Dantrolene improves survival after ventricular fibrillation by mitigating impaired calcium handling in animal models

BACKGROUND

Resistant ventricular fibrillation, refibrillation. and diminished myocardial contractility are important factors leading to poor survival after cardiac arrest. We hypothesized that dantrolene improves survival after ventricular fibrillation (VF) by rectifying the calcium dysregulation caused by VF.

METHODS AND RESULTS

VF was induced in 26 Yorkshire pigs for 4 minutes. Cardiopulmonary resuscitation was then commenced for 3 minutes, and dantrolene or isotonic saline was infused at the onset of cardiopulmonary resuscitation. Animals were defibrillated and observed for 30 minutes. To study the effect of VF on calcium handling and its modulation by dantrolene, hearts from 14 New Zealand rabbits were Langendorff-perfused. The inducibility of VF after dantrolene administration was documented. Optical mapping was performed to evaluate diastolic spontaneous calcium elevations as a measure of cytosolic calcium leak. The sustained return of spontaneous circulation (systolic blood pressure ≥60 mm Hg) was achieved in 85% of the dantrolene group in comparison with 39% of controls (P=0.02). return of spontaneous circulation was achieved earlier in dantrolene-treated pigs after successful defibrillation (21 ± 6 s versus 181 ± 57 s in controls, P=0.005). The median number of refibrillation episodes was lower in the dantrolene group (0 versus 1, P=0.04). In isolated rabbit hearts, the successful induction of VF was achieved in 83% of attempts in controls versus 41% in dantrolene-treated hearts (P=0.007). VF caused diastolic calcium leaks in the form of spontaneous calcium elevations. Administration of 20 μmol/L dantrolene significantly decreased spontaneous calcium elevation amplitude versus controls. (0.024 ± 0.013 versus 0.12 ± 0.02 arbitrary unit [200-ms cycle length], P=0.001).

CONCLUSIONS

Dantrolene infusion during cardiopulmonary resuscitation facilitates successful defibrillation, improves hemodynamics postdefibrillation, decreases refibrillation, and thus improves survival after cardiac arrest. The effects are mediated through normalizing VF-induced dysfunctional calcium cycling.

Effects of Chronic Gap Junction Conduction–Enhancing Antiarrhythmic Peptide GAP-134 Administration on Experimental Atrial Fibrillation in Dogs

Background— Abnormal intercellular communication caused by connexin dysfunction may contribute to atrial fibrillation (AF). The present study assessed the effect of the gap junction conduction–enhancing antiarrhythmic peptide GAP-134 on AF inducibility and maintenance in a dog model of atrial cardiomyopathy.

Methods and Results— Twenty-four dogs subject to simultaneous atrioventricular pacing (220 bpm for 14 days) were randomly assigned to placebo treatment (PACED-CTRL; 12 dogs) or oral GAP-134 (2.9 mg/kg BID; PACED-GAP-134; 12 dogs) starting on day 0. UNPACED-CTRL (4 dogs) and UNPACED-GAP-134 (4 dogs) served as additional control groups. Change in left atrial (LA) systolic area from baseline to 14 days was calculated using transoesophageal echocardiography. At 14 days, animals underwent an open-chest electrophysiological study. PACED-CTRL dogs (versus UNPACED-CTRL) had a shorter estimated LA wavelength (8.0�1.4 versus 24.4�2.5 cm, P <0.05) and a greater AF vulnerability (mean AF duration, 1588�329 versus 25�34 seconds, P <0.05). Oral GAP-134 had no effect on AF vulnerability in UNPACED dogs. Compared with PACED-CTRL dogs, PACED-GAP-134 dogs had a longer estimated LA wavelength (10.2�2.8 versus 8.0�1.4 cm, respectively, P <0.05). Oral GAP-134 did not significantly reduce AF inducibility or maintenance in the entire group of 24 PACED dogs; in a subgroup of dogs (n=11) with less than 100% increase in LA systolic area, oral GAP-134 reduced AF induction from 100% to 40% and mean AF duration from 1737�120 to 615�280 seconds ( P <0.05).

Conclusions— Oral GAP-134 reduces pacing-induced decrease in LA wavelength and appears to attenuate AF vulnerability in dogs with less atrial mechanical remodeling. Gap junction modulation may affect AF in some circumstances.

