Differential effects of defibrillation on systemic and cardiac sympathetic activity

Expert consensus on acute management of ventricular arrhythmias - VT network Austria

The Arrhythmia Working Group of the Austrian Society of Cardiology (ÖKG) has set the goal of systematically structuring and organizing the acute care of patients with ventricular arrhythmias (VA), i.e. ventricular tachycardia (VT) or ventricular fibrillation (VF) in Austria. Within a consensus paper, national recommendations on the basic diagnostic work-up of VA (12-lead ECG, medical history, family history, laboratory analyses, echocardiography, search for reversible causes, ICD interrogation), as well as further medical treatment and therapeutic measures (indication of coronary angiography, ablation therapy) are established. Since acute ablation of VT is indicated in the current ESC guidelines as a class IB indication for scar-associated incessant VT or electrical storm (ES; ≥ 3 ICD therapies in 24 h) as well as for ischemic cardiomyopathy (iCMP) with recurrent ICD shocks, organizational measures must be taken to ensure that these guidelines can be implemented. Therefore, a VT network will be established covering all areas in Austria, consisting of primary and secondary VT centers. Organizational aspects of an acute VT network are defined and should subsequently be implemented by the participating hospitals. All electrophysiologic centers in Austria that deal with VT ablation are to be integrated into the network in the medium-term. Centers that co-operate in the network are divided into primary and secondary VT centers according to predefined criteria.

The Effects of Shock from Defibrillation Threshold Testing on Cardiac Systolic and Diastolic Function

BACKGROUND

Inappropriate implantable cardioverter defibrillator (ICD) shocks are associated with increased overall mortality. However, it remains unclear whether shocks from defibrillation threshold (DFT) testing directly impair cardiac function.

METHODS

DFT testing was performed in 34 patients who underwent ICD/cardiac resynchronization therapy with a defibrillator implantation/generator exchange. Heart rate and cardiac function, including left ventricular (LV) systolic pressure, LV end-diastolic pressure, peak positive and negative dp/dt ( + dp/dt and -dp/dt, respectively) of LV pressure, and the tau index, were assessed with a Mikro-Cath™ diagnostic pressure catheter (CD Leycom, Zoetermeer, the Netherlands). These parameters were measured before and 1 minute, 3 minutes, 5 minutes, 10 minutes, and 15 minutes after DFT testing.

RESULTS

Peak positive dp/dt increased over baseline at each interval (976 ± 229 mm Hg/s vs 1,039 ± 258, 1,049 ± 245, 1,042 ± 247, 1,037 ± 259, and 1,034 ± 254 mm Hg/s, respectively; P < 0.01). Furthermore, peak negative dp/dt (-1,140 ± 397 mm Hg/s vs -1,185 ± 447, 1,193 ± 435, -1,195 ± 434, -1,189 ± 449, and -1,186 ± 459 mm Hg/s, respectively; P < 0.01) and the tau index (65.1 ± 18.5 vs 62.5 ± 16.8*, 62.4 ± 15.9(**) , 63.0 ± 16.8*, and 62.8 ± 18.7*, respectively; *P < 0.05, (**) P < 0.01) decreased compared to those at baseline at each interval.

CONCLUSION

Shock after DFT testing improved LV systolic and diastolic function immediately, especially in patients with preserved LV ejection fraction.

Not just any ICD device in patients with long-QT syndrome

Patients with LQT syndrome are prone to lifethreatening arrhythmias. After surviving such an event, implantation of an ICD is indicated. There are, however, special subtle demands in the treatment of these patients. In this case report we describe our findings in a patient with LQT1 syndrome, and the pitfalls that can and must be avoided. (Neth Heart J 2007;15:418-21.).

Is there an association between external cardioversions and long-term mortality and morbidity? Insights from the Atrial Fibrillation Follow-up Investigation of Rhythm Management study

BACKGROUND

Cardiac electric therapies effectively terminate tachyarrhythmias. Recent data suggest a possible increase in long-term mortality associated with implantable cardioverter-defibrillator shocks. Little is known about the association between external cardioversion episodes (ECVe) and long-term mortality. We sought to assess the safety of repeated ECVe with regard to cardiovascular mortality and morbidity.

