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Biomedical subjects

S Osswald

Publications and source records attributed to S Osswald.

At least 55 records · Page 3Linked to original sources
PubMed1996

[Drug therapy of cardiac insufficiency: status 1995].

Congestive heart failure is a frequent disorder with an estimated prevalence of 0.4-2% in the general population. Despite recent advances in our understanding of the pathophysiology of this disorder and new developments in its treatment, the prognosis of heart failure remains poor. All patients with heart failure should undergo diagnostic evaluation to determine the type of cardiac dysfunction, establish its etiology and orient treatment. Angiotensin converting enzyme (ACE) inhibitors, diuretics and digoxin are the standard therapy for chronic congestive heart failure caused by systolic dysfunction. ACE inhibitors are indicated in all stages of heart failure, even in asymptomatic patients. Diuretics should be added in the presence of fluid retention. Digoxin remains an important component in the management of refractory symptoms and atrial fibrillation. Symptomatic improvement and reduced morbidity have been shown with all these drugs. However, improved survival has been documented for ACE inhibitors only. Currently, numerous drugs with different mechanisms of action are being evaluated in ongoing clinical trials. Promising results have been published, mainly with beta-receptor blockers and newer positive inotropic substances. Rapidly growing evidence from basic research will advance our understanding of heart failure and hopefully pave the way for new preventive and therapeutic strategies in the near future.

Adrenergic beta-Antagonists↗
PubMed1996

[Intracoronary ultrasound: scientific aspects and clinical possibilities].

The recent development of miniaturized ultrasound devices incorporated at the tip of flexible angiographic catheters permits, for the first time in vivo, visualization of the full circumference of the vessel wall from a single tomographic view, similar to a histological study. Potential advantages of intracoronary ultrasound as compared to coronary angiography include characterization of the intramural anatomy of the vessel wall in normal and atherosclerotic segments as well as quantification of luminal dimensions and severity of stenoses using planimetry even in vessels with complex plaque morphology. Intracoronary ultrasound has therefore been called the new gold standard for vascular imaging. The method has been validated in vitro and in vivo and is highly reproducible. The complication rate of intracoronary ultrasound imaging is low. In addition to research applications, there are several emerging clinical applications for intracoronary ultrasound in the diagnosis of coronary artery disease, for instance for angiographically indeterminate lesions, in the assessment of transplant vasculopathy or in planning and guiding of coronary interventional procedures.

Coronary Angiography↗
PubMed1996

[Assessment of ventricular arrhythmias].

In the evaluation of patients with ventricular arrhythmias, those patients with asymptomatic ventricular arrhythmias, who usually comprise a low-risk population, have to be differentiated from patients with symptomatic ventricular arrhythmias (presyncopal symptoms, syncope, cardiac arrest). In general, patients with asymptomatic ventricular arrhythmias should not be treated with antiarrhythmic drugs; however, patients with recent myocardial infarction and asymptomatic ventricular arrhythmias, which may indicate an increased risk of sudden death, should undergo further risk stratification, since some of them might benefit from preventive antiarrhythmic therapy with a beta-blocking agent of amiodarone. In contrast to asymptomatic patients, patients with symptomatic ventricular arrhythmias are at high risk for sudden death, and, if functional status does not mandate against active therapy, these patients should undergo coronary angiography and electrophysiologic evaluation. Revascularization procedures and specific antiarrhythmic measures such as antiarrhythmic drug therapy, ablative therapy (surgical resection or transcatheter radiofrequency ablation of the arrhythmogenic focus) or the implantation of a cardioverterdefibrillator (ICD) are frequently needed in such patients. Consequently, in this high-risk population, early referral to a cardiac center with an electrophysiologic laboratory is recommended, whereas it should be strongly mandated against empirical antiarrhythmic drug therapy.

Adrenergic beta-Antagonists↗
PubMed1996

Intermittent pacemaker dysfunction caused by digital mobile telephones.

