identified the vast majority of cases that would require further detailed assessment of LVEF in early follow-up.
In common with other National and International guidelines, current NICE guidance relies heavily on LVEF as the primary determinant for ICD need.18 The use of qualitative assessments of LV function, as in our study, and the inherent problems in converting these into an LVEF, highlight the potential difficulties of the assessment of LVEF. Accurate and reproducible estimation of LVEF is an essential pre-requisite for any potential ICD screening programme, and it may be that the more widespread use of other imaging modalities needs to be considered.
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Conclusions |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
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This study highlights the current significant under-provision of ICD therapy for the primary prevention of SCD in the UK. The latest published UK ICD data give a new implantation rate of
40/million/year. Combining our results with published data for NICE secondary prevention indications gives a combined ICD indication incidence of 105–115/million/year. In order to improve the uptake of primary prevention device therapy, the implementation of clinical pathways that enable the systematic identification and early assessment of potential candidates are needed. Implantation rates for primary prevention indications are unlikely to significantly improve until there is widespread introduction of such programmes. Conflict of interest: P.R.R. has received Honoraria and research grants from Medtronic, St Jude, Sorin and Boston Scientific.
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References |
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