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Biomedical subjects

J R Windle

Publications and source records attributed to J R Windle.

18 recordsLinked to original sources
PubMed1995

The quality of life of patients with life-threatening arrhythmias.

BACKGROUND: The treatment of life-threatening arrhythmias with amiodarone or an implantable cardioverter/defibrillator prolongs patient survival but with significant comorbidity. Previous studies have shown diminished health status and increased psychologic distress and inferred a diminished quality of life; however, a multidimensional analysis of quality of life, including patient perception, has not been performed. METHODS: One hundred four consecutive patients were surveyed regarding patient demographics, health status, psychologic distress, and patient-perceived quality of life. The patients were treated with amiodarone (n = 30) with an implantable cardioverter/defibrillator (n = 45) and the remainder were reference patients (n = 29). RESULTS: This study confirms that patients who survive life-threatening arrhythmias have diminished health status and increased psychologic distress; however, patient-perceived quality of life is preserved. These patients report a better perceived quality of life (as measured by the Quality of Life Index) than the reference group (22.3 +/- 4.0 vs 20.5 +/- 4.4, P < .05) and their scores are similar to those of normal healthy volunteers (mean score, 21.9). The improved quality of life scores were not dependent on treatment modality (22.1 +/- 4.0 vs 22.4 +/- 4.1 for medical vs surgical groups, respectively). CONCLUSIONS: Patient-perceived quality of life is maintained in patients who survive life-threatening arrhythmias despite their diminished health status and increased psychologic distress. Measured quality of life is independent of treatment modality. Thus, caution must be exercised in assuming a diminished quality of life in patients who have survived a life-threatening cardiac event.

Aged↗
PubMed1995

Defibrillator patch electrode constriction: an underrecognized entity.

Pericardial constriction associated with the placement of intrapericardial defibrillator patches is a rare occurrence that is reported only one tenth as often in defibrillator patients as in patients undergoing other types of cardiac operations. Although this discrepancy may be attributable to a lower incidence of constriction with the defibrillator patch electrode procedure, it may also indicate a failure to recognize that progressive right heart failure and signs of low cardiac output that could be due to pericardial constriction and not progressive systolic dysfunction. Because surgical removal of the patches and decortication of the epicardial surface is the only effective therapy, it is important to recognize this uncommon, but profoundly debilitating entity.

Adult↗
PubMed1995

Clinical comparison of acute single to dual chamber pacing in chronotropically incompetent patients with left ventricular dysfunction.

Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimics the normal electrical and hemodynamic activity of the heart. This reasoning has been used to justify the higher initial costs and increased complexity of dual chamber system. This study was designed to determine if objective criteria could be identified during acute testing justify implanting a dual chamber instead of a single chamber system in patients with left ventricular dysfunction. Eight patients with DDDR pacemakers (implanted for chronotropic incompetence) and left ventricular dysfunction underwent exercise radionuclide angiography and graded exercise treadmill testing. Each patient performed the tests in the single (VVIR) and dual (DDDR) chamber modes in a randomized, blinded fashion. We found that objective parameters such as ejection fraction (31% +/- 13% vs 31% +/- 10%), exercise tolerance (6.1 +/- 2.7 min vs 6.3 +/- 2.9 min), oxygen consumption (VO2) (941 +/- 286 mL/min vs 994 +/- 314 mL/min), carbon dioxide production (VCO2) (995 +/- 332 mL/min vs 1054 +/- 356 mL/min), and maximum attainable workload (43 +/- 24 W vs 46 +/- 22 W) did not differ between the single and dual chamber pacing modes. These findings suggest that in the acute setting, the additional cost and complexity of dual chamber, rate responsive pacing cannot be justified by objective improvements in exercise tolerance in patients with underlying left ventricular dysfunction.

Aged↗
PubMed1994

Defibrillator twiddler's syndrome.

