Electrode pad size, transthoracic impedance and success of external ventricular defibrillation

Electrode pad size is an important determinant of transthoracic current flow during external countershock. Self-adhesive, dual function electrocardiogram/defibrillator pads were used to assess the effect of electrode pad size on defibrillation success with low energy (200 J) shocks. The study analyzed 123 cardiac arrests due to primary ventricular fibrillation (VF) in 105 patients (74 men, 31 women) ages 40 to 84 years (mean 64). Transthoracic impedance was measured before defibrillation using a low amplitude 30-kHz current passed through the chest by way of the electrocardiogram/defibrillator pads applied anteroanteriorly. Pad diameters were small (8/8 cm) in 26 cardiac arrests, intermediate (8/12 cm) in 63 arrests and large (12/12 cm) in 34 cardiac arrests. Transthoracic impedance decreased with increasing pad size (112 +/- 17 vs 92 +/- 22 vs 72 +/- 14 omega, respectively, p = 0.0001). Only the first episode of primary VF during a cardiac arrest was analyzed. A single shock of 200 J (delivered energy) was successful in 8 of 26 (31%) arrests using small pads, in 40 of 63 (63%) with intermediate pads and in 28 of 34 (82%) with large pads (p = 0.0003). A second 200-J shock increased the cumulative defibrillation rates to 12 of 26 (46%), 50 of 63 (79%) and 33 of 34 (97%), respectively (p less than 0.0001). In primary VF, larger self-adhesive electrocardiogram/defibrillator pads are associated with a lower transthoracic impedance and improved defibrillation success rates with low energy shocks.     

Experimental evaluation and initial clinical application of new self-adhesive defibrillation electrodes

We evaluated the efficacy of self-adhesive electrode pads for defibrillation and cardioversion in animals and patients. In 11 anesthetized dogs, the success rate of shocks given to terminate electrically-induced ventricular fibrillation was similar for both self-adhesive electrode pads and hand-held electrode paddles; success rate approached 100% at energies of 125-150 joules. Eighty patients undergoing defibrillation or elective cardioversion received shocks from self-adhesive pads. In all but 2 patients defibrillation or cardioversion was achieved at least once using these pads. The pads were equally effective from either apex-anterior or apex-posterior positions. The transthoracic impedance using self-adhesive pads was 75 +/- 21 ohms, similar to transthoracic impedance we previously reported when using standard hand-held paddles. No complications occurred with the use of the pads. We conclude that self-adhesive electrode pads are effective for defibrillation and cardioversion.     

Initial experience with a microprocessor controlled current based defibrillator.

Intramyocardial current flow is a critical factor in successful ventricular defibrillation. The main determinants of intramyocardial current flow during transthoracic countershock are the selected energy and the transthoracic impedance of the patient. To optimise the success of the first shock and to titrate energy dosage according to each patient's transthoracic impedance, a microprocessor controlled current based defibrillator was developed. It was compared with a conventional energy based protocol of 200 J (delivered energy), 200 J, then 360 J if required in 42 consecutive episodes of ventricular fibrillation in 33 men and seven women. The mean (SD) predicted transthoracic impedance was 69.9 (14.0) omega. First shock success with the standard protocol was 80.9%, and first or second shock success was 95.2%. The microprocessor controlled current based defibrillator automatically measured transthoracic impedance and calculated the energy required to develop a selected current in each patient. A current protocol of 30 A, 30 A, then 40 A, if required, was used in 29 men and 12 women with 41 episodes of ventricular fibrillation. Transthoracic impedance (mean 65.1 (15.9) omega) was similar to that in the energy protocol group and success rates for first shock (82.9%) and first or second shocks (97.5%) were also similar. The mean delivered energy per shock with the current based defibrillator for first or second shock success was significantly less (144.8 J) with the energy protocol (200 J). The mean peak current of successful shocks was also significantly reduced (29.0 v 31.9 A). A current based defibrillator titrates energy according to transthoracic impedance; it has a success rate comparable to conventional defibrillators but it delivers significantly less energy and current per shock.     