OBJECTIVES: This study was designed to evaluate possible interactions between digital mobile telephones and implanted pacemakers. BACKGROUND: Electromagnetic fields may interfere with normal pacemaker function. Development of bipolar sensing leads and modern noise filtering techniques have lessened this problem. However, it remains unclear whether these features also protect from high frequency noise arising from digital cellular phones. METHODS: In 39 patients with an implanted pacemaker (14 dual-chamber [DDD], 8 atrial-synchronized ventricular-inhibited [VDD(R)] and 17 ventricular-inhibited [VVI(R)] pacemakers), four mobile phones with different levels of power output (2 and 8 W) were tested in the standby, dialing and operating mode. During continuous electrocardiographic monitoring, 672 tests were performed in each mode with the phones positioned over the pulse generator, the atrial and the ventricular electrode tip. The tests were carried out at different sensitivity settings and, where possible, in the unipolar and bipolar pacing modes as well. RESULTS: In 7 (18%) of 39 patients, a reproducible interference was induced during 26 (3.9%) of 672 tests with the operating phones in close proximity (<10 cm) to the pacemaker. In 22 dual-chamber (14 DDD, 8 VDD) pacemakers, atrial triggering occurred in 7 (2.8%) of 248 and ventricular inhibition in 5 (2.8%) of 176 tests. In 17 VVI(R) systems, pacemaker inhibition was induced in 14 (5.6%) of 248 tests. Interference was more likely to occur at higher power output of the phone and at maximal sensitivity of the pacemakers (maximal vs. nominal sensitivity, 6% vs. 1.8% positive test results, p = 0.009). When the bipolar and unipolar pacing modes were compared in the same patients, ventricular inhibition was induced only in the unipolar mode (12.5% positive test results, p = 0.0003). CONCLUSION: Digital mobile phones in close proximity to implanted pacemakers may cause intermittent pacemaker dysfunction with inappropriate ventricular tracking and potentially dangerous pacemaker inhibition.

Aged↗
PubMed1996

Differences of disease progression in congestive heart failure due to alcoholic as compared to idiopathic dilated cardiomyopathy.

In patients with alcoholic cardiomyopathy there is evidence that mild heart failure is reversible if patients abstain from alcohol, but there is no consensus whether the disease is progressive once structural myocardial dilation has evolved. The aim of the present study was to compare the long-term course of congestive heart failure due to alcoholic and idiopathic dilated cardiomyopathy. Of 75 patients with overt congestive heart failure, 23 had alcoholic cardiomyopathy and were compared to 52 patients with idiopathic cardiomyopathy. The mean age was 48 +/- 12 years. Despite medical therapy, heart failure class New York Heart Association III-IV was present in 52% of patients with alcoholic and 47% of patients with idiopathic cardiomyopathy (not significant). Their mean left ventricular ejection fraction was 30 +/- 12% vs 28 +/- 12% and left ventricular end-diastolic volumes were 264 +/- 125 ml and 254 +/- 100 ml respectively (not significant). Overall survival at 1, 5 and 10 years was 100%, 81% and 81% for the group with alcoholic dilated cardiomyopathy and 89%, 48% and 30% for the group with idiopathic cardiomyopathy, respectively (P = 0.041), and the difference was even greater for transplant-free survival P = 0.005). Clinical and invasive signs of left and right heart failure as well as left ventricular dimensions were predictive of a fatal outcome; however, symptom duration and left ventricular volumes were only predictive in patients with idiopathic cardiomyopathy, suggesting that in the two patient groups different mechanisms may lead to death. Mortality in patients with severe congestive heart failure and left ventricular dilatation due to alcoholic cardiomyopathy is significantly lower than that in patients with idiopathic cardiomyopathy and similar degrees of heart failure. Thus, despite structural changes inherent in marked left ventricular dilatation, disease progression in alcoholic dilated cardiomyopathy is different from that in idiopathic cardiomyopathy and thus may have implications for the choice of therapy.

Adult↗
PubMed1996

Benefits and limitations of rate adaptive pacing under laboratory and daily life conditions in patients with minute ventilation single chamber pacemakers.

