Immediate countershock versus cardiopulmonary resuscitation before countershock in a 5-minute swine model of ventricular fibrillation arrest

STUDY OBJECTIVE: Prior laboratory and clinical studies demonstrate that cardiopulmonary resuscitation (CPR) preceding countershock of prolonged ventricular fibrillation (VF) increases the likelihood of successful cardiac resuscitation. The lower limit of VF duration at which time preshock CPR provides no benefit has not been specifically studied. The purpose of this study was to compare countershock and cardiac resuscitation outcome between immediate countershock of VF of 5-minute duration and CPR without drug therapy before countershock in a swine model. METHODS: VF was induced in anesthetized and instrumented swine. After 5 minutes of VF, animals received 1 of 2 treatments. Animals in group 1, a "historical" control group (n=20), received immediate countershock followed by CPR and repeated shocks if needed. Group 2 animals (n=11) received CPR for 90 seconds preceding countershock, then continued CPR and repeated countershock if necessary. Drugs were not administered to either group, and resuscitation efforts were discontinued if a perfusing rhythm was not restored within 10 minutes of the first countershock. First shock success rate (defined as termination of VF), the number of shocks required to terminate VF, and the cardiac resuscitation rate were compared between groups. RESULTS: The first shock terminated VF in 13 of 20 group 1 animals and 2 of 11 group 2 animals (P =.023). All but 1 animal in group 1 developed pulseless electrical activity after countershock. All but 1 animal in group 1 were eventually successfully resuscitated with CPR and repeated shocks if necessary. Four group 2 animals could not be resuscitated (P =.042). CONCLUSION: Although effective in improving outcome of prolonged VF, CPR preceding countershock of VF of 5-minute duration does not improve the response to the first shock, decrease the incidence of postshock pulseless electrical activity, or the rate of return of circulation. In this study, CPR preceding countershock resulted in a significantly lower cardiac resuscitation rate.     

Use of naloxone during cardiac arrest and CPR: potential adjunct for postcountershock electrical-mechanical dissociation

Naloxone has been shown to increase arterial pressure in hemorrhagic and septic shock. To determine if naloxone has salutary effects during cardiac arrest with conventional closed-chest cardiopulmonary resuscitation (CPR), ten dogs were studied during 20 minutes of ventricular fibrillation (VF) and CPR and during a 30-minute postcountershock period. Central aortic (Ao) and right atrial (RA) systolic and end-diastolic (EDP) pressures, instantaneous Ao-RA pressure difference (coronary perfusion pressure), and electromagnetic Ao flow were measured. Ao and RA samples were analyzed during a control period and at five-minute intervals during CPR for PO2, PCO2, and pH. During VF, a piston-cylinder device was used to perform anteroposterior sternal depressions and positive pressure ventilations (100% O2) at standard rates and ratios. After 15 minutes of CPR, animals were randomized and given either naloxone (5 mg/kg) or epinephrine (1 mg). Defibrillation was attempted five minutes later using 1 J/kg and then, if necessary, 2, 4, 8, 12, and 16 J/kg until VF was terminated or the maximum energy dose was reached. If VF persisted or if countershock resulted in asystole or a nonperfusing rhythm (electrical-mechanical dissociation [EMD]), the alternate drug (naloxone or epinephrine) was then given. Measured systolic pressures, coronary perfusion pressures, aortic flow, and blood gases were not significantly different during the control period or at five, ten, and 15 minutes of VF and CPR between animal groups prior to drug administration. When compared to hemodynamic values measured at 15 minutes, naloxone had no significant effect on pressures or aortic flow measured five minutes after administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanical "cough" cardiopulmonary resuscitation during cardiac arrest in dogs