Long-term complications of internal cardioverter defibrillators have generally involved inappropriate shocks or hardware malfunctions. The present case documents a new problem of internal cardioverter defibrillator lead disruption resulting from patient-induced rotation of the generator in its pocket, similar to the previously reported pacemaker twiddler's syndrome. However, unlike the usual early symptoms of pacemaker nonfunction, the first symptomatic manifestation of the defibrillator twiddler's syndrome may be an inappropriate internal cardioverter defibrillator discharge or more importantly, unrescued sudden death. Careful attention to patient complaints about the internal cardioverter defibrillator generator and being alert to subtle lead changes on chest radiographs may allow the clinician to recognize this syndrome before a major, possibly fatal event.

Defibrillators, Implantable↗
PubMed1994

Options in managing the patient with high defibrillation thresholds.

The desired defibrillation threshold (DFT) obtained during intraoperative testing of an implantable cardioverter defibrillator (ICD) should be 10 J lower than the maximal energy delivered by the ICD generator. Of the 206 patients undergoing ICD implantation since December 1986, 8 (3.9%) have had initial DFTs with less than the 10-J safety margin using the standard large patch-large patch configuration. Patches were implanted by left thoracotomy in 6 and sternotomy in 1, and 1 had implantation of a transvenous defibrillation lead and subcutaneous patch. Of note, 6 (75%) of the 8 patients with high DFTs had prior open heart operations, half were on a regimen of long-term amiodarone therapy, and the mean left ventricular mass index was quite large but not significantly greater than that of patients with low DFTs. Multiple techniques was tried to improve the DFTs in this group. Satisfactory DFTs were eventually obtained in 7 (88%); the threshold was lowered from a mean of 41.4 +/- 3.8 J to 26.9 +/- 8.8 J (p = 0.002). The most effective techniques were addition of a superior vena cava lead attached by a Y connector to one of the large patch leads in some patients and conversion to a biphasic-waveform generator in 2 others. Adding a third epicardial lead did not lower the DFTs. There were no major postoperative complications or deaths attributable to these supplemental procedures. Using these techniques, satisfactory DFTs were obtained in almost all patients with an ICD.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Scatter diagram analysis: a new technique for discriminating ventricular tachyarrhythmias.

With the increasing flexibility allowed by implantable cardioverter defibrillators that use tiered therapy, it is important to match the therapy with the arrhythmia. In this article we present scatter diagram analysis, a new computationally efficient two-channel algorithm for distinguishing monomorphic ventricular tachycardia (VT) from polymorphic ventricular tachycardia and ventricular fibrillation (VF). Scatter diagram analysis plots the amplitude from one channel versus the amplitude from another channel on a graph with a 15 x 15 grid. The fraction (percentage) of the 225 grid blocks occupied by at least one sample point is then determined. We found that monomorphic VT traces nearly the same path in space and occupies a smaller percentage of the graph than a nonregular rhythm such as polymorphic VT or VF. Scatter diagram analysis was tested on 27 patients undergoing intraoperative implantable cardioverter defibrillator testing. Passages of 4.096 seconds were obtained from rate (bipolar epicardial) and morphology (patch) leads, and digitized at 125 Hz. Scatter diagram analysis distinguished 13 episodes of monomorphic VT (28.6% +/- 4.0%) from 27 episodes of polymorphic VT or VF (48.0% +/- 8.2%) with P < 0.0005. There was overlap in only one monomorphic VT episode and one polymorphic VT or VF episode.

Algorithms↗
PubMed1994

Clinical applications of signal-averaged electrocardiography in patients after myocardial infarction.

