Implantable loop recorders in Clinical practice

Little is known on the prevalence of ILR in the clinical practice for patients with unexplained syncope. Solano et al (1) have estimated that 5% of all patients referred to two tertiary centres for the evaluation of syncope and 28% of those with unexplained syncope had received an ILR after complete work-up. In the multicentre ESGSY2 study, of 269 patients referred to the Emergency Department, 1% were implanted with an ILR (2). In the multicentre SUP study, of 700 patients referred to specialised syncope facilities, 4% finally received ILR implantation (3).

I - European guidelines for patients with unexplained syncope

The European Society of Cardiology and European Heart Rhythm Association have recently published documents containing recommendations on the appropriate use of ILRs in patients with syncope (4,5). In both documents, the recommendations for ILR in patients with unexplained syncope are similar; they are reported in table 1.

Table 1 Indications for ILR in patients with unexplained syncope

Class I recommendations. ILR is indicated in:

• In an initial phase of the work-up, instead of the completion of conventional investigations in patients with recurrent syncope of uncertain origin and absence of high risk criteria which require immediate hospitalisation or intensive evaluation. This is particularly the case for patients with recurrent syncope of uncertain origin who have a likely recurrence within battery longevity of the device,( ie. ³ 3 episodes of syncopes in last 2 years) : level of evidence A.
   
• High risk patients in whom a comprehensive evaluation did not demonstrate a cause of syncope or lead to a specific treatment; patients who have clinical or ECG features suggesting arrhythmic syncope : level of evidence B.

Class II A recommendations. ILR may be indicated:

• To assess the contribution of bradycardia before embarking on cardiac pacing in patients with suspected or certain neurally-mediated syncope presenting with frequent or traumatic syncopal episodes : level of evidence B.

Class II B recommendations. ILR may be indicated: 

• In selected “difficult” cases of patients with transient loss of consciousness of uncertain syncopal origin in order to definitely exclude an arrhythmic mechanism : level of evidence C.

II - Potential impact of European guidelines

In the multicentre, prospective and observational SUP study (3), the real world practice of 9 Italian hospitals equipped with a Syncope Unit was photographed. Among 700 consecutive patients investigated for syncope, the diagnosis remained unexplained in 159 cases at the end of full conventional work-up.

In an ad-hoc sub-study (6), authors compared the prevalence of ILR actually implanted (as per indication of the physician investigator) with that estimated using restricted criteria based on Class I recommendations of the recently published ESC (4) and EHRA (5) guidelines. The implant of ILR was considered potentially appropriate when the patient had one of these characteristics:

1. Unexplained syncope and structural heart disease or coronary artery disease
2. Unexplained syncope in patients with bundle branch block
3. Unexplained syncope in patients with absence of significant structural heart disease, age ³ 40 and ³ 3 episodes of syncope during the last two years.  

These criteria are probably more restrictive than those of class I of the guidelines because, contrary to guideline recommendations, patients without cardiac disease were included only if they had had ³ 3 episodes of syncope in the previous two years and age ³ 40 years.

Of 159 patients with unexplained syncope, 110 (69%) had appropriate criteria for implantation of  ILR according to guidelines. On the contrary, ILR had been actually implanted in 28 (18%) patients, p<0,0001 versus estimated criteria (Table 2).  Seven (25%) of these patients had potentially inappropriate ILR implantation according to the adopted criteria.

Table 2.  Relationship between observed and estimated ILR indications

III - Real world versus recommendation-based incidence

In the SUP study (3), the observed incidence of implanted ILR was 30 per million inhabitants per year (95% confidence interval 23–39), a figure which is very similar to that of 34 per million inhabitants per year calculated by Solano et al (1) in patients with unexplained syncope. These figures seem therefore to be representative of the real world practice in Italy. On the contrary, the estimated incidence according to predefined criteria based on class I indications of the EHRA and ESC guidelines (4,5) is 118 ILRs per million inhabitants per year (95% confidence interval 103–134). How much the dissemination of the guidelines will be able to fill the gap between the observed and estimated incidence is a matter for future studies.

Conclusion:

The conclusion of this study was that there is discrepancy between clinical practice and standardised class I indications for ILR in patients with unexplained syncope. Two thirds of patients with unexplained syncope had potentially appropriate indications for implantation of ILR. The estimated indications were four times higher than those observed.