Hemodynamic findings during ventricular fibrillation (VF) and closed-chest cardiopulmonary resuscitation (CPR) are similar to those described during VF and vigorous coughing. Interventions during CPR that mimic the physiologic events of coughing (high intrathoracic pressure and high intraabdominal pressure) improve perfusion during VF and CPR. An external circulatory assist apparatus was devised to emulate cough physiology, i.e., simultaneous pulsatile increases in intrathoracic pressure (pneumatic vest), intraabdominal pressure (abdominal binder) and airway pressure (high-pressure airway inflation). In this study, vest/binder CPR was compared with conventional CPR during 30 minutes of VF and artificial support in 18 randomized dogs. Defibrillation and long-term (more than 24 hours) survival were chosen as end points. During VF and artificial support, aortic and right atrial (RA) pressures, the instantaneous aortic-RA pressure difference (coronary perfusion pressure) and blood gas levels were measured. After 30 minutes of VF and administration of 1 mg of epinephrine, countershock was attempted. Systolic aortic and RA pressures, mean aortic-RA pressure difference and blood gas levels were not significantly different between dogs that were successfully resuscitated and those that were not. However, peak diastolic coronary perfusion pressure (peak diastolic aortic-RA pressure) for survivors averaged 23 +/- 6 mm Hg, but only 6 +/- 10 mm Hg for nonsurvivors (p less than 0.001). A peak diastolic coronary perfusion pressure 16 mm Hg or greater had a positive and negative predictive value for a successful outcome of 1.00. Only 1 of 9 conventional CPR dogs survived 24 hours; 7 of 9 dogs supported with the vest/binder device were alive and neurologically normal at 24 hours (p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperkalemia and ionized hypocalcemia during cardiac arrest and resuscitation: possible culprits for postcountershock arrhythmias?

STUDY OBJECTIVE: Early countershock of ventricular fibrillation (VF) has been shown to improve immediate and long-term outcome of out-of-hospital cardiac arrest. However, studies indicate that countershock of prolonged VF most commonly results in asystole or a nonperfusing bradyarrhythmia (pulseless electrical activity [PEA]), which rarely respond to current therapy. The cause of these postcountershock rhythm disturbances is not well understood but may be related to electrical injury of the globally ischemic myocardium or to local metabolic abnormalities that impair impulse formation and cardiac contraction. The purpose of this study was to evaluate changes in serum potassium and free calcium homeostasis during cardiac arrest and advanced cardiac life support (ACLS) interventions. METHODS: After sedation, intubation, anesthesia, and instrumentation, VF was induced in 13 dogs. After 7.5 minutes of VF, animals were immediately countershocked, standard closed-chest CPR was initiated, and epinephrine was administered (1 mg in repeated doses if necessary). RESULTS: Ten animals could not be resuscitated despite 20 minutes of ACLS interventions. In these animals, a progressive increase in serum potassium was observed from the onset of ACLS to the termination of resuscitation efforts (4.3+/-.6 to 6.0+/-.8 mEq/L, P<.01). A significant increase was observed within 10 minutes of beginning ACLS measures. This was accompanied by a decrease in ionized calcium concentration over the same period (4.95+/-.40 to 3.44 mg/dL, P<.01). The decrease in ionized calcium was significant within 5 minutes of ACLS interventions. Nine of these 10 animals had either postcountershock asystole or PEA at the termination of resuscitative efforts. The increase in potassium was not related to acidemia. Successfully resuscitated animals did not demonstrate these electrolyte changes. CONCLUSION: Ionized hypocalcemia and hyperkalemia occur during prolonged resuscitative efforts and may be related to dysfunctional transcellular ionic transport mechanisms. These cations play important roles in cardiac electrical and contractile activity and may play a role in refractory postcountershock rhythm disturbances.     

Postcountershock pulseless rhythms: response to CPR, artificial cardiac pacing, and adrenergic agonists