Quantitative assessment of brain microvascular and tissue oxygenation during cardiac arrest and resuscitation in pigs

Cardiac arrest is associated with a very high rate of mortality, in part due to inadequate tissue perfusion during attempts at resuscitation. Parameters such as mean arterial pressure and end-tidal carbon dioxide may not accurately reflect adequacy of tissue perfusion during cardiac resuscitation. We hypothesised that quantitative measurements of tissue oxygen tension would more accurately reflect adequacy of tissue perfusion during experimental cardiac arrest. Using oxygen-dependent quenching of phosphorescence, we made measurements of oxygen in the microcirculation and in the interstitial space of the brain and muscle in a porcine model of ventricular fibrillation and cardiopulmonary resuscitation. Measurements were performed at baseline, during untreated ventricular fibrillation, during resuscitation and after return of spontaneous circulation. After achieving stable baseline brain tissue oxygen tension, as measured using an Oxyphor G4-based phosphorescent microsensor, ventricular fibrillation resulted in an immediate reduction in all measured parameters. During cardiopulmonary resuscitation, brain oxygen tension remained unchanged. After the return of spontaneous circulation, all measured parameters including brain oxygen tension recovered to baseline levels. Muscle tissue oxygen tension followed a similar trend as the brain, but with slower response times. We conclude that measurements of brain tissue oxygen tension, which more accurately reflect adequacy of tissue perfusion during cardiac arrest and resuscitation, may contribute to the development of new strategies to optimise perfusion during cardiac resuscitation and improve patient outcomes after cardiac arrest.

Effects of Renal Artery Denervation on Ventricular Arrhythmias in a Postinfarct Model

BACKGROUND

The therapeutic potential of renal denervation (RDN) for arrhythmias has not been fully explored. Detailed mechanistic evaluation is in order. The objective of the present study was to determine the antiarrhythmic potential of RDN in a postinfarct animal model and to determine whether any benefits relate to RDN-induced reduction of sympathetic effectors on the myocardium.

METHODS AND RESULTS

Pigs implanted with single-chamber implantable cardioverter defibrillators to record ventricular arrhythmias (VAs) were subjected to percutaneous coronary occlusion to induce myocardial infarction. Two weeks later, a sham or real RDN treatment was performed bilaterally using the St Jude EnligHTN basket catheter. Parameters of ventricular remodeling and modulation of cardio-renal sympathetic axis were monitored for 3 weeks after myocardial infarction. Histological analysis of renal arteries yielded a mean neurofilament score of healthy nerves that was significantly lower in the real RDN group than in sham controls; damaged nerves were found only in the real RDN group. There was a 100% reduction in the rate of spontaneous VAs after real RDN and a 75% increase in the rate of spontaneous VAs after sham RDN (P=0.03). In the infarcted myocardium, presence of sympathetic nerves and tissue abundance of neuropeptide-Y, an indicator of sympathetic nerve activities, were significantly lower in the RDN group. Peak and mean sinus tachycardia rates were significantly reduced after RDN.

CONCLUSIONS

RDN in the infarcted pig model leads to reduction of postinfarction VAs and myocardial sympathetic effectors. This may form the basis for a potential therapeutic role of RDN in postinfarct VAs.

Docosahexaenoic Acid, but Not Eicosapentaenoic Acid, Supplementation Reduces Vulnerability to Atrial Fibrillation

Background—

The potential health benefits of ω-3 polyunsaturated fatty acids (PUFAs) usually are studied using a combination of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). This combination reduces vulnerability to experimentally induced atrial fibrillation (AF). It is unknown whether EPA and DHA have differential effects when taken alone. Using a model of pacing-induced atrial hemodynamic overload, we investigated the individual effects of EPA and DHA on vulnerability to AF and atrial remodeling.

Methods and Results—

Thirty-four dogs were randomized into 3 groups, all of which underwent simultaneous atrial and ventricular pacing at 220 beats per minute for 14 days. One group received purified DHA (≈1 g/d) orally for 21 days beginning 7 days before pacing began. Similarly, 1 group received ≈1 g/d purified EPA. In a third (control) group (No-PUFAs), 8 dogs received ≈1 g/d olive oil, and 12 were unsupplemented. Electrophysiological and echocardiographic measurements were taken at baseline and 21 days. Atrial tissue samples were collected at 21 days for histological and molecular analyses. Persistent AF inducibility was significantly reduced by DHA compared with No-PUFAs median [25–75 percentiles], 0% [0%–3%] for DHA versus 3.1% [2.2%–11%] for No-PUFAs; P =0.007) but not by EPA (3.4% [1.9%–8.9%]). DHA also reduced atrial fibrosis compared with No-PUFAs (11±6% versus 20±4%, respectively; P <0.05), whereas EPA did not (15±5%; P >0.05).

