RESUMO
BACKGROUND: Although overdrive pacing for treating atrial flutter is well established, the efficacy of device-based atrial pacing for treating spontaneous atrial tachyarrhythmias in patients with implantable cardioverter defibrillators (ICD) is unknown. This study evaluated the efficacy of novel pacing therapies for treating atrial tachyarrhythmias in patients receiving a dual-chamber ICD to treat ventricular tachyarrhythmias. METHODS AND RESULTS: A Jewel AF ICD was implanted in 537 patients with ventricular arrhythmia who were followed for 11.4+/-8.2 months (74% had a documented history of atrial tachyarrhythmias). The device discriminated atrial tachycardia (AT) from atrial fibrillation (AF) on the basis of cycle length and regularity, and it used 3 different methods of overdrive atrial pacing (Ramp, Burst+, and 50-Hz burst) to treat AT episodes and one method (50-Hz burst) to treat AF episodes. Pacing successfully terminated 59% of 1500 spontaneous AT episodes in 127 patients and 30% of 880 AF episodes in 101 patients (P<0.001). With AT and AF episodes combined, pacing efficacy was 48%. Pacing efficacy was significantly reduced at AT cycle lengths =220 ms and AF cycle lengths =160 ms (P<0.01) The median time from pacing to AT/AF termination was 1.1 minute for the pacing successes and 96 minutes for the failures (P<0.001). CONCLUSIONS: Atrial pacing terminated 48% of AT/AF episodes in patients with a history of ventricular arrhythmias. Pacing efficacy was greater for device-classified AT than AF. Pacing efficacy was significantly influenced by tachycardia cycle length. Successful pacing significantly reduces the time required for AT/AF termination.
Assuntos
Fibrilação Atrial/terapia , Flutter Atrial/terapia , Estimulação Cardíaca Artificial/métodos , Desfibriladores Implantáveis , Taquicardia/terapia , Idoso , Algoritmos , Fibrilação Atrial/fisiopatologia , Flutter Atrial/fisiopatologia , Técnicas Eletrofisiológicas Cardíacas , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Taquicardia/fisiopatologia , Resultado do Tratamento , Disfunção Ventricular/terapiaRESUMO
OBJECTIVES: We postulated that ventricular arrhythmias may arise from the heterogeneous washout of ischemic metabolites. Our objective was to investigate the distribution of extracellular potassium concentration ([K+]o) during myocardial ischemia and reperfusion and to correlate this distribution with regional differences in myocardial blood flow. BACKGROUND: Our previous study showed that reperfusion after a brief period of ischemia resulted in heterogeneous reflow of the ischemic myocardium. METHODS: The changes in regional myocardial blood flow, midmyocardial [K+]o and electrogram duration were quantitated in 14 dogs undergoing 20 min of left anterior descending coronary artery occlusion and 1 min of reperfusion. Regional myocardial blood flow was measured by using 15-microns radioactive microspheres in 1- to 1.5-g full thickness myocardial samples. The [K+]o was measured with intramyocardial K(+)-sensitive electrodes. RESULTS: During coronary occlusion, the ischemic zone exhibited a reduction in regional blood flow to 0.13 +/- 0.06 ml/g per min and increases in [K+]o to 9.3 +/- 2.6 mmol/liter and electrogram duration to 131.8 +/- 38.6% of control. Heterogeneous reduction in regional blood flow at various sites in the ischemic zone had fair correlations with variable increases in [K+]o (r = -0.70) and electrogram duration (r = -0.75). During min 1 of reperfusion, regional blood flow ranged from two to more than seven times baseline, resulting in a disorganized spatial distribution of perfusion with islands of high and low blood flows. Associated with the heterogeneous early reperfusion regional myocardial blood flow, [K+]o and electrogram duration changed at different rates toward normal. Whereas correlation between regional blood flow and [K+]o or standardized electrogram duration was fair during ischemia, this correlation was poor during early reperfusion. CONCLUSIONS: Spatial heterogeneity in regional myocardial blood flow during myocardial ischemia and early reperfusion is associated with heterogeneity in [K+]o and electrophysiologic characteristics, which in turn may play an important role in the genesis of arrhythmias arising from the ischemic and reperfused myocardium.