Clinically, countershock of ventricular fibrillation (VF) may result in asystole or a pulseless rhythm in more than 50% of attempts. We conducted a study to assess the effects of immediate artificial pacing, CPR, and adrenergic drug therapy in the management of postcountershock pulseless rhythms. Thirty-four episodes of VF followed by countershock were studied in eight anesthetized dogs. Transducer-tipped catheters were positioned in the ascending aorta (Ao) and right atrium (RA). A bipolar pacing catheter was advanced to the apex of the right ventricle and a catheter for measurement of coronary sinus blood flow (CSQ) (continuous thermodilution technique) was positioned in the coronary sinus. VF was induced electrically and a countershock at 400 J was given two minutes later; CPR was not performed during VF episodes. Countershock was followed by asystole or a pulseless rhythm in all animals. Immediate endocardial pacing (0.1 to 5 mA) of bradyarrhythmias produced electrical capture but did not result in arterial pressure pulses in any animal. After pacing, CPR was performed for two minutes or until restoration of spontaneous circulation (ROSC). During CPR, the diastolic coronary perfusion gradient (Ao-RA) was 20 +/- 7 mm Hg (mean +/- SD) and CSQ was 14 +/- 7 mL/min/100 g (53% +/- 43% of control). ROSC followed CPR of less than two minutes duration in 24% of VF study episodes. If ROSC did not follow two minutes of CPR, 1 mg epinephrine, or 50 micrograms or 100 micrograms isoproterenol was given IV.(ABSTRACT TRUNCATED AT 250 WORDS)     

QTc interval and survival in 75-year-old men and women from the general population.

AIMS: The study concerns the relationship of the corrected QT (QTc) interval to 6.4 years of survival and to measures of cardiac function, such as echocardiographic variables and plasma levels of brain natriuretic peptide (BNP), in 75-year-old people. METHODS AND RESULTS: QTc was measured in a 12-lead electrocardiogram (ECG) in 210 men and 223 women, comprising a randomly selected sample from the general population (70% participation rate). The Sicard 440/740 computer-analysis program, with Hodges' formula for heart rate-based QT correction, was used. The optimal cut-off point for predicting survival according to the receiver operating characteristic curve was found between 429 and 430 ms. Individuals with a QTc interval of > or =430 ms (n = 115) had decreased survival when compared with those with shorter QTc interval (n = 318); the relative risk was 2.4 (95% confidence interval 1.5-3.7). The predictive ability of QTc reflects an association between QTc and the following variables: BNP, left ventricular mass, and left ventricular ejection fraction (but not diastolic filling patterns). Both Hodges' and Bazett's formulae for heart rate correction of the QT interval were useful for predicting survival. The median QTc was 415 ms using Hodges' formula and 430 ms with Bazett's formula. The QRS component of QTc predicted survival better than the rest of the QTc interval and was approximately as useful as the QTc interval itself. CONCLUSION: The computer-derived QTc obtained from the ordinary 12-lead ECG identifies high-risk individuals among elderly people from the general population.     

肥厚型心肌病合并心房颤动患者射频消融术后心律失常复发心电指标的预测

目的:探讨心电指标f QRS与QTc联合是否能更好预测肥厚型心肌病(HCM)合并心房颤动患者导管消融术后的复发。方法:纳入在北京安贞医院行导管消融术的HCM合并心房颤动患者共120例(阵发/持续性心房颤动72/48)。消融策略包括:阵发性心房颤动患者行双侧肺静脉隔离(PVI);持续性心房颤动患者行PVI加左心房顶、二尖瓣峡部和三尖瓣峡部线性消融。术前评估基线心电图,f QRS定义为常规12导联心电图中至少两个连续导联的QRS波存在≥2个R波或者R波的波顶或S波的波谷出现顿挫波。采用Bazett公式校正QT间期。术后定期随访,复发定义为导管消融术后心电图或动态心电图记录的任何类型的>30 s的房性快速性心律失常。结果:59.2%(71/120)患者f QRR阳性。f QRS最常见于下壁导联(81.7%)。QTc间期(443.90±38.59)ms。平均随访13.4个月,窦性心律维持率为42.5%。多因素Cox回归分析表明,f QRS阳性(HR=1.922,95%CI:1.151~3.210,P=0.012)和QTc>448 ms(HR=1.982,95%CI 1.155~3.402,P=0.013)分别是术后复发的危险因素。f QRS和QTc联合能更好预测心房颤动术后复发。结论:f QRS和QTc延长是HCM合并心房颤动患者导管消融术后复发的独立预测因素。f QRS和QTc联合可用于预测该类患者心房颤动射频术后转归。     

