AVE4454B--a novel sodium-hydrogen exchanger isoform-1 inhibitor--compared less effective than cariporide for resuscitation from cardiac arrest.

We compared the efficacy of the novel sodium-hydrogen exchanger (NHE-1) inhibitor AVE4454B with cariporide for resuscitation from ventricular fibrillation (VF) assessing the effects on left ventricular myocardial distensibility during chest compression, myocardial function after the return of spontaneous circulation, and survival. Three groups of 10 rats each were subjected to 10 min of untreated VF and resuscitation attempted by providing chest compression for up to 8 min with the depth of compression adjusted to attain an aortic diastolic pressure between 26 and 28 mmHg (to secure a coronary perfusion pressure above 20 mmHg) followed by electrical shocks. Rats received AVE4454B (1 mg/kg), cariporide (1 mg/kg), or vehicle control immediately before chest compression. We observed that NHE-1 inhibition (NHEI) preserved left ventricular myocardial distensibility during chest compression evidenced by less depth of compression required to attain the target aortic diastolic pressure corresponding to (mean ± standard deviation) 14.1 ± 1.1 mm in the AVE4454B group (P < 0.001 versus control), 15.0 ± 1.4 mm in the cariporide group (P < 0.01 versus control), and 17.0 ± 1.2 mm in controls. When the depth of compression was related to the coronary perfusion pressure generated-an index of left ventricular distensibility-only the cariporide group attained statistical significance. Postresuscitation, both compounds ameliorated myocardial dysfunction evidenced by lesser reductions in mean aortic pressure and the maximal rate of left ventricular pressure increase as well as earlier normalization of left ventricular end-diastolic pressure increases. This effect was associated with improved survival corresponding to 55% in the AVE4454B group (not significant) and 70% in the cariporide group (P < 0.01 versus control by Gehan-Breslow analysis) at 240 min postresuscitation. An inverse correlation was found between plasma cytochrome c and indices of left ventricular function at 240 min postresuscitation suggesting that NHEI exerts beneficial effects in part by attenuating mitochondrial injury. We conclude that cariporide is more effective than AVE4454B for resuscitation from cardiac arrest given its more prominent effect on preserving left ventricular myocardial distensibility and promoting survival.

Cariporide given during resuscitation promotes return of electrically stable and mechanically competent cardiac activity.

UNLABELLED: Episodes of ventricular fibrillation (VF) and myocardial dysfunction commonly occur after cardiac resuscitation compromising the return of stable circulation. We investigated in a pig model of VF whether limiting Na(+)-induced cytosolic Ca(2+) overload using the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) inhibitor cariporide promotes resuscitation with stable circulation. METHODS: VF was electrically induced in 20 male pigs and left untreated for 6 min after which CPR was initiated and continued for 8 min before attempting defibrillation. Pigs were randomized to receive 3-mg/kg cariporide (n=10) or 0.9%-NaCl (n=10) before chest compression. RESULTS: Seven of 10 pigs in each group were successfully resuscitated and survived 2h. Cariporide ameliorated post-resuscitation ventricular ectopic activity such that fewer singlets (5+/-5 vs. 26+/-21; p<0.05) and fewer bigemini (1+/-3 vs. 33+/-25; p<0.05) were observed during the initial 5 min post-resuscitation. Additionally, cariporide-treated pigs did not require additional post-resuscitation shocks for ventricular tachycardia or recurrent VF (0.0+/-0.0 vs. 5.3+/-7.8 shocks; p=0.073). During the initial 60 min cariporide-treated pigs had higher, cardiac index (6.1+/-0.7 vs. 4.4+/-1.1L/min/m(2); p<0.01), left ventricular stroke work index (45+/-9 vs. 36+/-10 gmm/beat/m(2); p<0.05), and numerically higher mean aortic pressure (104+/-11 vs. 91+/-12 mmHg; p=0.054). CONCLUSION: Cariporide administered at the start of chest compression may help restore electrically and mechanically stable circulation after resuscitation from cardiac arrest.

