Results are expressed as 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. Linear regression models were used to analyze the number of implants and devices implanted per million population, the total number of implants, and the number of implants for primary prevention in each center.

In 2021, 198 hospitals participated in this registry. This is the highest number of participating hospitals since the registry began and easily exceeds that of the previous years (173 in 2020, 172 in 2019, 173 in 2018, and 181 in 2017; the latter was the previous peak). The data of the 198 hospitals are visible in table 1. Figure 1 shows the total number of implanting centers, the rate per million population, and the total number of implants per autonomous community according to the data submitted to the registry. In 2021, 23 centers implanted ≥ 100 devices (5 hospitals exceeded 200 implanted units), 74 centers implanted between 11 and 99, and 101 centers implanted 10 or less, of which 28 implanted only 1.

Figure 1.

Distribution of implantation activity by autonomous community in 2021: number of implantation centers/rate per million population/total number of implants. Mean rate=158 implants/million population.

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The name of the hospital performing the procedure was recorded in 99.9% of forms (table 1). Most procedures (6749, 90%) were performed in publicly-funded health centers.

The total number of implants reported to the registry and those estimated by Eucomed in the last 10 years are shown in figure 2. In 2021, 7496 implants were recorded (both first implants and replacements). This figure represents a historic high for the registry and a 6.3% increase vs the previous year (7056 units recorded in 2020). In addition, the data provided by Eucomed (7743 implants in 2021) also show the highest number of implants in registry history, with a 9% increase in units implanted in 2021 and a 5% increase vs the last 2 years (2020 and 2021).

Figure 2.

Total number of implants recorded and those estimated by the European Medical Technology Industry Association from 2012 to 2021. ICD, implantable cardioverter-defibrillator.

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Changes in the implantation rate per million population in the last 10 years according to registry and Eucomed data are shown in figure 3. According to the data from Eucomed, the total implantation rates were 163 implants/million population in 2021, 150 in 2020, and 157 in 2019. Despite the increase detected in the ICD implantation rate per million population in Spain, this number is still much lower than the average ICD implantation rate in Europe. For example, in Europe in 2020 (a year with reduced hospital activity due to the COVID-19 pandemic), the mean implantation rate was 285 units/million population.10

Figure 3.

Total number of implants notified per million population and number estimated by Eucomed from 2012 to 2021. Eucomed: European Confederation of Medical Suppliers Associations; ICD, implantable cardioverter-defibrillator.

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Figure 4 shows the number of ICD implants by month between 2018 and 2021. The figure illustrates the implantation dynamic during the year and reveals the recovery in the number of units implanted in March after the end of the peak COVID-19 incidence observed in the winter of 2021. The impact of the other COVID-19 waves in 2021 was lower and activity remained above that of previous years in the rest of the year.

Figure 4.

Number of implants per month from 2018 to 2021.

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This information was available in 6067 forms (81% of devices included in the registry). First implants represented 4268, or 70.3% of the total. The rate of first implants per million population was 110.

The mean age of all of the patients included in the registry was 63.5 ± 13.5 (3-94) years in 2021, which is higher than the average age in 2020 (62.2 ± 13.4 [5-95] years). The mean age at first implantation was 63.2 ± 13.5 years (61.0 ± 13.1 years in 2020). Once again, and as in previous years, patients were overwhelming male: they represented 81.2% of all patients and 82% of first implants.

The most frequent underlying cardiac condition in first implant patients was ischemic heart disease (56.8%), followed by dilated cardiomyopathy (26.8%), hypertrophic cardiomyopathy (9.2%), primary conduction abnormalities (Brugada syndrome and long QT syndrome; 2.6%), arrhythmogenic right ventricular cardiomyopathy (1.8%), and valve diseases (1.4%) (figure 5).

Figure 5.

Type of heart disease prompting implantation (first implants). ARVD, arrhythmogenic right ventricular dysplasia; Others, patients with more than 1 diagnosis.

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figure 6 shows the left ventricular systolic function data (available in 43.7% of submitted forms). Left ventricular ejection fraction was > 50% in 17.5% of patients, from 41% to 50% in 8.1%, from 36% to 40% in 9%, from 31% to 35% in 21.6%, and ≤ 30% in 43.7%. These values were similar when patients were grouped by first implants and replacements.

Figure 6.

