When Less Is More: Safety and Efficacy of a Subcutaneous ICD

The recently approved subcutaneous implantable cardioverter-defibrillator (S-ICD) offers the advantage of no need for intravenous and intracardiac leads or their associated risks and shortcomings. This is important because lead malfunction caused by conductor failure or insulation breach occurs in up to 40% of indwelling transvenous leads at 8 years after implantation. Failure occurs more commonly in active young patients or in patients with longer life expectancy who expose the leads to greater cumulative physical stress.

However, while a completely subcutaneous electrode configuration can treat potentially lethal ventricular tachyarrhythmia, its major disadvantage is its inability to provide bradycardia rate support and antitachycardia pacing to terminate ventricular tachycardia.

So where are we with a completely subcutaneous electrode configuration to treat potentially lethal ventricular tachyarrhythmia?

The first-generation device raised concerns about an increased risk of pocket infection, battery longevity, and inappropriate shocks compared with the newest transvenous ICD (T-ICD) systems. No study to date directly compared the T-ICD and the S-ICD in patients indicated for ICD therapy as primary prevention of SCD.

Recently, Aziz et al. published a State-of-the-Art paper in JACC on the subcutaneous defibrillator.¹ Clinical experience does suggest that its use be considered in relatively younger patients (i.e., age < 40 years), those at increased risk for bacteremia, patients with indwelling intravascular hardware at risk for endovascular infection, or patients with compromised venous access.

At the 2015 ESC meeting in London, new European guidelines were released covering the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death.² The new document notes that a subcutaneous ICD may be a useful alternative to a transvenous defibrillator when venous access is difficult, after the removal of a transvenous defibrillator due to infections, or in very active younger patients, otherwise fit, with smaller body weight and not a lot of subcutaneous tissue.

Registry Data

Even more recently in JACC, Burke et al. presented the largest, most comprehensive study with the longest follow-up of efficacy in the treatment of spontaneous ventricular tachycardia/ventricular fibrillation (VT/VF) episodes by the S-ICD.³ The data emerged from a pooled analysis of the IDE Study (the S-ICD System IDE Clinical Investigation) and the EFFORTLESS (Boston Scientific Post Market S-ICD; see Figure) Registry (total for both: n = 876).

The pooled cohort analysis confirms that the favorable outcomes achieved with the S-ICD in early studies continue for up to 3 years post-implantation. In addition, the rates of inappropriate shocks, infection, and overall complications improved in the most recently implanted patients.

In brief, the success of shock therapy after up to five shocks for ventricular tachyarrhythmias was 98.2%, and the estimated 3-year inappropriate shock rate was 13.1%. For comparison, that’s similar to the 11.5% rate reported in a substudy of MADIT II (Multicenter Automatic Defibrillator Implantation Trial II).⁴ However, as Anne B. Curtis, MD, FACC, and Hiroko Beck, MD, FACC, of the University at Buffalo, NY, wrote in an accompanying editorial comment in JACC, inappropriate shocks have been reduced in more recent studies to < 5% in T-ICD systems with the use of newer algorithms for programming that incorporate longer detection times and/or higher rate cutoffs.5

Estimated all-cause mortality was 4.7% at 3 years with a total of 26 deaths, which was 2.9% of patients who underwent implantation, with only one known arrhythmic death (0.1%) (due to Loeffler’s syndrome). Device-related complications occurred in 11.1% of patients at 3 years, but there was no S-ICD–related endocarditis or bacteremia. That’s not to say infection did not occur: infection was a leading complication of S-ICD implantation, with 1.7% of patients requiring extraction due to infection. Again, for perspective, compare that to an earlier study,⁶ in which there was a 5% risk of infection; so the 1.7% reported in EFFORTLESS is a significant improvement.

Obviously, the system does not provide pacing, except for up to 30 seconds of post-shock ventricular pacing. For this reason, the study methods excluded patients who had episodes of VT of <170 beats/min that could potentially be terminated by anti-tachycardia pacing. Therefore, the index arrhythmia for the secondary prevention patients in this study was predominantly VF or polymorphic VT.

The S-ICD would also not be appropriate in the occasional patient whose arrhythmia might be suppressed by overdrive pacing. Plus, another broad category of patients for whom the S-ICD would not be appropriate includes patients who require pacing for bradycardia, atrioventricular block, or cardiac resynchronization therapy. One answer: future generations of the S-ICD system may incorporate features that accommodate these pacing requirements by using Bluetooth and leadless pacing technology.