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.     

Initial experience with a microprocessor controlled current based defibrillator

Intramyocardial current flow is a critical factor in successful ventricular defibrillation. The main determinants of intramyocardial current flow during transthoracic countershock are the selected energy and the transthoracic impedance of the patient. To optimise the success of the first shock and to titrate energy dosage according to each patient's transthoracic impedance, a microprocessor controlled current based defibrillator was developed. It was compared with a conventional energy based protocol of 200 J (delivered energy), 200 J, then 360 J if required in 42 consecutive episodes of ventricular fibrillation in 33 men and seven women. The mean (SD) predicted transthoracic impedance was 69.9 (14.0) omega. First shock success with the standard protocol was 80.9%, and first or second shock success was 95.2%. The microprocessor controlled current based defibrillator automatically measured transthoracic impedance and calculated the energy required to develop a selected current in each patient. A current protocol of 30 A, 30 A, then 40 A, if required, was used in 29 men and 12 women with 41 episodes of ventricular fibrillation. Transthoracic impedance (mean 65.1 (15.9) omega) was similar to that in the energy protocol group and success rates for first shock (82.9%) and first or second shocks (97.5%) were also similar. The mean delivered energy per shock with the current based defibrillator for first or second shock success was significantly less (144.8 J) with the energy protocol (200 J). The mean peak current of successful shocks was also significantly reduced (29.0 v 31.9 A). A current based defibrillator titrates energy according to transthoracic impedance; it has a success rate comparable to conventional defibrillators but it delivers significantly less energy and current per shock.     

Determinants of successful transthoracic defibrillation and outcome in ventricular fibrillation.

OBJECTIVE--To examine factors determining defibrillation success and outcome in patients with ventricular fibrillation. DESIGN--Observational prospective study of age, sex, transthoracic impedance, site of cardiac arrest, ventricular fibrillation duration and amplitude, primary or secondary ventricular fibrillation, aetiology, number of shocks to correct ventricular fibrillation, and drug treatment. SETTING--A teaching hospital and a mobile coronary care unit with a physician. PATIENTS--70 consecutive patients (50 male, 20 female) mean age 66.5 years. INTERVENTIONS--Before the first countershock was administered transthoracic impedance using a 30 kHz low amplitude AC current passed through 8 cm/12 cm self-adhesive defibrillator electrode pads applied in the anteroapical position was measured. The first two shocks were 200 J delivered energy (low energy) and further shocks of 360 J (high energy) were given if required. MAIN OUTCOME MEASURES--Countershock success and outcome from ventricular fibrillation. RESULTS AND CONCLUSIONS--First shock success was significantly greater in inhospital arrests (37/53) than in out-of-hospital arrests (5/17) and in those receiving antiarrhythmic treatment (13/15, 86.7%) v (27/51, 52.9%). Transthoracic impedance was similar in those who were successfully defibrillated with one or two 200 J shocks (98.7 (26) omega) and those who required one or more 360 J shocks (91.4 (23) omega). Success rates with two 200 J shocks were similar in those patients with "high" transthoracic impedance (that is, greater than 115 omega) and those with transthoracic impedance (less than or equal to 115 omega) (8/12 (67%) v 44/58 (76%]. Fine ventricular fibrillation was significantly more common in the patients with a transthoracic impedance of greater than 95 omega (41% (13/32] than in those with a transthoracic impedance less than or equal to 95 omega (13% (5/38]. Death during arrest was significantly more common in patients who needed high energy shocks (14/18 (78%] than in those who needed low energy shocks (16/52 (31%]. Multiple regression analysis identified ventricular fibrillation with an amplitude of greater than or equal to 0.5 mV, age less than or equal to 70 years, and arrests that needed less than or equal to two shocks for defibrillation, in rank order as independent predictors of survival to discharge.     