In conclusion, signal-averaged electrocardiography is a useful, noninvasive technique to identify patients after myocardial infarction at risk for future arrhythmic events, especially in conjunction to existing tools, such as 24 hour ambulatory monitoring, echocardiography, nucleotide angiography and coronary angiography. It has a limited positive predictive value, but has an excellent negative predictive value. The optimum time to do signal-averaged electrocardiograms after myocardial infarction is unclear, 6 to 14 days after myocardial infarction has the highest sensitivity. Time domain analysis remains the most common method used to record late potentials. The definition of late potential and the scoring of a high resolution electrocardiogram as normal and abnormal have not yet been resolved. The criteria proposed by the Task Force Committee of the European Society of Cardiology, the American Heart Association and the American College of Cardiology (see introduction) should be observed at present. Many studies on signal-averaging were done in the prethrombolytic era. In patients who have received thrombolytic therapy, the positive predictive value of signal-averaged electrocardiograms has decreased. There are other limitations in applying signal averaging technique. The faster the ventricular tachycardia is induced in electrophysiological studies, the shorter is the late potential. Thus, a faster tachycardia which causes sudden cardiac death may not be detected by late potentials. The management strategies for patients who have abnormal signal-averaged electrocardiograms after myocardial infarction have not be defined. One should note that any management strategy has to prove that it improves prognosis. More prospective, randomized clinical trials are required to address these issues.

Arrhythmias, Cardiac↗
PubMed1993

Effects of flecainide on ectopic atrial automaticity and conduction.

BACKGROUND: Previous studies have shown that class Ic antiarrhythmic agents are effective in suppressing ectopic atrial rhythms and accessory pathway conduction. METHODS AND RESULTS: To explore the potential mechanisms for their effectiveness, we investigated the concentration-dependent effects of the Ic agent flecainide acetate (0.5 to 10 micrograms/mL) on atrial ectopic automaticity and exit conduction in isolated rabbit tricuspid valves. This experimental model consists of three major cell types as defined anatomically and by intracellular recordings: pacemaker, transitional, and working atrial muscle. Simultaneous recordings from these cell types before and during flecainide superfusion (n = 7) showed that the drug produced a slight, concentration-dependent slowing of pacemaker-transitional conduction but elicited third-degree transitional-working atrial muscle block in six of seven preparations at 10 micrograms/mL. Flecainide caused a significant dose-dependent reduction in the initial phase of diastolic depolarization of pacemaker cells but produced only a small, biphasic change in spontaneous pacemaker cycle length. It also caused a significant prolongation in action potential duration in pacemaker and transitional cells and reduction in upstroke velocity in atrial cells. Of note in four additional preparations, flecainide caused a concentration-dependent upward shift in the strength-duration curve for atrial fibers. CONCLUSIONS: These data suggest that flecainide has little direct effect on ectopic atrial automaticity but rather causes exit conduction slowing and block between transitional and atrial muscle fibers. The mechanism for the induction of block is likely due to a decrease in atrial excitability creating a greater electrical load on generated impulses.

Animals↗
PubMed1990

Late potentials and inducible ventricular tachycardia in surgically repaired congenital heart disease.

We compared signal-averaged electrocardiography with invasive electrophysiological study in patients after surgical repair of congenital heart disease to determine if potentially useful correlations exist between the two methods for assessment of risk for ventricular tachycardia. Thirty-one patients (age, 1-49 years; mean, 10.6 years) with congenital heart disease repaired with right ventriculotomy or postrepair right bundle branch block (77% postoperative tetralogy of Fallot) who had electrophysiological study were studied with signal-averaged electrocardiography. Patients were classified by electrophysiological study results as having no inducible ventricular tachycardia, nonsustained ventricular tachycardia, or sustained ventricular tachycardia. Signal-averaged electrocardiograms were examined for the duration of low-amplitude (less than or equal to 40 microV) QRS signal, duration of total QRS, and root-mean-square voltage of the terminal 40 msec of the QRS. Low-amplitude terminal root-mean-square voltage of 100 microV or less had 91% sensitivity and 70% specificity for ventricular tachycardia inducible by electrophysiological study. Similar sensitivity but less specificity were seen using the criterion of 20 msec or more total low-amplitude QRS signal (initial plus terminal) or using total QRS duration of 128 msec or more. There was a weaker association between terminal low-amplitude QRS signal of 15 msec or more and inducible ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1989

Fast Fourier transformation of the entire low amplitude late QRS potential to predict ventricular tachycardia.