Assuntos
Arritmias Cardíacas/etiologia , Circulação Coronária/fisiologia , Sistema de Condução Cardíaco/fisiopatologia , Traumatismo por Reperfusão Miocárdica/etiologia , Potássio/metabolismo , Animais , Arritmias Cardíacas/metabolismo , Cães , Eletrocardiografia , Espaço Extracelular/metabolismo , Feminino , Masculino , Microesferas , Traumatismo por Reperfusão Miocárdica/metabolismo , Miocárdio/metabolismoRESUMO
OBJECTIVE: The aim was to investigate the influence of the sympathetic nervous system on the native collateral circulation in the intact heart. METHODS: Experiments were performed on 10 open chest dogs anaesthetised with alpha chloralose. The left anterior descending coronary artery was cannulated and embolised with 25 microns microspheres. Collateral resistance was determined from measurements of aortic pressure and retrograde flow. Additional haemodynamic measurements included left ventricular pressure and blood flow in the circumflex coronary artery. RESULTS: Coronary embolisation decreased retrograde resistance from 41.5(SEM 6.0) to 20.1(1.9) mm Hg.ml-1.min-1 (P < 0.01). Left stellate stimulation for 60 s (10 Hz) significantly increased circumflex blood flow and decreased circumflex resistance from 2.1(0.3) to 1.6(0.2) mm Hg.ml-1.min-1. Retrograde resistance during sympathetic stimulation decreased from 19.7(1.8) mm Hg.ml-1.min-1 (P < 0.01). Transient occlusion of descending aorta resulted in changes in perfusion pressure and retrograde flow that were similar to those observed during stellate stimulation. Stellate stimulation after beta blockade with timolol (0.1 mg.kg-1) increased circumflex resistance from 1.9(0.2) to 2.3(0.3) mm Hg.ml-1.min-1 (P < 0.01) but did not alter retrograde resistance. CONCLUSIONS: The sympathetic nervous system does not have a direct effect on native coronary collateral vessels. Increased sympathetic input to the heart does not result in a coronary steal phenomenon. The primary determinant of flow and resistance in the native collateral network during sympathetic activation is the arterial perfusion pressure.
Assuntos
Circulação Colateral/fisiologia , Circulação Coronária/fisiologia , Sistema Nervoso Simpático/fisiologia , Animais , Pressão Sanguínea/fisiologia , Doença das Coronárias/fisiopatologia , Cães , Estimulação Elétrica , Fenômenos Eletromagnéticos , Embolia , Feminino , Masculino , Perfusão , Fluxo Sanguíneo Regional/fisiologiaRESUMO
OBJECTIVE: The aim was to investigate the influence of the sympathetic nervous system on the induction of mechanical and electrical alternans in the intact canine heart. METHODS: Experiments were performed on 8 open-chest dogs anesthetized with sodium pentobarbital. A micromanometer-tipped catheter was used to measure left ventricular pressure, dp/dt and the time constant of isovolumic relaxation. Rapid atrial pacing was used to induce alternans and the left stellate ganglion was stimulated electrically to alter sympathetic tone. The longest pacing cycle length that showed a significant alternation in peak systolic pressure was defined as the alternans threshold. Electrical alternans was detected by comparing the ST-T area in the surface ECG (lead II) on alternate beats. RESULTS: The alternans threshold was 305(s.e.m. 10.4) ms under control conditions and decreased to 271(12.1), 225(33.4), and 177(6.2)ms, as the frequency of left stellate stimulation was increased to 1, 2, and 5 Hz, respectively (P < 0.001). Tau and peak -dp/dt began to alternate at the same pacing cycle length as peak +dp/dt and peak systolic pressure. Electrical alternans was only observed during mechanical alternans and the ST-T area of the strong beat was 243(143)% greater than the ST-T area of the weak beat (P < 0.001). Timolol (1 mg.kg-1) blocked the effect of left stellate stimulation (1 and 2 Hz) on mechanical and electrical alternans. CONCLUSIONS: Left sympathetic activation causes a frequency-dependent reduction in the threshold cycle length for global mechanical and electrical alternans. Alternation in relaxation occurs at the same pacing cycle length as does alternation in contraction. Repolarization alternans in the surface ECG appears to reflect underlying mechanical events.
