Distribution of excitation frequencies on the epicardial and endocardial surfaces of fibrillating ventricular wall of the sheep heart.
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Tissue heterogeneities may play an important role in the mechanism of ventricular tachycardia (VT) and fibrillation (VF) and can lead to a complex spatial distribution of excitation frequencies. Here we used optical mapping and Fourier analysis to determine the distribution of excitation frequencies in >20 000 sites of fibrillating ventricular tissue. Our objective was to use such a distribution as a tool to quantify the degree of organization during VF. Fourteen episodes of VT/VF were induced via rapid pacing in 9 isolated, coronary perfused, and superfused sheep ventricular slabs (3x3 cm(2)). A dual-camera video-imaging system was used for simultaneous optical recordings from the entire epi- and endocardial surfaces. The local frequencies of excitation were determined at each pixel and displayed as dominant frequency (DF) maps. A typical DF map consisted of several (8.2+/-3.6) discrete areas (domains) with a uniform DF within each domain. The DFs in adjacent domains were often in 1:2, 3:4, or 4:5 ratios, which was shown to be a result of an intermittent Wenckebach-like conduction block at the domain boundaries. The domain patterns were relatively stable and could persist from several seconds to several minutes. The complexity in the organization of the domains, the number of domains, and the dispersion of frequencies increased with the rate of the arrhythmia. Domain patterns on the epicardial and endocardial surfaces were not correlated. Sustained epicardial or endocardial reentry was observed in only 3 episodes. Observed frequency patterns during VT/VF suggest that the underlying mechanism may be a sustained intramural reentrant source interacting with tissue heterogeneities. (+info)
Comparative effects of pretreatment with captopril and losartan on cardiovascular protection in a rat model of ischemia-reperfusion.
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OBJECTIVES: We sought to assess the comparative effects of pretreatment with captopril and losartan on myocardial infarct size and arrhythmias in a rat model of ischemia-reperfusion. BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) inhibit the renin-angiotensin system in different ways. However, the comparative effects of pretreatment with ACE inhibitors or ARBs on acute myocardial infarct size and arrhythmias are unknown. METHODS: We randomly assigned 117 female Sprague-Dawley rats into three groups: group N was the normal control; group C was given 40 mg/kg body weight per day of captopril in drinking water; and group L was given 40 mg/kg per day of losartan in drinking water. After 10 weeks of pretreatment, 25 rats in each group were subjected to 17 min of left anterior descending coronary artery occlusion and 2 h of reperfusion with hemodynamic and electrocardiographic monitoring. Fourteen rats in each group had blood samples drawn and aortic rings removed to study vascular reactivity. RESULTS: Mortality during ischemia and reperfusion was lower in combined groups L and C than in group N (4.2% vs. 19.2%, p = 0.042). Rats treated with losartan had significantly higher levels of angiotensin II in their plasma. Hemodynamic variables were not significantly different among the three groups. The thresholds of ventricular fibrillation (VF) before occlusion and after reperfusion were significantly higher in groups L and C than in group N (1.99 +/- 0.24 and 1.93 +/- 0.27 vs. 1.23 + 0.17 mA, p = 0.04; 2.13 +/- 0.25 and 1.78 +/- 0.22 vs. 0.95 +/- 0.11 mA, p = 0.001). The average episodes of ventricular tachycardia (VT) and VF per rat were significantly less in groups L and C than in group N (0.96 +/- 0.2 and 1.2 +/- 0.3 vs. 2.8 + 0.4 mA, p < 0.001). Myocardial infarct size was significantly smaller in groups L and C than in group N (34 +/- 3% and 35 +/- 3% vs. 44 +/- 3%, p = 0.031, 0.043). Endothelium-dependent vasorelaxation induced by a calcium ionophore (A23187) was increased in both groups but was only statistically significant in group C (p = 0.020). CONCLUSIONS: Losartan and captopril have similar cardiovascular protective effects in a rat model of ischemia-reperfusion. They increased the threshold of VF, decreased mortality and decreased episodes of VT and VF, as well as decreased myocardial infarct size. (+info)
Effect of beta-blocker therapy on severe ventricular arrhythmias in patients with idiopathic dilated cardiomyopathy.