In their accompanying editorial, Curtis and Beck wrote: “We now know that removing the transvenous lead from the ICD system can be done safely and effectively, and yields a potentially life-saving, but less invasive, system that is appropriate for many patients.”⁵

References

1. Aziz S, Leon AR, El-Chami MF. J Am Coll Cardiol. 2014;63:1473-9.
2. Priori SG, Blomström-Lundqvist C, Mazzanti A, et al. Eur Heart J. 2015 Aug 29. pii:ehv316. [Epub ahead of print]
3. Burke MC, Gold MR, Knight BP, et al. J Am Coll Cardiol. 2015;65:1605-15.
4. Daubert JP, Zareba W, Cannom DS, et al. J Am Coll Cardiol. 2008;51:1357-65.
5. Curtis AB, Beck H. J Am Coll Cardiol. 2015;65:1616-8.
6. Olde Nordkamp LRA, Abkenari LD, Boersma LVA, et al. J Am Coll Cardiol. 2012;60:1933-9.

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Sounds Like a Winner: Honing Auscultation Skills

Dramatic breakthroughs in transcatheter treatment of valvular disease have occurred. Indeed, one of the presentations at the 2015 TCT (Transcatheter Cardiovascular Therapeutics) meeting in October was Transcatheter Treatment of All Four Heart Valves—We’re Closer than You Think! To benefit from these changes, however, early recognition and follow-up of valve disease is critical. Cardiac auscultation is the most common means of initial detection.

Unfortunately, you can’t hear what you’re missing and there has been concern among medical educators for a couple of decades that differentiating normal and abnormal heart sounds is an important clinical skill that is being lost. Results from a landmark study by Mangione et al. showed that the median rate of identification of 12 pre-recorded cardiac sounds was only 20% for medical students, 19% for medical residents, and 22% for cardiology fellows.¹ This low level of proficiency changed little with years of standard classroom training and was never better than that of third-year medical students. (As you likely know, the standard approach for teaching cardiac auscultation consists of a 1- or 2-hour classroom lecture. Yes, that’s all.)

Nor was this poor performance in cardiac auscultation limited to physicians in training. Two primary care studies a decade or more ago found that attending physicians correctly identified < 40% of auscultatory findings.^2,3 Things have gotten better by now, right? Well, at ESC.15, Michael J. Barrett, MD, FACC, Lehigh Valley Health Network, Allentown, PA, presented the results of the largest survey of cardiologists’ auscultation skills in the last 20 years. A total of 1,098 cardiologists were tested from 2011 to 2014. Participants chose either a set of basic or advanced murmurs (Table 1).

The Power of Repetition

This was not just a test of current skills. Barrett and colleagues previously reported that repetitions of four basic cardiac murmurs dramatically improved proficiency in recognizing cardiac murmurs by medical students (from about 20% at baseline to nearly 90% accuracy after intensive training; p < 0.001).4 This effect was equally robust whether the students listened to the repetitions in a monitored setting in a classroom or in unmonitored setting on their own time.

In this new study, pre- and post-tests were performed using recorded sounds from different patients. Intervention consisted of listening to 400 repetitions of each murmur while viewing relevant images including phonocardiograms, echoes, etc. Training time averaged 90 minutes.

At baseline, cardiologists failed to identify more than half of basic and about one third of advanced pre-recorded murmurs. However, skills improved significantly after the 90-minute training session for both basic and advanced murmurs (Table 2).

In noting the power of repetition, Barrett et al. wrote, “The fact that listening to heart sounds repetitively improves auscultatory proficiency is not surprising if one considers auscultation to be an auditory pattern recognition skill that is best learned through repetition rather than through didactic teaching. While a lecture format may be an effective means of learning pathophysiology, we believe auditory recognition requires intensive repetition to achieve proficiency.”⁴

However, recognizing heart sounds is not like riding a bicycle. Pyschoacoustic studies suggest that such skills have a shelf life of about 1 year, meaning you should annually refresh your skills and test yourself again to assure continuing recognition of basic and advanced murmurs.

According to Patrick T. O’Gara, MD, MACC, ACC past president and a co-investigator on the study, “These findings confirm the widely held view that auscultation skills among cardiologists have eroded over time.” However, as shown in this new study presented at ESC.15, Dr. O’Gara said, “These skills can improve with repetition and training. Accurate auscultation is the first step in the cost-effective evaluation of patients with suspected valvular heart disease.”

References:

1. Mangione S, Nieman L, Gracely E, et al. Ann Intern Med. 1993;119:47-54.
2. Paauw DS, Wenrich MD, Curtis JR, et al. JAMA. 1995;274:1380-2.
3. Roy JD, Sargeant J, Gray J, et al. J Contin Educ Health Prof. 2002;22:152-9.
4. Barrett MJ, Lacey CS, Sekara AE, et al. Chest. 2004;126:470-5.

Keywords: CardioSource WorldNews Interventions, Cardiovascular System, Defibrillators, Implantable, Heart Auscultation, Heart Valves, Life Expectancy

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