METHODS AND RESULTS

We analyzed the data of the 4060 patients from the AFFIRM (Atrial Fibrillation Follow-up Investigation of Rhythm Management) trial. In particular, associations of ECVe with all-cause mortality, cardiovascular mortality, and hospitalizations after ECVe were studied. Over an average follow-up of 3.5 years, 660 (16.3%) patients died, 331 (8.2%) from cardiovascular causes. A total of 207 (5.1%) and 1697 (41.8%) patients had low ejection fraction and nonparoxysmal atrial fibrillation, respectively; 2460 patients received no ECVe, whereas 1600 experienced ≥ 1 ECVe. Death occurred in 412 (16.7%), 196 (16.5%), 39 (13.5%), and 13 (10.4%) of patients with 0, 1, 2, and ≥ 3 ECVe, respectively. There was no significant association between ECVe and mortality within any of the 4 subgroups defined by ejection fraction and atrial fibrillation type, although myocardial infarction, coronary artery bypass graft, and digoxin were significantly associated with death (estimated hazard ratios, 1.65, 1.59, and 1.62, respectively; P < 0.0001). ECVe were associated with increased cardiac hospitalization reported at the next follow-up visit (39.3% versus 5.8%; estimated odds ratio, 1.39; P < 0.0001).

CONCLUSIONS

In the AFFIRM study, there was no significant association between ECVe and long-term mortality, even though ECVe were associated with increased hospitalizations from cardiac causes. Digoxin, myocardial infarction, and coronary artery bypass graft were significantly associated with mortality.

The pharmacology of electrical stimulation in the heart: Where devices meet drugs

Both cardiac electrical stimulation and cardiac pharmacological agents exert effects by acting upon ion channels, secondary messengers and autonomic nerve terminals. Defining the common substrates between devices and drugs provides the evaluation tools to warn of unsafe interactions with pacemakers, defibrillators or detection of cardiac arrhythmias. This review describes substrates of drug-device interaction, reviews research on drug-like effects of devices, and provides a framework for how the physiology of interaction translates to streamlined clinical trials.:

DC cardioversion of persistent atrial fibrillation: A comparison of two protocols

BACKGROUND

Current guidelines for transthoracic direct-current cardioversion (DCCV) of atrial fibrillation (AF) recommend a step-up energy protocol. The aim of this study was to compare such a protocol with a protocol involving a high initial energy shock, anteroposterior paddle position and reversal of shock polarity, on cardioversion efficacy, total energy delivery, use of sedation and patient tolerability.

METHODS

261 patients (mean age 71+/-10 years, 62% male) referred for elective DCCV of persistent AF were enrolled. Patients were randomised to either protocol A: (1) 200 J anteroapical, (2) 360 J anteroapical, (3) 360 J anteroposterior; or protocol B: (1) 360 J anteroapical, (2) 360 J anteroposterior, and (3) 360 J posteroanterior. All procedures were performed under sedation with intravenous diazepam.

RESULTS

Protocol B improved shock success rates (protocol A first shock success rate=42%, protocol B=68%, p<0.001; protocol A second shock success rate=72%, protocol B 86%, p=0.006; protocol A third shock success rate=83%, protocol B=92%, p=0.03) and required fewer shocks to achieve sinus rhythm (1.3+/-0.6) compared with protocol A (1.6+/-0.7, p<0.001). There were no differences in cumulative energy used (protocol A 473+/-286 J, protocol B 436+/-273 J, p=0.24) or sedation requirements (protocol A diazepam 22.1+/-9.0 mg, protocol B 21.7+/-8.9 mg, p=0.75). Both protocols were equally well tolerated by patients.

CONCLUSION

High initial energy increased success rates and decreased the number of shocks but resulted in similar cumulative energy delivery, sedation use and patient tolerability compared with a conventional step-up protocol.

Predictive value of heart rate variability for the recurrence of chronic atrial fibrillation after electrical cardioversion

BACKGROUND

The relation between heart rate variability (HRV) and occurrence of atrial fibrillation (AF) in paroxysmal AF has been well studied, but there are controversial observations regarding the relation of HRV parameters to the recurrence of chronic AF after cardioversion.

HYPOTHESIS

The present study compared HRV parameters of patients with chronic AF on the second day of cardioversion with a healthy control group and investigated their predictive value for AF recurrence.

METHODS

Forty-one patients with chronic AF (> 3 months), who had various underlying cardiovascular disorders, were enrolled to the study. Of these, 31 patients were successfully cardioverted by external direct current shock, but 27 patients fulfilled the entry criteria. Twenty healthy subjects served as a control group. On the second day of restoration of sinus rhythm, 24-h Holter recording was obtained and the following time-domain indices of HRV were measured: SDNN (the standard deviation of the mean RR interval expressed in ms), SDANN (the SD of the averages of RR intervals in all 5-min segments of the 24-h recording), rMSSD (the root mean square of differences of successive RR intervals), and pNN50 (the percentage of adjacent RR intervals that differed by more than 50 ms). Patients were followed-up for 6 weeks for recurrence of AF.

