Defibrillation efficacy and pain perception of two biphasic waveforms for internal cardioversion of atrial fibrillation

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.

"Beauty is a light in the heart": the transformative potential of optogenetics for clinical applications in cardiovascular medicine

Optogenetics is an exciting new technology in which viral gene or cell delivery is used to inscribe light sensitivity in excitable tissue to enable optical control of bioelectric behavior. Initial progress in the fledgling domain of cardiac optogenetics has included in vitro expression of various light-sensitive proteins in cell monolayers and transgenic animals to demonstrate an array of potentially useful applications, including light-based pacing, silencing of spontaneous activity, and spiral wave termination. In parallel to these developments, the cardiac modeling community has developed a versatile computational framework capable of realistically simulating optogenetics in biophysically detailed, patient-specific representations of the human heart, enabling the exploration of potential clinical applications in a predictive virtual platform. Toward the ultimate goal of assessing the feasibility and potential impact of optogenetics-based therapies in cardiovascular medicine, this review provides (1) a detailed synopsis of in vivo, in vitro, and in silico developments in the field and (2) a critical assessment of how existing clinical technology for gene/cell delivery and intra-cardiac illumination could be harnessed to achieve such lofty goals as light-based arrhythmia termination.

See the light: can optogenetics restore healthy heartbeats? And, if it can, is it really worth the effort?

Cardiac optogenetics is an exciting new methodology in which light-sensitive ion channels are expressed in heart tissue to enable optical control of bioelectricity. This technology has the potential to open new avenues for safely and effectively treating rhythm disorders in the heart with gentle beams of light. Recently, we developed a comprehensive framework for modeling cardiac optogenetics. Simulations conducted in this platform will provide insights to guide in vitro investigation and steer the development of therapeutic applications - these are the first steps toward clinical translation. In this editorial, we review literature relevant to light-sensitive protein delivery and intracardiac illumination to provide a holistic feasibility assessment for optogenetics-based arrhythmia termination therapy. We then draw on examples from computational work to show that the optical control paradigm has undeniable advantages that cannot be attained with conventional electrotherapy. Hence, we argue that cardiac optogenetics is more than a flashy substitute for current approaches.

Transthoracic versus transesophageal cardioversion of atrial fibrillation under light sedation: a prospective randomized trial

BACKGROUND

Electrical cardioversion (ECV) of atrial fibrillation (AF) is limited by a 5-10% failure rate and by the expense arising from a perceived need for general anesthesia. A transesophageal approach using light sedation has been proposed as a means of augmenting the success rate and avoiding the need for general anesthesia. We hypothesized that the high rate of success and the lower energy requirement associated with biphasic cardioversion might eliminate any advantage of the transesophageal approach.

METHODS

We randomly assigned 60 patients attending for ECV of persistent AF to a transesophageal or a transthoracic approach. Sedation of moderate depth was achieved with intravenous midazolam. The dose of midazolam was titrated in the same manner in both groups.

RESULTS

Sinus rhythm was restored in 29/30 patients (97%) in each group using a similar number of shocks for both groups (1.3 +/- 0.6 transesophageal vs 1.4 +/- 0.7 transthoracic, P = NS) with a similar procedure duration (14.1 +/- 8.2 minutes vs 13.8 +/- 7.5 minutes, P = NS). Both groups received similar doses of midazolam (4.2 +/- 2.7 mg vs 4.4 +/- 2.8 mg, P = NS) and both reported a similar discomfort score in (0.9 +/- 1.3 vs 1.1 +/- 1.8, P = NS). No complication occurred in either group.

CONCLUSION

AF may be cardioverted safely and effectively by either a transthoracic or a transesophageal approach. The use of sedation of moderate depth renders cardioversion by either approach acceptable. As transesophageal ECV shows no clear advantage, transthoracic cardioversion should remain the approach of first choice.

Outpatient oesophageal-precordial electrical cardioversion of atrial fibrillation: an effective and safe technique to restore sinus rhythm

OBJECTIVE

External electrical cardioversion is commonly used in the management of atrial fibrillation (AF), but usually involves general anaesthesia. We tested the efficacy, safety and tolerability of a minimally invasive cardioversion technique, not requiring general anaesthesia, performed on an outpatient basis.

METHODS

We performed outpatient oesophageal cardioversion in 87 consecutive patients (mean age: 67.5 +/- 9.6 years; weight: 77.47 +/- 12.34 kg; left atrium diameter: 46.25 +/- 6.85 mm; LVEF: 55.5 +/- 16%) with persistent AF (mean duration: 6.99 +/- 11.55 months). A biphasic shock was delivered via an oesophageal decapolar lead (cathode) and two precordial patches (anode) under a mild sedation (midazolam 2.5-5 mg). In the first 25 patients, a step-up protocol (from 10 to 100 J) was performed whereas, in the other 62, a first shock at 50 J and a second one at 100 J, were delivered.

RESULTS

Patients described the level of discomfort caused by the procedure according a five-grade scale. Cardioversion was achieved in 97.7% of patients using a mean effective energy of 51.2 +/- 15.7 J. In 88.5% of patients, sinus rhythm was restored by using 50 J or less. No complications occurred and no patient required hospital admission. Mean discomfort score was 1.56 +/- 0.74 out of 5. Sinus rhythm persisted in 62.6% of patients at the 1-month follow-up.

