TENS in patients with ICDs

Stimulated by Subhail Arain et al 2023.[1]

TENS – transcutaneous electrical nerve stimulation
ICD – implanted cardioverter defibrillator
EA – electroacupuncture
CRT – cardiac resynchronisation therapy
ECG – electrocardiogram
EMI – electromagnetic interference
VT – ventricular tachycardia
VF – ventricular fibrillation
AEs – adverse events

key to acronyms

As a keen proponent of EA and of safe and effective practice,[2] I have often been asked about the safety of EA in patients with ICDs and pacemakers. I was aware that the device manuals all stated that EA was contraindicated in any patient with a pacemaker, but I had also found myself performing EA on a patient that had not included the fitting of a pacemaker under surgery on the past medical history form. I discovered the pacemaker by accident on about the 4^th session of EA, when the patient removed his shirt and I saw the classic scar and swelling below the left clavicle. Despite the discovery I carried on applying EA. I figured that the treatment location in his right hip girdle was too far away to influence the pacemaker, he was lying down, and he had already had several uneventful sessions.

It wasn’t until I learned more about modern pacemakers and ICDs that I became more cautious and embarked on some experiments with the late Professor John W Thompson, who was also a great advocate of EA and renowned expert in the use of TENS. We were able to perform some measurements on one normal subject (me) and concluded that pairs of needles close together in a limb were probably safe, but that stimulation across the chest did have the potential to confuse an implanted device with a sensing lead.[3]

John organised for us to meet with a cardiologist in his university hospital to plan a study on patients with implanted CRT devices who required battery changes. Unfortunately, the medical physics guy came late to the meeting, had not read our detailed protocol, and proceeded to be so obstructive that it was impossible to continue. I had flown up from London for the meeting and was astonished. We did not pursue the study and John died in 2012.[4]

I did learn something though. While we were waiting for Mr Obstructive, I was chatting with the cardiologist and learned a couple of key facts about modern CRT. First, I was shocked to hear that some paced patients would have no rhythm without pacing. I had thought that we all have at least a ventricular rhythm, but apparently that is not the case. Second, ICDs modify their sensitivity the longer the time lapse from the previous R wave (the big upward deflection in the QRS complex of the ECG). Both these things left me with an increased sense of caution about patients subject to fancy modern CRT.

So, it should be clear now why I had to highlight this paper on the safety of TENS in such patients. The authors acknowledge that TENS is considered to be contraindicated in patients with ICDs, but modern devices now have better filtering and noise protection algorithms, so they should be less affected by EMI.

The authors recruited 107 patients with ICDs and proceeded to apply TENS at two different positions on the thorax at two different stimulation modes. One position was paravertebral placement of pads at the base of the neck (C7), just as might be used for lower neck pain. The second position was deliberately high risk, with the pads placed in the 5^th intercostal space on the left anterior chest wall. The protocols were 80Hz constant stimulus or a 2Hz burst stimulus, with the intensity gradually increased to the maximum comfortable level.

Patients were lying down, and the ICD therapy function was manually deactivated before TENS stimulation.

Of the 107 patients, EMI occurred in 17 (15.9%). Only one of these was associated with stimulation at the neck. There were only 2 tests where the device interpreted the EMI as being VT or VF, and hence there was a significant risk of triggering defibrillation if this function had not been turned off. Unfortunately, each was from a different position, so it was not possibly to say that neck stimulation appeared to be without risk.

So, the bottom line has not changed. We still should seek advice from the patient’s cardiologist and perform a test of stimulation under monitoring. But the safety parameters are improving.

It is a shame that they did not perform stimulation below the waist or across pads placed in the same limb, as this would be less likely to create EMI, and might have allowed us to say that these sites of stimulation are relatively safe. We will have to wait a little longer, but this is a welcome start, and not something I was expecting to see.

I am sure some readers have questions about the relative risk of EA and TENS in this situation. Well, the intensities of electrical stimulation are considerably lower with EA – between 3 and 10 times lower. The needles are clearly a greater risk physically than the pads and most AEs related to EA derive from the needle insertion rather than the electrical stimulus. Penetrating needles could theoretically get closer to a sensing lead, but as these are inside the heart, I would hope that we are a long way away most of the time, so this difference would be irrelevant. On the whole there is likely to be less risk of EMI from EA than from TENS, but we still need to do that study.

References

1          Suhail Arain S, Cretnik A, Huemer M, et al. Risk of occurrence of electromagnetic interference from the application of transcutaneous electrical nerve stimulation on the sensing function of implantable defibrillators. Europace 2023;25:euad206. doi:10.1093/europace/euad206

2          Cummings M. Safety aspects of electroacupuncture. Acupunct Med 2011;29:83–5. doi:10.1136/acupmed-2011-010035

3          Thompson JW, Cummings M. Investigating the safety of electroacupuncture with a Picoscope. Acupunct Med 2008;26:133–9. doi:10.1136/aim.26.3.133

4          Filshie J. John Warburton Thompson. Acupunct Med 2013;31:331–2. doi:10.1136/acupmed-2013-010436

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Declaration of interests MC