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Beta-blocker therapy has been shown to improve cardiac function and prognosis in patients with idiopathic dilated cardiomyopathy (DCM). However, whether beta-blockers reduce severe ventricular arrhythmias and sudden cardiac death has not been clarified. The present study was designed to investigate the effects of beta-blockers on non-sustained ventricular tachycardia (VT) and sudden cardiac death in patients with DCM. Sixty-five patients with DCM treated with diuretics, digitalis and angiotensin-converting enzyme inhibitors were assigned to receive beta-blockers (n = 33) or not (n = 32). Mean follow-up was 53+/-30 months. The echocardiographic indices of cardiac function, the incidence of non-sustained VT on Holter monitoring electrocardiograms, and sudden cardiac death rate were compared between the 2 groups. Comparable improvement in cardiac function on echocardiograms was found in the 2 treatment groups. The patient group treated with beta-blockers showed a significant reduction in the prevalence of VT (from 43 to 15%, p<0.05) and the development of new episodes of VT (5 vs. 16%) compared to the group without beta-blockers. The sudden cardiac death rate did not differ between the 2 groups. The results of the present study suggest that beta-blockers are effective in reducing severe ventricular arrhythmias in patients with DCM. (+info)
Spatial heterogeneity in refractoriness as a proarrhythmic substrate: theoretical evaluation by numerical simulation.
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Spatial heterogeneity in the refractoriness of the ventricular myocardium due to a regionally prolonged refractory period has often been observed in patients with cardiovascular disease as the substrate for functional reentrant tachyarrhythmias. The present study sought to determine how functional reentrant activity could occur due to the spatial heterogeneity, using numerical simulation. Spatial heterogeneity in the refractoriness was introduced into a two-dimensional array by the regionally prolonged refractory period expressed as a square cluster. Double stimulation, conducted from a single source, was introduced into 4 types of matrices, which differed in their level of spatial heterogeneity. A pseudoelectrocardiogram was calculated from these matrices. Spiral waves were initiated in all the matrices except for the lowest heterogeneous matrix. A vulnerable window of the coupling interval, which induced spiral waves, was observed and was wider in proportion to the level of the heterogeneity. A higher level of heterogeneity and more limited range of coupling intervals were required to sustain the spiral waves. Furthermore, in the pseudoelectrocardiogram, sustained spiral waves exhibited a waveform like that in torsades de pointes (TdP) and their transformation into ventricular fibrillation (VF). Spatial heterogeneity in refractoriness due to a regionally prolonged refractory period could be a substrate for functional reentrant tachyarrhythmias, possibly including TdP and VF. (+info)
Resuscitation from fulminant myocarditis associated with refractory ventricular fibrillation.
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Resuscitation was possible in a case of fulminant myocarditis with refractory ventricular fibrillation (Vf) using a percutaneous cardiopulmonary support system (PCPS). A 46-year old Japanese man suddenly experienced cardiopulmonary dysfunction shortly after the onset of flu symptoms, was promptly diagnosed as having fulminant myocarditis and PCPS was immediately initiated. On the second day in the hospital, refractory Vf occurred, which lasted for approximately 2h despite repeated efforts to terminate it. Finally, a large dose of steroids was administered. From the third day of hospitalization and onwards, the Vf disappeared totally. The patient completely recovered from such a serious state in 6 months. During the following 3 years, he has had no clinical symptoms of worsening. As in this case demonstrates, most myocarditis is curable and invasive measures are very helpful in rescuing patients from the fulminant type with refractory Vf. (+info)
Development of a novel biomarker of free radical damage in reperfusion injury after cardiac arrest.
