Safety and efficacy of intravenous diltiazem in atrial fibrillation or atrial flutter

This study examines the efficacy of various doses of intravenous diltiazem to control the ventricular response during atrial fibrillation or atrial flutter. Control of the ventricular response of patients with atrial fibrillation and a rapid ventricular response can provide patients with relief of symptoms and improve hemodynamics. Eighty-four consecutive patients with atrial fibrillation or atrial flutter, or both, received an intravenous bolus dose of diltiazem followed by a continuous infusion of diltiazem at 5, 10, and 15 mg/hour. The mean ventricular response and blood pressure were monitored. Overall, 94% of patients (79 of 84) responded to the bolus dose with a > 20% reduction in heart rate from baseline, a conversion to sinus rhythm, or a heart rate < 100 beats/min. Seventy-eight patients received the continuous infusion. After 10 hours of infusion, 47% of patients (confidence interval [CI]: 36%, 59%) had maintained response with the 5 mg/hour infusion, 68% (CI: 57%, 79%) maintained response after the infusion was titrated to 10 mg/hour, and 76% (CI: 66%, 85%) after titration from the 5 and 10 mg/hour infusion to the 15 mg/hour dose. For the 3 diltiazem infusions studied, mean (+/- SD) heart rate was reduced from a baseline value of 144 +/- 14 beats/min to 98 +/- 19, 107 +/- 25, 107 +/- 22, 101 +/- 22, 91 +/- 17, and 88 +/- 18 beats/min at infusion times 0, 1, 2, 4, 8, and 10 hours, respectively. By the end of the infusion, 18% of patients (14 of 78) had conversion to sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety of pacemaker implantation in patients with transvenous (nonthoracotomy) implantable cardioverter defibrillators

While several reports have documented the safety of implantation of transvenous pacemakers in patients with epicardial patch-based implantable cardioverter defibrillators (ICDs), the implantation of transvenous pacemakers in patients with transvenous (nonthoracotomy) ICDs has not been well-described. We present three patients with transvenous ICDs who subsequently underwent implantation of transvenous pacemakers without complication. Technical considerations and a testing, protocol for detection of pacemaker-ICD interactions are discussed.

Lessons learned from data logging in a multicenter clinical trial using a late-generation implantable cardioverter-defibrillator. The Guardian ATP 4210 Multicenter Investigators Group

OBJECTIVES

This study examined patterns of implantable cardioverter-defibrillator use as documented by data logging.

BACKGROUND

Implantable cardioverter-defibrillators are accepted therapy for malignant ventricular tachyarrhythmias; however, relatively little is known about their patterns of use. Incorporation of data-storage capacities into these devices provides insight into long-term defibrillator function.

METHODS

Stored data-logging information was retrieved from 401 implanted cardioverter-defibrillators in 393 patients over an average of 303 days of follow-up.

RESULTS

A total of 91,443 detections were recorded in 299 patients. One hundred-six patients (26%) had detections due to supraventricular tachycardias, electrical noise or other causes, resulting in inappropriate therapy delivery to 92 patients (23%). Two hundred eighty-one patients recorded 66,276 episodes of ventricular tachycardia or ventricular fibrillation. Of these, 74.4% episodes terminated spontaneously without any delivered therapy, 22.1% terminated after antitachycardia pacing, and 1.7% terminated after shock therapy. Antitachycardia pacing was activated without formal testing in 47% of all patients receiving this therapy and was successful in 96% of all episodes receiving this therapy. Acceleration of tachycardia to shock therapy occurred in 1.3% of all episodes and in 30.5% of patients receiving antitachycardia pacing. Thirty-four patients (8.7%) died during follow-up. Mortality was associated with patient age, heart failure functional class at implantation and frequency of shocks received during follow-up (all p < or = 0.05).