Assuntos
Estimulação Cardíaca Artificial , Estimulação Elétrica , Coração/fisiologia , Sistema Nervoso Simpático/fisiologia , Animais , Cães , Eletrocardiografia , Feminino , Coração/efeitos dos fármacos , Átrios do Coração , Masculino , Simpatolíticos/farmacologia , Sístole , Timolol/farmacologia , Pressão Ventricular/efeitos dos fármacos , Pressão Ventricular/fisiologiaRESUMO
We used complex demodulation of cardiac interval and systolic arterial blood pressure oscillations in the low-frequency band (0.04 to 0.14 Hz) to investigate baroreceptor control of heart rate. Baroreflex sensitivity was defined as the instantaneous amplitude of complex-demodulated oscillations in the RR interval divided by the instantaneous amplitude of complex-demodulated oscillations in systolic blood pressure. We evaluated the method using both simulated and actual data obtained from 33 healthy nonsmokers during supine and standing postures. To test the validity and reliability of the method, we compared the mean values of baroreflex sensitivity calculated using complex demodulation with the values obtained using power spectral analysis and sequential analysis of spontaneous variations in blood pressure and RR interval. All three methods applied to the simulated data yielded the same values of baroreceptor sensitivity. Mean values of baroreflex sensitivity assessed by complex demodulation of the actual data were similar to those calculated by both power spectral analysis and sequential analysis (13.9 +/- 5.2 versus 13.7 +/- 6.7 or 14.3 +/- 6.5 ms/mm Hg for supine and 7.3 +/- 2.8 versus 7.0 +/- 3.0 or 7.2 +/- 2.8 ms/mm Hg for standing, respectively). In addition, a significant correlation existed between the values obtained by complex demodulation and power spectral analysis (r = .97, P = .0001) and sequential analysis (r = .98, P = .0001). Furthermore, complex demodulation-derived baroreflex sensitivity fluctuated across time during both the supine and standing postures, and this could not be discerned by power spectral analysis. The results indicate that complex demodulation provides a dynamic assessment of baroreflex sensitivity and may be a useful tool in exploring reflex autonomic control of the cardiovascular system.
Assuntos
Barorreflexo/fisiologia , Eletrocardiografia/métodos , Frequência Cardíaca/fisiologia , Adulto , Humanos , Masculino , Pessoa de Meia-Idade , PosturaRESUMO
This study examined the relationship between breath pentane and plasma lipid peroxide levels sampled simultaneously in patients with stable angina (n = 17), unstable angina (n = 23), and controls (n = 10). Plasma lipid peroxides were measured in venous blood as the adduct formed between thiobarbituric acid and malondialdehyde (MDA) using high performance liquid chromatography. Pentane was measured in end-expiratory air using gas chromatography. MDA concentrations in stable (1.81 +/- 0.84 mumol/l) and unstable (1.5 +/- 1.23 mumol/l) angina were not different. However, both groups had significantly (p < 0.005) elevated MDA levels compared to controls (0.41 +/- 0.26 mumol/l). Breath pentane was 0.20 +/- 0.12 nmol/l in controls and not different from stable angina (0.26 +/- 0.20 nmol/l) or unstable angina (0.15 +/- 0.07 nmol/l). When the data from all three groups were combined, there was no correlation between pentane and MDA (rho = -0.09, p = 0.54). In five of the unstable angina patients treated with balloon angioplasty, MDA in pulmonary arterial blood rose by 69 +/- 15% (p < 0.01), and breath pentane rose by 73 +/- 20% (p < 0.01) immediately after balloon deflation. One minute after balloon deflation MDA and pentane had returned to preinflation levels. The results suggest that basal levels of pentane are less useful than MDA as an index of lipid peroxidation in patients with coronary artery disease. However, breath pentane appears to be a sensitive index of reperfusion-induced lipid peroxidation.
Assuntos
Angina Pectoris/metabolismo , Angina Instável/metabolismo , Hemiterpenos , Peróxidos Lipídicos/sangue , Isquemia Miocárdica/metabolismo , Pentanos/análise , Respiração , Adulto , Idoso , Angina Pectoris/sangue , Angina Instável/sangue , Biomarcadores/análise , Biomarcadores/sangue , Butadienos/análise , Colesterol/sangue , Feminino , Humanos , Masculino , Malondialdeído/sangue , Pessoa de Meia-Idade , Isquemia Miocárdica/sangue , Valores de Referência , Fumar , Triglicerídeos/sangueRESUMO
Sinus node dysfunction is a disorder of impulse generation and impulse conduction. Previous works have emphasized that the dysfunction occurs not only within the sinus node but also within the escape pacemaker. Adrenergic and cholinergic mechanisms, as well as pulsations and pressure within the sinus node artery, play an important role in normal sinus node activity. Although perinodal fibers act as a buffer zone for sinoatrial conduction, their role in man is yet to be clarified. During normal sinus node activity, pacemaker shifts from the sinus node to the crista terminalis have been shown to occur. Following sinus node destruction, similar shifts do occur. Clinical methods of determining sinus node function, such as the sinus node recovery time and sinus atrial conduction time, are useful but have limitations. Dynamic electrocardiographic monitoring provides the best clinical method available for detecting sinus node dysfunction. Digitalis appears to improve the parameters of sinus node function by increasing the automaticity of latent atrial pacemakers. The atrial arrhythmia of sinus node dysfunction appears to be related to the characteristics of latent atrial pacemaker and "enhanced" cholinergic tone.