Rate adaptive pacing has been shown to improve hemodynamic performance and exercise tolerance during acute testing. However, there remain concerns about its benefit in daily life and possible complications incurred by unnecessary pacing. This double-blind crossover study compared the benefit of rate adaptive (SSIR) versus fixed rate (SSI) pacing under laboratory and daily life conditions in 20 rate incompetent patients with minute ventilation single chamber pacemakers (META II). The heart rate (HR) response during three different exercise tests (treadmill, bicycle ergometry, walking test) was correlated with the Holter findings during daily life in either pacing mode. The maximal HR was significantly higher in the SSIR-mode compared to the SSI-mode, both during laboratory testing (treadmill: 123 +/- 15 vs 93 +/- 29 beats/min; ergometry: 118 +/- 15 vs 89 +/- 27 beats/min; walking test: 127 +/- 9 vs 95 +/- 26 beats/min, all P values < 0.01) as well as during daily life (Holter: 126 +/- 13 vs 103 +/- 24 beats/min, P < 0.01). On Holter, the average HR (71 +/- 14 vs 71 +/- 8 beats/min) and the percentage of paced rhythm (54% vs 62%, SSI- vs SSIR-mode, P = NS) were not different in either mode. However, despite a 30% rate gain in the SSIR-mode, the exercise capacity remained unchanged, and only 38% of patients preferred the SSIR-mode. Minute ventilation pacemakers provide a physiological rate response to exercise. Irrespective of the protocol used, the findings of laboratory testing are comparable to those during daily life. However, patient selection for rate adaptive single chamber pacing should be made with caution, since the objective benefit of restoring normal chronotropy may subjectively be negligible for most patients.

Aged↗
PubMed1996

VDD(R) pacing: short- and long-term stability of atrial sensing with a single lead system.

BACKGROUND: Recent studies have shown that the atrial signal can reliably be sensed for VDD(R) pacing via atrial floating electrodes incorporated in a single-pass lead. However, there remains concern about the long-term stability of atrial sensing and proper VDD function under real-life conditions. This study investigated the long-term reliability of atrial sensing and atrioventricular synchronous pacing using a new single lead VDD(R) pacing system. METHODS AND RESULTS: In 20 consecutive patients (ages 71 +/- 14 years) with normal sinus node function and high-degree heart block, a single lead VDD(R) pacemaker (Unity, Intermedics) was implanted. Atrial sensing was studied at implantation, at discharge, and at 1, 3, 6, 12, and 18 months of follow-up. At implant, the measured P wave amplitude was 2.3 +/- 1.2 mV. By telemetry, the atrial sensing threshold was 0.79 +/- 0.41 mV at discharge, 0.75 +/- 0.43 mV at 1 month, 0.73 +/- 0.43 mV at 3 months, 0.76 +/- 0.41 mV at 6 months, 0.79 +/- 0.41 mV at 12 months, and 0.77 +/- 0.35 mV at 18 months of follow-up (P = NS). Appropriate VDD pacing was assessed by the percentage of correct atrial synchronization (PAS = atrial triggered ventricular paced complexes divided by total number of ventricular paced complexes) during repeated Holters. PAS was 99.99% +/- 0.01% at 1 month, 99.99% +/- 0.02% at 3 months, and 99.98% +/- 0.05% at 12 months of follow-up (P = NS). No atrial oversensing with inappropriate ventricular pacing was observed, neither during isometric arm exercise testing nor spontaneously during Holter monitoring. CONCLUSION: The long-term stability of atrial sensing with almost 100% correct atrial synchronous tracking and the lack of inappropriate pacing due to atrial oversensing make the new Unity VDD(R) system a highly reliable single lead pacing system. In view of the lower costs and the ease of single lead implantation, this system may offer an interesting alternative to DDD pacemakers in patients with normal sinus node function.

Aged↗
PubMed1996

Review of cardiac events in USAF aviators.