CONCLUSIONS

Most ventricular tachyarrhythmia detections by this noncommitted implantable cardioverter-defibrillator resolve spontaneously, whereas the majority receiving therapy can be treated with antitachycardia pacing. Mortality after implantable cardioverter-defibrillator implantation is associated with age, heart failure class and frequency of shocks received during follow-up. Data-logging capabilities provide valuable insights into the patterns of defibrillator use.

Refractive Indices of Fluids Related to Alternative Refrigerants

As part of a comprehensive program to develop suitable methods of chemical analysis for alternative refrigerants and their products, we have compiled a database of spectral, chromatographic, and physical property data that can aid in compound identification. As a small part of this effort, we have measured the refractive indices of a number of such fluids for which data were unavailable. The measurements were performed on a commercially available, digital Abbe refractometer that was modified for the relatively low temperature measurements (0 °C to 20 °C) that are sometimes required with these samples.

Flecainide: its value and danger

Flecainide is an important addition to the therapeutic armamentarium because it is a potent agent for the treatment of paroxysmal supraventricular tachycardia in patients without structural heart disease. Flecainide also may be useful in patients with debilitating nonsustained ventricular arrhythmias in the absence of structural heart disease. It is rarely useful in the management of life-threatening sustained ventricular arrhythmias.

Sensing/pacing lead complications with a newer generation implantable cardioverter-defibrillator: worldwide experience from the Guardian ATP 4210 clinical trial

OBJECTIVES

This report describes the sensing/pacing lead complications that developed during a worldwide clinical trial of a new implantable cardioverter-defibrillator.

BACKGROUND

The reliability of the leads used for sensing and pacing with the implantable cardioverter-defibrillator has not been adequately studied.

METHODS

The Guardian ATP 4210 was implanted in 302 patients. The sensing/pacing leads consisted of either two unipolar epicardial electrodes or a bipolar endocardial electrode from a variety of manufacturers.

RESULTS

During a mean follow-up period of 380 days, 39 patients (12.9%) required reoperation because their device developed sensing/pacing lead system complications. The most common clinical presentation was device oversensing (multiple tachycardia or noise detections or inappropriate shocks), which was observed in 27 patients, whereas elevated pacing thresholds were seen in 10 patients. Forty-one (11.8%) of 347 implanted lead systems required revision. The mean time to revision was 156 +/- 145 days. Actuarial lead survival rate at 1 and 3 years was 89% and 79%, respectively. Epicardial lead systems required significantly (p < 0.05) more revision than did endocardial systems, but when adapter problems were excluded, the revision rates of epicardial and endocardial leads were similar. Causes of lead system failures included adapter connection problems, lead dislodgement and insulation disruption. Predictors of lead revision were use of an epicardial lead system or an adapter.

CONCLUSIONS

A high rate of sensing/pacing lead complications was found with this newer generation implantable cardioverter-defibrillator. The enhanced diagnostic and data storage capabilities of this implantable cardioverter-defibrillator facilitated the recognition and troubleshooting of these complications. These findings emphasize the need for careful surveillance and testing of implantable cardioverter-defibrillator sensing/pacing leads during follow-up.

Can amiodarone pulmonary toxicity be predicted in patients undergoing implantable cardioverter defibrillator implantation?

