Results are expressed as the mean ± standard deviation or median [interquartile range], depending on the distribution of the variable. Continuous quantitative variables were analyzed using analysis of variance or the Kruskal-Wallis test, whereas qualitative variables were analyzed using the chi-square test.

In total, 203 centers participated in the Spanish implantable cardioverter-defibrillator registry for 2024, representing a 12.7% increase from 2023 and the highest participation in the history of the registry (180 centers in 2023). The participating hospitals are listed in table 1. Figure 1 shows the rate per million population and the total number of implants per autonomous community according to the data submitted to the registry. In 2024, 1 center implanted more than 300 ICD devices, 6 centers implanted more than 200 devices (6 in 2023), and 31 implanted more than 100 devices (29 in 2023). A total of 68 centers (the same number as in 2023) implanted between 11 and 99 devices, while 104 centers (83 in 2023) implanted ≤ 10, of which 26 (26 in 2023) implanted only 1 device. Most of the devices were implanted in public hospitals.

Figure 1.

Distribution of implant activity reported to the Heart Rhythm Association of the Spanish Society of Cardiology by autonomous community in 2024. Rate per million population/total number of implants reported.

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The total number of implants reported to the registry by the implanting centers and those estimated by Eucomed in the last 10 years are shown in figure 2. In 2024, 8793 implants were recorded (including first implants and replacements), marking a historic high for the registry and representing a 7% increase vs the previous year (8219 implants recorded in 2023). In addition, the data provided by Eucomed (8975 implants in 2024) also show the highest numbers of implants since the inception of the registry, with a 5.3% increase in devices billed in 2024 compared with 2023. Changes in the implantation rate per million population in the last 10 years according to both registry and Eucomed data are shown in figure 3. The total rate of implants recorded in 2024 was 186 implants/million population. These values exceed those reported to the registry and available in Eucomed in previous years (177 implants/million population according to Eucomed in 2023, 168 in 2022, 163 in 2021, and 150 in 2020).

Figure 2.

Total number of implants recorded and Eucomed estimates from 2015 to 2024. Eucomed, European Medical Technology Industry Association; ICD, implantable cardioverter-defibrillator.

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Figure 3.

Number of implants recorded per million population and Eucomed estimates from 2015 to 2024. Eucomed, European Medical Technology Industry Association; ICD, implantable cardioverter-defibrillator.

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Information distinguishing first implants and replacements (as well as the data presented in the following sections) was recorded in 3398 forms from the ICD Technical Report (37% of all implants) and 4135 forms extracted from the CardioDispositivos platform (45% of all implants). First implants comprised 76.3% of devices implanted, while replacements represented 19.7%; the remaining 3.5% corresponded to device upgrade procedures. The percentage of first implants exceeded that of previous years (72% of all implants in 2023, 71.9% in 2022, and 70.3% in 2021). This figure equals a rate of first implants per million population of 133.9 (121.5 in 2023, 116 in 2022, and 110 in 2021).

In 2024, the mean age of the patients included in the registry was 63.3 ± 15 (range, 2-93) years. Similar to previous years, the mean age of first ICD recipients was slightly lower: 61.7 ± 15 years. As in previous registries, patients were predominantly male, representing 75% of all patients.

The underlying heart diseases in the registry patients (first implants and replacements) are shown in figure 4. Ischemic heart disease was the most frequent underlying cardiac condition in first implant patients (49.7%), followed by dilated cardiomyopathy (24.9%), hypertrophic cardiomyopathy (10.9%), primary electrical diseases (Brugada syndrome, long QT syndrome, and catecholaminergic ventricular tachycardia; 2.8%), arrhythmogenic right ventricular cardiomyopathy (2.8%), and valve disease (0.9%).

Figure 4.

Underlying heart disease. ARVC, arrhythmogenic right ventricular cardiomyopathy. *Patients with more than 1 diagnosis.

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Left ventricular systolic function data were provided for 51% of patients. As shown in figure 5, 15.1% of first implant patients had a left ventricular ejection fraction (LVEF) > 50%, 10.1% had an LVEF between 41% and 50%, 9.7% had an LVEF between 36% and 40%, 22.9% had an LVEF between 31% and 35%, and 42.2% had an LVEF ≤ 30%.

Figure 5.

Left ventricular ejection fraction (LVEF) values of patients in the registry (total and first implants).

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Most registry patients (72.3%) were in New York Heart Association (NYHA) class II, followed by NYHA III (16.9%), NYHA I (9.2%), and NYHA IV (1.6%).

The baseline rhythm shown by patients at implantation was mainly sinus rhythm (80.6%), followed by atrial fibrillation (16.2%) and pacemaker rhythm (3.2%).

