Computerized medical records in the Department of Veterans Affairs.

The VA Medical Center in Washington, DC, was the nexus for a number of computerization projects that were initiated by the Department of Veterans Affairs. The culmination of these initiatives is a software package that presents the complete electronic patient record in an easy-to-use graphic user interface. This record combines text data from the legacy data base, diagnostic images from patient procedures, electrocardiograms from a commercial server, an Internet connection, and a hospital web site with pertinent reference information. The information is available in over 1000 places in the hospital and can be accessed remotely using a remote access server. The computerization of the medical record has improved hospital efficiency, has made physician access to patient information more reliable, has opened new opportunities for patient education, and has given healthcare providers more time to care for patients.

Smoking and obesity are associated with the progression of aortic stenosis.

OBJECTIVE: The purpose of the study was to identify clinical predictors of progression of aortic stenosis. BACKGROUND: The natural history of valvular aortic stenosis includes a latency period followed by an unpredictable progression. Recent investigations have shown an association between risk factors for atherosclerosis and the presence of aortic stenosis. The authors hypothesized that atherosclerosis risk factors are also associated with the progression of aortic stenosis. METHODS: In a retrospective study, patients with a diagnosis of aortic stenosis were identified by continuous wave Doppler and a follow-up study of at least 6 months. Clinical data at the time of the index echocardiogram were obtained from review of patients' medical records. Independent risk factors for the progression of aortic stenosis were identified by stepwise logistic regression analysis. RESULTS: One hundred twenty-three patients were identified, and complete data were obtained for 87 patients (mean age, 70.7 +/- 10 years; men, 81%; mean follow-up, 2.54 +/- 1.6 years). The initial gradient was mild in 61% of patients and moderate in 31%. The mean rate of progression was 6.3 +/- 13 mm Hg/year. Mild aortic stenosis in 36% of patients at the time of the index echocardiogram progressed to moderate or severe over an average of 2.9 +/- 2.0 years. Independent clinical factors associated with a progression of 5 mm Hg/year or greater included a history of smoking (relative risk [RR] = 3.06; 95% confidence interval [CI] = 1.09-8.61; p = 0.034) and body mass index (RR = 1.16; 95% CI = 1.03-1.30; p = 0.013). Hypertension, diabetes, cholesterol, age, gender, and coronary artery disease were not independently associated with progression. CONCLUSIONS: Body mass index and a history of smoking are independent predictors of significant progression of aortic stenosis, defined as > 5 mm Hg/year. The rate of progression of aortic stenosis is variable. However, a substantial number of patients have progression of even initially mild aortic stenosis within a relatively short period of time. The effect of controlling atherosclerosis risk factors on the rate of progression of aortic stenosis remains to be determined.

Severity of coronary artery disease in black and white male veterans and likelihood of revascularization.

BACKGROUND: Many reports in the literature have found the use of invasive cardiac procedures in black patients to be less common than in white patients. These reports tend to have small numbers of black patients compared with white patients or rely on the information contained in claims or administrative data. METHODS AND RESULTS: Cardiac catheterization reports were reviewed in a Veterans Administration hospital that serves a large number of black patients. After review of the medical histories and hemodynamic and angiographic findings in 726 black and 734 white male veterans, data were collected to determine recommended and actual therapy. Death was assessed after a 4- to 10-year follow-up period. White patients were more likely to have significant coronary artery lesions than black patients. Multivariate analysis showed that the likelihood of patients actually having percutaneous transluminal coronary angioplasty or coronary artery bypass surgery did not differ by ethnicity when controlling for disease extent or severity. Coronary artery bypass surgery was associated with decreased mortality rates for both black and white patients. Although short-term death in blacks was not different from whites, blacks had an increased long-term risk for death. CONCLUSIONS: After coronary angiography, black veterans and white veterans appear to undergo revascularization procedures related to the severity of disease. The decreased long-term life expectancy of black men as compared with whites is not necessarily explained by the presence of or treatment for coronary artery disease in this population.