Conclusions—

DHA is more effective than EPA in attenuating AF vulnerability and atrial remodeling in structural remodeling–induced AF.

Characterization of the ultrashort-TE (UTE) MR collagen signal

Although current cardiovascular MR (CMR) techniques for the detection of myocardial fibrosis have shown promise, they nevertheless depend on gadolinium-based contrast agents and are not specific to collagen. In particular, the diagnosis of diffuse myocardial fibrosis, a precursor of heart failure, would benefit from a non-invasive imaging technique that can detect collagen directly. Such a method could potentially replace the need for endomyocardial biopsy, the gold standard for the diagnosis of the disease. The objective of this study was to measure the MR properties of collagen using ultrashort TE (UTE), a technique that can detect short T2* species. Experiments were performed in collagen solutions. Via a model of bi-exponential T2* with oscillation, a linear relationship (slope = 0.40 ± 0.01, R(2) = 0.99696) was determined between the UTE collagen signal fraction associated with these properties and the measured collagen concentration in solution. The UTE signal of protons in the collagen molecule was characterized as having a mean T2* of 0.75 ± 0.05 ms and a mean chemical shift of -3.56 ± 0.01 ppm relative to water at 7 T. The results indicated that collagen can be detected and quantified using UTE. A knowledge of the collagen signal properties could potentially be beneficial for the endogenous detection of myocardial fibrosis.

Study of the Effects of Epinephrine on Cerebral Oxygenation and Metabolism During Cardiac Arrest and Resuscitation by Hyperspectral Near-Infrared Spectroscopy

OBJECTIVES

Epinephrine is routinely administered to sudden cardiac arrest patients during resuscitation, but the neurologic effects on patients treated with epinephrine are not well understood. This study aims to assess the cerebral oxygenation and metabolism during ventricular fibrillation cardiac arrest, cardiopulmonary resuscitation, and epinephrine administration.

DESIGN

To investigate the effects of equal dosages of IV epinephrine administrated following sudden cardiac arrest as a continuous infusion or successive boluses during cardiopulmonary resuscitation, we monitored cerebral oxygenation and metabolism using hyperspectral near-infrared spectroscopy.

SETTINGS

A randomized laboratory animal study.

SUBJECTS

Nine healthy pigs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Our study showed that although continuous epinephrine administration had no significant impact on overall cerebral hemodynamics, epinephrine boluses transiently improved cerebral oxygenation (oxygenated hemoglobin) and metabolism (cytochrome c oxidase) by 15% ± 6.7% and 49% ± 18%, respectively (p < 0.05) compared with the baseline (untreated) ventricular fibrillation. Our results suggest that the effects of epinephrine diminish with successive boluses as the impact of the third bolus on brain oxygen metabolism was 24.6% ± 3.8% less than that of the first two boluses.

CONCLUSIONS

Epinephrine administration by bolus resulted in transient improvements in cerebral oxygenation and metabolism, whereas continuous epinephrine infusion did not, compared with placebo. Future studies are needed to evaluate and optimize the use of epinephrine in cardiac arrest resuscitation, particularly the dose, timing, and mode of administration.

Experimental studies of atrial fibrillation: a comparison of two pacing models

Rapid ventricular pacing (RVP) is a well-established animal model of atrial fibrillation (AF). However, this model is limited by a high mortality rate and severe heart failure. The purpose of our study was to assess a new canine model of inducible AF. We performed acute, short-term, simultaneous atrioventricular pacing (SAVP) and RVP (in random order) in 14 dogs for 30 s. SAVP produced more echocardiographic pulmonary venous flow reversal, a greater increase in mean pulmonary capillary wedge pressure, and a significantly greater decrease in left atrial emptying function (-84.4 +/- 38.6% vs. -23.7 +/- 27.1%, P < 0.05) than RVP. Thirty dogs were randomized to three, longer-term, study groups: eight dogs in the control group (no pacing), eight dogs in the RVP group (2 wk at 240 beats/min followed by 3 wk at 220 beats/min), and fourteen dogs in the SAVP group (2 wk at 220 beats/min). SAVP induced less left ventricular dysfunction but more left atrial dysfunction than RVP. SAVP dogs had similar atrial effective refractory periods as RVP dogs but more heterogeneity in conduction and more AF inducibility (83% vs. 40%, P < 0.05) and maintenance (median 1,660 vs. 710 s, P < 0.05) than RVP dogs. SAVP induced more collagen turnover and was associated with a significantly greater increase in type III collagen in the atria compared with RVP dogs (6.9 +/- 1.5 vs. 4.8 +/- 1.6, respectively, P < 0.05 vs. 1.1 +/- 0.7 in unpaced control dogs). In conclusion, the SAVP model induced profound mechanical and substrate atrial remodeling and reproducible sustained AF. This new model is clinically relevant and may be useful for testing AF interventions.