Value of initial ECG findings and plasma drug levels in cyclic antidepressant overdose

Electrocardiographic changes and quantitative plasma drug levels associated with cyclic antidepressant (TCA) overdose have been the subject of many reports in the medical literature. Heart rate, QRS duration, QT interval, and most recently, the terminal 40 ms QRS (T40) axis have been reported to be valuable indicators in TCA overdose. The value of plasma drug levels and their ability to predict complications has been debated. To evaluate the discriminant and predictive abilities of ECG parameters and quantitative drug levels in a large series of TCA overdoses, we retrospectively reviewed the charts of all overdose patients admitted to ICU in our facility during a 30-month study period. The TCA-positive group (187) had statistically significant differences (P less than .001) from the TCA-negative group (171) in heart rate, QRS duration, QTc, and T40 axis. However, none of these parameters could correctly classify more than 66% of cases. The sensitivity and specificity of the T40 axis were found to be only 29% and 83%, respectively. Correlation coefficients for plasma quantitative TCA levels by ECG parameter yielded an R of less than .33 in all cases. QRS duration of 100 ms or more and heart rate of 100 or more, or TCA level of 1,000 ng/mL or more, were present in all of a few patients with complications. We conclude that ECG parameters cannot be relied on to include or exclude the diagnosis of TCA overdose and that TCA levels do not correlate with ECG parameters.     

Ventricular fibrillation during colonoscopy: a case report--colonoscopy in high-risk patients should be performed with ECG monitoring

While ventricular premature contractions have been noted during colonoscopy (CS), ventricular fibrillation (VF) is rare. We recently had a patient who developed VF during CS and recovered without any sequelae despite severe complications after cardiopulmonary resuscitation (CPR). If electrocardiogram (ECG) monitoring had been done during CS, a direct current shock defibrillation could have been accomplished and prevented complications. CS in high-risk patients should be done with ECG monitoring.     

Electrocardiographic predictors of right ventricular volume measured by magnetic resonance imaging late after total repair of tetralogy of Fallot.

BACKGROUND: Right ventricular dysfunction occurs in many patients with significant pulmonary valve regurgitation late after initial total repair of tetralogy of Fallot. Methods to predict which of these patients are at increased risk of late morbidity and mortality are not yet known. HYPOTHESIS: This study evaluated electrocardiographic (ECG) predictors of severe right ventricular dilatation determined by magnetic resonance imaging (MRI) volumes in patients with tetralogy of Fallot late after initial corrective repair. METHODS: We retrospectively reviewed the ECGs and MRI right ventricular volume measurements of 20 patients (age 4.4 to 19.3 years, mean 10.0 years) with significant pulmonary valve regurgitation late after repair of tetralogy of Fallot. All patients had enlarged, hypokinetic right ventricles by echocardiography. The patients were grouped based on an indexed right ventricular end-diastolic volume (RVEDV/BSA) of < 102 ml/m2 (Group 1) or > or = 102 ml/m2 (Group 2). We determined the sensitivity, specificity, positive and negative predictive values of QRS duration, and mean frontal plane QRS axis for predicting right ventricular volumes. RESULTS: A maximal QRS duration of > or = 150 ms or a northwest quadrant frontal plane QRS axis had 85% sensitivity, 86% specificity, 92% positive predictive value, and 75% negative predictive value for predicting an RVEDV/BSA of > or = 102 ml/m2. The mean QRS duration was significantly longer in Group 2 than in Group 1 patients (156 ms vs. 125 ms, p = 0.005). CONCLUSIONS: In patients late after repair of tetralogy of Fallot with significant pulmonary valve regurgitation a maximal manually measured QRS duration of > or = 150 ms and/or a frontal plane QRS northwest quadrant axis can predict patients with marked right ventricular enlargement. The presence of either of these findings on the ECG signifies patients who require further evaluation and consideration for pulmonary valve replacement.     

Left ventricular electromechanical delay in patients with heart failure and normal QRS duration and in patients with right and left bundle branch block.