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

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New York Heart Association (NYHA) functional class was reported in 29% of submitted forms. Most patients were in NYHA class II (61.7%), followed by NYHA III (26.2%), NYHA I (10.9%), and NYHA IV (1.2%). Once again, the distribution of this variable was similar in the overall and first implantation groups.

With data from 52.1% of forms, the baseline cardiac rhythm was primarily sinus (79.2%), followed by atrial fibrillation (17.1%) and pacemaker rhythm (3.6%). The remaining patients had other rhythms (eg, atrial flutter and other arrhythmias).

Figure 7 shows the clinical arrhythmia prompting ICD implantation (recorded in 25.9% of forms submitted to the registry). For first implants, most patients had no documented clinical arrhythmias (72.6%), whereas 11.9% had sustained monomorphic ventricular tachycardia, 7.4% had nonsustained ventricular tachycardia, and 6.1% had ventricular fibrillation.

Figure 7.

Distribution of arrhythmias prompting implantation (total and first implants). 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 60% of patients), followed by syncope, sudden cardiac death, and other symptoms (figure 8).

Figure 8.

Clinical presentation of the arrhythmia in the registry patients (first implants and total). SCD, sudden cardiac death.

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Information on the electrophysiological studies performed before ICD implantation was provided in 52.7% of forms. These studies were performed in 296 patients (7.5%), mainly those with ischemic heart disease or dilated cardiomyopathy and in 31.8% of patients with Brugada syndrome. Sustained monomorphic ventricular tachycardia was the most common induced arrhythmia (49.5%), followed by ventricular fibrillation (14.7%), nonsustained ventricular tachycardia (7.5%), and, to a lesser extent, other arrhythmias (3.6%). No arrhythmia was induced in 24.5% of the electrophysiological studies.

Data on patients’ clinical history were available in 17.8% of submitted forms. Regarding cardiovascular risk factors and the most relevant medical history of the patients undergoing ICD implantation, the most important findings were as follows: hypertension, 67.9%; hypercholesterolemia, 12.8%; smoking, 4.5%; diabetes mellitus, 43.3%; history of atrial fibrillation, 40%; kidney failure, 18.8%; history of sudden cardiac death, 12.6%; and history of stroke, 9.6%.

The QRS duration interval was reported for 29.8% of first implant patients (mean, 126.5ms). Of these, it was > 140ms in 32.9% of the patients, and 78.8% of these patients had a resynchronization-defibrillator device (ICD-CRT).

Device indications and their changes over time are shown in table 2. These data were provided in 59.4% of forms in 2021. Ischemic heart disease was the most frequent reason for ICD implantation in Spain, accounting for 51.4% of first implants in 2021. Among ischemic heart disease patients, the most common indication was primary prevention (69.4%). The second most common reason for ICD implantation was dilated cardiomyopathy (27.1% of all first implants) and, as can be seen in table 2, the absolute number of first implants reduced in 2021 vs previous years (619 in 2021 vs 1242 in 2020, 925 in 2019, 803 in 2018, and 830 in 2017). In the less common heart diseases, the most frequent indication was primary prevention.

The implantation indication was reported in 66.2% of the forms. Primary prevention of sudden cardiac death was the main indication for first implants in most patients (86.4%) and its number greatly exceeded that recorded in previous years (72.7% in 2020, 65.1% in 2019, 65.7% in 2018, and 62% in 2017 and 2016) (table 3).

The implantation setting and specialist performing the procedure were recorded in 60% of forms; 85.9% of procedures were performed in electrophysiology laboratories and 13.2% in operating rooms. Cardiac electrophysiologists performed 83.5% of implants, surgeons performed 6.6%, and both together performed 4.5%. Other specialists and intensivists were involved in 0.9% and 4.3%, respectively.

Transvenous ICD generator placement was reported for 66.3% of first implants, with a subcutaneous location in 98.2% of cases and subpectoral in the remaining 1.8%. These figures were 98.2% and 1.7%, respectively, for all devices implanted.

The type of device implanted is shown in table 4 (information reported in 78.3% of forms submitted to the registry). Among first implants performed in 2021 and in previous years, the data show a reduced percentage of subcutaneous ICD and dual-chamber ICD implants, a similar percentage of CRT-ICD implants, and an increased percentage of single-chamber ICD implants.

The most frequent cause of ICD generator replacement was battery depletion (88.5%), with complications prompting 7.3% of replacements. A change in indication prompted 4.1%.