Assuntos
Arritmias Cardíacas/fisiopatologia , Sistema Nervoso Autônomo/fisiopatologia , Nó Sinoatrial , Arritmias Cardíacas/tratamento farmacológico , Glicosídeos Digitálicos/uso terapêutico , Frequência Cardíaca/efeitos dos fármacos , Humanos , Condução Nervosa/efeitos dos fármacos , Sistema Nervoso Parassimpático/fisiopatologia , Período Refratário Eletrofisiológico/efeitos dos fármacos , Nó Sinoatrial/efeitos dos fármacos , Nó Sinoatrial/fisiologia , Nó Sinoatrial/fisiopatologiaRESUMO
Experiments were performed to determine the importance of sympathetic blockade vs a direct myocardial effect as a mechanism for the antifibrillatory action of bretylium. The ventricular fibrillation (VF) threshold was determined in open-chest, anesthetized dogs by scanning the vulnerable period with either a single electrical stimulus (10 ms) or a train of electrical stimuli (14 pulses, 4 ms, 100 Hz). Using the train-of-pulses technique, the VF threshold increased from 6.8 +/- 0.6 mA to 29.7 +/- 6.4 mA 15 minutes after a 10-mg/kg intravenous bolus of bretylium (p less than 0.001, n = 8). There was no further significant change in the train-of-pulses VF threshold at 2 or 4 hours. Beta-adrenergic blockade with timolol (0.2 mg/kg) increased the train-of-pulses VF threshold from 6.7 +/- 1.6 mA to 24.5 +/- 5.2 mA (p less than 0.01 n = 8) and prevented any further significant change in response to bretylium. When single electrical pulses were used to scan the vulnerable period, bretylium at doses of 10 mg/kg (n = 8) and 100 mg/kg (n = 6) did not alter the VF threshold over a 4-hour observation period. The administration of timolol, alone or in combination with bretylium, did not significantly alter the single-pulse VF threshold. The failure of bretylium to alter the single-pulse VF threshold was not dependent on the site of stimulation. Stimulation of the right sympathetic cardiac nerves showed that 15 minutes of bretylium treatment was sufficient to completely inhibit adrenergic neuronal transmission to the myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Compostos de Bretílio/farmacologia , Tosilato de Bretílio/farmacologia , Fibrilação Ventricular/fisiopatologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Estimulação Cardíaca Artificial/métodos , Cães , Relação Dose-Resposta a Droga , Estimulação Elétrica/métodos , Eletrocardiografia , Frequência Cardíaca/efeitos dos fármacos , Contração Miocárdica/efeitos dos fármacos , Timolol/farmacologia , Fibrilação Ventricular/tratamento farmacológicoRESUMO
Ventricular multiple extrasystoles and fibrillation were induced in open chest dogs by the delivery of either a single electrical pulse or a train of pulses to the right ventricle during the vulnerable period of the cardiac cycle. Bipolar epicardial electrodes delivered current while bipolar plunge electrodes recorded the activation complexes at various distances from the stimulation site. At stimulus intensities below the threshold for multiple ventricular responses, the electrograms recorded from muscle adjacent to the stimulation site showed fragmented activation complexes that lasted considerably longer than the control complexes. At stimulus intensities that evoked multiple ventricular extrasystoles or fibrillation, the fragmented electrical activity became continuous and bridged the diastolic interval between successive ectopic complexes. The continuous fractionated electrical activity that preceded the appearance of multiple extrasystoles and fibrillation was recorded only from electrodes placed within a few millimeters of the stimulating electrodes and could be evoked only by stimulation during the vulnerable period. Disappearance of the fractionated local electrical activity during a run of extrasystoles was followed immediately by the resumption of a normal rhythm. In addition, the fractionated continuous electrical activity that appeared after delivery of a single stimulus during the vulnerable period could be abolished by the delivery of a second stimulus during the protective zone. The presence of continuous local electrical activity before the development of multiple extrasystoles and fibrillation provides strong evidence that the ventricular fibrillation threshold technique operates by producing local reentrant activity.