AIMS: We sought to define the reference values of intra-left ventricular (LV) electromechanical delay (EMD), and to assess the prevalence (and pattern) of intra-LV dyssynchrony in patients with heart failure (HF) and normal QRS and in patients with right and left bundle branch block. METHODS AND RESULTS: We used tissue Doppler imaging echocardiography and a six-LV wall model to study LV EMD in 103 patients [41 with HF and normal QRS, 22 with right bundle branch block (RBBB), and 40 with left bundle branch block (LBBB)], and in 59 controls. In controls, the median intra-LV EMD was 17 ms, (inter-quartile range 13-30); 95% of controls had a value < or =41 ms. Patients showed a longer intra-LV EMD than controls: 33 ms (20-57) in patients with normal QRS, 32 ms (23-50) in RBBB patients, and 50 ms (30-94) in LBBB patients. Intra-LV dyssynchrony (defined as intra-LV EMD >41 ms) was present in 39, 36, and 60% of the patients, respectively. On average, HF patients showed the same pattern of activation as controls, from the septum to the posterior wall, but activation times were significantly prolonged. In RBBB patients the activation sequence was directed from inferior to anterior and in LBBB from anterior to inferior wall. CONCLUSIONS: Left ventricular dyssynchrony was present in several patients with HF and normal QRS, and in patients with RBBB; conversely, 40% of LBBB patients showed values of LV EMD within the normal range. Left ventricular activation sequence was different between groups. Assessment of LV synchronicity by means of imaging techniques may be more important than QRS duration or morphology in selecting patients for cardiac resynchronization treatment.     

Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model

OBJECTIVE: We sought to compare the defibrillation efficacy of a low-energy biphasic truncated exponential (BTE) waveform and a conventional higher-energy monophasic truncated exponential (MTE) waveform after prolonged ventricular fibrillation (VF). BACKGROUND: Low energy biphasic countershocks have been shown to be effective after brief episodes of VF (15 to 30 s) and to produce few postshock electrocardiogram abnormalities. METHODS: Swine were randomized to MTE (n = 18) or BTE (n = 20) after 5 min of VF. The first MTE shock dose was 200 J, and first BTE dose 150 J. If required, up to two additional shocks were administered (300, 360 J MTE; 150, 150 J BTE). If VF persisted manual cardiopulmonary resuscitation (CPR) was begun, and shocks were administered until VF was terminated. Successful defibrillation was defined as termination of VF regardless of postshock rhythm. If countershock terminated VF but was followed by a nonperfusing rhythm, CPR was performed until a perfusing rhythm developed. Arterial pressure, left ventricular (LV) pressure, first derivative of LV pressure and cardiac output were measured at intervals for 60 min postresuscitation. RESULTS: The odds ratio of first-shock success with BTE versus MTE was 0.67 (p = 0.55). The rate of termination of VF with the second or third shocks was similar between groups, as was the incidence of postshock pulseless electrical activity (15/18 MTE, 18/20 BTE) and CPR time for those animals that were resuscitated. Hemodynamic variables were not significantly different between groups at 15, 30 and 60 min after resuscitation. CONCLUSIONS: Monophasic and biphasic waveforms were equally effective in terminating prolonged VF with the first shock, and there was no apparent clinical disadvantage of subsequent low-energy biphasic shocks compared with progressive energy monophasic shocks. Lower-energy shocks were not associated with less postresuscitation myocardial dysfunction.     

Effect of application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success.