INTRODUCTION: The purpose of this study was to define the cardiac event rate in the U.S. Air Force (USAF) aviator population. METHODS: Several sources of information were reviewed to search for individual USAF active duty pilots and navigators who had cardiac events (defined as myocardial infarction, angina and sudden cardiac death), while on unrestricted flying duties during the years 1988-92. Source investigated included: USAF physical disability, casualty and medical evaluation board records, and records from the Aeromedical Consultation Service at Brooks AFB, TX. RESULTS: There were 38 total cardiac events, with an average of 7.6 events per year. Myocardial infarctions occurred in 23 aviators, angina in 7 and sudden death in 8. The ages ranged from 31-53 yr with an average age of 44 yr. The 5-yr average annual event rate by age group was 0.0054% (30-34 yr), 0.018% (35-39 yr), 0.038% (40-44 yr), 0.14% (45-49 yr), and 0.13% (50-54 yr). CONCLUSIONS: Although the total number of cardiac events in our aviator population is low, the cardiac event rate in the older age groups is of concern and may warrant a more intensive screening program for that population.

Adult↗
PubMed1995

[Initial clinical results with a novel implantable cardioverter-defibrillator: a prospective evaluation in 3 Swiss university hospitals].

The most important technical improvements of implantable cardioverter-defibrillators (ICD) of the latest generation comprise more sophisticated antitachycardia pacing options, stored intracardiac electrograms and biphasic shock capabilities which virtually always allow ICD implantation without thoracotomy. The present study summarizes the first clinical experience with these new devices. In 37 consecutive symptomatic (near sudden death 17, syncope 16, pre-syncope 4) patients aged 56 +/- 10 years with refractory ventricular arrhythmias (presenting arrhythmia: ventricular fibrillation 14, ventricular tachycardia 22, not documented 1), an ICD (Jewel PCD 7219, Medtronic) was implanted. Coronary artery disease was present in 21, dilated cardiomyopathy in 5, valvular heart disease in 2 and various conditions in 8 patients; the mean left ventricular ejection fraction was 43 +/- 18%. In 29 patients (78%), the ICD was inserted in a pectoral and in 8 (22%) in an abdominal position. A non-thoracotomy lead (NTL) configuration was successfully implanted in 36/37 patients (97%) (purely transvenous systems in 30, in combination with subcutaneous patch electrode in 6). Surgical complications comprised one pneumothorax, one hemorrhage and one death due to sepsis; during a mean follow-up of 5 +/- 3 months, another patient died of heart failure and 2 revisions (5.4%) for lead problems (1 connector, 1 SQ-patch) became necessary. In 23/37 patients (62%), the ICD was activated after 74 +/- 89 days post implant. 22 of these 23 patients (96%) received one or more appropriate shocks (9 +/- 22 shocks per patient). The actuarial survival was 95% at 6 months. In the present study, an ICD of the newest generation was successfully implanted without thoracotomy in > or = 97% and with purely transvenous systems in > or = 84%. Compared to older systems, this has made the implantation procedure remarkably easier and will most likely lead to a further reduction in mortality and morbidity. Despite the relatively short follow-up, the high incidence of appropriate ICD utilization underscores the high recurrence rate of arrhythmias in this population and suggests that the ICD may be very effective in preventing unnecessary rehospitalizations.

Aged↗
PubMed1995

Limitations and late complications of third-generation automatic cardioverter-defibrillators.