Assuntos
Função Ventricular , Animais , Cães , Estimulação Elétrica , Eletrocardiografia , Eletrodos , Frequência Cardíaca , Sístole , Fatores de Tempo , Fibrilação Ventricular/etiologiaRESUMO
This study investigated the effects of therapeutic and subtoxic doses of digoxin on the risk of ventricular tachycardia (VT) after graded, transthoracic shocks in anesthetized dogs. A series of direct current shocks (5, 10, 25, 50, 75, 100, 150 and 200 J) was delivered to 33 normal dogs and 6 dogs with a healed (32 +/- 7 days) myocardial infarct (MI). In 10 untreated dogs, the duration of post-shock VT was highly reproducible when 3 separate series of shocks were delivered at 2-hour intervals. In 6 normal dogs treated with oral digoxin (0.5 mg/day for 5 to 7 days), a series of shocks delivered before and during treatment (serum levels 1.5 +/- 0.5 ng/ml) resulted in the same duration of post-shock VT. In 18 normal and 6 dogs with MI, a series of shocks was given before and 90 minutes after a therapeutic dose of digoxin (0.05 mg/kg intravenously). At this dose of digitalis (serum level 2.5 +/- 1.0 ng/ml), there was no difference in the duration of post-shock VT in either normal dogs or dogs with MI. A third series of shocks was given after achieving subtoxic digitalization with additional intravenous digoxin (0.01 mg/kg) every 30 minutes until a premature ventricular stimulus evoked a repetitive ventricular response. The subtoxic doses of digitalis (serum levels 13.9 +/- 4.7 ng/ml) increased the duration of post-shock VT in both normal dogs (100%) and dogs with MI (700%) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Arritmias Cardíacas/etiologia , Digoxina/toxicidade , Cardioversão Elétrica/efeitos adversos , Animais , Arritmias Cardíacas/induzido quimicamente , Digoxina/administração & dosagem , Cães , Relação Dose-Resposta a Droga , Eletrocardiografia , Ventrículos do Coração/fisiopatologia , Infarto do Miocárdio/tratamento farmacológico , Infarto do Miocárdio/fisiopatologia , Risco , Taquicardia/induzido quimicamente , Taquicardia/etiologiaRESUMO
The ventrolateral cardiac nerve in the dog is a primary branch of the left sympathetics and represents a direct neural link between the central nervous system and the heart. Its electric excitation elicits characteristic shifts in pacemaker and tachydysrhythmias related to its explicit innervation of the inferior atrial, atrioventricular (A-V) junctional and ventricular tissues. Total denervation of the canine heart, sparing the ventrolateral cardiac nerve, produced a long-term model in which only these portions of the heart retained their sympathetic innervation. The trained unanesthetized model dog was subjected to severe exercise in order to determine the effects of elevated levels of sympathetic tone upon these important regions of the conduction system. Reproducible tachydysrhythmias were elicited in all six animals completing the regimen of periodic testing over a period of 136 to 378 days after operation. The abnormal rhythms consisted of shifting cardiac pacemakers and supraventricular A-V junctional and ventricular tachycardias with frequent premature systoles. Comparable abnormalities were not observed in a similarly tested sham-operated animal or in dogs with a totally denervated heart. The exercise-induced dysrhythmias gradually disappeared with time, presumably in relation to autonomic reinnervation of the heart. The characteristic patterns of ventrolateral cardiac nerve and upon its presumed influence upon Purkinje fiber and A-V nodal automaticity and temporal dispersion of refractoriness in myocardial tissues.
Assuntos
Arritmias Cardíacas/fisiopatologia , Sistema de Condução Cardíaco/cirurgia , Complicações Pós-Operatórias/fisiopatologia , Animais , Nó Atrioventricular/fisiopatologia , Fibras Autônomas Pós-Ganglionares/cirurgia , Denervação , Cães , Estimulação Elétrica , Eletrocardiografia , Teste de Esforço , Feminino , Átrios do Coração/inervação , Ventrículos do Coração/inervação , Masculino , Contração Miocárdica , Regeneração Nervosa , Nó Sinoatrial/cirurgia , Sistema Nervoso Simpático/fisiopatologia , Transmissão Sináptica , Taquicardia/fisiopatologiaRESUMO
Coronary angiography with Renografin 76 (RG76) occasionally results in ventricular fibrillation (VF). Angiovist 370 (AV370) is a contrast medium similar to RG76 except the calcium-sequestering agents, sodium citrate and EDTA in RG76 have been replaced by calcium EDTA. To determine whether these sequestering agents contribute to contrast medium-induced VF, a comparison was made of the effects of intracoronary injections of RG76, AV370, and saline solutions containing sodium citrate and EDTA (CIT/EDTA) and calcium EDTA (CA EDTA) on myocardial conduction, local QT intervals, and incidence of spontaneous and induced VF in 32 dogs. Four milliliters of RG76 produced a 111 +/- 12-ms increase in local QT intervals, compared with a 73 +/- 8-ms increase with AV370 (p less than 0.001). Spontaneous VF occurred in 12 of 16 six-milliliter injections of RG76, compared with 4 of 16 injections of AV370 (p less than 0.02) An early-cycle premature impulse applied after every fourth beat induced VF in 15 of 16 four-milliliter injections of RG76 compared with 5 of 16 injections of AV370 (p less than 0.01). As the premature beat conducted through the left anterior descending region, conduction slowing and fractionation occurred, which was less with AV370 than with RG76. The CIT/EDTA solution produced a greater increase in QT intervals (77 +/- 5 ms) than the CA EDTA solution (29 +/- 3 ms) or 0.9% saline solution alone (28 +/- 2 ms) (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Cálcio/farmacologia , Citratos/farmacologia , Meios de Contraste/farmacologia , Diatrizoato de Meglumina/efeitos adversos , Diatrizoato/análogos & derivados , Diatrizoato/efeitos adversos , Fibrilação Ventricular/fisiopatologia , Animais , Ácido Cítrico , Diatrizoato/farmacologia , Diatrizoato de Meglumina/farmacologia , Cães , Combinação de Medicamentos/farmacologia , Ácido Edético , Eletrocardiografia , Feminino , Masculino , Radiografia , Fibrilação Ventricular/diagnóstico por imagemRESUMO