STUDY OBJECTIVE: To examine the effect of the application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success. METHODS: A prospective, randomized, controlled pilot study was carried out in an experimental animal laboratory, involving 32 mixed-breed swine weighing 36.5 to 55.7 kg each. Ventricular fibrillation (VF) was induced, and the animals were randomly allocated to 1 of 4 groups, with 8 animals per group. Animals in groups I and II remained in VF for 30 seconds; those in groups III and IV remained in VF for 5 minutes. At the end of the VF period, up to 3 countershocks were given. In groups I and III, countershocks were delivered through the self-adhesive defibrillator pads alone; in groups II and IV, they were delivered through the defibrillator pads with 25 lb of applied force. Any animal without return of spontaneous circulation after 3 countershocks was given epinephrine after 1 minute of CPR, followed by 1 additional minute of CPR and 1 additional countershock if required. RESULTS: The main measurements included baseline and countershock transthoracic impedance, cumulative countershock success rate, and 30-minute survival rate. Application of 25 lb of force to the defibrillator pads significantly decreased transthoracic impedance, compared with baseline values (group II, 15. 1% decrease; group IV, 16.1% decrease). The first-shock success rate was higher when force was applied during the countershock (87.5% versus 50% for groups II and I, respectively; 62.5% and 37.5% for groups IV and III, respectively). In the animals who experienced 5 minutes of VF, there were greater rates of success after the second, third, and fourth countershocks when force was applied (group IV) than when no force was applied (group III). Groups I and II (VF for 30 seconds) demonstrated 100% survival at 30 minutes. Group IV had a higher 30-minute survival rate (3/8 animals) than did group III (1/8). However, the rates of countershock success and 30-minute survival were not statistically different among the groups. CONCLUSION: Application of force to self-adhesive defibrillator pads decreases transthoracic impedance during countershock. This effect may contribute to improving the countershock success rate.     

心肌梗死急性期QRS波增宽预测远期心脏性猝死发生的价值

目的探讨急性心肌梗死后早期无创性指标左心室射血分数(LVEF)、QRS波时限和QTc间期预测远期心脏性猝死(SCD)发生的价值。方法采集289例急性心肌梗死后存活患者在急性期(<30 d)超声测定LVEF、体表心电图测定QRS波时限和QTc间期的数据,临床随访观察远期(>1年)发生的SCD事件。LVEF降低的界值为35%,QRS波增宽的界值为110 ms,QTc间期延长的界值为450 ms(男)/460 ms(女)。根据随访结果将患者分为SCD组和幸存组。结果在心肌梗死后平均(15±3)个月内,15例(5.2%)患者发生SCD。与幸存组患者相比,SCD组患者的LVEF明显降低[35%(28%～52%)比50%(33%～60%),P<0.0001],QRS波时限明显延长[115(88～152)ms比105(91～126)ms,P=0.0222],而两组患者QTc间期差异无统计学意义[458(416～513)ms比450(394～493)ms,P=0.1836]。SCD组患者中LVEF降低、QRS波增宽和QTc间期延长的比率依次为40%、67%和60%。生存分析提示,LVEF降低(26.1%比3.4%,P<0.0001)和QRS波增宽(9.7%比2.7%,P=0.0098)患者远期SCD发生率增加。多元Logistic回归分析显示,LVEF降低[RR:6.0(2.0～17.8),P=0.0011]和QRS波增宽[RR:3.1(1.0～9.0),P=0.0345]均为SCD发生的独立危险因素。结论急性心肌梗死后早期QRS波增宽能独立预测远期SCD的发生。     

The mortality predictive power of discharge electrocardiogram after first acute myocardial infarction

The prognostic value of discharge ECG was studied in 457 patients after their first acute myocardial infarction. Thirteen different ECG variables were studied on the discharge ECG. When cumulative 4-year survival rates were calculated by standard life-table method for each variable individually, the following variables had statistically significant prognostic power: PTF (P terminal force), PTFA (P terminal frontal axis), AF (atrial fibrillation), ST depression, ST elevation, QRS duration, and the combination block (LBBB/RBBB + LAHB/LPHB). The variables with no statistically significant predictive power were: QTc, LBBB or RBBB, LAHB or LPHB, AV block, T wave angle, T negativity, and sigma R. The relative risks for the most important variables in the discrete life-table model were: PTF 3.4, QRS duration 3.3, ST depression 2.6, PTFA 2.5, and ST elevation 2.2. In further analysis a model with only three ECG variables (PTF, ST depression, and ST elevation) was developed which stratified the study population in categories with 1.9% to 75.5% estimated 4-year survival rates.     