BACKGROUND: This study examines the limitations and complex management problems associated with the use of tiered-therapy, implantable cardioverter-defibrillators (ICDs). METHODS AND RESULTS: The study group comprises the first 154 patients undergoing implantation of tiered-therapy ICDs at our institution. Pulse generators from three different manufacturers were used. In 39 patients, a complete nonthoracotomy lead system was used. The perioperative mortality was 1.3%. Of these 154 patients, 37% experienced late postoperative problems. Twenty-one patients required system revision within 36.5 months (mean, 8.57 +/- 11.3) of surgery. Reasons for revision were spurious shocks due to electrode fractures (3) or electrode adapter malfunction (2), inadequate signal from endocardial rate-sensing electrodes (3), superior vena cava or right ventricular coil migration (5), failure to correct tachyarrhythmias due to a postimplant rise in defibrillation threshold (5), or pulse generator failure (3). One of these patients required system removal for infection after revision of an endocardial lead. A further 32 patients received inappropriate shocks for atrial fibrillation with a rapid ventricular response or sinus tachycardia. Two of these patients also received shocks for ventricular tachycardia initiated by antitachycardia pacing triggered by atrial fibrillation. Ventricular pacing for bradycardia was associated with inappropriate shocks due to excessive autogain in 2 patients. CONCLUSIONS: Despite the major diagnostic and therapeutic advantages of tiered-therapy ICDs, a significant proportion of patients continue to experience hardware-related complications or receive inappropriate shocks.

Algorithms↗
PubMed1995

Electrocardiographic pseudo-infarct patterns after implantation of cardioverter-defibrillators.

Postoperative electrocardiographic (ECG) changes are frequently present after insertion of implantable cardioverter-defibrillators (ICD) and may mimic perioperative myocardial infarction (MI). The purpose of this study was to assess the incidence and clinical significance of postoperative ECG changes in relation to clinical, laboratory, and implantation data. In 25 (16%) of 156 patients undergoing ICD implantation, significant ECG changes (> or = 50% reduction in R-wave amplitude in > or = 3 leads or new Q waves in > or = 2 leads) were present 1 to 3 days after the operation and persisted at hospital discharge in 12 (8%). Presence of thoracotomy, the total number of induced ventricular fibrillation episodes, and the number of defibrillation shocks required during defibrillation threshold (DFT) testing correlated with postoperative ECG changes. Other factors associated with a significant R-wave loss in the lateral precordial leads included left-sided pleural effusion, lung infiltrates or atelectasis, and large defibrillator patch electrodes over the left ventricle or the lateral chest wall. Myocardial necrosis documented by elevated cardiac enzymes occurred in 6 (5%) of 151 patients without significant ECG changes and in 3 (12%) with (p value not significant). However, postoperative ECG changes associated with elevated enzymes were indistinguishable from changes unrelated to necrosis. Therefore the sensitivity and specificity of the surface ECG for detection of MI after ICD placement is poor. Multiple factors such as thoracotomy, myocardial injury from DFT testing, electric insulation, or shielding of the heart may contribute to the development of electrocardiographic pseudo-infarct patterns.

Aged↗
PubMed1995

Ventricular pacing induced ventricular tachycardia in patients with implantable cardioverter defibrillators.

Appropriately timed noncompetitive ventricular pacing potentially may initiate ventricular tachycardia in patients prone to these arrhythmias. The combination of bradycardia pacing and stored electrograms in a currently available cardioverter defibrillator provides an opportunity to evaluate the occurrence of such pacing induced ventricular tachycardia. During a surveillance period of 18.7 +/- 11.4 months, stored electrograms documented 302 episodes of ventricular tachycardia in 77 patients. Five patients (6.5%) demonstrated 25 episodes (1-16 per patient) of ventricular tachycardia that were immediately preceded by an appropriately paced ventricular beat (8.3% of all episodes of ventricular tachycardia). All five patients had prior myocardial infarctions and a history of monomorphic ventricular tachycardia occurring both spontaneously and in response to programmed electrical stimulation. Antitachycardia pacing terminated pacing induced ventricular tachycardia in 22 episodes; in one episode antitachycardia pacing accelerated ventricular tachycardia. In two cases shock therapy was aborted for nonsustained ventricular tachycardia. We conclude that, in selected nonsustained ventricular tachycardia. We conclude that, in selected postinfarction patients with recurrent sustained monomorphic ventricular tachycardia treated with implantable cardioverter defibrillators, appropriately timed ventricular pacing may induce ventricular tachycardia.

Aged↗
PubMed1995

Subclavian crush syndrome complicating transvenous cardioverter defibrillator systems.