CONCLUSIONS

Outpatient oesophageal cardioversion is a safe, acceptable and effective way to cardiovert patients with AF. It may be a useful alternative to external cardioversion. A relatively high starting energy (50 J) was demonstrated to be superior to a low-energy step-up technique.

Plateau waveform shape allows a much higher patient shock energy tolerance in AF patients

OBJECTIVES

To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients.

BACKGROUND

Previous studies have indicated that reduced amplitude waveforms would be less painful than a conventional (65/65% tilt) biphasic waveform. Computer modeling suggested that a moderately long (10-12 msec) plateau (flat topped) shock waveform would deliver equivalent effectiveness with the lowest possible peak amplitude.

METHODS

We enrolled 27 patients at two sites with persistent AF with a total of 220 shocks delivered during internal atrial cardioversion using an interleaved crossover design. Patient response was scored in three ways: (1) a verbally reported discomfort score, (2) visual analog scale (VAS), and (3) a blinded observer reporting a contraction score.

RESULTS

All scores were significantly reduced (P < 0.0001) by the plateau waveform with impressive statistics: Verbal discomfort (3.51 +/- 0.13 to 2.89 +/- 0.12), VAS (7.00 +/- 0.56 to 5.91 +/- 0.36), and contraction scores (1.94 +/- 0.12 to 1.62 +/- 0.12). The average pain threshold shift (TS) for the Verbal score was 2.34, while that for the VAS score was 2.30. (This means that the patient typically could tolerate 2.34 times as much energy with the plateau waveform for the same level of verbally reported discomfort.) The contraction TS was less at 1.57. Response scores were also corrected for the shock sequence number to control for the sensitization effect from multiple shocks. This increased the TS for the Verbal score to 3.58, but the shock number was not significant for the VAS. A pulmonary artery electrode return was associated with lower pain compared with a coronary sinus position.

CONCLUSION

A plateau shaped biphasic waveform resulted in significantly increased shock energy pain tolerances. Controlling for session sensitization, patients tolerated over three times as much energy for the same verbally reported discomfort score.

Psychophysiologic and affective parameters associated with pain intensity of cardiac cardioverter defibrillator shock discharges

OBJECTIVE

Pain caused by intracardiac shock discharge of an implanted cardioverter defibrillator (ICD) is an important clinical issue in the treatment of ICD patients. The present study aimed to examine whether the strength of perceived shock pain is influenced by affective and psychophysiologic parameters.

METHODS

Among 204 ICD patients drawn from the German Heart Center Munich, 95 patients (46.6%) experienced > or =1 shock discharge. Pain perception (PPC) was measured by a visual analog scale ranged from 0 to 100 points. Standard instruments were administered to measure psychological distress. A startle paradigm was assessed to measure psychophysiologic arousal with skin conductance responses (SCR) and electromyogram responses (EMG) as dependant variables. Classification and regression tree (CART) analysis was applied to assess the effects of psychodiagnostic and psychophysiologic parameters on pain perception.

RESULTS

Mean ICD shock PPC was 53.7 points (SD 31.6), with a median of 59.0 points (interquartile range 30-80). Pain intensity was highly associated with shock discomfort (p < .001) but was largely uninfluenced by clinical and sociodemographic factors. CART analysis revealed patients with one shock and low EMG magnitude (< or =4.15 muV) as subclass with the lowest mean PPC (21.9 points; 95% confidence interval [CI], 4.6-39.1), whereas patients with >one shock experience and an anxiety score >7 (Symptom Checklist-90) expressed the highest mean PPC (74.8 points; 95% CI, 60.5-89.2). Without heightened anxiety, an increased EMG amplitude and impaired EMG habituation yielded a mean PPC of 71.2 (95% CI, 61.6-80.9).

CONCLUSIONS

Augmented PPC of ICD shocks is predominantly associated with the number of perceived shocks, postshock anxiety, and accompanied by heightened levels of EMG magnitude and impaired EMG habituation, which points to sensitization of central neural structures.

Internal defibrillation with minimal skeletal muscle activation: A new paradigm toward painless defibrillation

BACKGROUND

Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue.

OBJECTIVES

The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system.

METHODS

Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration.

RESULTS

Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J.

CONCLUSION

Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.

Minimum energy single-shock internal atrial defibrillation in sheep

Well-tolerated internal atrial defibrillation shocks must be below the pain threshold, which has been estimated to be less than 1 Joule. Defibrillation of the atria with low energy is made possible by delivering shocks at the low end of the defibrillation dose-response curve. We studied low-energy defibrillation in sheep to test the hypothesis that the energy that defibrillates the atria 10% of the time (ED10) is less than 1 Joule. The ED10 was estimated in seven sheep with rapid pacing induced chronic atrial fibrillation (AF). Low-energy defibrillation shocks were delivered from coronary sinus (CS) to superior vena cava (SVC) and the ED10 and ED50 (energy that defibrillates the atria 50% of the time) were then calculated using logistic regression. The mean ratio of ED10 to ED50 was 0.50, indicating that on average, the ED10 was equal to half of the ED50. ED10 shocks had energies ranging from 1.2 to 5.8 Joules. These results suggest that painless single-shock low-energy defibrillation may not be feasible.