Sensory Transcutaneous Electrical Stimulation Fails to Decrease Discomfort Associated With Neuromuscular Electrical Stimulation in Healthy Individuals

Tetanizing prepulse: A novel strategy to mitigate implantable cardioverter-defibrillator shock-related pain

BACKGROUND

Skeletal muscle activation has been implicated as the source of pain associated with implantable cardioverter-defibrillator shocks. We hypothesized that the skeletal muscle response to defibrillatory shocks could be attenuated with a tetanizing prepulse immediately before biphasic shock delivery.

OBJECTIVE

The purpose of this study was to test the ability of tetanizing prepulses to reduce the skeletal muscle activation associated with defibrillation.

METHODS

Seven adult pigs were studied. A left ventricular coil and subcutaneous dummy can in the right thorax were used to deliver either pure biphasic waveforms or test waveforms consisting of a tetanizing pulse of high-frequency alternating current (HFAC) ramped to an amplitude of 5-100 V over 0.25-1 second, immediately followed by a biphasic shock of approximately 9 J (ramped HFAC and biphasic [rHFAC+B]). We used limb acceleration and rate of force development as surrogate measures of pain. Test and control waveforms were delivered in sinus rhythm and induced ventricular fibrillation to test defibrillation efficacy.

RESULTS

Defibrillation threshold energy was indistinguishable between rHFAC+B and pure biphasic shocks. Peak acceleration and rate of force development were reduced by 72% ± 7% and 71% ± 22%, respectively, with a 25-V, 1-second rHFAC+B waveform compared with pure biphasic shocks. Notably, rHFAC+B with a 9-J biphasic shock produced significantly less skeletal muscle activation than a 0.1-J pure biphasic shock.

CONCLUSION

A putative source of implantable cardioverter-defibrillator shock-related pain can be mitigated using a tetanizing prepulse followed by biphasic shock. Human studies will be required to assess true pain reduction with this approach.

The reliability of hand-held dynamometry for strength assessment during electrically induced muscle contractions

OBJECTIVES

To determine inter- and intra-tester reliability of strength measurements during maximal electrically induced contractions (MEIC) using a hand-held dynamometer (HHD).

METHODS

Thirty-seven healthy young female adults, mean age (SD) 23.4 (2.4) years, were tested by two examiners during two sessions, with order of examiners randomized. Biphasic pulses (phase duration--300 µs; pulse frequency--75 Hz) were employed in order to induce contractions of the quadriceps femoris muscle at a maximally tolerated current level. Strength of maximal voluntary isometric contractions (MVIC) and of MEIC was recorded with a HHD utilizing a stabilization belt.

RESULTS

Good to excellent inter- and intra-tester reliability were determined with intra-class correlation coefficients ranging between 0.8 and 0.9, and no bias in the Bland-Altman plots. The 95% repeatability ranged between 8.7 and 13.0 kg for the MVIC and MEIC, and between 20.7 and 25.6% for the % MVIC.

CONCLUSION

Our results confirm previous findings indicating good to excellent reliability of quadriceps femoris muscle MVIC assessment with a HHD. However, a high 95% repeatability range indicates the HHD is not sufficiently reliable as an indicator of the force level attained during electrically induced contractions. Other methods need to be investigated to assist in determining whether MEIC have reached therapeutic levels.