Zoniporide preserves left ventricular compliance during ventricular fibrillation and minimizes postresuscitation myocardial dysfunction through benefits on energy metabolism.

OBJECTIVE: To investigate whether sodium-hydrogen exchanger isoform-1 (NHE-1) inhibition attenuates myocardial injury during resuscitation from ventricular fibrillation through effects on energy metabolism, using an open-chest pig model in which coronary perfusion was controlled by extracorporeal circulation. DESIGN: Randomized controlled animal study. SETTING: University research laboratory. SUBJECTS: Male domestic pigs. INTERVENTIONS: Ventricular fibrillation was electrically induced and left untreated for 8 mins, after which extracorporeal circulation was started and its flow adjusted to maintain a coronary perfusion pressure of 10 mm Hg. After 10 mins of extracorporeal circulation, restoration of spontaneous circulation was attempted by epicardial defibrillation and gradual reduction in extracorporeal flow. Two groups of eight pigs each were randomized to receive the NHE-1 inhibitor zoniporide (3 mg.kg-1) or vehicle control immediately before starting extracorporeal circulation. MEASUREMENTS AND MAIN RESULTS: Identical extracorporeal flows (approximately = 9% of baseline cardiac index) were required in zoniporide and control groups to attain the target coronary perfusion pressure, resulting in comparable left anterior descending coronary artery blood flow (9 +/- 1 and 10 +/- 1 mL.min-1) and resistance (0.10 +/- 0.01 and 0.10 +/- 0.01 dyne.sec.cm(-5)). Yet zoniporide prevented reductions in left ventricular volume and wall thickening while favoring higher myocardial creatine phosphate to creatine ratios (0.14 +/- 0.03 vs. 0.06 +/- 0.01, p < .05), lower myocardial adenosine (0.7 +/- 0.1 vs. 1.3 +/- 0.2, p < .05), and lower myocardial lactate (80 +/- 9 vs. 125 +/- 6 mmol.kg-1, p < .001). Postresuscitation, zoniporide-treated pigs had higher left ventricular ejection fraction (0.57 +/- 0.07 vs. 0.29 +/- 0.05, p < .05) and higher cardiac index (4.8 +/- 0.4 vs. 3.4 +/- 0.2 L.min-1.m-2, p < .05). CONCLUSIONS: Zoniporide ameliorated myocardial injury during resuscitation from ventricular fibrillation through beneficial effects on energy metabolism without effects on coronary vascular resistance and coronary blood flow.

Myocardial protection by erythropoietin during resuscitation from ventricular fibrillation.

Human recombinant erythropoietin (rhEPO) can protect the myocardium during ischemia and reperfusion. We investigated whether rhEPO could ameliorate previously identified functional myocardial abnormalities that develop during resuscitation from cardiac arrest, using a rat model of ventricular fibrillation (VF) and closed-chest resuscitation. VF was electrically induced and maintained, untreated, for 10 minutes. Chest compression and ventilation were then started and electrical defibrillation was attempted 8 minutes later. Rats were randomized to receive rhEPO (5000 U/kg) in the right atrium at baseline, 15 minutes before induction of VF (rhEPOBL -15-min), or at 10 minutes of VF, immediately before the start of chest compression (rhEPOVF 10-min), or to receive 0.9% NaCl solution instead (control). rhEPO given at the time of resuscitation (rhEPOVF 10-min group) -- but not at baseline -- prompted more effective chest compression, yielding higher coronary perfusion pressures for a given compression depth (1.95 +/- 0.27 mm Hg/mm; P < 0.05 in comparison with rhEPOBL -15-min [1.63 +/- 0.23 mm Hg/mm] and control [1.62 +/- 0.26 mm Hg/mm], by Dunnett's multicomparison method). Post-resuscitation, rats in the rhEPOVF 10-min group displayed higher mean aortic pressure associated with numerically higher cardiac index, stroke work index, and systemic vascular resistance index. rhEPO may rapidly induce myocardial protection during resuscitation from cardiac arrest.

Limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation prevents excess mitochondrial Ca2+ accumulation and attenuates myocardial injury.