Cerebral Hemodynamics and Metabolism During Cardiac Arrest and Cardiopulmonary Resuscitation Using Hyperspectral Near Infrared Spectroscopy

BACKGROUND

Maintaining cerebral oxygen delivery and metabolism during cardiac arrest (CA) through resuscitation is essential to improve the survival rate while avoiding brain injury. The effect of CA and cardiopulmonary resuscitation (CPR) on cerebral and muscle oxygen delivery and metabolism is not clearly quantified.

METHODS AND RESULTS

A novel hyperspectral near-infrared spectroscopy (hNIRS) technique was developed and evaluated to measure cerebral oxygen delivery and aerobic metabolism during ventricular fibrillation (VF) CA and CPR in 14 pigs. The hNIRS parameters were measured simultaneously on the dura and skull to investigate the validity of non-invasive hNIRS measurements. In addition, we compared the hNIRS data collected simultaneously on the brain and muscle. Following VF induction, oxygenated hemoglobin (HbO2) declined with a 9.9 s delay and then cytochrome-c-oxidase (Cyt-ox) decreased on average 4.4 s later (P<0.05). CPR improved cerebral metabolism, which was reflected by an average 0.4 μmol/L increase in Cyt-ox, but had no significant effect on HbO2, deoxygenated hemoglobin (HHb) and tissue oxygen saturation (tSO2). Cyt-ox had greater correlation with HHb than HbO2. Muscle metabolism during VF and CPR was significantly different from that of the brain. The total hemoglobin concentration (in the brain only) increased after ~200 s of untreated CA, which is most likely driven by cerebral autoregulation through vasodilation.

CONCLUSIONS

Overall, hNIRS showed consistent measurements of hemodynamics and metabolism during CA and CPR.

Establishing a multicenter, preclinical consortium in resuscitation: A pilot experimental trial evaluating epinephrine in cardiac arrest

BACKGROUND

Large animal studies are an important step in the translation pathway, but single laboratory experiments do not replicate the variability in patient populations. Our objective was to demonstrate the feasibility of performing a multicenter, preclinical, randomized, double-blinded, placebo-controlled cardiac arrest trial. We evaluated the effect of epinephrine on coronary perfusion pressure (CPP) as previous single laboratory studies have reported mixed results.

METHODS

Forty-five swine from 5 different laboratories (Ann Arbor, MI; Baltimore, MD; Los Angeles, CA; Pittsburgh, PA; Toronto, ON) using a standard treatment protocol. Ventricular fibrillation was induced and left untreated for 6 min before starting continuous cardiopulmonary resuscitation (CPR). After 2 min of CPR, 9 animals from each lab were randomized to 1 of 3 interventions given over 12 minutes: (1) Continuous IV epinephrine infusion (0.00375 mg/kg/min) with placebo IV normal saline (NS) boluses every 4 min, (2) Continuous placebo IV NS infusion with IV epinephrine boluses (0.015 mg/kg) every 4 min or (3) Placebo IV NS for both infusion and boluses. The primary outcome was mean CPP during the 12 mins of drug therapy.

RESULTS

There were no significant differences in mean CPP between the three groups: 14.4 ± 6.8 mmHg (epinephrine Infusion), 16.9 ± 5.9 mmHg (epinephrine bolus), and 14.4 ± 5.5 mmHg (placebo) (p = NS). Sensitivity analysis demonstrated inter-laboratory variability in the magnitude of the treatment effect (p = 0.004).

CONCLUSION

This study demonstrated the feasibility of performing a multicenter, preclinical, randomized, double-blinded cardiac arrest trials. Standard dose epinephrine by bolus or continuous infusion did not increase coronary perfusion pressure during CPR when compared to placebo.