High dispersion of ventricular repolarization after an implantable defibrillator shock predicts induction of ventricular fibrillation as well as unsuccessful defibrillation.

OBJECTIVES: To test the hypothesis that post-shock dispersion of repolarization (PSDR) is higher in T wave shocks that induce ventricular fibrillation (VF) than in those that do not, as well as in implantable cardioverter defibrillator (ICD) defibrillation shocks which fail to terminate VF when compared with those that are successful. BACKGROUND: Ventricular fibrillation has been linked to the presence of dispersion of repolarization, which facilitates reentry. Most of the studies have been done in animals, and the mechanism underlying the generation and termination of VF in humans is speculative and remains to be determined. METHODS: Monophasic action potentials (MAPs) were recorded simultaneously from the right ventricular outflow tract (RVOT) and the right ventricular apex (RVA) in 27 patients who underwent implantation and testing of an ICD. T wave shocks were used to induce VF while the termination was attempted using internal defibrillator shocks. The post-shock repolarization time (PSRT) was measured in both the RVA and RVOT MAPs, and the difference between the two recordings was defined as the PSDR. The averages of PSDR were compared between the successful and unsuccessful inductions and terminations of VF. RESULTS: T wave shocks that induced VF generated a greater PSDR (93.4 +/- 85.1 ms) than the unsuccessful ones (45.1 +/- 55.9 ms, p < 0.001). On the other hand, shocks that failed to terminate VF were associated with a greater PSDR (59.9 +/- 41.2 ms) than shocks that terminated VF (21.1 +/- 20.1 ms), p < 0.001. CONCLUSIONS: A high PSDR following a T wave shock is associated with induction of VF; while following a defibrillating shock, it is associated with its failure and the continuation of VF. Conversely, a low PSDR is associated with failure of a T wave shock to induce VF and successful termination of VF by a defibrillating shock.

Class III drugs and congestive heart failure: focus on the congestive heart failure-survival trial of antiarrhythmic therapy.

Patients with congestive heart failure frequently have ventricular arrhythmias on ambulatory electrocardiographic recordings and sudden cardiac death is seen in almost 50% of such patients. Many antiarrhythmic agents have been approved to suppress the arrhythmia in an effort to improve survival. Some sodium-channel blockers not only failed to improve survival but have been shown to be harmful. This led to the development of potassium-channel blockers, such as d-sotalol, amiodarone, dofetilide, and azimilide. d-Sotalol was associated with excess mortality in patients with left ventricular dysfunction; amiodarone seems to be potentially beneficial; and dofetilide has a neutral effect on mortality. The Sudden Cardiac Death Heart Failure Trial (SCD HEFT) is testing the implantable cardioverter defibrillator (ICD) against amiodarone and placebo. The ICDs appear to be superior to antiarrhythmic drugs in certain high-risk patients, although not proved in unstratified patients with heart failure.

Effects of amiodarone on tumor necrosis factor-alpha levels in congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy.