Determinants of successful transthoracic defibrillation and outcome in ventricular fibrillation

OBJECTIVE--To examine factors determining defibrillation success and outcome in patients with ventricular fibrillation. DESIGN--Observational prospective study of age, sex, transthoracic impedance, site of cardiac arrest, ventricular fibrillation duration and amplitude, primary or secondary ventricular fibrillation, aetiology, number of shocks to correct ventricular fibrillation, and drug treatment. SETTING--A teaching hospital and a mobile coronary care unit with a physician. PATIENTS--70 consecutive patients (50 male, 20 female) mean age 66.5 years. INTERVENTIONS--Before the first countershock was administered transthoracic impedance using a 30 kHz low amplitude AC current passed through 8 cm/12 cm self-adhesive defibrillator electrode pads applied in the anteroapical position was measured. The first two shocks were 200 J delivered energy (low energy) and further shocks of 360 J (high energy) were given if required. MAIN OUTCOME MEASURES--Countershock success and outcome from ventricular fibrillation. RESULTS AND CONCLUSIONS--First shock success was significantly greater in inhospital arrests (37/53) than in out-of-hospital arrests (5/17) and in those receiving antiarrhythmic treatment (13/15, 86.7%) v (27/51, 52.9%). Transthoracic impedance was similar in those who were successfully defibrillated with one or two 200 J shocks (98.7 (26) omega) and those who required one or more 360 J shocks (91.4 (23) omega). Success rates with two 200 J shocks were similar in those patients with "high" transthoracic impedance (that is, greater than 115 omega) and those with transthoracic impedance (less than or equal to 115 omega) (8/12 (67%) v 44/58 (76%]. Fine ventricular fibrillation was significantly more common in the patients with a transthoracic impedance of greater than 95 omega (41% (13/32] than in those with a transthoracic impedance less than or equal to 95 omega (13% (5/38]. Death during arrest was significantly more common in patients who needed high energy shocks (14/18 (78%] than in those who needed low energy shocks (16/52 (31%]. Multiple regression analysis identified ventricular fibrillation with an amplitude of greater than or equal to 0.5 mV, age less than or equal to 70 years, and arrests that needed less than or equal to two shocks for defibrillation, in rank order as independent predictors of survival to discharge.     

Self-adhesive preapplied electrode pads for defibrillation and cardioversion

The efficacy of self-adhesive electrode pads for defibrillation and cardioversion was assessed in 80 patients who received 267 shocks from self-adhesive pads. In all but two patients, defibrillation or cardioversion was achieved at least once. The pads were equally effective when used in the apex-anterior or apex-posterior position. The transthoracic impedance using self-adhesive pads was 75 +/- 21 ohms (mean +/- standard deviation), which is similar to previously reported transthoracic impedance in defibrillation, using standard hand-held electrode paddles of 67 +/- 36 ohms. It is concluded that self-adhesive electrode pads are effective for defibrillation and cardioversion.     

Automated impedance-based energy adjustment for defibrillation: experimental studies

In defibrillation, current flow depends on the energy selected and the transthoracic impedance. If transthoracic impedance is high, current flow may be inadequate to defibrillate. We developed a method by which high transthoracic impedance is automatically compensated for by an increase in operator-selected energy when impedance is high. Transthoracic impedance was predicted in advance of the first shock by passing a low-level current between the defibrillator electrodes during the defibrillator charge cycle; a microprocessor monitored current flow and determined impedance. In 28 mongrel dogs we manipulated transthoracic impedance by placing glycerin-soaked gauze pads between the paddle electrodes and the chest. If the predicted impedance exceeded a preset value, the delivered energy was automatically increased by 40% or 100%. Using this impedance-based energy adjustment technique, we found significant improvements in current flow and success rate of shocks when energy was automatically increased to compensate for high transthoracic impedance. The use of transthoracic impedance as a basis for energy adjustment appears a promising technique to minimize the hazards of high electrical energy; it allows low-energy shocks in most patients while avoiding inappropriate low energies in patients with high impedance. Clinical trials are justified.     