Implantable cardioverter defibrillator (ICD) implantation is rapidly becoming accepted as primary therapy for malignant ventricular arrhythmias. Many patients undergoing ICD implantation are on concomitant antiarrhythmic drugs to decrease shock frequency, slow tachycardia rate, and suppress supraventricular arrhythmias. Amiodarone is a potent antiarrhythmic agent that is also frequently used in the treatment of patients with refractory ventricular arrhythmias. Ten to forty percent of patients undergoing ICD implantation will also be taking amiodarone. It has been reported to cause pulmonary toxicity in about 5% of patients per year. Acute amiodarone toxicity presenting as adult respiratory distress syndrome has been reported much less frequently. Although perioperative morbidity due to amiodarone has been described, the risk, predictability, and consequences of acute pulmonary toxicity from amiodarone in patients undergoing ICD implantation have not been previously described. We reviewed the records of 99 consecutive patients undergoing ICD implantation at our institution from October 1987 to April 1992. Thirty-nine patients were taking 480 +/- 230 mg of amiodarone (median 400 mg, lower 20th percentile 400 mg, upper 80th percentile 800 mg) for 291 +/- 554 days prior to ICD implantation. Ten patients taking amiodarone developed acute pulmonary toxicity clinically manifesting as diffuse pulmonary infiltrates on chest radiography and adult respiratory distress syndrome with hypoxia (arterial pO2 < 60 mmHg) without evidence of pneumonia or elevated pulmonary capillary wedge pressure (PCW < or = 15 mmHg). Of the 60 patients not taking amiodarone none developed adult respiratory distress syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Procainamide: a perspective on its value and danger

Procainamide remains one of the most widely used antiarrhythmic agents in clinical practice. Currently, it is widely used alone or in combination with class I agents (eg, mexiletine or tocainide) to prevent recurrent ventricular tachycardia or symptomatic nonsustained ventricular tachycardia. Procainamide is also used for short-term treatment of ventricular tachycardia and a variety of supraventricular tachycardias, primarily atrial flutter and atrial fibrillation. Long-term procainamide therapy is limited by a number of systemic side effects, primarily lupus-like syndrome, gastrointestinal disturbances, and autoimmune blood dyscrasias. Procainamide levels can be useful in initial dose titrations; however, QRS and QT interval measurements help prevent drug toxicity. It is recommended that patients being started on antiarrhythmic therapy with procainamide be admitted to the hospital for monitoring to ensure that their QT interval is not excessively prolonged.

Radiofrequency catheter ablation of sinus node reentrant tachycardia

Sinus node reentrant tachycardia is a relatively uncommon (5%-15%) form of recurrent paroxysmal supraventricular tachycardia (SVT). We describe a case of symptomatic sinus node reentrant tachycardia in a 67-year-old male with ischemic heart disease, congestive heart failure, and depressed ventricular function. Adenosine administered during an electrophysiology study caused prolongation of the tachycardia cycle length due to atrial cycle length prolongation (without atrio-His prolongation) prior to tachycardia termination. Right atrial mapping revealed the earliest site of atrial activation in the high lateral right atrium just below the superior vena cava. Low energy (10 and 20 W) radiofrequency lesions were applied at this site with termination of the tachycardia within 3 seconds of radiofrequency energy delivery. Tachycardia could not be reinduced after delivery of the radiofrequency lesions. The sinus node function immediately and 6 weeks after radiofrequency catheter ablation remained normal and the patient was without clinical recurrence of SVT. Mapping of sinus node reentrant tachycardia and elimination of the reentrant circuit with radiofrequency catheter ablation is possible without causing sinus node dysfunction. Adenosine causes prolongation of the atrial cycle length followed by termination of sinus node reentrant tachycardia.

Doppler echocardiographic assessment of an impedance-based dual-chamber rate-responsive pacemaker

Rate-responsive pacing allows patients with chronotropic incompetence to achieve more physiologic heart rate responses to exercise. One sensor currently being investigated uses impedance-derived measurements of changes in right ventricular stroke volume to alter the pacing rate. Correlation of pacemaker-derived measurements of stroke volume with an accepted method of stroke volume measurement has not been performed. The relative changes in impedance-derived stroke volume were compared in 10 patients with an impedance-based dual-chamber rate-responsive pacemaker (Precept DR, Cardiac Pacemakers, Inc.) with simultaneous Doppler echocardiographic measurements of right and left ventricular stroke volume. These comparisons were made during pacing at 2 heart rates (70 and 100 beats/min) and 3 AV intervals (150, 200 and 250 ms) while in a supine resting state, during lower body negative pressure to -30 mm Hg, and while performing 25% maximal handgrip. Pacemaker-derived stroke volume decreased by 7 to 11% and Doppler time-velocity integral measurements decreased by 14 to 19% in response to an increase in pacing rate (p = NS). There was also no significant difference by either technique in the mean stroke volume change when the atrioventricular interval was varied. Both techniques detected a decrease in stroke volume during lower body negative pressure, ranging from -7 to -20% by pacemaker, and -17 to -38% by Doppler. Overall, the pacemaker stroke volume measurements responded in an appropriate direction to each intervention, signaling the pacemaker's ability to detect directional change in stroke volume. The Precept DR may aid in the programming of parameters such as atrioventricular interval and heart rate by allowing for optimization of stroke volume in individual patients.