UNLABELLED: Subclavian crush syndrome, described with pacemaker leads implanted via subclavian puncture, may occur when conductor fractures and insulation breaches develop by compression of a lead between the first rib and clavicle. We reviewed our experience in 164 patients who underwent intended implantation of transvenous defibrillator systems to determine the clinical relevance of subclavian crush syndrome in defibrillator patients. Venous access was obtained via subclavian puncture in 114 patients (70%) and via cephalic cut-down in 50 patients (30%). Nonthoracotomy lead systems, with or without subcutaneous patch, were successfully implanted in 131 of 164 patients (79.9%). Thoracotomy was required in 32 patients (19.5%) and subxiphoid patch in 1 patient (0.6%). Over a mean of 12.9 months (range 1-62 months), 3 patients (1.8%) required revision of the rate sensing lead/coil or superior vena cava coil after development of lead compression fractures in the region of the clavicle and first rib. In all 3 patients the leads had been implanted via subclavian puncture (2.6% of patients in whom the subclavian technique was utilized). Two patients presented with spurious shocks. One patient was asymptomatic. CONCLUSIONS: When venous access is obtained via subclavian puncture, subclavian crush syndrome may develop in patients with transvenous defibrillator systems. Patients may be asymptomatic and lead fractures may go unrecognized. When implanting transvenous defibrillator systems, strong consideration should be given to obtaining venous access primarily via the cephalic cut-down technique.

Aged↗
PubMed1994

A comparison of VVIR and DDDR pacing following cardiac transplantation.

UNLABELLED: We compared the clinical course of patients paced in VVIR versus DDDR mode to determine the most appropriate method of pacing following cardiac transplantation. Pacemaker implantation was required in 9 of 90 orthotopic cardiac transplants (10%). Indications included sinus bradycardia or sinus arrest (8 patients) and AV node dysfunction (1 patient). VVIR pacemakers were implanted in four patients and DDDR in five patients. DDDR patients: The mean P wave was 1.7 mV and the mean atrial stimulation threshold was 0.8 V (at 0.5 msec). During follow-up of 20 months, two atrial lead complications developed (29% of leads in 33% of patients). No lead complications were directly related to endomyocardial biopsy. VVIR patients: All four patients developed VA conduction with mean VA time 180 msec (160-240 msec). Two patients developed pacemaker syndrome. CONCLUSIONS: VA conduction and pacemaker syndrome may develop in cardiac transplant recipients paced in the VVIR mode. Dual chamber pacing is technically feasible and preferable following cardiac transplantation.

Adult↗
PubMed1994

Treatment of ventricular tachycardia by transcatheter radiofrequency ablation in patients with ischemic heart disease.

BACKGROUND: Recurrent sustained ventricular tachycardia (VT) is not responsive to antiarrhythmic drugs in the majority of patients, who therefore need therapy with nonpharmacological methods. We evaluated prospectively the feasibility, safety, and efficacy of transcatheter radiofrequency (RF) ablation of VT in 21 selected patients with ischemic heart disease and VT. METHODS AND RESULTS: Twenty-one patients with ischemic heart disease and recurrent, drug-refractory VT documented by 12-lead ECG were selected who had sufficient hemodynamic tolerance of VT to undergo transcatheter mapping. Documented clinical VT was reproduced by programmed cardiac stimulation (PCS), and the site of origin was localized by a combination of techniques, including pace mapping, activation-sequence mapping, recordings of middiastolic potentials, and application of resetting and entrainment principles. RF current at 55 V was applied (3.8 +/- 3.1 applications per patient) for as long as 30 seconds at a time to target sites. Twenty-four distinct clinical VTs (mean cycle length, 445 +/- 52 milliseconds) were mapped and ablated in 21 patients. In 17 of 21 patients (81%), the procedure was acutely successful, and the target clinical VT could no longer be induced by PCS after the procedure, whereas in 4 patients, clinical VT remained inducible. By contrast, VTs with shorter cycle length and different QRS morphology than the ablated VT could still be induced by PCS in 12 of 21 patients. One patient died in intractable congestive heart failure 10 days after the procedure, and the remaining 20 are alive at the end of the follow-up period. The majority of the patients continued to be treated with at least one additional mode of antiarrhythmic therapy; 12 patients were still taking antiarrhythmic drugs, and 9 patients received an implantable cardioverter/defibrillator. During a mean follow-up period of 13.2 +/- 5.0 months, 9 of 20 patients (45%) had recurrent VT. In 4 patients, the recurrent VT was different than the previously ablated one. Clinical VT recurred in all 4 patients in whom RF ablation had been acutely unsuccessful. Four patients with recurrent VT underwent repeat RF ablation procedures that were acutely successful and had no further recurrence. CONCLUSION: Transcatheter RF ablation is feasible but has only moderately high efficacy in a small, selected group of patients with ischemic heart disease and drug-refractory, highly frequent, hemodynamically tolerated, sustained VT. In the majority of the patients, this treatment technique is palliative rather than definitive, and many of the patients continue to require other methods of antiarrhythmic therapy.