Tumor necrosis factor-alpha (TNF-alpha) has been implicated in the pathogenesis of congestive heart failure and may be associated with an increase in mortality. A recent in vitro study showed that amiodarone decreases TNF-alpha production by human blood mononuclear cells in response to lipopolysaccharide. However, no previous clinical studies have determined the effect of chronic amiodarone therapy on TNF-alpha levels. Thus, the purpose of this study was to determine whether amiodarone affects TNF-alpha levels in patients with ischemic and nonischemic cardiomyopathy. TNF-alpha levels were analyzed by an enzyme-linked immunoassay using plasma samples at baseline, 1, and 2 years of follow-up in New York Heart Association class III patients (n = 40 in each of the placebo and amiodarone groups, mean ejection fraction 0.25+/-0.09) who were randomized in the Congestive Heart Failure-Survival Trial of Antiarrhythmic Therapy, a multicenter, double-blind, placebo-controlled study in which the effect of amiodarone on survival was investigated. TNF-alpha levels were elevated in both groups of patients at baseline, 6.6+/-3.1 and 7.7+/-5.3 pg/ml in the amiodarone and placebo groups, respectively (p = 0.3). There were no significant differences in demographic or clinical variables between the 2 groups. Amiodarone treatment was associated with a significant increase in TNF-alpha levels in patients with ischemic cardiomyopathy, 12.7+/-12.5 and 6.8+/-3.7 pg/ml in the amiodarone and placebo groups, respectively (p = 0.03) at 1 year. No change in TNF-alpha levels was observed in patients with nonischemic cardiomyopathy. In contrast to the in vitro data, amiodarone treatment is associated with an increase in TNF-alpha levels in patients with ischemic cardiomyopathy. This increase is not associated with an adverse effect on survival.

Prevalence and significance of nonsustained ventricular tachycardia in patients with premature ventricular contractions and heart failure treated with vasodilator therapy. Department of Veterans Affairs CHF STAT Investigators.

OBJECTIVES: This study sought to determine the prevalence and significance of nonsustained ventricular tachycardia (NSVT) in patients with premature ventricular contractions (PVCs) and heart failure treated with vasodilator therapy. BACKGROUND: Heart failure patients with ventricular arrhythmia and NSVT have a significantly increased risk of premature cardiac death. Recently there has been the question of whether these arrhythmias are expressions of a severely compromised ventricle or are they independent risk factors. We, therefore, determined the prevalence and significance of NSVT in patients with PVCs and heart failure and on vasodilator therapy. METHODS: Twenty-four hour ambulatory recordings were done at randomization, at 2 weeks, at months 1, 3, 6, 9 and 12 and then every 6 months in 674 patients with heart failure and on vasodilator therapy. The median period of follow-up was 45 months (range 0 to 54). RESULTS: Nonsustained ventricular tachycardia was present in 80% of all patients. Patients without (group 1) and with (group 2) NSVT were balanced for variables: age, etiology of heart disease, New York Heart Association (NYHA) functional class, use of amiodarone and diuretics and left ventricular diameter by echocardiogram. However, group 1 patients had significantly less beta-adrenergic blocking agent use and higher ejection fraction (EF) (p < 0.002 and p < 0.001, respectively). Survival analysis for all deaths showed a greater risk of death among group 2 patients (p=0.01). Similarly, sudden death was increased in group 2 patients (p=0.02, risk ratio 1.8). After adjusting for the above variables, only EF (p=0.001) and NYHA class (p=0.01) were shown to be independent predictors of survival. Nonsustained ventricular tachycardia showed a trend (p=0.07) as an independent predictor for all-cause mortality but not for sudden death. Only EF was an independent predictor for sudden death. CONCLUSIONS: Nonsustained ventricular tachycardia is frequently seen in patients with heart failure and may be associated with worsened survival by univariate analysis. However, after adjusting other variables, especially for EF, NSVT was not an independent predictor of all-cause mortality or sudden death. These results have serious implications in that suppression of these arrhythmias may not improve survival.

Effects of moderate intensity exercise on serum lipids in African-American men with severe systemic hypertension.