RESULTS

After cardioversion, SDNN and SDANN were found to be significantly lower in the AF group than in the control group (86.4 +/- 31.7 ms vs. 142.1 +/- 40.2 ms, and 57 +/- 17.4 ms vs. 124.4 +/- 37.7 ms, p < 0.001 and p < 0.001, respectively). The indices of vagal modulation of heart rate (rMSS and pNN50) were not different between the AF group and the control group. Recurrence of AF was observed in 15 patients. In these patients, all HRV parameters were significantly depressed compared with those with maintained sinus rhythm. Logistic regression analysis revealed that only decreased pNN50 was an independent predictor of AF relapse (relative risk = 1.5, p = 0.02, 95% confidence interval 1.1-2.2). There was also a trend toward a shortened SDNN as a predictor of AF recurrences.

CONCLUSION

Suppressed HRV parameters and decreased vagal tone are probably a risk factor for AF recurrences after cardioversion to sinus rhythm in a specific subset of patients with chronic AF.

Myocardial injury, neurohormonal activation and inflammation after internal atrial defibrillation

BACKGROUND

The effects of patient-activated atrial defibrillation on subclinical myocardial injury are unknown. Using biochemical markers, this study assessed the effect of a single internal atrial shock delivered by the implantable atrial defibrillator on myocardial damage, neurohormonal activation and inflammation.

METHODS

Twelve patients were implanted with a dual chamber defibrillator for the sole indication of drug refractory symptomatic persistent atrial fibrillation (AF). All had maximum defibrillation energy programmed to maximise the first shock success rate. Creatine kinase isoenzyme, troponin T, cortisol, catecholamines, C-reactive protein and brain natriuretic peptide were measured (i) during sinus rhythm, (ii) 8 h after onset of spontaneously occurring AF (before cardioversion) and (iii) 8 h following successful patient activated cardioversion.

RESULTS

There was no change in creatine kinase, troponin T, cortisol or C-reactive protein during AF or following internal cardioversion. Brain natriuretic peptide levels rose from a median value of 56 pg/ml during sinus rhythm (inter-quartile range 14-92 pg/ml) to 133 pg/ml during AF (30-262 pg/ml), p=0.002. There was a decrease 8 h after cardioversion to baseline (52 and 40-189 pg/ml), p=0.01. There were increases in serum adrenaline and noradrenaline levels during AF from 0.43 (0.12-0.61) to 0.58 pg/ml (0.39-0.80 pg/ml), p=0.002 and from 2.06 (1.61-2.59) to 2.83 nmol/l (2.43-3.46 nmol/l), p=0.02, respectively. These figures reverted to baseline levels 8 h post-cardioversion.

CONCLUSIONS

Internal atrial defibrillation does not result in myocardial injury. The onset of AF results in sympathetic activation and increased brain natriuretic peptide levels, which resolve following restoration of sinus rhythm.

Exaggerated electrodermal startle responses after intracardiac shock discharges in patients with implanted cardioverter defibrillators

OBJECTIVE

We studied whether repetitive intracardiac shock discharges of implantable cardioverter defibrillators (ICDs) provoke an enduring enhancement of startle responses.

METHODS

The study population comprised 134 patients with an ICD. Among those, 67 patients had experienced shock delivery. Thirty-five patients had received five or more shocks. We used the startle reflex paradigm, which consisted of 15 acoustic stimuli (95 dB, 1000 Hz, 500 ms duration). Skin conductance response was measured using a constant 0.5 V through 8-mm electrodes placed on each subject's nondominant palm. Response magnitude was calculated by subtracting the baseline response level of the 2 seconds immediately preceding tone onset from the maximum response level within 1 to 4 seconds after tone onset. The left orbicularis oculi electromyogram (EMG) response was calculated by subtracting the mean EMG level during the 2 seconds immediately preceding tone onset from the highest EMG level measured within 40 to 200 ms after tone onset. Habituation was defined by the response slope of the regression equation and by the number of trials required to reach the nonresponse criterion.

RESULTS

Although EMG response measures of magnitude and habituation failed to yield differences between study groups, patients who had experienced five or more ICD shocks exhibited a significantly larger skin conductance response magnitude in comparison to the patients who had experienced fewer than five shocks (median, interquartile range: 0.364, 0.209-0.618 vs. 0.512, 0.375-0.791; Mann-Whitney U test, p =.007). Poorer habituation in the group with five or more shocks in comparison with the low shock group was confirmed both by the number of trials needed to reach the nonresponse criterion (median, interquartile range: 10, 5-14 vs. 5, 2-13; p =.003) and by the response slope (median, interquartile range: 0.209, 0.116-0.274 vs. 0.262, 0.181-0.332; p =.008). After controlling for potential confounding factors (age, anxiety, aversiveness of stimuli, time since last shock experience, and use of beta-adrenoceptor antagonists), intracardiac shock discharges had the strongest impact on augmented skin conductance response magnitude (adjusted odds ratio = 3.0, 95% confidence interval = 1.3-7.2, p =.01) and impaired habituation (adjusted odds ratio = 2.8, 95% confidence interval = 1.2-6.3; p =.015).