Coronary angiography occasionally results in ventricular fibrillation. To compare the fibrillatory propensity of conventional ionic and nonionic contrast media, we measured QT intervals and performed programmed electrical stimulation during intracoronary injection of Renografin 76 (R76), Hypaque 76 (H76), and iopamidol (IOP) in 16 open chest dogs. In ten dogs the incidence of ventricular fibrillation following induction of a single premature ventricular beat after every fourth atrial paced beat was 19/20 with R76, 8/20 with H76, and 0/20 with IOP (P less than .001). When two premature beats were induced, the incidence of ventricular fibrillation was 20/20 with R76, 19/20 with H76, and 1/20 with IOP (P less than .001). In six additional dogs, the mean prolongation of the QT interval was 170 +/- 20 msec with R76, 105 +/- 14 msec with H76, and 63 +/- 9 msec with IOP (P less than .001). Thus, programmed electrical stimulation readily induces ventricular fibrillation during intracoronary injection of conventional ionic contrast media. The incidence of ventricular fibrillation parallels the amount of QT interval prolongation produced. H76, which lacks EDTA and sodium citrate, is less fibrillatory than R76. However, the nonionic medium IOP appears far less fibrillatory than either R76 or H76.
Assuntos
Angiografia/efeitos adversos , Meios de Contraste/efeitos adversos , Fibrilação Ventricular/induzido quimicamente , Animais , Meios de Contraste/administração & dosagem , Diatrizoato/efeitos adversos , Diatrizoato de Meglumina/efeitos adversos , Cães , Combinação de Medicamentos/efeitos adversos , Estimulação Elétrica/métodos , Eletrocardiografia , Feminino , Íons , Iopamidol , Ácido Iotalâmico/efeitos adversos , Ácido Iotalâmico/análogos & derivados , Masculino , Contração Miocárdica/efeitos dos fármacos , Fibrilação Ventricular/diagnósticoRESUMO
Thirty patients with drug refractory ventricular tachycardia (RVT) were studied between 1 week and 5 years after myocardial infarction with coronary agniography and left ventriculography. They were divided into four groups: (1) inoperable, five patients; (2, a) operated, with primary left ventricular failure, five patients; (2, b) operated with primary RVT, not mapped, 15 patients; (2, c) operated, with mapping, five patients. The mortality rate in group 1 was 100%, and in group 2, a it was 80%. In group 2, b, despite aggressive drug therapy and operation, including aneurysmectomy, coronary revascularization, and intra-aortic balloon pumping when appropriate, the mortality rate wad intraoperative mapping in group 2, c. Arrhythmogenic foci were identified and removed in four. There was one operative death (20%) and four patients are alive from 12 to 27 months after operation, three of whom are asymptomatic. Intraoperative epicardial mapping is an important adjunct to surgery for RVT.
Assuntos
Procedimentos Cirúrgicos Cardíacos , Infarto do Miocárdio/complicações , Taquicardia/fisiopatologia , Idoso , Cateterismo Cardíaco , Ponte Cardiopulmonar , Eletrofisiologia , Seguimentos , Ventrículos do Coração/diagnóstico por imagem , Ventrículos do Coração/fisiopatologia , Ventrículos do Coração/cirurgia , Humanos , Masculino , Pessoa de Meia-Idade , Infarto do Miocárdio/cirurgia , Radiografia , Taquicardia/diagnóstico por imagem , Taquicardia/etiologiaRESUMO
BACKGROUND: Symptomatic improvement of a patient's hemodynamic condition during intraaortic balloon counterpulsation (IABC) is considered to result largely from a reduction in afterload. Afterload can be accurately quantified by arterial input impedance measurements. Here we report the effect of IABC on arterial impedance in humans. METHODS: To characterize the effects of IABC on arterial input impedance, impedance measurements were obtained using aortic annulus Doppler flow and pressure from the aortic balloon catheter. Impedance spectra were compared between the cardiac cycles preceding and following the cycle with IABC in 25 patients. RESULTS: Intraaortic balloon counterpulsation increased stroke volume (23%; p = 0.001), reduced myocardial oxygen demand (11%; p = 0.02), and decreased the aortic pressure at the onset of systole (16%; p = 0.001). There was also a decrease in systemic vascular resistance (24%; p = 0.001), characteristic arterial impedance (21%; p = 0.002), and pulse wave reflection (20%; p = 0.006). Linear regression analysis showed that an increase in stroke volume was predicted only by the decrease in systemic vascular resistance (r = -0.81; p = 0.001). CONCLUSIONS: The reduction in systemic vascular resistance appeared to be the major mechanism by which IABC improved cardiac pumping efficiency. This effect may result from the passive distention of the peripheral vascular bed due to the propagation of the balloon-augmented diastolic pressure through the arterial system.