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In a porcine model of cardiopulmonary resuscitation (CPR), we investigated changes in the plasma levels of 8-iso-PGF(2alpha), a marker for oxidative injury, and 15-keto-dihydro-PGF(2alpha), an inflammatory response indicator during the post-resuscitation period after cardiac arrest. Twelve piglets were subjected to either 2 or 5 min (VF2 and VF5 group) of ventricular fibrillation (VF) followed by 5 min of closed-chest CPR. Six piglets without cardiac arrest were used as controls. In VF5 group, 8-iso-PGF(2alpha) in the jugular bulb plasma (draining the brain) increased four-fold. Jugular bulb 8-iso-PGF(2alpha) in the control group remained unchanged. The 15-keto-dihydro-PGF(2alpha) also increased four-fold in the VF5 group. Thus, 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) measurements in jugular bulb plasma may be used as biomarkers for quantification of free radical catalyzed oxidative brain injury and inflammatory response in reperfusion injury. (+info)
Canadian implantable defibrillator study (CIDS) : a randomized trial of the implantable cardioverter defibrillator against amiodarone.
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BACKGROUND: Patients surviving ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) are at a high risk of death due to a recurrence of arrhythmia. The implantable cardioverter defibrillator (ICD) terminates VT or VF, but it is not known whether this device prolongs life in these patients compared with medical therapy with amiodarone. METHODS AND RESULTS: A total of 659 patients with resuscitated VF or VT or with unmonitored syncope were randomly assigned to treatment with the ICD or with amiodarone. The primary outcome measure was all-cause mortality, and the secondary outcome was arrhythmic death. A total of 328 patients were randomized to receive an ICD. A thoracotomy was done in 33, no ICD was implanted in 18, and the rest had a nonthoracotomy ICD. All 331 patients randomized to amiodarone received it initially. At 5 years, 85.4% of patients assigned to amiodarone were still receiving it at a mean dose of 255 mg/day, 28.1% of ICD patients were also receiving amiodarone, and 21.4% of amiodarone patients had received an ICD. A nonsignificant reduction in the risk of death was observed with the ICD, from 10.2% per year to 8.3% per year (19.7% relative risk reduction; 95% confidence interval, -7.7% to 40%; P=0.142). A nonsignificant reduction in the risk of arrhythmic death was observed, from 4.5% per year to 3.0% per year (32.8% relative risk reduction; 95% confidence interval, -7.2% to 57.8%; P=0.094). CONCLUSIONS: A 20% relative risk reduction occurred in all-cause mortality and a 33% reduction occurred in arrhythmic mortality with ICD therapy compared with amiodarone; this reduction did not reach statistical significance. (+info)
Ventricular defibrillation with triphasic waveforms.
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BACKGROUND: It has been reported that triphasic defibrillation waveforms cause less myocardial injury than biphasic waveforms. This study compared the defibrillation thresholds (DFTs) of triphasic and biphasic waveforms. METHODS AND RESULTS: ++DFTs were determined for a transvenous lead system and a 300-microF-capacitor defibrillator. In 8 pigs (group 1), DFTs were determined for 5 triphasic waveforms with tilts of 80%, 83%, and 86% and for 1 biphasic waveform. DFTs were determined in another 8 pigs (group 2) for 2 triphasic and 4 biphasic waveforms with tilts of 43%, 49%, and 56%. In both groups, a biphasic waveform from a 140-microF-capacitor defibrillator was also evaluated, and both shock polarities were tested for each waveform. In group 1, with the 300-microF-capacitor defibrillator, the leading-edge voltage and energy stored at DFT were significantly lower for triphasic waveforms with phase-duration ratios of 50/33/17 and an anode at the right ventricular electrode for phase 1 than for biphasic waveforms (P<0.001). In group 2, the stored energy of triphasic waveforms with 56% and 49% tilt was significantly lower than that of biphasic waveforms with the same tilts for anodal but not cathodal phase 1 at the right ventricular electrode. Electrode polarity significantly affected the DFT of triphasic waveforms for both studies. CONCLUSIONS: Some 80% tilt triphasic waveforms defibrillate more efficiently than biphasic waveforms with a 300-microF-capacitor defibrillator. The triphasic waveforms for both groups were not superior to 140-microF-capacitor biphasic waveforms. The efficacy of triphasic waveforms depends on phase durations and electrode polarity. (+info)