Evaluation of a new defibrillation pathway--the tongue-epigastric route. I. Experimental studies in dogs

The purpose of this study was to determine the efficacy of a tongue-epigastric defibrillation route in anesthetized dogs. Ventricular fibrillation was induced by rectangular pulses passed down a transvenous catheter into the right ventricle. Three groups of dogs were studied. Group I (15 dogs) received shocks from a 12 cm2 tongue electrode, a 50 cm2 circular, gelled self-adhesive electrode pad placed on the epigastrium and standard transthoracic defibrillator paddle electrodes. Shocks were given at energy levels of 50 to 460 joules (delivered energy, 50 ohm resistance). The success of the tongue-epigastric shocks in achieving defibrillation, and the resistance and current flow were determined at each energy level and compared with the same energy shocks from the standard transthoracic electrodes. In Group II (five dogs), comparisons were made between the 12 cm2 tongue electrode used in the first group of dogs and a larger tongue electrode of 40 cm2. In Group III (five dogs), intracardiac current flow (potential gradient) with tongue-epigastric and standard transthoracic electrodes was studied. In Group I, defibrillation success with the tongue-epigastric electrodes ranged from no success at 50 to 100 joules to 83% success at 460 joules. With standard transthoracic electrodes, success rates ranged from 65% at 50 joules to 100% at 300 joules. At all energies tested, the resistance was significantly higher and current significantly lower using tongue-epigastric compared with transthoracic electrodes. The higher tongue-epigastric resistance is probably related to the longer interelectrode distance; the correlation between interelectrode distance (x, in centimeters) and resistance (y, in ohms) in these dogs was y = 2.2x + 29.6, r = 0.78.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy of nifekalant hydrochloride in the treatment of fatal ventricular arrhythmia in patients with ischemic heart disease

Ventricular tachycardia (VT), which causes hemodynamic instability, and ventricular fibrillation (VF) sometimes occur in patients with severe underlying cardiovascular disease such as myocardial ischemia or infarction, and are associated with high mortality. This report presents the efficacy of nifekalant hydrochloride (nifekalant), a pure class III antiarrhythmic agent, in treating life-threatening ventricular arrhythmia in such patients. From June 2000, when nifekalant became commercially available in Japan, to May 2003, 30 ischemic heart disease (IHD) patients with VT/VF resistant to direct-current (DC) countershock received nifekalant in our hospital. These 30 patients served as the nifekalant group in this study. As a control group, we also included 33 IHD patients with VT/VF that had been resistant to DC countershock upon or during hospitalization between January 1996 and May 2000 before nifekalant became commercially available. No significant differences were observed in patient background factors and treatments between the two groups. The rates of death within 48 hours of occurrence of VT/VF were significantly lower in the nifekalant group (7%, 2/30) than in the control group (27%, 9/33; P < 0.03). The rates of cardiac death during hospitalization were also significantly lower in the nifekalant group (40%, 12/30) than in the control group (67%, 22/33; P < 0.03). The rates of survival until hospital discharge were significantly higher in the nifekalant group (57%, 17/30) than in the control group (30%, 10/33; P < 0.03). Multivariate analysis of all 63 patients revealed nifekalant administration was the factor that significantly improved the mortality (odds ratio for cardiac death, 0.26; 95% confidence interval (CI), 0.07 to 0.95; P = 0.041). Nifekalant improves the prognosis for life-threatening ventricular arrhythmia in IHD patients.     

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.     