The prevalence of systemic hypertension and its cardiovascular consequences is higher in African-Americans than in whites. Low to moderate intensity aerobic exercise lowers blood pressure (BP) in African-American patients with severe hypertension. It is not known whether such exercise can improve lipid metabolism in these patients. Thirty-six African-American men with established essential hypertension, aged 35 to 76 years, were randomly assigned to an exercise (n = 17) or no exercise (n = 19) group. The exercise group exercised for 16 weeks, 3 times/week, at 60% to 80% of maximum heart rate. After 16 weeks, peak oxygen uptake in the exercise group improved (21+/-4 vs 23+/-3 ml/kg/min; p <0.001). Body weight did not change. Exercise intensity correlated with high-density lipoprotein (HDL) cholesterol changes from baseline to 16 weeks (r = 0.65; p <0.01) and was the strongest predictor of these changes (R2 = 0.4; p = 0.009). Lipoprotein-lipid changes in the 2 randomized groups did not differ significantly. A 10% increase in HDL cholesterol--42+/-19 versus 46+/-19 mg/dl; p = 0.003--noted in 10 patients who exercised > or = 75% of maximal heart rate suggested the existence of an exercise intensity threshold. Thus low to moderate intensity aerobic exercise may not be adequate to modify lipid profiles favorably in patients with severe hypertension. However, substantial changes in HDL cholesterol were noted in patients exercising at intensities > or = 75% of age-predicted maximum heart rate, suggesting an exercise-intensity threshold.

Value of the electrocardiogram in determining cardiac events and mortality in myotonic dystrophy.

Electrocardiograms were recorded at baseline and regular intervals in 53 patients with myotonic dystrophy who were followed for a mean of 6.3 +/- 4.0 years. Patients with cardiac events had a significantly prolonged PR interval (p <0.001), a later age of onset of neuromuscular symptoms (p <0.05), and were older (p <0.005).

Pulmonary effect of amiodarone in patients with heart failure. The Congestive Heart Failure-Survival Trial of Antiarrhythmic Therapy (CHF-STAT) Investigators (Veterans Affairs Cooperative Study No. 320).

OBJECTIVES: The purpose of this study was to evaluate the pulmonary effects of amiodarone in patients with heart failure, in those with chronic obstructive pulmonary disease (COPD) and in those undergoing a surgical procedure. BACKGROUND: Amiodarone has been known to cause pulmonary complications; especially in those with COPD and in those undergoing a surgical procedure. METHODS: Patients receiving vasodilator therapy for congestive heart failure were prospectively randomized to placebo or amiodarone at 800 mg/day for 14 days, 400 mg/day for 50 weeks and then 300 mg/day thereafter. Chest X-ray film and pulmonary function tests with diffuse capacity of carbon monoxide (DLCO) were obtained at baseline and annually. The power to detect a 20% difference in DLCO at 1 year exceeded 90% in all patients and in those with COPD (two-sided alpha = 0.05). The sample allowed a 75% power to detect pulmonary complications (1% vs. 5%) between the two treatment groups. RESULTS: There was no difference in baseline characteristics between patients randomized to amiodarone (n = 269) or placebo (n = 250). The DLCO measurements at randomization were 18.3 +/- 6.9 and 17.7 +/- 7.6 ml/min per mm Hg for the amiodarone and placebo groups, respectively (p = 0.3). At 1 and 2 years, DLCO measurements were 17.7 +/- 7.0 and 18.3 +/- 7.7 ml/min per mm Hg for the amiodarone group and 17.9 +/- 7.2 and 18.2 +/- 7.2 for the placebo group, respectively. There were no significant differences between the groups, with corresponding p values of 0.73 ad 0.96 at years 1 and 2, respectively. Among patients with COPD, DLCO measurements at randomization were 17.9 +/- 6.7 and 15.8 +/- 6.8 ml/min per mm Hg for the amiodarone and placebo groups, respectively. At years 1 and 2, DLCO measurements were 16.6 +/- 7.8 and 17.8 +/- 9.5 ml/min per mm Hg for the amiodarone group and 16.5 +/- 6.6 and 16.3 +/- 7.0 ml/min per mm Hg for the placebo group, with corresponding p values of 0.95 and 0.48, respectively. There was no difference in survival free of noncardiac or perioperative deaths between patients assigned to amiodarone or placebo. Pulmonary fibrosis was diagnosed in four patients (1.1%) treated with amiodarone and in three patients (0.8%) receiving placebo. CONCLUSIONS: Our study shows that amiodarone can be safely used, with an acceptable pulmonary toxicity, in patients with heart failure.