BACKGROUND: intracellular Na+ accumulation during ischemia and reperfusion leads to cytosolic Ca2+ overload through reverse-mode operation of the sarcolemmal Na+ -Ca2+ exchanger. Cytosolic Ca2+ accumulation promotes mitochondrial Ca2+ (Ca2+ m) overload, leading to mitochondrial injury. We investigated whether limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation (VF) attenuates Ca2+ m overload and lessens myocardial dysfunction in a rat model of VF and closed-chest resuscitation. METHODS: hearts were harvested from 10 groups of 6 rats each representing baseline, 15 min of untreated VF, 15 min of VF with chest compression given for the last 5 min (VF/CC), and 60 min postresuscitation (PR). VF/CC and PR included four groups each randomized to receive before starting chest compression the new NHE-1 inhibitor AVE4454B (1.0 mg/kg), the Na+ channel blocker lidocaine (5.0 mg/kg), their combination, or vehicle control. The left ventricle was processed for intracellular Na+ and Ca2+ m measurements. RESULTS: limiting sarcolemmal Na+ entry attenuated cytosolic Na+ increase during VF/CC and the PR phase and prevented Ca2+ m overload yielding levels that corresponded to 77% and 71% of control hearts at VF/CC and PR, without differences among specific Na+ -limiting interventions. Limiting sarcolemmal Na+ entry attenuated reductions in left ventricular compliance during VF and prompted higher mean aortic pressure (110 +/- 7 vs. 95 +/- 11 mmHg, P < 0.001) and higher cardiac work index (159 +/- 34 vs. 126 +/- 29 g x m x min(-1) x kg(-1), P < 0.05) with lesser increases in circulating cardiac troponin I at 60 min PR. CONCLUSIONS: Na+ -limiting interventions prevented excess Ca2+ m accumulation induced by ischemia and reperfusion and ameliorated myocardial injury and dysfunction.

Circulating levels of cytochrome c after resuscitation from cardiac arrest: a marker of mitochondrial injury and predictor of survival.

Ca(2+) overload and reactive oxygen species can injure mitochondria during ischemia and reperfusion. We hypothesized that mitochondrial injury occurs during cardiac resuscitation, causing release of cytochrome c to the cytosol and bloodstream while activating apoptotic pathways. Plasma cytochrome c was measured using reverse-phase HPLC and Western immunoblotting in rats subjected to 4 or 8 min of untreated ventricular fibrillation and 8 min of closed-chest resuscitation followed by 240 min of postresuscitation hemodynamic observation. A sham group served as control. Plasma cytochrome c rose progressively to levels 10-fold higher than in sham rats 240 min after resuscitation (P < 0.01), despite reversal of whole body ischemia (decreases in arterial lactate). Cytochrome c levels were inversely correlated with left ventricular stroke work (r = -0.40, P = 0.02). Western immunoblotting of left ventricular tissue demonstrated increased levels of 17-kDa cleaved caspase-3 fragments in the cytosol. Plasma cytochrome c was then serially measured in 12 resuscitated rats until the rat died or cytochrome c returned to baseline. In three survivors, cytochrome c rose slightly to

Cariporide minimizes adverse myocardial effects of epinephrine during resuscitation from ventricular fibrillation.