Disposable defibrillator electrodes

The transthoracic impedance to direct-current defibrillation discharge of the half-sinusoidal waveform was compared using recently marketed disposable defibrillator electrode pads (SAF-D-FIB and DEFIB-PADS) with electrode paste as the interfaces between the defibrillator paddle electrode and chest wall. Twenty-four mongrel dogs with an average weight of 17.3 kilograms were used. Half were shocked with the defibrillator meter setting at 100 watt-seconds (mean delivered energy, 59 watt-seconds) and half at 400 watt-seconds (mean delivered energy, 205 watt-seconds). Each animal received six shocks with both paste and one of the sets of disposable pads. The sequence of shocks was changed in alternate animals. At a meter setting of 100 watt-seconds, the mean impedance using SAF-D-FIB was 59 +/- 6 ohms compared to 46 +/- 6 ohms with paste (p less than 0.001), while that encountered with DEFIB-PADS was 57 +/- 5 ohms compared to 50 +/- 5 ohms with paste (p less than 0.01). At settings of 400 watt-seconds, the impedances encountered were also significantly higher with the disposable electrode (p less than 0.01). The output of many defibrillators in use today is inadequate for consistent defibrillation of adult patients weighing more than 50 to 80 kilograms. Since a minimal peak current per unit of body weight is required for ventricular defibrillation and since a higher transthoracic impedance results in a lower delivered peak current, one should use the paddle electrode-chest wall interface that results in the lowest impedance to defibrillator discharge. The impedance encountered with disposable electrodes is significantly higher than that encountered with electrode paste. Therefore, we do not recommend the use of these disposable electrodes for defibrillation or elective cardioversion.     

Precountershock cardiopulmonary resuscitation improves ventricular fibrillation median frequency and myocardial readiness for successful defibrillation from prolonged ventricular fibrillation: a randomized,controlled swine study

STUDY OBJECTIVE: After prolonged ventricular fibrillation (VF), precountershock cardiopulmonary resuscitation (CPR) will improve myocardial "readiness" for defibrillation compared with immediate defibrillation. METHODS: After 10 minutes of untreated VF, 32 swine (27+/-1 kg) were randomly assigned to receive immediate countershocks (DEFIB), CPR for 3 minutes followed by countershocks (CPR), or CPR for 3 minutes plus intravenous epinephrine followed by countershocks (CPR+EPI). VF waveform was evaluated by fast Fourier transformation. RESULTS: VF amplitude and median frequency by fast Fourier transformation decreased during the untreated VF interval in all groups, and the median frequency subsequently increased during each minute of precountershock CPR. Although the VF median frequency in the 3 groups did not differ after 10 minutes of untreated VF (8.9+/-0.8 Hz versus 8.4+/-0.5 Hz versus 7.3+/-0.5 Hz, respectively), immediately before the first shock the VF median frequency was much lower in the DEFIB group than in either the CPR or CPR+EPI groups (8.9+/-0.8 Hz versus 13.1+/-0.8 Hz versus 13.8+/-0.9 Hz, respectively; P <.01). None of the 10 animals in the DEFIB group attained return of spontaneous circulation after the first set of shocks versus 5 of 10 animals in the CPR group and 6 of 12 animals in the CPR+EPI group (DEFIB versus each CPR group; P <.05). Cardiac output 1 hour after resuscitation was substantially worse in the DEFIB group than in the CPR or CPR+EPI groups (74+/-7 mL/kg per minute versus 119+/-7 mL/kg per minute versus 104+/-15 mL/kg per minute; P <.05). CONCLUSION: Precountershock CPR can result in substantial physiologic benefits compared with immediate defibrillation in the setting of prolonged VF. Moreover, these benefits can be attained with or without the addition of intravenous epinephrine.     

Transthoracic impedance to defibrillator discharge. Effect of electrode size and electrode-chest wall interface

Transthoracic impedance of man to direct current defibrillator discharge has been reported to vary from 27 to 110 ohms. This study was designed to determine the effect of paddle electrode size and paddle electrode-chest wall interface on transthoracic impedance. Paddle electrode diameters studied were 4.5, 8.0, and 12.8 cm. There was a progressive decrease in impedance with increasing paddle electrode size. Paddle electrode-chest wall interfaces used were none, electrode cream, saline-soaked gauze pads, and electrode paste. The transthoracic impedance was progressively decreased with these interfaces regardless of paddle electrode size.This study suggests that when using direct current defibrillators or cardioverters, large paddle electrodes should be used with electrode paste as interface to accomplish maximum reduction in transthoracic impedance.     