Of the 891 replacements providing this information, 1.6% were performed before 6 months. In addition, 30.2% of forms provided information on the status of leads, which were malfunctioning in 19 patients.

With data on 57.0% of implants, the most widely used programming was VVI (47.7%), followed by DDD (24.5%), VVIR (5.0%), DDDR (6.34%), and others (6.3%), which were largely algorithms or modes to prevent ventricular pacing.

At least 1 ventricular fibrillation induction test was conducted in 292 patients (10%). Defibrillation testing was largely performed in patients with subcutaneous ICD implantation and in just 12 patients during transvenous ICD implantation. The mean number of shocks delivered was 1.07. Thus, in the overwhelming majority of cases, correct device functioning was evaluated and not the threshold.

Complication data were recorded in 31.5% of forms. There were 19 complications: 9 suboptimal positions of the left ventricular lead, 2 pneumothoraces, 2 deaths, 1 coronary sinus dissection, and 5 unspecified complications. As in previous years, the mortality rate was very low, at 0.03%.

Over the period evaluated, there has been a gradual increase in the number of ICDs implanted vs previous years, with isolated reductions in 2011 to 2012, 2017, and 2020. In 2020, there was a 4% decrease in ICD implants vs 2018 and 2019 (the years with the highest recorded activity before 2021) as a consequence of the reduced hospital activity related to the COVID-19 pandemic. A recovery in ICD implant-related activity was seen in 2021. Nonetheless, somewhat of an impact of the COVID-19 pandemic on ICD implants could still be seen during January and February, with the recovery in March coinciding with the end of the third wave in Spain. Thus, March showed 29% and 20% increases in ICD implants vs February and January, respectively, and was the month with the highest number of implants in all of 2021. In general, 2021 can be considered a year of recovery and a resumption of the activity growth curve seen in 2018 and 2019. Despite this growth, the mean ICD implantation rate per million population in Spain (163 implants) is the lowest of all European Union countries and continues to be far from the European average, which was 285 implants per million population in 2020, despite the reduced activity also seen that year in Europe.14

ICD implants in Spain continue to be less frequent than expected given the scientific evidence supporting the clinical practice guidelines.1–3 This situation is not specific to Spain and its consequences were highlighted in a study performed in Sweden15 that showed that just 10% of patients with a primary prevention indication for an ICD for sudden cardiac death (according to European Society of Cardiology guidelines) between 2000 and 2016 ultimately received the device. ICD implantation was associated with mortality reductions of 27% in the first year of follow-up and 12% at 5 years. Another European registry also showed the benefit of ICDs in the primary prevention of sudden cardiac death in both ischemic and nonischemic patients, with a 27% reduced risk of death during a mean follow-up of 2.5 years.16 Our registry results also show the clear underuse of ICD therapy in Spain and highlight the importance of the adoption of new measures to increase ICD use in patients who would benefit from the devices.

This latest registry confirms the increase in primary prevention indications detected in recent years, with an 86.4% rate of prophylactic implants (table 3). The rate of prophylactic implantation has increased by 51% in the last 10 years. For the first time, our rate is similar to that of Europe, where primary prevention is the leading indication for ICD implantation, with rates of about 80%.17,18

Regarding the types of devices implanted in Spain, there was a stabilization in the percentage of first implants of CRT-ICDs at about 30%, as well as a fall in dual-chamber ICD implants. In addition, the data showed a drop in the percentage of first implants of subcutaneous ICDs (7.3% in 2021), after peaks of 8.3% and 8.1% were reached in 2019 and 2020, respectively. The reduced percentage of subcutaneous ICDs was followed by an increase in single-chamber ICD devices, which were the most frequently implanted type of device in Spain (52.6% of all first implants). Although the publication in 2020 of the Praetorian19 and Untouched20 studies, which obtained positive results for subcutaneous ICDs, might have led to a gradual increase in their use, this has not been found in Spain. These figures can probably be explained by factors such as the higher cost per unit or the safety alerts experienced by these devices in recent years.

