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Biomedical subjects

D S Cannom

Publications and source records attributed to D S Cannom.

At least 19 recordsLinked to original sources
PubMed1992

A critical appraisal of indications for the implantable cardioverter defibrillator (ICD).

The implantable cardioverter defibrillator (ICD) is a remarkably effective therapy for reducing sudden cardiac death in patients with malignant ventricular arrhythmias. The indications for implantation of the ICD were approved in 1985 by the United States Food and Drug Administration; it could be implanted in patients who have experienced cardiac arrest or in those with recurrent ventricular arrhythmias which are not suppressed by anti-arrhythmic drugs in the electrophysiology laboratory. These established indications have not changed in the last seven years. In the near future, the release of third-generation ICDs (with antitachycardia pacing) will likely further expand indications for the device. Many patients with stable ventricular tachycardia who have not had syncope or cardiac arrest will receive a third-generation defibrillator. Also, three clinical trials now in progress--CABG-PATCH, Multicenter Automatic Defibrillator Implantation Trial (MADIT) and Multicenter Unsustained Tachycardia Trial (MUSTT)--are studying "pre-event" patients with low ejection fraction and electrical instability; some of the patients in each trial are being prospectively randomized to the ICD. Within the next five years we will have a better understanding of the role of ICD therapy in such patients. Until these studies are completed, it is important that the indications for the ICD not be expanded.

Arrhythmias, Cardiac↗
PubMed1988

Predictors of automatic implantable cardioverter defibrillator discharge for life-threatening ventricular arrhythmias.

Data from 100 patients with life-threatening ventricular arrhythmias and automatic implantable cardioverter defibrillators (AICDs) were analyzed to determine if clinical, angiographic and electrophysiologic variables are predictive of AICD discharge. During a median follow-up period of 18 months, 45% of patients experienced greater than or equal to 1 device discharge during a documented ventricular arrhythmia or in association with presyncope or syncope ("appropriate" AICD discharge). Univariate predictors of appropriate AICD discharge included depressed left ventricular ejection fraction (p = 0.0007), inducible sustained ventricular arrhythmia at electrophysiologic study performed in the absence of antiarrhythmic drugs (p = 0.009), fewer number of extrastimuli required for induction at this study (p = 0.001), inducible sustained arrhythmia at electrophysiologic study performed on the discharge antiarrhythmic regimen (p = 0.0005) and fewer extrastimuli required for this induction (p less than 0.0001). Multivariate analysis identified the induction of a sustained ventricular arrhythmia by 1 or 2 extrastimuli during electrophysiologic study performed on the discharge regimen as the only independent predictor among the variables analyzed (p less than 0.0001). The probability of appropriate AICD discharge at 18 months was 86% for patients who had a sustained arrhythmia induced with 1 or 2 extrastimuli versus 15% for those requiring 3 extrastimuli for arrhythmia induction and 13% for patients without inducible sustained arrhythmias.

Arrhythmias, Cardiac↗
PubMed1988

The automatic implantable cardioverter-defibrillator: efficacy, complications and survival in patients with malignant ventricular arrhythmias.

Ninety-four patients underwent surgery for automatic implantable cardioverter-defibrillator implantation. Ninety patients were discharged from the hospital with the device and were followed up for a mean period of 17 +/- 10 months. Forty-six patients experienced at least one discharge of the device under circumstances consistent with a malignant ventricular arrhythmia. One sudden death occurred. Complications included perioperative death (3 patients), post-operative ventricular tachycardia (12 patients) and atrial fibrillation (8 patients), perioperative myocardial infarction (1 patient) and device discharges for sinus tachycardia and supraventricular arrhythmias (17 patients). Six and 12 month survival rates by life table analysis were 98.7 and 95.4%, respectively. Thus, the automatic implantable cardioverter-defibrillator is a highly effective and relatively low risk treatment modality for patients with refractory life-threatening ventricular arrhythmias.

Adolescent↗
PubMed1988

Postoperative infection with the automatic implantable cardioverter defibrillator: clinical presentation and use of the gallium scan in diagnosis.

This report describes three patients with infection involving an automatic implantable cardioverter defibrillator. All three patients presented with fever, fluid in the pulse generator pocket, leukocytosis and an elevated erythrocyte sedimentation rate. A gallium scan, together with aspiration and culture of the fluid from the pocket, confirmed the diagnosis in each case.

Candidiasis↗
PubMed1986

Implantation of the automatic implantable cardioverter defibrillator (AICD): practical aspects.