The clinical arrhythmias prompting ICD implantation (available in 2812 of forms submitted to the registry) are shown in figure 6. Most patients had no documented clinical arrhythmias (65.9%), whereas 8.8% had sustained monomorphic ventricular tachycardia (SMVT), 5.3% had nonsustained ventricular tachycardia, 1.1% had polymorphic ventricular tachycardia, and 6.6% had ventricular fibrillation (VF).

Figure 6.

Distribution of arrhythmias prompting implantation (total and first implants) in 2024. BVT, bidirectional ventricular tachycardia; NSVT, nonsustained ventricular tachycardia; PVT, polymorphic ventricular tachycardia; SMVT, sustained monomorphic ventricular tachycardia; VF, ventricular fibrillation.

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The most frequent clinical presentation in patients with ICD implantation was asymptomatic (in about 50.6% of patients), followed by SCD, syncope, “other symptoms”, and palpitations (figure 7).

Figure 7.

Clinical presentation of arrhythmias in registry patients (total and first implants).

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In a small percentage of cases (6.5%), an electrophysiological study was conducted before ICD implantation. Such studies were most commonly performed for ischemic heart disease, dilated cardiomyopathy, Brugada syndrome, and arrhythmogenic right ventricular cardiomyopathy. SMVT was the most common induced arrhythmia (40.6%), followed by VF (30%), nonsustained ventricular tachycardia (24.1%), and, to a lesser extent, other arrhythmias (5.1%).

Hypertension was present in 52.1% of the patients included in the implantable cardioverter-defibrillator registry, as well as hypercholesterolemia in 47.4%, smoking in 34%, diabetes in 30.1%, a history of atrial fibrillation in 30%, renal impairment in 11.6%, a family history of SCD in 9.1%, and a history of stroke in 5.9%.

QRS duration was reported for 33.3% of first implants and averaged 95.8 ms. The duration was > 120 ms in 41.8% of patients, most of whom received a CRT-ICD.

Device indications and their changes over time are shown in table 2. Ischemic heart disease was the most common cardiac condition prompting ICD implantation in Spain. Among patients with ischemic heart disease, the most common indication was primary prevention. The second most common reason for ICD implantation was dilated cardiomyopathy. However, as can be seen in table 2, there has been a continued decline in first ICD implants for this condition. For the less common heart diseases, the most frequent indication was primary prevention.

As in previous years, primary prevention of SCD was the main indication for first ICD implants (75.4%), followed by SMVT (12%), syncope (6.6%), and SCD (5.8%) (table 3).

The implantation setting and specialist performing the procedure were recorded in 91% and 91.2% of forms, respectively. Overall, 83% of procedures were performed in electrophysiology laboratories and 16% in operating rooms. In 59% of cases, an electrophysiologist implanted the device. Of the remainder, a surgeon implanted 7.7%, an intensivist implanted 3.3%, and, as stated in the forms, other professionals implanted the remaining 30%.

Transvenous ICD generator placement was reported in 85% of forms: subcutaneous in 87% of cases and subpectoral in the remaining 13%.

The types of implanted devices are shown in table 4. An increase was seen in the percentage of subcutaneous ICD implantation, reaching 9% of all implants. The most frequently implanted devices were single-chamber ICD devices (37.2%), followed by CRT-ICD devices (36.2%) and dual-chamber ICD devices (17.6%).

As in previous years, the most frequent reason for ICD generator replacement was battery depletion (82%), followed by an upgrade (15% of cases). In addition, replacement was due to device dysfunction or infection in the remaining 3%. Finally, 57 instances of generator dysfunction and 43 of lead dysfunction were reported to the registry.

With data on 73.3% of implants, the most commonly used pacing mode was VVI (47.5%), followed by DDD (21.1%), VVIR (5.7%), and DDDR (3.5%). Resynchronization was specified in 11.9% of cases and other modes in the remaining 10.4%. These other modes typically reflect algorithms or modes to prevent ventricular pacing. Finally, VF induction testing was performed in 210 patients following ICD implantation.

Complication data were included in 94.1% of forms. A total of 36 complications were recorded: 9 subacute lead dislodgements, 7 ventricular arrhythmias, 5 coronary sinus dissections, 5 cardiac tamponades, 2 hemorrhages, 1 perforation, and 7 unspecified complications; no cases of pneumothorax or death were reported.

In 2024, 203 centers submitted data to the registry, a 12.7% increase compared with 2023. In addition, this year has seen the highest level of hospital participation in the implantable cardioverter-defibrillator registry, reflecting almost all implants performed in Spain.

Since the registry began, the number of implanted ICD devices has progressively increased, with periodic reductions in 2011/2012, 2017, and 2020. As a result of the COVID-19-related reduction in clinical activity, there was a 4% decrease in ICD implants in 2020 vs previous years. Clinical activity normalized in 2021. Since then, the number of ICD implants in Spain has grown each year, with 2024 showing the highest number of implants in registry history.