OBJECTIVE: Epinephrine given during closed-chest resuscitation increases blood flow across the coronary and cerebral circuits. However, epinephrine worsens reperfusion arrhythmias and intensifies postresuscitation myocardial dysfunction. We investigated whether cariporide-a selective sodium-hydrogen exchanger isoform-1 inhibitor-could ameliorate such adverse effects without diminishing its vasopressor actions. DESIGN: Randomized animal study. SETTING: University-based animal laboratory. SUBJECTS: Twenty-four anesthetized male domestic pigs (29-43 kg). INTERVENTIONS: Ventricular fibrillation was electrically induced and left untreated for 8 mins. Pigs were randomized to receive after 2 mins of chest compression a 3 mg/kg bolus of cariporide (n = 8), a 0.02 mg/kg bolus of epinephrine (n = 8), or a combination of cariporide and epinephrine (n = 8). Additional doses of epinephrine were given if the coronary perfusion pressure decreased below 15 mm Hg. Successfully resuscitated pigs were observed for 72 hrs. MEASUREMENTS AND MAIN RESULTS: The averaged coronary perfusion pressure was higher in the epinephrine (34 +/- 11 mm Hg, p = .001) and cariporide/epinephrine (35 +/- 10 mm Hg, p < .001) groups compared with the cariporide group (15 +/- 6 mm Hg). All pigs in the epinephrine and cariporide/epinephrine groups but only six in the cariporide group were successfully resuscitated and survived 72 hrs. During the immediate postresuscitation period, four of eight pigs in the epinephrine group had episodes of recurrent ventricular fibrillation or pulseless ventricular tachycardia requiring additional electrical shocks (7.0 +/- 6.4) but none in the cariporide and cariporide/epinephrine groups (chi-square, p = .008). Myocardial dysfunction occurred early after return of spontaneous circulation but only in the epinephrine group. CONCLUSIONS: The combined administration of cariporide and epinephrine prompted adequate pressor effects during chest compression and facilitated reestablishment of cardiac activity without episodes of recurrent ventricular fibrillation or transient myocardial dysfunction as with epinephrine alone.

Cariporide potentiates the effects of epinephrine and vasopressin by nonvascular mechanisms during closed-chest resuscitation.

BACKGROUND: The efficacy of vasopressor therapy during closed-chest resuscitation is limited and decreases over time. We previously reported that sodium-hydrogen exchanger isoform-1 inhibition during ventricular fibrillation (VF) using cariporide ameliorates ischemic contracture and enhances the efficacy of chest compression. We currently investigated whether cariporide could potentiate pressor responses to epinephrine and vasopressin. METHODS: VF was induced and left untreated for 12 min in two series of 16 rats each. Chest compression was then started and the depth adjusted within the initial 2 min to attain an aortic diastolic pressure between 26 and 28 mm Hg. In one series, rats received boluses of epinephrine (150 microg/kg); in the other series, rats received boluses of vasopressin (0.8 U/kg) to maintain the aortic diastolic pressure > 25 mm Hg. Within each series, rats were randomized to receive a 3 mg/kg bolus of cariporide or 0.9% NaCl immediately before starting chest compression. Defibrillation was attempted at 20 min of VF (8 min of chest compression). RESULTS: Cariporide prompted higher and more sustained coronary perfusion pressures in both the epinephrine group (37 +/- 5 mm Hg vs 29 +/- 7 mm Hg, p < 0.05) and the vasopressin group (36 +/- 5 mm Hg vs 28 +/- 6 mm Hg +/- SD, p < 0.02) even though fewer additional vasopressor doses were required. After resuscitation, cariporide-treated rats had less ventricular ectopic activity, better hemodynamic function, and improved survival scores. In separate experiments, in situ perfusion of the aorta excluded a vascular-mediated effect of cariporide. CONCLUSION: Cariporide enhanced the hemodynamic efficacy of vasopressor agents and improved resuscitation outcomes probably as a result of enhanced forward blood flow without effect on the peripheral vasculature.

Cariporide enables hemodynamically more effective chest compression by leftward shift of its flow-depth relationship.

When given during closed-chest resuscitation, cariporide (4-isopropyl-methylsulfonylbenzoyl-guanidine methanesulfonate; a selective inhibitor of the Na(+)/H(+) exchanger isoform-1) enables generation of viable perfusion pressures with less depth of compression. We hypothesized that this effect results from greater blood flows generated for a given depth of compression. Two series of 14 rats each underwent 10 min of untreated ventricular fibrillation followed by 8 min of chest compression before defibrillation was attempted. Compression depth was adjusted to maintain an aortic diastolic pressure (ADP) between 26 and 28 mmHg in the first series and between 36 and 38 mmHg in the second series. Within each series, rats were randomized to receive cariporide (3 mg/kg) or NaCl (0.9%; control) before chest compression was started. Blood flow was measured using 15-mum fluorescent microspheres. Less depth of compression was required to maintain the target ADP when cariporide was present in both series 1 (13.6 +/- 1.2 vs. 16.6 +/- 1.2 mm; P < 0.001) and series 2 (15.3 +/- 1.0 vs. 18.9 +/- 1.5 mm; P < 0.001). Despite less compression depth, the cardiac index in cariporide-treated rats was comparable to control rats in series 1 (11.1 +/- 0.7 vs. 11.3 +/- 1.4 ml.min(-1).kg(-1); P = not significant) but higher in series 2 (15.5 +/- 2.3 vs. 9.9 +/- 1.4 ml.min(-1).kg(-1); P < 0.05). Increases in compression depth (from series 1 to series 2) increased myocardial, cerebral, and adrenal blood flow in cariporide-treated rats. We conclude that cariporide enhances the efficacy of closed-chest resuscitation by leftward shift of the flow-depth relationship.