Measurement of ventricular electrogram amplitude during intraoperative induction of ventricular tachyarrhythmias

Adequate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF) is necessary for proper functioning of an implantable cardioverter defibrillator (ICD). Several ICDs currently undergoing investigation have programmable fixed gain sensitivity for tachycardia detection. If intracardiac electrogram amplitude decreases below the programmed sensitivity during VT or VF, detection of a ventricular arrhythmia may be delayed or missed. The mean amplitude of intracardiac electrograms (ICEGM) recorded with bipolar epicardial or transvenous sensing leads was measured in 63 patients during induced VT and VF recorded in the operating room at the time of ICD implantation. The mean amplitude of the ICEGM during 41 episodes of VF in 15 patients decreased from 14.9 +/- 0.9 mV during sinus rhythm to 8.8 +/- 0.7 mV at 1 second, 9.7 +/- 0.7 mV at 5 seconds, and 9.4 +/- 0.7 mV at 10 seconds (p < 0.0001 vs sinus rhythm ICEGM) with endocardial leads. The mean amplitude of the ICEGM recorded during 173 episodes of VF in 43 patients with epicardial leads decreased from 10.4 +/- 0.3 mV in sinus rhythm to 7.8 +/- 0.3 mV at 1 second, 8.3 +/- 0.3 mV at 5 seconds and 8 mV at 10 seconds (p <0.0001 vs sinus rhythm ICEGM). The mean amplitude of epicardial and transvenous ICEGMs recorded during 34 episodes of monomorphic VT decreased from 18.5 +/- 1.8 mV (epicardial) and 14.4 +/- 2.0 mV (transvenous) during sinus rhythm (p = 0.15, epicardial vs transvenous) to 16.0 +/- 1.7 mV (epicardial) and 13.7 +/- 1.9 mV (transvenous) at 10 seconds (< 10% of baseline amplitude).(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiographic abnormalities after radiofrequency catheter ablation of accessory bypass tracts in the Wolff-Parkinson-White syndrome

Repolarization abnormalities on surface electrocardiograms have been described after loss of ventricular preexcitation in some patients with the Wolff-Parkinson-White syndrome. Radiofrequency catheter ablation of overt accessory pathways provides a unique opportunity to study this phenomenon. In this study, serial electrocardiograms were obtained before and after radiofrequency ablation of manifest accessory pathways in 19 patients, of concealed accessory pathways in 6 and after radiofrequency atrioventricular nodal modification in 12. Seven patients undergoing manifest right-sided accessory pathway ablation had left superior frontal plane T-wave axis deviations after ablation (-42 +/- 13 degrees). No patient with a manifest left-sided or concealed accessory pathway, or atrioventricular nodal modification had T-wave abnormalities after ablation; however, left anterior fascicular block and incomplete right bundle branch block each occurred in 1 patient with left accessory pathway ablation. Repolarization abnormalities observed after ablation were similar to T-wave abnormalities during the absence of preexcitation before ablation and persisted up to 5 weeks after the procedure. Patients with repolarization abnormalities after ablation had significantly longer preexcited QRS durations than those without such changes, suggesting that the initial contribution of the pathway to ventricular activation is an important determinant of T-wave changes after ablation. The proposed mechanism for repolarization abnormalities after ablation is the phenomenon of T-wave "memory."