Aged↗
PubMed1994

Relation between shock-related myocardial injury and defibrillation efficacy of monophasic and biphasic shocks in a canine model.

BACKGROUND: Certain biphasic waveforms with specific time ratios of positive and negative components require less energy for successful defibrillation of the fibrillating ventricles than monophasic waveforms. However, if more efficient waveforms were also to be associated with more injurious effects on myocardial function, they might not provide a true biological advantage. This study investigates the relation between defibrillation efficacy and potential toxicity of monophasic and asymmetric, single capacitor, biphasic waveforms with equal durations of positive and negative components. METHODS AND RESULTS: The myocardial lactate extraction rate (LER) was used to measure the injurious effects on myocardial oxidative metabolism of two synchronized 35-J shocks in sinus rhythm. LER, mean arterial pressure (MAP) and, in a subset of experiments, cardiac output (CO) and coronary blood flow (CBF) were measured at baseline, 30 seconds, 60 seconds, 90 seconds, 150 seconds, 300 seconds, and 600 seconds after the shocks. In 12 dogs, three different waveforms (M 10: monophasic 10 milliseconds; BI 10: biphasic 10 milliseconds; BI 20: biphasic 20 milliseconds) were tested as series of two consecutive shocks (60 seconds apart) resulting in a total of 36 sets of data. At baseline, LER was 25 +/- 11%. After monophasic shocks, LER decreased significantly more than after biphasic shocks (LER at 150 seconds: M 10: -6 +/- 31% versus BI 10: 21 +/- 15% versus BI 20: 21 +/- 16%; M 10 versus BI 10 and M 10 versus BI 20, P < .05) and showed also a slower recovery (LER at 300 seconds: M 10: 1 +/- 24% versus BI 10: 20 +/- 11% versus BI 20: 20 +/- 15%; M 10 versus BI 10 and M 10 versus BI 20, P < .05). The maximal decrease in LER was 41 +/- 27% for M 10 compared with 18 +/- 15% for BI 10 and 15 +/- 11% for BI 20 (both, M 10 versus BI 10 and M 10 versus BI 20, P < .05). There was a similar decrease in CO and MAP, with the lowest MAP after monophasic shocks. The maximal decrease in MAP was significantly greater after M 10 compared with BI 20 (-29 +/- 15 mm Hg versus -13 +/- 11 mm Hg, P < .05). The defibrillation threshold was 18.6 +/- 8 J for M 10 compared with 11.5 +/- 4.0 J for BI 10 (P < .05) and 15.0 +/- 6.1 J for BI 20, respectively (P = NS). CONCLUSIONS: Our results suggest that these specific biphasic waveforms are associated with less injurious effects on myocardial oxidative metabolism and hemodynamic performance. Given their higher defibrillation efficacy as well, biphasic waveforms may provide important long-term benefits in patients receiving frequent shocks from implantable cardioverter-defibrillators.

Animals↗