Self-adhesive monitor/defibrillation pads improve prehospital defibrillation success

We compared self-adhesive, dual-function monitor/defibrillation electrode pads to standard chest monitoring leads and hand-held electrode paddles in the management of prehospital ventricular fibrillation in a single urban paramedic service. Shocks were delivered more quickly following paramedic arrival with self-adhesive pads than with hand-held paddles (1.6 vs 2.5 min; P less than .001). Ventricular fibrillation was terminated more frequently when shocks were delivered using the self-adhesive pads (55 of 58 patients, 95%) than when shocks were delivered using hand-held paddles (49 of 69 patients, 71%; P less than .005). Initial shocks delivered with self-adhesive pads were especially effective, converting 40 of 58 (69%) patients to an organized rhythm on the first or second shock; this was true of only 24 of 69 (35%) patients shocked with hand-held paddles (P less than .001). Patient survival to hospital admission improved when self-adhesive pads were used: 30 of the 58 (52%) patients shocked with self-adhesive pads achieved hospital admission, while only 21 of 69 patients (30%; P less than .025) survived to admission when hand-held paddles were used. In addition, electrical artifact that interfered with accurate rhythm interpretation was far more prevalent when standard monitoring electrodes were used, including artifact that resulted in inappropriate shock delivery (23% of patients monitored with standard electrodes vs 3% of patients monitored with self-adhesive pads; P less than .005). Self-adhesive monitor/defibrillation pads are superior to standard monitoring leads and hand-held electrode paddles in the management of prehospital ventricular fibrillation.     

Role of a catheter lead system for transvenous countershock and pacing during electrophysiologic tests: an assessment of the usefulness of catheter shocks for terminating ventricular tachyarrhythmias

The practicality and safety of using a single catheter system for transvenous countershock, programmed stimulation and ventricular pacing during electrophysiologic tests were evaluated in 13 patients with inducible sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). The efficacy and patient toleration of transvenous countershock were compared with other methods of arrhythmia termination. The same lead was used for programmed stimulation at the right ventricular apex and for VT termination by pacing methods during serial testing (20 ± 15 days [mean ± standard deviation]). Synchronized countershock using energies that patients found tolerable (0.01 to 5 J) terminated 31 of 50 episodes (62%) of induced VT. Episodes of VT cardioverted with these low energies were distinguished from other episodes by a longer cycle length (352 ± 62 ms versus 297 ± 50 ms, p < 0.004). Among paired episodes of VT matched for patient, date of induction, morphologic characteristics, cycle length and drugs administered, pacing methods (single extrastimuli and bursts of rapid pacing) were just as effective as low-energy countershock for VT termination (25 of 25 versus 21 of 25, difference not significant). Transvenous countershock was uniformly effective for termination of ventricular flutter and VF when sufficient energy was used (range 5 to 30 J, mean 20.4 ± 7.7). This required interfacing leads to a defibrillation unit. VT acceleration occurred during 7 of 50 synchronized low-energy cardioversion attempts (14%). There was no evidence of myocardial injury as a result of shocks as high as 30 J, but patients required increasing sedation when energy exceeded 0.5 J.Thus, a single catheter system can be used for programmed stimulation, ventricular pacing and countershock during electrophysiologic tests. Low-energy countershock (0.01 to 5 J) is no more effective than pacing methods for VT termination and is tolerated less well. The most practical use of this catheter system, including any implantable unit, may be for slightly higher energy (5 to 30 J) countershock termination of repeated episodes of very rapid VT or VF, in which pacing techniques are ineffective. This method may be safer and less traumatic than conventional transthoracic countershock.     