Optimal timing for electrical defibrillation after prolonged untreated ventricular fibrillation.

OBJECTIVE: It currently is recommended that electrical shocks be delivered immediately on recognition of ventricular fibrillation. However, decreased effectiveness of this approach has been reported after prolonged intervals of untreated ventricular fibrillation. We investigated the optimal strategy for successful defibrillation after prolonged untreated ventricular fibrillation by using a rat model of ventricular fibrillation and closed-chest resuscitation. DESIGN: Controlled, randomized, laboratory study. SETTING: Research laboratory at a VA hospital. SUBJECTS: Seventy pentobarbital anesthetized Sprague-Dawley rats. INTERVENTIONS: After 10 mins of untreated ventricular fibrillation, four groups of rats were randomized to receive electrical shocks (which we designated as "experimental shocks") immediately before or at 2, 4, or 6 mins of chest compression. Unsuccessfully defibrillated rats received additional shocks (which we designated as "rescue shocks") after 8 mins of chest compression. MEASUREMENTS AND MAIN RESULTS: The number of rats that restored spontaneous circulation after the experimental shocks increased with increasing duration of the predefibrillatory interval of chest compression (0 of 8, 0 of 8, 2 of 8, and 7 of 8, respectively, p <.005). Two additional groups then were randomized to receive repetitive experimental shocks at 2, 4, and 6 mins or a single attempt at 6 mins of chest compression. Although a comparable number of rats restored spontaneous circulation in each group, rats subjected to repetitive defibrillation attempts had more intense postresuscitation ectopic activity and worse survival. Two final groups were used to investigate whether inhibition of the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) could facilitate return of spontaneous circulation during repetitive defibrillation attempts. Although spontaneous circulation was restored earlier in more rats subjected to NHE-1 inhibition, the differences were statistically insignificant. NHE-1 inhibition, however, replicated previously reported resuscitation and postresuscitation benefits. The optimal predefibrillation interval of chest compression was approximately 6 mins, and this coincided with partial return of the amplitude and frequency characteristics of the ventricular fibrillation waveform to those present immediately after induction of ventricular fibrillation. CONCLUSIONS: Improved outcome after prolonged untreated ventricular fibrillation may result from strategies that provide chest compression before attempting defibrillation and avoid early and repetitive defibrillation attempts. The amplitude and frequency characteristics of the ventricular fibrillation waveform could help identify the optimal timing for attempting electrical defibrillation.

Myocardial protection during resuscitation from cardiac arrest.

PURPOSE OF REVIEW: Successful treatment of cardiac arrest requires that an electrically stable and mechanically competent cardiac activity be promptly reestablished. However, many interventions used to attempt to reestablish cardiac activity may also inflict additional myocardial injury and, in turn, compromise resuscitability. In this review, we examine mechanisms of such myocardial injury and discuss potential new strategies for myocardial protection during resuscitation from cardiac arrest. RECENT FINDINGS: Efforts are currently directed at understanding underlying mechanisms of myocardial injury associated with current resuscitation methods, with the purpose of developing alternative approaches that are safer and more effective. These new approaches include, among others, the development of alternative low-energy defibrillation waveforms, methods for optimizing the timing for attempting defibrillation, and the use of vasopressor agents devoid of beta-agonist effects. There is also interest in understanding the role that activation of pathways of ischemic and reperfusion injury could play during resuscitation from cardiac arrest. To this end, activation of the sarcolemmal sodium-hydrogen exchanger isoform 1 seems to play an important role. Other potentially important pathways involve adenosine metabolism, activation of potassium ATP channels, and generation of oxygen radical species. These pathways may become novel pharmacologic targets for cardiac resuscitation. SUMMARY: The growing body of research in these areas is bringing hope that in a not so distant future new approaches and interventions for cardiac resuscitation could be available for resuscitation of humans in various clinical settings.