Assuntos
Balão Intra-Aórtico , Resistência Vascular , Idoso , Idoso de 80 Anos ou mais , Ponte Cardiopulmonar , Ponte de Artéria Coronária , Feminino , Cardiopatias/fisiopatologia , Cardiopatias/cirurgia , Hemodinâmica , Humanos , Masculino , Pessoa de Meia-Idade , Volume SistólicoRESUMO
Pentane and isoprene concentrations were analyzed in single end-expiratory breath samples using gas chromatography. Breath analysis was performed in 15 patients with acute myocardial infarction, 15 patients with stable angina, and 15 healthy control subjects. The two patient groups were well matched for age, sex, smoking habits, hypertension and serum cholesterol levels. There was no significant difference in breath pentane concentration in the acute myocardial infarction group (0.29 +/- 0.03 nmol/l) (mean +/- SEM) compared to the group with stable angina (0.31 +/- 0.03 nmol/l) or the control group (0.36 +/- 0.04 nmol/l). However, breath isoprene concentration was higher (p < 0.01) in the acute myocardial infarction group (11.4 +/- 1.2 nmol/l), compared to both the stable angina group (7.7 +/- 0.5 nmol/l) and the control group (7.1 +/- 1.0 nmol/l). There was no difference in either the pentane or isoprene concentrations between the control group and the group with stable angina. Since pentane is thought to be an index of lipid peroxidation, the results do not support the presence of enhanced lipid peroxidation in acute myocardial infarction in the absence of thrombolytic therapy or primary angioplasty. The mechanism responsible for isoprene elevation in acute myocardial infarction is unknown.
Assuntos
Butadienos/análise , Hemiterpenos , Infarto do Miocárdio/metabolismo , Pentanos/análise , Adulto , Idoso , Idoso de 80 Anos ou mais , Angina Pectoris/metabolismo , Testes Respiratórios , Butadienos/metabolismo , Cromatografia Gasosa , Eletrocardiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Pentanos/metabolismoRESUMO
To investigate the effects of autonomic nerve activation on electrophysiological properties of ischemic atrial myocardium, experiments were performed in 10 open chest adult dogs anesthetized with xylazine and alpha-chloralose. Ischemia was created in the right atrial free wall by ligation of one or more branches of the right coronary artery. Bipolar electrograms were recorded from multiple sites in the ischemic and non-ischemic zones. The atria were paced at 400 ms and 180 ms to assess conduction properties. One hour after ligation, delayed activation, electrogram fractionation, and electrogram alternans were observed in the ischemic zone. All local conduction abnormalities were heart rate dependent in that they were only observed at a pacing cycle length of 180 ms. The average duration of ischemic zone electrograms was significantly prolonged from 17.7+/-1.6 ms to 26.4+/-1.6 ms (P<0.001). Right and left vagal stimulation significantly shortened the electrogram duration in the ischemic zone from 26.4+/-1.6 ms to 19.7+/-1.1 ms (P<0.01) and 20.0+/-1.1 ms (P<0.01), respectively. Ischemia-induced electrogram alternans was eliminated completely. During right and left stellate stimulation, electrogram duration was not altered and alternans was still present. In conclusion, vagal stimulation in this canine model improves local conduction in ischemic myocardium in the right atrium. This effect may be mediated by a reversal of the ischemia-induced membrane depolarization and a shortening of refractoriness in the atrium during vagal activation.