Effects of amiodarone on the circadian pattern of sudden cardiac death (Department of Veterans Affairs Congestive Heart Failure-Survival Trial of Antiarrhythmic Therapy).

Some antiarrhythmic drugs have been shown to influence the circadian pattern of sudden cardiac death (SCD). The effect of chronic amiodarone therapy on this pattern is unknown. This study determines the circadian pattern of deaths in the Congestive Heart Failure-Survival Trial of Antiarrhythmic Therapy (CHF-STAT) and compares the distribution of SCD between the amiodarone and the placebo arms of the trial. CHF-STAT was a multicenter trial that determined whether amiodarone reduces mortality in patients with heart failure and asymptomatic ventricular arrhythmias. The time of death was retrospectively analyzed in patients who died from pump failure and SCD. In patients who died suddenly, the circadian pattern of deaths was compared between patients receiving amiodarone and those receiving placebo. In CHF-STAT, 274 patients died during follow-up. The time of death was available in 65 of the 74 patients who died from pump failure, and in 96 of the 139 patients who died suddenly. There was a circadian variation of all SCDs compared with other deaths with a distinct peak during the morning (p = 0.04). A similar morning peak of sudden cardiac death was found in both the amiodarone (n = 42) and the placebo (n = 54) groups, and the overall circadian pattern did not differ between them (p = 0.16). In contrast, death from pump failure occurred equally distributed over time. Thus, SCD occurs predominantly during the morning, whereas death from heart failure does not exhibit a morning peak. Amiodarone does not influence the circadian pattern of SCD.

Effects of aerobic training on exaggerated blood pressure response to exercise in African-Americans with severe systemic hypertension treated with indapamide +/- verapamil +/- enalapril.

Hypertensive patients are likely to have an exaggerated blood pressure (BP) response during physical exertion. When moderate aerobic exercise was added to medical antihypertensive therapy in patients with severe hypertension, excessive elevations in BP during physical exertion were attenuated even with a modest reduction in BP at rest.

A second defibrillator chest patch electrode will increase implantation rates for nonthoracotomy defibrillators.

Nonthoracotomy defibrillator systems can be implanted with a lower morbidity and mortality, compared to epicardial systems. However, implantation may be unsuccessful in up to 15% of patients, using a monophasic waveform. It was the purpose of this study to prospectively examine the efficacy of a second chest patch electrode in a nonthoracotomy defibrillator system. Fourteen patients (mean age 62 +/- 11 years, ejection fraction = 0.29 +/- 0.12) with elevated defibrillation thresholds, defined as > or = 24 J, were studied. The initial lead system consisted of a right ventricular electrode (cathode), a left innominate vein, and subscapular chest patch electrode (anodes). If the initial defibrillation threshold was > or = 24 J, a second chest patch electrode was added. This was placed subcutaneously in the anterior chest (8 cases), or submuscularly in the subscapular space (6 cases). This resulted in a decrease in the system impedance at the defibrillation threshold, from 72.3 +/- 13.3 omega to 52.2 +/- 8.6 omega. Additionally, the defibrillation threshold decreased from > or = 24 J, with a single patch, to 16.6 +/- 2.8 J with two patches. These changes were associated with successful implantation of a nonthoracotomy defibrillator system in all cases. In conclusion, the addition of a second chest patch electrode (using a subscapular approach) will result in lower defibrillation thresholds in patients with high defibrillation thresholds, and will subsequently increase implantation rates for nonthoracotomy defibrillators.

Effect of amiodarone on clinical status and left ventricular function in patients with congestive heart failure. CHF-STAT Investigators.