Signal averaged ECG and mechanisms of sudden death

The aim of signal averaged electrocardiography is to detect late potentials (LP) which are markers of ventricular tachycardia. As sudden death is often due to ventricular fibrillation which can complicate ventricular tachycardia, some workers have suggested that the presence of LP may increase the risk of sudden death. We analysed the results of signal averaged ECG in 17 subjects who died suddenly and compared them with 8 patients who died from ventricular tachycardia. These two groups of patients were part of a general population of 450 subjects who underwent programmed ventricular stimulation and signal averaged ECG by Simson's method (25 Hz filter). Three parameters of this ECG were analysed: total QRS duration (Dur QRS), amplitude of the signal 40 ms before its termination (V 40), and the duration of the terminal activity less than 40 microV (Dur LP). The criteria of diagnosis of Lp were: Dur QRS greater than or equal to 120 ms, V 40 less than or equal to 20 microV, Dur LP greater than or equal to 40 ms. The results of signal averaged ECG of patients who died suddenly were different to those of patients who died from VT: Dur QRS 116 +/- 40 vs 140 +/- 25 ms, V 40 27 +/- 24 vs 7 +/- 8 microV, Dur LP 39 +/- 27 vs 59 +/- 14 ms. Only 8 patients who died suddenly had LP (47%) whereas all patients who died of VT had LP. A correlation was observed between the presence of LP and 2 factors: the LV ejection fraction which was significantly lower in patients with LP (28 +/- 8 vs 46 +/- 19%) and the results of programmed ventricular stimulation: patients with induced sustained VT less than 270/mn usually had LP (15/16). LP were usually absent (4/6) in cases of ventricular flutter (VT greater than or equal to 270/mn) or induced VF. The presence of LP in 2 patients could signify a risk of developing VT later on. In conclusion, 9/17 patients who died suddenly did not have LP. The risk of sudden death due to primary VF or V flutter cannot be predicted. Other causes of VF are even harder to identify.     

Electrocardiographic Markers of Late Sudden Death Risk in Postoperative Tetralogy of Fallot Children

Late Sudden Death Risk in Postoperative TOF. Following surgery for tetralogy of Fallot (TOP), children may develop late onset ventricular arrhythmias. Many patients have both depolarization and repolarization abnormalities, including right bundle branch block (RBBB) and QT prolongation. The goal of this study was to improve prospective risk-assessment screening for late onset sudden death. Resting ECG markers including QRS duration, QTc, JTc, and interlead QT and JT dispersion were statistically analyzed to identify those patients at risk for ventricular arrhythmias and sudden cardiac death. To determine predictive markers for future development of arrhythmia, we examined 101 resting ECGs in patients (age 12 ± 6 years) with postoperative TOF and RBBB, 14 of whom developed late ventricular tachycardia (VT) or sudden death. These ECGs were also compared with an additional control group of 1000 age- and gender-matched normal ECGs. The mean QRS (± SD) in the VT group was 0.18 ± 0.02 seconds versus 0.14 ± 0.02 seconds in the non-VT group (P < 0.01). QTc and JTc in the VT group was 0.53 ± 0.05 seconds and 0.33 ± 0.03 seconds compared with 0.50 ± 0.03 seconds and 0.32 ± 0.03 seconds in the non-VT group (P = NS). There was no increase in QT dispersion among TOF patients with VT or sudden death compared with control patients or TOF patients without VT, although JT dispersion was more common in the TOF groups. A prolonged QRS duration in postoperative TOF with RBBB is more predictive than QTc, JTc, or dispersion indexes for identifying vulnerability to ventricular arrhythmias in this population, while retaining high specificity. The combination of both QRS prolongation and increased JT dispersion had very good positive and negative predictive values. These results suggest that arrhythmogenesis in children following TOF surgery might involve depolarization in addition to repolarization abnormalities. Prospective identification of high-risk children may be accomplished using these ECG criteria.     