Despite this increase, the mean ICD implantation rate per million population (186 implants per million) in Spain is the lowest of all European Union countries and remains far below the European average of 317 implants per million population in 2024. According to these figures, ICD implants in Spain remain less frequent than expected given the scientific evidence underpinning clinical practice guidelines.1–3 This situation is not unique to Spain, with studies performed in other health care systems showing ICD treatment rates much lower than expected according to guidelines. In this regard, data from various American databases demonstrate ICD and CRT-ICD implantation percentages of 15% and 41% of theoretical indications according to clinical practice guidelines.16 A study performed in Sweden17 revealed that only 10% of patients with an ICD indication for primary prevention of SCD (according to European Society of Cardiology guidelines) between 2000 and 2016 ultimately received a device.15 In that study, ICD implantation was associated with mortality reductions of 27% in the first year of follow-up and 12% at 5 years. Recently published observational data that consider the experience of patients already treated with drugs such as sacubitril-valsartan and sodium-glucose cotransporter type 2 inhibitors also show the underuse of ICD devices (8.4% of all theoretical indications) and a highly significant reduction in mortality in ICD recipients during a 5-year follow-up (37.6% vs 44.7% in those who did not receive an ICD, with a risk reduction of 24.3%; P < .001).18 These data indicate that the main consequence of ICD underuse is an increase in mortality in patients who could benefit from this therapy. The Spanish implantable cardioverter-defibrillator registry shows the clear underuse of ICD therapy in Spain. While the reasons are unclear, the results highlight the need for new measures to increase ICD use in patients who would benefit from the therapy.

Primary prevention of SCD was the main reason for ICD implantation in Spain. This indication accounted for 75.4% of first implants in 2024. These values are similar to those of recent years, at more than 70%, and are comparable to those of our neighboring countries, where primary prevention is the main indication for ICD implantation, with values at about 80%.19,20

In 2024, a change was detected in the type of device implanted. First, the percentage of single-chamber ICD devices fell (37.2% of first implants vs percentages exceeding 45% in 2023 and before). Moreover, the percentage of CRT-ICD devices recovered, and the number of both dual-chamber and subcutaneous ICD devices increased (9% in 2024). The inability of subcutaneous ICD devices to use antitachycardia pacing to treat ventricular arrhythmias has represented a barrier to the greater use of these devices. Nonetheless, in May 2024, the evaluation was published of a new modular system that includes a subcutaneous ICD and a leadless pacemaker with the capacity for wireless communication between the 2 devices.21 This system permits antitachycardia pacing. Assessment of the system showed the safety and efficacy of the combined use of the 2 devices, as well as the reliability of their intercommunication.18 Finally, a new extravascular ICD received CE mark approval in the European Union in 2021. This defice enables ventricular pacing to deliver pause-prevention pacing and antitachycardia therapies.22 Throughout 2024, the use of this device (rarely implanted in 2023) gradually increased. This would also have contributed to the rise in subcutaneous ICD implants.

The most frequent ICD indication in 2024 was once again ischemic heart disease, followed by dilated cardiomyopathy. Together, these 2 conditions represent 75% of all ICD indications prompting implantation in Spain. As in previous years, ICD therapy exhibited lower use in patients with dilated cardiomyopathy, largely as a result of the fall in the number of implants in primary prevention (table 2). Various publications may explain these figures. In addition to the DANISH study,23 the guidelines of the European Society of Cardiology for the diagnosis and treatment of heart failure from 2021 3 and for the management of patients with ventricular arrhythmias and the prevention of SCD from 2022 2 have reduced the level of recommendation for ICD devices in the primary prevention of SCD in patients with nonischemic dilated cardiomyopathy (IIa A). However, the indication for ICD therapy in dilated cardiomyopathy remains controversial. The heart failure guidelines acknowledge possible benefits of ICD devices in patients with dilated cardiomyopathy and age < 70 years, in whom a publication from the same study showed a 30% reduction in mortality.3 In addition, the guidelines include the results of a meta-analysis including the DANISH trial, in which ICD was found to reduce all-cause mortality in patients with nonischemic cardiomyopathy.24 Moreover, the guidelines for the management of patients with ventricular arrhythmias recommend the use of genetic analysis to identify mutations associated with an elevated risk of SCD and detect late gadolinium enhancement on cardiac magnetic resonance to improve the risk stratification of SCD in patients with dilated cardiomyopathy.2 In 2023, the European Society of Cardiology published new clinical practice guidelines for the management of cardiomyopathies.25 These guidelines define a new entity, nondilated left ventricular cardiomyopathy, which involves ventricular dysfunction or the presence of gadolinium enhancement without ventricular dilatation. The guidelines consider ICD implantation (IIa C recommendation) in both dilated and nondilated cardiomyopathy in the presence of mutations associated with an elevated risk of SCD or late gadolinium enhancement on cardiac magnetic resonance in patients with LVEF both below and above 35%. Finally, a Spanish cost-effectiveness analysis24 of ICD devices in the primary prevention of SCD showed that ICD therapy is associated with reduced all-cause death in both ischemic heart disease (hazard ratio = 0.70; 95% confidence interval, 0.58-0.85) and nonischemic heart disease (hazard ratio = 0.79; 95% confidence interval, 0.66-0.96). Using probabilistic analysis, the study estimated cost-effectiveness ratios of 19 171 euros per quality-adjusted life year (QALY) in patients with ischemic heart disease, 31 084 euros/QALY in patients with nonischemic dilated cardiomyopathy, and 23 230 euros/QALY in individuals younger than 68 years.26 These results confirm the cost-effectiveness of ICD devices in the primary prevention of SCD in patients with left ventricular dysfunction of both ischemic and nonischemic origin, particularly in patients younger than 68 years.