Most patients who are resuscitated from an episode of sudden cardiac death or one of sustained ventricular tachycardia (VT) can now be treated using serial electrophysiologic testing as a guide to drug therapy. Recurrence rates are low if an antiarrhythmic regimen can be found which prevents induction of VT. Patients failing serial drug testing have a high recurrence rate (approximately 50%/year). Most clinicians now refer such patients for either experimental antiarrhythmic therapy or electrical intervention. The most promising of the electrical interventions (including tachycardia converting pacemakers and intraoperative mapping) has been the automatic implantable cardioverter defibrillator (AICD). Only recently has the AICD been released from investigative status by the Food and Drug Administration. It can be implanted safely and with favorable clinical outcome if the techniques of implantation are well understood and used often. The text incorporates the authors' experience in implanting nearly 200 devices and is intended as a practical guide to the use of the AICD.

Electric Countershock↗
PubMed1984

Clinical and induced ventricular tachycardia in a patient with myotonic dystrophy.

A 20 year old patient with myotonic dystrophy presented with hemodynamically significant ventricular tachycardia at a rate of 230 beats/min requiring cardioversion. Two days later, the identical tachycardia was reproducibly initiated and terminated in the electrophysiology laboratory using two extrastimuli in the right ventricle. Trials of procainamide and quinidine were not successful in controlling the induced rhythm and amiodarone was administered. On restudy with amiodarone, ventricular fibrillation was induced using a single extrastimulus. This case suggests that ventricular tachyarrhythmias may contribute to the known cardiac morbidity and mortality in myotonic dystrophy.

Adult↗
PubMed1983

Control of sudden recurrent arrhythmic deaths: role of amiodarone.

Patients resuscitated after out-of-hospital cardiac arrest have electrical instability of the myocardium, with 30% to 40% propensity for recurrent arrest in the first year. About 85% to 90% of such patients have complex ventricular ectopy and runs of ventricular tachycardia; in 70% to 80%, ventricular tachycardia or fibrillation are inducible by programmed electrical stimulation. The attempt to control recurrent cardiac arrest using these parameters and conventional antiarrhythmic drugs has yielded conflicting or variable results. Amiodarone was therefore studied in 40 consecutive patients (with previous cardiac arrests) in whom conventional antiarrhythmic therapy had proved ineffective or was not tolerated. The mean ejection fraction of the group was 0.29 +/- 0.12. At a mean follow-up of 16 months (range 5 to 40 months) six patients had died, three from heart failure, one from liver failure (not drug induced), and two from sudden (presumably arrhythmic) death. Late occurrences of arrhythmia were found in two patients (complicated by digitalis intoxication in one). Ambulatory ECG recordings showed that amiodarone had a potent suppressant effect on ventricular ectopy and runs of VT, but electrophysiologic studies demonstrated that it did not inhibit inducible VT/VF in greater than 65% despite an excellent clinical outcome. Limiting adverse reaction was seen in only one patient; other relatively minor side effects occurred in 10% to 15% of patients receiving maintenance therapy. Our data provide further evidence for the effectiveness of amiodarone in life-threatening ventricular arrhythmias, with a potential for the prolongation of survival in patients resuscitated after out-of-hospital cardiac arrests.

Amiodarone↗
PubMed1983

Orthogonal electrogram sensing.

Intracardiac electrogram sensing is the afferent limb of demand pacing systems. Under- and over-sensing at the ventricular level has been demonstrated in almost 50% of implanted unipolar pulse generators, and atrial electrogram sensing problems are more common. A unique dedicated sensor employing noncontacting and circumferentially placed orthogonal electrodes was tested at both the atrial and ventricular levels. Electrograms demonstrated voltages similar to those recorded from contacting electrodes, but with complete far-field rejection of signals from the opposite chamber. Orthogonal electrograms allowed for activation sequencing and capture verification as well.

Electric Conductivity↗
PubMed1983

Orthogonal ventricular electrogram sensing.