BACKGROUND: Although trials of amiodarone therapy in patients with congestive heart failure have produced discordant results with regard to effects on survival, most studies have reported a significant rise in left ventricular ejection fraction during long-term therapy. In the present study, we determined whether this increase in ejection fraction is associated with an improvement in the symptoms and/or physical findings of heart failure or a reduction in the number of hospitalizations for heart failure. METHODS AND RESULTS: In the Department of Veterans Affairs cooperative study of amiodarone in congestive heart failure, 674 patients with New York Heart Association class II through IV symptoms and ejection fractions of < or = 40% were treated with amiodarone or placebo for a median of 45 months in a randomized, double-blind, placebo-controlled protocol. Clinical assessments and radionuclide ejection fraction were performed at baseline and after 6, 12, and 24 months. Compared with the placebo group, ejection fraction increased more in the amiodarone group at each time point (8.1 +/- 10.2% [mean +/- SD] versus 2.6 +/- 7.9% at 6 months, 8.0 +/- 10.9% versus 2.7 +/- 8.0% at 12 months, and 8.8 +/- 10.1% versus 1.9 +/- 9.4% after 24 months, all P < .001). However, this difference was not associated with greater clinical improvement, lesser diuretic requirements, or fewer hospitalizations for heart failure (11.1% for amiodarone and 13.6% for placebo group; overall relative risk in the amiodarone group, 0.81 [95% CI, 0.56 to 1.10], P = .18). Of note is the trend toward a reduction in the combined end point of hospitalizations and cardiac deaths (relative risk, 0.82 [CI, 0.65 to 1.03], P = .08), which was significant in patients with nonischemic etiology (relative risk, 0.56 [CI, 0.36 to 0.87], P = .01) and absent in the ischemic group (relative risk, 0.95). CONCLUSIONS: Although amiodarone therapy resulted in a substantial increase in left ventricular ejection fraction in patients with congestive heart failure, this was not associated with clinical benefit in the population as a whole. The substantial reduction in the combined end point of cardiac death plus hospitalizations for heart failure in the nonischemic group suggests possible benefit in these patients.

Regional cardiac compression due to a large anaerobic bacterial empyema.

Compression of the heart outside the pericardial sac is a rare cause of hemodynamic compromise and cardiac tamponade. We report an atypical case of regional cardiac compression caused by a large loculated anaerobic bacterial empyema.

Thermistor guided radiofrequency ablation of atrial insertion sites in patients with accessory pathways.

Radiofrequency ablation has gained acceptance in the treatment of patients with symptomatic Wolff-Parkinson-White syndrome. The purpose of this study was to characterize the relation between temperature and other electroconductive parameters in patients undergoing atrial insertion accessory pathway ablation utilizing a thermistor equipped catheter. The mean temperature and power at sites of atrial insertion ablation are lower than has been previously associated with creation of radiofrequency lesions in the ventricle. While high cavitary blood flow in the atrium may result in cooling, the thinner atrial tissue may require less energy to achieve adequate heating than ventricular myocardium.

Amiodarone in patients with congestive heart failure and asymptomatic ventricular arrhythmia. Survival Trial of Antiarrhythmic Therapy in Congestive Heart Failure.

BACKGROUND: Asymptomatic ventricular arrhythmias in patients with congestive heart failure are associated with increased rates of overall mortality and sudden death. Amiodarone is now used widely to prevent ventricular tachycardia and fibrillation. We conducted a trial to determine whether amiodarone can reduce overall mortality in patients with congestive heart failure and asymptomatic ventricular arrhythmias. METHODS: We used a double-blind, placebo-controlled protocol in which 674 patients with symptoms of congestive heart failure, cardiac enlargement, 10 or more premature ventricular contractions per hour, and a left ventricular ejection fraction of 40 percent or less were randomly assigned to receive amiodarone (336 patients) or placebo (338 patients). The primary end point was overall mortality, and the median follow-up was 45 months (range, 0 to 54). RESULTS: There was no significant difference in overall mortality between the two treatment groups (P = 0.6). The two-year actuarial survival rate was 69.4 percent (95 percent confidence interval, 64.2 to 74.6) for the patients in the amiodarone group and 70.8 percent (95 percent confidence interval, 65.7 to 75.9) for those in the placebo group. At two years, the rate of sudden death was 15 percent in the amiodarone group and 19 percent in the placebo group (P = 0.43). There was a trend toward a reduction in overall mortality among the patients with nonischemic cardiomyopathy who received amiodarone (P = 0.07). Amiodarone was significantly more effective in suppressing ventricular arrhythmias and increased the left ventricular ejection fraction by 42 percent at two years. CONCLUSIONS: Although amiodarone was effective in suppressing ventricular arrhythmias and improving ventricular function, it did not reduce the incidence of sudden death or prolong survival among patients with heart failure, except for a trend toward reduced mortality among those with nonischemic cardiomyopathy.