Short-term reproducibility over time of right ventricular pulse pressure as a potential hemodynamic sensor for ventricular tachyarrhythmias

The implantable cardioverter defibrillator (ICD) has been shown to effectively terminate episodes of ventricular tachyarrhythmias. Multiple investigators have suggested that the incorporation of hemodynamic sensors may allow ICDs to differentiate between hemodynamically unstable and stable ventricular tachyarrhythmias (VT), as well as differentiate ventricular from supraventricular tachycardias. Right ventricular (RV) pulse pressure has been shown to possess acceptable characteristics as a sensor for incorporation in ICDs. We sought to determine the short-term reproducibility of RV pulse pressure measurements by comparing RV pulse pressure measured during two separate episodes of VT in each of ten study patients. The mean VT cycle length for VT episode 1 was 293 +/- 15 msec, and was 298 +/- 15 msec for VT episode 2 (P = NS). The decrease in mean arterial pressure was 40 +/- 7 mmHg in episode 1 and 37 +/- 7 mmHg in episode 2 (P = NS). The decrease in RV pulse pressure during episode 1 was -13 +/- 2 mmHg, and -12 +/- 2 during episode 2 (P = NS). The decrease in RV pulse pressure during episodes of VT at two different times during a single electrophysiology study is highly reproducible, suggesting that RV pulse pressure may be a reliable sensor over time.

Implantation of cardioverter defibrillators in the post-sternotomy patient

In an attempt to minimize the hazards of redo sternotomy or thoracotomy in patients who have undergone previous cardiac procedures, a technique has been developed for cardioverter defibrillator implantation that involves dissection through a left subcostal incision and placement of extrapericardial defibrillation patches. This approach was used in 22 consecutive patients who required an implantable cardioverter defibrillator 4 to 156 months after previous median sternotomy. Defibrillation threshold energy was less than or equal to 20 J in every patient. Ninety-one percent of patients were extubated during the first 24 hours and were transferred out of the intensive care unit by the second postoperative day. One patient died of an acute myocardial infarction 3 days postoperatively (1/22, 4.5%). It was necessary to replace one lead for mechanical failure of an adapter, one patch required repositioning, and 1 patient needed drainage of a persistent pleural effusion (3/22, 13.6%). No further complications occurred during 3 to 27 months of follow-up. Advantages of the subcostal approach included prompt extubation, a single incision, and minimal morbidity. This approach is safe and effective, and is the method of choice for implantation of a cardioverter defibrillator in patients who have undergone prior sternotomy.

Failure of a second and third generation implantable cardioverter defibrillator to sense ventricular tachycardia: implications for fixed-gain sensing devices

Failure to sense ventricular tachycardia and/or ventricular fibrillation by implantable cardioverter defibrillators (ICDs) is rare. We report a case in which persistent undersensing of monomorphic and polymorphic ventricular tachycardia occurred with a second and third generation ICD using fixed-gain sensing. This occurred despite adequate R wave sensing during sinus rhythm. The use of an endocardial sensing lead did not correct the problem. Failure to sense ventricular tachycardia in the third generation device with fixed-gain sensing occurred late after implantation and was discovered only at follow-up electrophysiology testing of the ICD. This problem could not be corrected by reprogramming of the device, and was not related to lead dislodgement. Placement of a new device with an automatic-gain sensing algorithm and use of previously implanted epicardial leads with better sensing characteristics provided appropriate sensing of ventricular tachyarrhythmias. The case illustrates the importance of testing the sensing of all ventricular arrhythmias in patients with fixed-gain ICD's. Follow-up electrophysiology testing and evaluation of epicardial and endocardial leads may be necessary in certain cases to ensure adequate sensing of ventricular tachyarrhythmias late after implantation.