Assuntos
Átrios do Coração/fisiopatologia , Sistema de Condução Cardíaco/fisiopatologia , Coração/inervação , Isquemia Miocárdica/fisiopatologia , Nervo Vago/fisiopatologia , Animais , Cães , Feminino , MasculinoRESUMO
UNLABELLED: Defibrillation energy requirements of epicardial implantable cardioverter defibrillator systems are generally lower than endovascular systems currently used. The former has the disadvantage of requiring a thoracotomy and so has a greater morbidity and mortality than an endovascular procedure. The middle cardiac vein (MCV) is an epicardial structure that is accessible by a non-thoracotomy approach. This study investigated the merits of ventricular defibrillation from the middle cardiac vein. METHODS AND RESULTS. Defibrillation thresholds (DFT) were measured in 10 anesthetized pigs, weighing 34.5 +/- 44.1 kg (mean 39 kg). An Angeflex electrode (1.7 mm x 50 mm) was introduced via the left external jugular vein to the right ventricular apex. The MCV was identified with standard angiography techniques and a 4080 (Angeion Corp.) defibrillation electrode (1.6 mm x 65 mm) introduced into the vein. An active can was implanted in the left subpectoral region. The defibrillation thresholds (DFT) of the following defibrillation configurations were assessed using a modified four-reversal binary search: RV-->Can, RV + MCV-->Can and MCV-->Can. The DFT's for the three configurations were 15.5 +/- 2.8 J, 10.8 +/- 3.4 J and 13.7 +/- 2.4 J. Analysis of variance showed that the DFT with the RV + MCV combination was significantly less than the RV alone (p < 0.05) CONCLUSIONS: Defibrillation is possible through the MCV and that incorporating an electrode in the MCV with RV-Can configuration can reduce the DFT by 30%.
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Vasos Coronários , Cardioversão Elétrica/métodos , Animais , Cateterismo Periférico , Angiografia Coronária , Modelos Animais de Doenças , Eletrocardiografia , Feminino , Fluoroscopia , Suínos , Veias , Fibrilação Ventricular/terapiaRESUMO
UNLABELLED: The aim of this study was to identify the optimal position on the chest wall to place an implant able cardioverter defibrillator in a two-electrode system, consisting of a right ventricular electrode and active can. METHODS AND RESULTS: Defibrillation thresholds (DFT) were measured in 10 anaesthetised pigs (weight 33-45 kg). An Angeflextrade mark lead was introduced transvenously to the right ventricular apex. The test-can (43 cc) was implanted submuscularly in each of four locations: left pectoral (LP), right pectoral (RP), left lateral (LL) and apex (A). The sequence in which the four locations were tested was randomized. Ventricular fibrillation (VF) was induced using 60 Hz alternating current. Rectangular biphasic shocks were delivered 10 seconds after VF induction. The DFT was measured using a modified four-reversal binary search. The results of the four configurations were: LP, 14.6+/- 4.0 J; RP, 18.8+/- 4.2 J; LL, 14.7+/- 4.1 J; A, 14.9+/- 3.1 J. Repeated measures analysis of variance showed that the DFT of RP was significantly higher than LP, LL and A (p < 0.05). CONCLUSIONS: Implanting an active can in the RP position increases the DFT by 29% compared to LP, LL and A sites. The can position on the left thorax does not appear to have a significant influence on DFT.
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Desfibriladores Implantáveis , Animais , Estudos de Avaliação como Assunto , Feminino , Distribuição Aleatória , SuínosRESUMO
INTRODUCTION: Conventional implantable cardioverter defibrillators employ endocardial (shock) electrodes with a lead located in the right ventricular apex (RV) and a "hot-can" electrode located subcutaneously in the left pectoral region. In the event of a high defibrillation threshold (DFT) a third electrode is frequently employed in the superior vena cava (SVC). We report the comparison of conventional and novel locations of additional electrodes with the RV/Can configuration, in a porcine model. METHOD: In 12 anesthetized pigs (30-45 kg), endocardial defibrillation electrodes were randomized to the following locations: RV/Can, RV/Can + SVC, RV/Can + main pulmonary artery (MPA) and RV/Can + left pulmonary artery wedge position (PAW), RV/Can + high inferior vena cava (HIVC), RV/Can + Low inferior vena cava (LIVC). Ventricular fibrillation (VF) was induced using 60 Hz alternating current. After 10 seconds VF a rectangular biphasic shock was delivered by the ARD9000 (Angeion Corp). The DFT was determined for each configuration using a modified four-reversal binary search. All configurations were compared using a repeated measures analysis of variance (ANOVA) statistical test and the five 3-electrode configurations were compared to the RV/Can position using a Dunnett test. RESULTS: Mean DFTs: RV = 21.5 +/- 4.8 J, SVC = 16.8 +/- 4.7 J (p < 0.05 vs. RV), HIVC = 21.1 +/- 4.7 J (p <. 0.05), LIVC = 19.1 +/- 5.7 J (p <. 0.05 vs. RV), MPA = 16.0 +/- 5.8 J (p < 0.01), PAW = 17.5 +/- 4.6 J (p < 0.05 vs. RV). CONCLUSIONS: Relative to the RV/can configuration the addition of a third electrode in the PA, PAW or SVC significantly reduces the DFT in the pig. The addition of an electrode to the IVC did not significantly reduce the DFT in our model.