Factors associated with sources of influence/information in reducing red meat by elderly subjects.

A number of studies have found that health beliefs and social influences predict changes in dietary intake, including red meat. These studies have not determined what kinds of individuals are more likely to change their diets due to the advice of physicians, the advice of significant others, or because of mass-media exposure. We obtained data from 424 elderly Houstonians regarding whether they had attempted to reduce red meat consumption and if so, why. Social network, health status, food attitude and demographic variables are used to differentiate those who have made physician-induced changes from other sources of influence/information for change. Elderly subjects with smaller abdominal girth measurements are more likely to make red meat reductions regardless of the source of influence/information; those who believe in the efficacy of health foods are more likely to give physicians and mass media as sources of influence/information for red meat reductions. Men are more likely than women to report red meat reductions because of mass media and physician influences. Women who receive a greater amount of companionship from their social networks are more likely to change because of friends/relatives influences.

Optimization of biphasic waveforms for human nonthoracotomy defibrillation.

BACKGROUND: Biphasic waveforms reduce defibrillation threshold (DFT) in a wide variety of models. Although there are several human studies of long-duration, high-tilt biphasic waveform defibrillation, the specific biphasic waveform shape required to achieve optimal DFT reduction is unknown. METHODS AND RESULTS: This study tested the effect of single capacitor biphasic waveform tilt modification on DFT using a paired study design in 18 patients undergoing nonthoracotomy defibrillator implantation. Baseline DFT was obtained using a 65% tilt, simultaneous pulse, bidirectional monophasic shock from a right ventricular cathode to a coronary sinus or superior vena cava lead and a subscapular patch. The single-capacitor biphasic waveform shocks, delivered over the same pathways, consisted of either both phases at 65% tilt (65/65 biphasic waveform) to produce an overall tilt of 88% and a delivered energy 11% greater than monophasic shock or both phases at 42% tilt (42/42 biphasic waveform) to produce an overall tilt of 66% and delivered energy equal to monophasic shock. The 65/65 biphasic waveform reduced stored energy DFT 25%, from 16.2 +/- 4.4 J with monophasic shock to 12.1 +/- 5.3 J (P < .02); however, it did not significantly reduce the delivered energy DFT. In contrast, the 42/42 biphasic waveform required 49% less stored energy (16.2 +/- 4.4 J, monophasic shock, vs 8.3 +/- 3.3 J, biphasic waveform; P < .001) and 49% less delivered energy (14.2 +/- 3.8 J, monophasic shock, vs 7.3 +/- 2.9 J, biphasic waveform; P < .001) than monophasic shock for successful defibrillation. The 42/42 biphasic waveform delivered energy DFT was 4.6 +/- 5.2 J (39%) less than 65/65 biphasic waveform DFT (P < .002). CONCLUSIONS: DFT reduction is an inherent electrophysiological property of biphasic waveforms that is independent of delivered energy. Overall biphasic waveform tilt and the relative amplitudes of the waveform phases are important factors in defibrillation efficacy. Defibrillation with a 42/42 biphasic waveform is more efficacious than 65/65 biphasic waveform defibrillation; however, the optimal biphasic waveform remains unknown.