Sudden death in patients with congestive heart failure: future directions

Sudden, unexpected cardiac death continues to be a major clinical problem in patients with congestive heat failure. This review summarizes the current state of knowledge regarding the identification and management of these patients. The roles of ambulatory ECG monitoring, electrophysiological testing, signal-averaged ECG, and other methods of predicting increased risk of sudden death are discussed. The modes of sudden cardiac death and the potential mechanisms of ventricular arrhythmias in congestive heart failure are reviewed. Current therapeutic options including antiarrhythmic drugs, neurohormonal blockade, and automatic implantable cardioverter defibrillators are discussed. Finally, future directions and ongoing clinical investigations of the management of these complex patients are considered.

A prospective study of changes in right ventricular dP/dt during ventricular tachycardia

The automatic implantable cardioverter defibrillator (AICD) has significantly decreased mortality in high risk ventricular tachycardia (VT) patients. The AICD provides treatment based on ventricular rate, sometimes leading to high energy shocks in conscious patients with stable VT, or patients with sinus or supraventricular tachycardia. Other physiological parameters, such as maximal positive and negative systolic right ventricular (RV) dP/dt (RV + dP/dtmax, RV - dP/dtmax, respectively), may be included in detection algorithms for future implantable defibrillators. We studied frequency band limited positive and negative RV dP/dtmax before, during, and after 13 episodes of VT lasting at least 40 beats in duration in nine male patients. The mean (+/- SEM) RV + dP/dtmax, dropped by 120 +/- 28 mmHg/sec (P less than 0.001) during the first five beats of VT. RV + dP/dtmax then slowly rose toward baseline levels until a significant overshoot occurred during the first ten beats following VT termination (delta = 234 +/- 58 mmHg/second, P less than 0.002). RV + dP/dtmax correlated poorly with mean arterial pressure (r = 0.32, P greater than 0.1), systolic blood pressure (r = 0.19, P greater than 0.1), and VT cycle length (r = 0.34, P greater than 0.1). Conversely, RV - dP/dtmax rose during the first ten beats of VT (74 +/- 27 mmHg/sec, P greater than 0.05) and then slowly drifted back toward baseline levels. Like RV + dP/dtmax, RV - dP/dtmax overshot baseline levels during the recovery phase (-108 +/- 48 mmHg/sec, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of right ventricular impedance, pulse pressure and maximal dP/dt for determination of hemodynamic stability of ventricular arrhythmias associated with coronary artery disease

By monitoring hemodynamic parameters, a future generation of automatic implantable defibrillators will provide tiered therapy of ventricular arrhythmias according to the associated hemodynamic compromise. Changes in intracardiac impedance permit beat-to-beat assessment of ventricular volumes and make this parameter attractive as a rapid discriminator of hemodynamic compromise during arrhythmias. Beat-to-beat changes in right ventricular (RV) impedance were measured before, during and after 27 episodes of ventricular tachyarrhythmias induced in 17 men (64 +/- 7 years, mean +/- standard deviation; left ventricular ejection fraction 41 +/- 11%). Impedance was measured using a tripolar lead system and was compared to ventricular tachycardia cycle length, RV pulse pressure and maximum systolic RV dP/dt as indicators of systemic hemodynamic compromise. The average decreases in systolic blood pressure and mean arterial pressure during ventricular tachycardia were 48 +/- 23% and 46 +/- 26%, respectively (mean +/- standard deviation; p less than 0.001 for each). Right ventricular impedance decreased an average 39 +/- 22% from its baseline value (p less than 0.001) during ventricular tachycardia. The percent change in impedance from baseline during ventricular tachycardia correlated significantly with the percent decrease in systolic and mean arterial pressure (r = 0.45 and 0.42, respectively; both p less than 0.05). Right ventricular dP/dt correlated the most poorly of all parameters with changes in blood pressure while impedance X RV pulse pressure correlated best with changes in mean and systolic pressure (r greater than or equal to 0.82, p less than 0.001).