CONCLUSIONS

Intracardiac shock discharges are associated with augmented skin conductance responses and slower habituation, indicating sustained sympathetic arousability, which is presumably centrally mediated.

Impaired exercise-induced vasodilatation in chronic atrial fibrillation--role of endothelium-derived nitric oxide

Exercise capacity is often reduced in patients with atrial fibrillation (AF), but very few studies have focused on changes in endothelial function as a potential mechanism for the exercise limitation. The present study used using venous occlusion plethysmography to investigate whether nitric oxide (NO)-mediated vasodilatation is attenuated during exercise in patients with AF by measuring forearm blood flow (FBF) in 10 patients at rest and immediately after 2 levels of rhythmic handgrip exercise, before and after inhibition of NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA, 100 micromol). The measurements were repeated 1 day after restoration of sinus rhythm by cardioversion. FBF responses to graded doses of acetylcholine (ACh) were also observed before and after cardioversion. Heart rate decreased after cardioversion, but blood pressure did not change. FBF at rest was not affected by cardioversion, but at the highest level of exercise it increased from 28.4+/-2.3 ml x min(-1) x dl(-1) before to 39.4+/-3.2 ml x min(-1) x dl(-1) after cardioversion (p<0.05). L-NMMA significantly decreased FBF at rest (p<0.01) and depressed the increase in FBF response to exercise after (p<0.01), but not before cardioversion. The FBF response to ACh was also accelerated significantly after cardioversion. The present results provide new evidence that NO bioavailability is depressed at rest and during exercise in patients with AF.

Atrial fibrillation impairs endothelial function of forearm vessels in humans

BACKGROUND

Although there have been many studies on the effects of atrial fibrillation (AF) on cardiac function, few studies have been done on its effects on endothelial function. The present study was designed to examine the effects of AF on endothelial function in human subjects.

METHODS AND RESULTS

Changes in forearm blood flow (FBF) induced by acetylcholine and nitroglycerin were measured by using plethysmography in 14 patients with lone AF, 13 patients with AF and underlying heart disease, and 12 normal control subjects. In the patients, these measurements were repeated after cardioversion. Although baseline FBF was the same in the 3 groups, acetylcholine-induced increases in FBF were significantly smaller in both patient groups than in the control group, and FBF increases were particularly depressed in AF patients with underlying heart disease. After restoration of sinus rhythm by cardioversion, FBF response to the highest dose of acetylcholine increased by 46% in patients with lone AF (n = 10) and by 90% in AF patients with underlying heart disease (n = 11). Nitroglycerin-induced vasodilatation was the same in all 3 groups and was not affected by cardioversion.

CONCLUSIONS

These findings suggest that endothelium-dependent vasodilatation is impaired by AF and improves after sinus rhythm is restored.

Relation of autonomic modulation to recurrence of atrial fibrillation following cardioversion

The aim of this study was to investigate the time course of changes in autonomic nervous system activity in patients with long-standing atrial fibrillation (AF) following internal electrical conversion to sinus rhythm and to look for differences between patients who do and do not relapse. Time-domain indexes of heart rate variability were calculated from 24-hour Holter recordings on the day of conversion and 1 day and 1 month afterward for 22 patients with chronic (> 3 months) AF. Ten healthy subjects served as a control group. During the day of cardioversion the mean RR interval and its circadian variation differed significantly between controls and patients. The mean values of successive RR intervals that deviated by > 50% from the prior RR interval and the root-mean-square of successive RR interval differences--indexes of vagal modulation--were initially significantly higher in patients than in controls but showed a decrease (p < 0.05) by the second day (from 12.4 +/- 7% to 8.1 +/- 5% to 7.3 +/- 5% and from 49 +/- 9 to 39 +/- 12 to 41 +/- 11 ms, respectively) to levels similar to those of the controls (7.6 +/- 5% and 40 +/- 17 ms, respectively). Only these 2 indexes contained significant prognostic information about relapse: patients who later relapsed had higher initial values than those who did not, and these values remained high during the 2 days after conversion. In conclusion, this study provides data confirming that spontaneous chronic AF in humans results in a significant increase in vagal tone that is reversed with time after restoration of sinus rhythm. Persistently higher values of vagal tone are observed in patients who relapse, and are probably a predictor for recurrence.