Quantitative analysis of signal-averaged electrocardiograms

Quantitative analysis of the high frequency components of the terminal portion of the high-resolution surface QRS was performed in 119 normal subjects (N), 62 patients with ventricular tachycardia (VT) including 20 patients with sustained VT or VF (VTs/VF) and in 565 ischemic and nonischemic cardiac patients (NO-VT). High-resolution surface ECG (SAECG) was obtained during sinus rhythm with noise level below 0.4 microV by ART-1200EPX. The vector magnitude of the filtered and signal-averaged standard bipolar orthogonal leads X, Y, Z (V = square root of X2 + Y2 + Z2) were used for analysis. Total duration of the QRS (QRST), the duration of the low amplitude (40 microV) signals in the terminal portion of the QRS (D40) and the amplitude of the signals in the last 40 ms (V40) were measured at filter settings of both 25Hz and 40Hz by the computer. Specific values for each of the indices were identified at both 25Hz and 40Hz filterings, which could separate N as well as NO-VT from VTs/VF. They were greater than or equal to 120 ms for QRST, greater than or equal to 34 ms for D40 and less than or equal to 25 microV for V40 at 25Hz, greater than or equal to 120 ms for QRST, greater than or equal to 39 ms for D40 and less than or equal to 20 microV for V40 at 40 Hz filtering.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of conduction defects on the signal-averaged electrocardiographic determination of late potentials

To determine the effect of cardiac conduction defects on the signal-averaged electrocardiogram (ECG) and on its ability to noninvasively identify patients predisposed to ventricular tachycardia (VT), standard 12-lead ECGs and signal-averaged ECGs were obtained in 213 patients with normal conduction and 186 patients with various conduction defects. Sustained VT was induced by programmed stimulation or occurred spontaneously in 122 patients. Two-way analysis of variance showed that conduction defects and VT were associated with changes in 3 signal-averaged ECG parameters: duration of the filtered QRS, duration of the terminal QRS under 40 microV and the mean amplitude of the terminal 40 ms of the QRS. Stepwise multiple logistic regression identified 3 variables that distinguished the patient with VT with a sensitivity of 62%, a specificity of 63% and a positive predictive accuracy of 63%. These 3 variables, listed in order of importance, were conduction defect score, duration of the filtered QRS and mean amplitude of the terminal 40 ms of the QRS. These data indicate that conduction defects have systematic effects on signal-averaged ECG parameters independent of those seen in patients predisposed to VT. These effects mandate the adjustment of the definitions of late potentials in the presence of conduction defects.     

Nifekalant hydrochloride administration during cardiopulmonary resuscitation improves the transmural dispersion of myocardial repolarization: experimental study in a canine model of cardiopulmonary arrest.

BACKGROUND: Because nifekalant hydrochloride (NIF) displayed a superior defibrillating effect on ventricular tachycardia/fibrillation (VT/VF) in cardiopulmonary arrest (CPA) patients, despite some QT prolongation, its effect on transmural dispersion of repolarization (TDR) in the left ventricle (LV) in an animal model of CPA was investigated. METHODS AND RESULTS: Eight beagle dogs were created with a myocardial infarction under anesthesia, and then VT/VF induction by continuous stimulation and cardiopulmonary resuscitation (CPR) were repeated. NIF (0.3 mg/kg) was administered under acidotic conditions (pH 7.26). The QTc interval measured by Y-lead ECG showed no significant prolongation before and after NIF. The activation recovery interval (ARI) measured by 64-lead LV surface mapping showed minimum ARI prolongation (40%) by NIF without maximum ARI prolongation, and as a result the ARI dispersion decreased by 67%. The repolarization time (RPT) with the plunge electrode showed 13-19% prolongation in the subendocardium and subepicardium with CPR, but NIF prolonged the RPT in the middle layer alone (17%), and as a result Plunge-TDR decreased by 82% (n=8, p<0.05). CONCLUSIONS: Administration of NIF during CPR decreased the TDR by RPT prolongation selectively in the middle layer. Because the subendocardial and subepicardial RPTs after CPR were already prolonged before NIF administration, it may have been the reason why the QT-prolonging effect of NIF was not reflected in the body surface ECG.