Exacerbation of doxorubicin cardiotoxicity by digoxin administration in an experimental rabbit model

The relationship between digoxin administration and the development of doxorubicin cardiomyopathy was evaluated in a chronic experimental rabbit model. We graded the myocardial pathology by conventional light microscopic histologic techniques. Additionally, myocardial fibrosis was quantified by hydroxyproline determinations and myocardial cellular damage by technetium-99m pyrophosphate uptake. Twenty-four rabbits were studied: 6 control, 6 doxorubicin-treated, and 12 digoxin-doxorubicin-treated. Mortality in the digoxin-doxorubicin group was 50%. All other rabbits lived throughout the entire experiment. The severest grades of histologic lesions were seen only in the digoxin-doxorubicin group. Myocardial hydroxyproline content was greater (p less than 0.05) in the digoxin-doxorubicin group than in the doxorubicin or control groups. Myocardial technetium-99m pyrophosphate content was also significantly greater (p less than 0.05) in the digoxin-doxorubicin group than in controls. In conclusion, the pretreatment and continued administration of digoxin, together with doxorubicin, increased the severity of myocardial damage and reduced longevity in this experimental model of doxorubicin cardiotoxicity.

Long-term oral therapy of congestive heart failure with phosphodiesterase inhibitors

The existing management of severe chronic congestive heart failure carries a dismal prognosis. Mortality over 6 months is 50% by some estimates. This fact, coupled with increasing concern for the safety and efficacy of the digitalis glycosides, has stimulated an intense search for new oral cardiotonic agents suitable for chronic administration. Despite the ability of many phosphodiesterase inhibiting agents to affect profound hemodynamic improvements acutely after oral or intravenous administration, none of the four agents here reviewed in 30 clinical trials has been adequately proven to provide benefit over conventional long-term therapy of severe heart failure. The four drugs to have undergone long-term clinical trials are amrinone, milrinone, enoximone (MDL 17043), and piroximone (MDL 19,025). For amrinone, inefficacy was revealed through carefully designed, placebo-controlled studies despite initial enthusiasm generated by open uncontrolled trials. Enoximone has suffered rapid attenuation of its hemodynamic effectiveness in most studies, and piroximone failed in its only long-term trial. Therefore, final judgment on most of these agents must await completion of controlled clinical trials, and any initial optimism stimulated by the current uncontrolled studies should be met with reservation.

Hospital-based DME: a balance between control and entrepreneurship

Achieving a balance between controlling the activity of a hospital-based DME company, and allowing its entrepreneurial manager to build it into a strong revenue-generating business, is possible. The payoff over the long term can more than make up for any near-term negative cash flow.

The effects of dihydroxyfumarate on isolated rabbit papillary muscle function: evidence for an iron dependent non-hydroxyl radical mechanism

To delineate the active free radical species mediating the toxic effects of autoxidizing dihydroxyfumarate (DHF), isolated rabbit right ventricular papillary muscles were exposed to 4.5 mM DHF in the presence of FeCl3, ADP and bovine albumin. In the absence of free radical scavengers a 47.3 +/- 11.5% (mean +/- standard deviation) depression in contractile force was noted over 60 minutes. Neither the combination of superoxide dismutase (SOD) 3,200 u/cc and catalase (CAT) 2,950 u/cc nor mannitol 0.1 M provided statistically significant protection. Deferoxamine mesylate (DFX) 10 mg/cc (15 mM) did provide significant protection of muscle function both in the presence and absence of SOD and CAT (p less than 0.01). The degree of protection conferred by DFX alone was statistically similar to that of DFX with SOD and CAT. This data suggests the involvement of an iron-oxygen complex not dependent on superoxide or hydrogen peroxide for its formation and not readily scavenged by mannitol. The perferryl ion may be representative of such a species. Alternatively, a reactive complex similar to the 'Crypto-OH' radical proposed by Youngman may be formed by the reaction of DHF with iron and oxygen.