The most frequent indication in 2020 continued to be ischemic heart disease (56.8%), followed by dilated cardiomyopathy (26.8%). These data consolidate the stabilization observed in 2019 in the percentage of patients with dilated cardiomyopathy as the heart disease prompting the ICD implantation after the reduction seen in previous years. This fall was largely due to lower use of ICD therapy in the primary prevention of sudden cardiac death, which fell drastically in Spain after the publication of the DANISH study.21 This phenomenon was also seen to a greater or lesser extent in other European countries.22 Recently, the European Society of Cardiology guidelines for the diagnosis and treatment of heart failure, released in 2021,23 decreased the level of recommendation for ICD in the primary prevention of sudden cardiac death in patients with nonischemic dilated cardiomyopathy (IIa A), largely due to the results of the DANISH study. However, the same guidelines recognize a possible benefit of ICDs in patients with dilated cardiomyopathy and age < 70 years, who were found, in the same study, to have a 30% reduction in mortality (hazard ratio [HR]=0.70; 95% confidence interval [95%CI], 0.51-0.96; P=.03).24 In addition, the guidelines consider the results of a meta-analysis including the DANISH trial, in which ICDs were found to reduce all-cause mortality in patients with nonischemic cardiomyopathy.25 In a recent cost-effectiveness analysis of ICD implantation for the primary prevention of sudden cardiac death in Spain, ICDs were associated with reduced all-cause mortality in both ischemic (HR=0.70; 95%CI, 0.58-0.85) and nonischemic (HR=0.79; 95%CI, 0.66-0.96) heart disease. The cost-effectiveness ratio estimated through probabilistic analysis was €19 171 per quality-adjusted life year (QALY) in patients with ischemic heart disease, €31 084 per QALY in patients with nonischemic dilated cardiomyopathy, and €23 230 per QALY in individuals younger than 68 years.26 These results confirm the efficacy of single-chamber ICDs in Spain in the primary prevention of sudden cardiac death in patients with left ventricular dysfunction of both ischemic and nonischemic origin, particularly in patients younger than 68 years.

The 2021 registry continues to show major differences among autonomous communities in the implantation rate per million population. Several autonomous communities showed higher rates than the average: Cantabria (384), Principality of Asturias (234), La Rioja (203), Extremadura (184), the Valencian Community (179), Galicia (174), Castile-La Mancha (173), Chartered Community of Navarre (170), Aragon (164), Community of Madrid (163), and Region of Murcia (159). Below average were Catalonia (151), Castile and León (143), the Basque Country (138), Andalusia (134), the Canary Islands (125), and the Balearic Islands (119). The difference between the communities with the highest and lowest implantation rates has increased to 265 units from 180 in 2020 and 139 in 2019. The disparity in ICD implantation rates among the different autonomous communities continues to be difficult to explain in the context of a supposedly uniform health care system such as that of Spain. 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 might call into question the equity of our health care system in an area as important as the prevention of sudden cardiac death.

In 2020 (the year with the greatest impact of the COVID-19 pandemic), the implantation rate in the countries participating in Eucomed was 285 per million population (303 in 2019, 302 in 2018, 307 in 2017, and 316 in 2016), including ICDs and ICD-CRTs. The countries with the highest implant numbers were the Czech Republic and Germany (474 and 445 devices per million population, respectively). Despite being compared with a year of reduced hospital activity in Europe, Spain continues to be the country with the lowest number of implants per capita (163 implants/million population in 2021).

There is no simple explanation for these differences. Our neighboring countries have the same regional differences27 seen in the Spanish registry. One possible explanation is the number of available arrhythmia centers, but that does not explain the relationship, at least in Spain, because communities with the highest number of available centers had lower implantation rates. Income does not seem to be 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 prevalences of cardiovascular diseases. Regardless, the low implantation rate in Spain might reflect a lower degree of adherence to clinical practice guidelines, which has been linked to increased mortality in patients with cardiovascular disease. This situation means that we must remain cognizant of the problem and do everything in our power to alleviate it.

In 2021, our registry collected data on 96.8% of all implants, which represents the vast majority of all ICDs implanted in Spain. As in previous years, completion of the different fields in the implantation form varied and was lower than desired. In addition, no follow-up data were collected from patients, which would permit more relevant clinical studies. Finally, the unequal completion of the data on ICD implantation-related complications and the absence of follow-up data probably underestimate the true rate of complications.

This is the 18th official report of the registry, and its extended durability is a credit to all of the participating members of the Heart Rhythm Association of the SEC. The use of the webpage for online completion of the implantation form for both ICDs and pacemakers, whose development involved the collaboration of the SEC and the Spanish Agency for Medicines and Health Products, strengthened in 2021, although its use varies among the different centers participating in the registry. This website enables the real-time recording of both types of implantable heart devices.