Sodium-hydrogen exchange inhibition during ventricular fibrillation: Beneficial effects on ischemic contracture, action potential duration, reperfusion arrhythmias, myocardial function, and resuscitability.

BACKGROUND: Inhibition of the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) is emerging as a promising novel strategy for ameliorating myocardial injury associated with ischemia and reperfusion. We investigated whether NHE-1 inhibition (with cariporide) could minimize mechanical and electrical myocardial abnormalities that develop during ventricular fibrillation (VF) and improve outcome using a porcine model of closed-chest resuscitation. METHODS AND RESULTS: Two groups of 8 pigs each were subjected to 8 minutes of untreated VF and randomized to receive either a 3-mg/kg bolus of cariporide or 0.9% NaCl immediately before an 8-minute interval of conventional closed-chest resuscitation. Cariporide prevented progressive increases in left ventricular free-wall thickness (from 1.0+/-0.2 to 1.5+/-0.3 cm with NaCl, P<0.001 versus 0.9+/-0.1 to 1.1+/-0.3 cm with cariporide, P=NS), maintained the coronary perfusion pressure above resuscitability thresholds (10+/-8 versus 19+/-3 mm Hg before attempting defibrillation, P<0.05), and increased resuscitability (2 of 8 versus 8 of 8, P<0.005). In 2 additional groups of 4 pigs each subjected to a briefer interval of untreated VF, cariporide ameliorated postresuscitation shortening of the action potential duration (APD) at 30%, 60%, and 90% repolarization (ie, APD60 at 2 minutes after resuscitation; 75+/-29 versus 226+/-16 ms, P<0.05), minimized postresuscitation ventricular ectopic activity preventing recurrent VF, and lessened postresuscitation myocardial dysfunction. CONCLUSIONS: NHE-1 inhibition may represent a highly potent novel strategy for resuscitation from VF that can ameliorate myocardial manifestations of ischemic injury and improve the effectiveness and outcome of closed-chest resuscitation.

Myocardial protection during ventricular fibrillation by inhibition of the sodium-hydrogen exchanger isoform-1.

Activation of the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) in response to the intense intracellular acidosis that develops during ischemia has been identified as an important mechanism of myocardial cell injury. NHE-1 inhibition in the quiescent (nonfibrillating) heart ameliorates functional manifestation of ischemia and reperfusion injury. We investigated in isolated heart and intact rat models of ventricular fibrillation whether NHE-1 inhibition, by using the selective inhibitor cariporide, could ameliorate myocardial abnormalities that develop during ventricular fibrillation and limit resuscitability and survival. In the isolated rat heart, cariporide significantly reduced the magnitude of ischemic contracture during ventricular fibrillation and the accompanying increases in coronary vascular resistance. Hearts that had received cariporide during ventricular fibrillation had no diastolic dysfunction after resuscitation and recovered their systolic function earlier. In intact rats, cariporide given immediately before starting chest compression allowed generation of a coronary perfusion pressure and end-tidal Pco2 comparable with control rats but with significantly less depth of compression. Cariporide had an unprecedented effect in this rat model, prompting spontaneous defibrillation after approximately 8 mins of chest compression. After resuscitation, rats treated with cariporide had significantly less ventricular ectopic activity, better hemodynamic function, and higher survival rates (22 of 24 [94%] vs. 15 of 24 [63%] in control rats, p <.05). We conclude that NHE-1 inhibition may represent a novel and highly effective form of treatment for resuscitation from ventricular fibrillation.