Blind source separation in characterizing ECG pre-shock waveforms during Ventricular Fibrillation

Ventricular Fibrillation (VF) is a cardiac arrhythmia for which the only available treatment option is defibrillation by electrical shock. Existing literature indicates that VF could be the manifestation of different sources controlling the heart with different degrees of organization. In this work we test the hypothesis that the pre-shock waveforms of successful and unsuccessful shock outcomes could be related to the number of independent sources present in these waveforms. The proposed method uses Blind Source Separation (BSS) to extract independent components in frequency direction from a pig database consisting of 20 pre-shock waveforms. The slope of the energy capture curve was used as an indicator to demonstrate the number of independent sources required to model the pre-shock waveforms. The results were also quantified by performing a linear discriminant analysis based classification achieving an overall classification accuracy of 75%. The results indicate that successful cases can be modeled with less number of independent sources compared to unsuccessful cases.

Abstract 152: Intrinsic Vascular Tone may be Necessary for Successful Resuscitation from Experimental Cardiac Arrest

Introduction: Survival rates from out-of-hospital cardiac arrest are often <10% despite performance of good quality CPR. We assessed the hypothesis that the effect of CPR on cardiac and brain perfusion may be dependent on factors other than thoracic compression force and ventilation.

Methods: Eighty healthy Yorkshire pigs (29±3 kg) were anesthetized and underwent 2-4 minutes of untreated ventricular fibrillation (VF), followed by guideline based CPR, then defibrillation. “Survivors” were pigs in sinus rhythm with aortic systolic pressure ≥30 mmHg 30 minutes after defibrillation; all others were “non-survivors”. Hemodynamic, ventilatory and defibrillation parameters were measured and tested for association with survival.

Results: Thirty four pigs survived (43%). During baseline and untreated VF, hemodynamic and blood gas parameters were not different between survivors and non-survivors. During CPR, compressions generated adequate left ventricular pressures in both groups (99±21 mmHg vs. 106±28 mmHg, survivors vs. non-survivors, P=ns). Compressions produced 28% higher peak aortic pressures in survivors than non-survivors (respectively 73±21 mmHg vs. 57±17 mmHg, P<0.005). During the decompression phase, nadir aortic pressures were 41% higher in survivors than non-survivors (respectively 24±7 mmHg vs. 17±5 mmHg, P<0.0001). Controlled manual bag ventilation during CPR resulted in significantly higher minute ventilation being delivered to survivors compared to non-survivors (4.8±2.3 L/min vs. 3.9±1.4 L/min, P<0.05). Coronary perfusion pressure, carotid blood flow, cerebral O 2 tension, and end tidal CO 2 were also higher in survivors.

Conclusions: Guideline based CPR in a uniform population of pigs undergoing a structured cardiac arrest and resuscitation protocol does not produce consistent results. Intravascular pressures, intrathoracic pressure and critical organ flow correlate with survival. During cardiac arrest, more emphasis may need to be placed on vascular support rather than powerful compressions.

The effects of long chain polyunsaturated fatty acids on local activation properties in dogs vulnerable to atrial fibrillation

Marine derived long chain polyunsaturated fatty acids (PUFAs) were found to have benefits in reducing inducibility and maintenance of atrial fibrillation (AF) in a dog model. This study was conducted to evaluate the effect of PUFAs on local atrial electrical conduction properties acquired via a multi-electrode plaque sutured to the posterior wall of the left atrium of the heart in these dogs. Eleven dogs underwent simultaneous atrioventricular pacing (SAVP) for 2 weeks, and were organized into 2 groups: 5 dogs received no PUFAs (SAVP-PLACEBO), 6 dogs received Eicosapentaenoic or Docosahexaenoic acid derived from fish oils (SAVP-PUFA), where PUFAs were given for 21 days, starting 1 week prior to pacing and during the 2 week pacing period. Three features were extracted, which were the average conduction velocity, average intra atrial conduction time, and total activation time. The PUFA group had a faster average conduction velocity (0.82±0.19 m/s) than the PLACEBO group (0.47±0.21 m/s, P=0.02). Using the average conduction velocity feature, classification was performed with a linear classifier and leave-one-out method. In the SAVP-PLACEBO group, 60% of the dogs were correctly classified, and 66% of the dogs were correctly classified in SAVP-PUFA group, leading to an overall classification accuracy of 63.5%.