As in previous years, the 2024 registry revealed considerable differences among autonomous communities in the implantation rate per million population (figure 1). As is evident from these figures, the autonomous community with the highest implantation rate implanted more than twice as many devices as the 2 autonomous communities with the lowest implantation rates. The disparity in the ICD implantation rate among the autonomous communities in the supposedly uniform Spanish health care system remains difficult to explain and indicates that the same criteria are not being applied to ICD implantation, despite the available evidence and the work of the SEC. These differences are not explained by income level or population density or by the different incidences of ischemic heart disease and heart failure among the autonomous communities. This situation calls into question the equity of the Spanish health care system in an area as important as the prevention of SCD.

Spain has the lowest ICD implantation rate per million population compared with the other European countries participating in Eucomed, where the European average in 2024 was 317 ICD devices per million population (including ICD and CRT-ICD devices). This figure is higher than that of previous years (310 in 2023, 300 in 2022, 297 in 2021, 285 in 2020, 303 in 2019, 302 in 2018, 307 in 2017, and 316 in 2016). The countries with the highest implant numbers were the Czech Republic, Germany, and Italy (474, 471, and 457 devices per million population, respectively). Spain remains the country with the lowest number of implants per capita (186 implants/million population in 2024). This figure is lower than that of the other European countries with low ICD implantation activity, such as Finland, Hungary, the United Kingdom, and Portugal (219, 219, 231, and 280 implants per million population in 2024, respectively).

There are probably many complex reasons for this situation. One possible explanation is the number of available arrhythmia units, but that does not explain the relationship, at least in Spain, because communities with the highest number of available units had lower implantation rates. The level of income does not seem to be a factor because countries with lower incomes than Spain, such as Ireland, the Czech Republic, and Poland, show much higher implantation rates. Nor can this disparity be explained by differences in the prevalence of cardiovascular diseases. For example, Mediterranean countries such as Greece (324 implants/million population), Portugal, and Italy show much higher implantation rates, with Italy in particular doubling the Spanish figures.

In 2024, the registry collected data on most ICD implants in Spain. As in previous years, completion of the different fields in the implantation form varied and was lower than desired. Although a web platform for recording both pacemaker and ICD device implantation has been available since 2019 (CardioDispositivos), reporting is inconsistent. In addition, the registry does not collect key ICD programming data that would be associated with patients’ morbidity and mortality, such as detection times, heart rate thresholds, and the intervals at which supraventricular rhythm discriminators operate, all of which help to reduce both appropriate and inappropriate therapies. Furthermore, no prospective follow-up data were collected from patients, which would permit more informative clinical studies. Finally, inconsistent reporting of ICD implantation-related complications and the absence of follow-up data likely underestimate the true complication rate.

This is the 21st official report of the registry, and its longevity is a credit to all participating members of the Heart Rhythm Association of the SEC. We are the only country that publishes, on an annual basis, data not only on ICD implants but also on pacemaker implants and ablations performed nationwide, a fact that should be a source of pride. At the same time, all hospitals should commit to ensuring the completeness of the data included in the registry. The use of CardioDispositivos, the online platform of the Spanish pacemaker registry and the Spanish implantable cardioverter-defibrillator registry, differs among Spanish implanting centers, despite the mandatory reporting requirement to provide data under Article 36 of Royal Decree 192/2023 of March 21.12 The viability of the registry relies on all participating centers recognizing the importance of submitting ICD- and pacemaker-related data to the designated platform. Improved adherence could serve as the basis for more in-depth studies enabling the planning of management, research, and innovation strategies in the Spanish health care system.