Inappropriate demand pacing is most commonly due to improper ventricular electrogram sensing. Filters and programmable sensitivities improve electrogram sensing of conducted beats, but paced electrograms cannot be sensed by conventional unipolar or bipolar systems. A permanent pacing lead with a standard tip electrode and three orthogonal 0.8 mm2 sensing electrodes located circumferentially 2 cm proximal to the pacing tip was tested in 22 patients. The tip electrode was placed in the right ventricular apex in standard pacing position. Orthogonal electrodes were not in contact with ventricular myocardium. Orthogonal ventricular electrograms from 54 electrode pairs were compared with unipolar tip electrograms during conducted rhythms and paced beats. Tip ventricular electrograms averaged 12.8 mV with 3.04 mVT waves. Orthogonally recorded ventricular electrograms during conducted beats averaged 8.86 mV with T waves of 1.57 mV. During pacing, tip ventricular electrograms were obscured by the stimulus artifact and repolarization events. Orthogonal ventricular electrograms, however, demonstrated small discrete stimuli of 1.99 mV followed by discrete ventricular electrograms of 9.19 mV and T waves of 1.9 mV. Orthogonal ventricular electrograms compared favorably with contacting tip electrograms during conducted beats and provided a redundant sensing capability. During pacing, orthogonal ventricular electrograms allowed the capability for capture verification. A new pacing catheter allows for improved ventricular electrogram sensing and capture verification.

Arrhythmias, Cardiac↗
PubMed1983

Amiodarone in refractory life-threatening ventricular arrhythmias.

Ninety-six patients with life-threatening ventricular arrhythmias refractory to two or more conventional agents were treated with amiodarone and followed for 6 to 40 months (mean, 15 months). Currently, 75 are alive and well. Seven patients died from nonarrhythmic and five from arrhythmic causes. Nonfatal arrhythmias recurred in four patients, one with early and three with late onset. Intolerable side effects occurred in five patients but heart failure was not aggravated by the drug. On 24-hour Holter recordings done before and serially during therapy in 72 patients, amiodarone eliminated episodes of ventricular tachycardia and complex ectopy and reduced total ectopic beat counts by 90% or more in all but 4 patients. In contrast, ventricular tachycardia inducible by programmed electrical stimulation was suppressed in only 50% of patients, but failure of such suppression did not compromise an excellent clinical outcome. Thus, amiodarone is highly effective in the prophylaxis of recurrent refractory life-threatening ventricular arrhythmias.

Acute Disease↗
PubMed1981

A new orthogonal lead for P synchronous pacing.

P synchronous pacing has long been identified as advantageous for patients with atrioventricular conduction defects and intact sinus node function. Prior endocavitary systems have been infrequently employed, because of unreliable P wave sensing from standard ring electrodes in the atrium or the requirement for a second atrial sensing lead. A single endocardial lead employing a unipolar ventricular stimulating electrode and an orthogonal P wave sensing design was developed and tested in 22 patients undergoing electrophysiologic study or pacemaker implantation. Thirteen centimeters from the stimulating tip of a standard permanent pacing lead, three or four electrodes with a surface area of one millimeter squared, equidistant from the tip, were placed circumferentially about the catheter. With the catheter tip normally placed in the right ventricular apex, atrial sensing electrodes were positioned in the mid-high lateral right atrium, adjacent to, but not affixed to, the right atrial wall. Bipolar orthogonal leads X and Y were obtained. In 22 patients, during sinus rhythm, atrial electrogram voltages in the X axis of 2.47 plus or minus 1.6 millivolts and 2.32 plus or minus 1.6 millivolts in the Y axis were recorded. QRS voltages of 0.078 millivolts and 0.073 millivolts, respectively, allowed dramatic ability to discriminate P from QRS complexes (P/QRS equals 32/1). There was no change in QRS or unipolar ventricular pacing. A single catheter designed for P synchronous pacing employing circumferentially placed atrial sensing electrodes has demonstrated unique atrial sensing voltages with excellent QRS signal rejection.

Cardiac Catheterization↗
PubMed1978

Relations between ventricular refractoriness and regional myocardial blood flow after acute coronary occlusion.

Myocardial ischemia has been associated with dispersion of ventricular refractory periods and this dispersion has been related to the ventricular arrhythmias seen with coronary occlusion. This study relates the degree of change in measured ventricular refractory period with the degree of regional myocardial blood flow abnormality after coronary occlusion. When regional myocardial blood flow is less than 70% of that of nonischemic areas, refractory periods are significantly (P less than 0.001) shortened. The greatest change in refractory periods occurs in areas with a regional myocardial blood flow that is 21 to 40% of that of nonischemic areas. Marked (less than 20%) and minimal (61 to 80%) reductions in regional myocardial blood flow are associated with less, but still significant, shortening of ventricular refractory periods. Thus dispersion of refractoriness can be related to the inhomogeneity of regional myocardial blood flow after acute coronary occlusion. Interventions designed to salvage ischemic myocardium by increasing regional myocardial blood flow may affect dispersion of ventricular refractory periods in complex and divergent ways.

Acute Disease↗