Evaluation of a new defibrillation pathway: tongue-epigastric/tongue-apex route. II. Impedance characteristics in human subjects

An automated device for defibrillation using a vertical shock pathway (tongue-epigastric or tongue-apex) has been developed. The energy requirements for defibrillation using vertical pathways are uncertain and will be determined largely by the impedance of the pathway. The purpose of this study was to determine the impedance characteristics of vertical defibrillation pathways in human subjects. Twenty patients undergoing elective cardioversion of atrial fibrillation or atrial flutter, or both, were studied. Patients received shocks from electrodes placed in tongue-epigastric or tongue-cardiac apex positions. The tongue electrode was a 12 cm2 metal plate fixed to a standard plastic oropharyngeal airway. The epigastric or cardiac apex electrode was a 40 cm2 self-adhesive pad. The electrodes were connected to a standard damped-sinusoidal waveform defibrillator. It was found that the two vertical shock pathways had substantially higher impedance than the standard transthoracic pathway: tongue-epigastric pathway 130 +/- 11 omega (SD), tongue-apex pathway 115 +/- 12 omega, transthoracic pathway 68 +/- 11 omega (p less than 0.05). The higher impedance is probably due to the longer interelectrode distances of vertical pathways: tongue-epigastric 33 +/- 3 cm, tongue-apex 28 +/- 3 cm, transthoracic 23 +/- 3 cm (p less than 0.05). Vertical pathway shocks were successful in the cardioversion of 15 of 20 patients. Four of the five patients in whom vertical shocks were unsuccessful subsequently underwent successful cardioversion by transthoracic shocks; the transthoracic shocks achieved a higher current because of lower impedance of the transthoracic route.(ABSTRACT TRUNCATED AT 250 WORDS)     

Predictive indices of successful cardiac resuscitation after prolonged arrest and experimental cardiopulmonary resuscitation

To determine if clinically accessible hemodynamic and blood gas measurements are of value in predicting outcome of countershock after prolonged ventricular fibrillation (VF) and artificial cardiopulmonary support, 14 dogs were studied during 30 minutes of VF using two randomly assigned closed-chest techniques. Seven dogs underwent conventional CPR; the other seven were supported with a pneumatic thoracic vest and abdominal binder, which were inflated synchronously with the airway. Ascending aortic (Ao), right atrial (RA), and instantaneous coronary perfusion pressures (Ao - RA) were measured at five-minute intervals. Ao and RA blood samples were analyzed at 10, 20, 25 and 30 minutes for PO2, PCO2, and pH. After 25 minutes, 1 mg epinephrine was given intravenously, and five minutes later defibrillation was attempted. If unsuccessful, repeated countershocks, conventional pharmacologic therapy, and artificial support were continued. If a perfusing spontaneous cardiac rhythm did not result within an additional 30 minutes, the experiment was terminated. Six animals developed a perfusing cardiac rhythm after one or more countershocks (Group 1); eight failed to develop a perfusing rhythm after repeated countershocks and an additional 30 minutes of resuscitative effort (Group 2). Five Group 1 dogs received vest/binder artificial support. When measured values were averaged over the study period, Group 1 was found to have a significantly greater Ao end-diastolic pressure (AoEDP) and peak diastolic coronary perfusion pressure (CPP) when compared to Group 2 (23 +/- 6 vs 14 +/- 8 mm Hg, P less than .05; and 22 +/- 6 vs 5 +/- 10 mm Hg, P less than .01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Significance of lung resistance-related protein in the clinical outcome of acute leukaemic patients with reference to P-glycoprotein

Lung resistance-related protein (LRP) overexpression in leukaemic blast cells from acute leukaemia patients and the effect of LRP or P-glycoprotein (P-gp) on the clinical outcome of acute leukaemia were investigated individually by dividing patients into four groups. The complete remission rate of group I (LRP and P-gp both negative) was 81.7%, group II (only LRP positive) 87.5%, group III (only P-gp positive) 87.1% and group IV (LRP and P-gp both positive) 40.0%. There were no statistical differences between group I and groups II or III, but a significant difference was observed between groups I, II or III and group IV. Median overall survival in group IV was significantly shorter (4.6 months) than in groups I, II or III, although no significant differences were observed between group I and groups II or III (18.9, 20.5 and 31.8 months). There was a tendency for disease-free survival in group III to be longer than that in groups I, II or IV. The reasons for these findings are discussed. Our present results indicate that the co-existence of LRP and P-gp strongly influenced the effectiveness of induction chemotherapy and long-term prognosis, whereas the isolated presence of LRP or P-gp did not.