Signal-averaged electrocardiograms (X, Y and Z leads) were acquired from 24 patients with coronary artery disease and recurrent ventricular tachycardia, 24 control patients with coronary artery disease and 23 normal subjects to assess the discriminant value of fast Fourier transformation of the entire late potential period of the QRS complex. Analysis of the vector magnitude in the temporal domain (25 to 250 Hz bandpass filters) measured high frequency QRS duration, the duration of terminal signals less than 40 microV and the root mean square voltage of the last 40 ms. Late potentials were defined as terminal signals greater than 25 Hz that were less than 40 microV. Analysis in the frequency domain used a 120 ms window that encompassed (had onset with) all of the late potential, but the mean value was first subtracted to eliminate a direct current component. High frequency spectral areas (60 to 120 Hz) and the percent high frequency (100 x [60 to 120 Hz/0 to 120 Hz]) were calculated. Results in both temporal and frequency domains were similar in control patients with coronary artery disease and normal subjects. Patients with ventricular tachycardia had a longer high frequency QRS complex (p less than 0.0001) and longer high frequency terminal signals less than 40 microV (p less than 0.0004), but not significantly lower voltage in the last 40 ms. The most useful temporal domain measurement was high frequency QRS duration (if greater than or equal to 120 ms, odds ratio = 8.2). Patients with ventricular tachycardia had increased high frequency spectral areas (p less than 0.0002) in the late potential, and the percent high frequency was especially increased (p = 0.0000; if percent high frequency greater than 3.1%, odds ratio = 18.4). The odds ratio and the area under the receiver operating characteristic curve were both greater for percent high frequency than for high frequency QRS duration (p less than 0.03). All patients with ventricular tachycardia had a high frequency QRS complex greater than or equal to 107 ms or percent high frequency greater than or equal to 3.1% (sensitivity 100%). For a high frequency QRS complex greater than or equal to 107 ms and percent high frequency greater than or equal to 3.1%, specificity was 96%. Therefore, high frequencies in late potentials, not their duration or reduced voltage, most usefully identify patients with coronary artery disease who are prone to ventricular tachycardia.

Adult↗
PubMed1986

Subthreshold conditioning stimuli prolong human ventricular refractoriness.

This study tested whether a subthreshold stimulus (Sc) inserted before a premature stimulus prolonged the right ventricular effective refractory period in humans, and whether the degree of effective refractory period lengthening was influenced by heart rate, Sc current intensity or Sc pulse duration. Sc at current intensity 10 mA and pulse width 2 ms prolonged mean effective refractory period from 255 ms to 277 ms (p less than 0.001, n = 20). The increase in effective refractory period was similar in 6 patients studied at pacing cycle lengths 600 (259 to 289 ms) and 400 ms (236 to 258 ms). When Sc current intensities were varied at 2, 5 or 10 mA at a constant pulse duration of 100 ms the effective refractory period progressively prolonged by 6, 40 and 81 ms respectively (p less than 0.02, n = 6). The pulse duration of Sc at a constant current of 10 mA significantly influenced effective refractory period prolongation. With Sc pulse durations of 2, 10, and 100 ms the effective refractory period prolonged by 16, 33 and 66 ms respectively (p less than 0.01, n = 7). Thus, subthreshold impulses prolong the effective refractory period in human right ventricular myocardium. The prolongation of effective refractory period depended on Sc current intensity and pulse duration but was independent of heart rate at the cycle lengths tested. The use of subthreshold stimuli as antiarrhythmic therapy may be feasible in some patients.

Adult↗
PubMed1986

Determination of the earliest site of ventricular activation in Wolff-Parkinson-White syndrome: application of digital continuous loop two-dimensional echocardiography.

Surgical and transcatheter ablation of accessory atrioventricular (AV) connections (Wolff-Parkinson-White syndrome) requires accurate localization of the accessory pathway. In a canine model of endocardial pacing, a continuous loop two-dimensional echocardiographic technique was developed for determining the earliest site of ventricular activation. This technique was then used to localize accessory AV connections in patients. Echocardiographic images were acquired on videotape and converted to a digital continuous loop format, from which the earliest site of systolic motion was determined. In six dogs, using six distinct endocardial sites, two blinded observers accurately identified the earliest site of ventricular activation in 31 (86%) of 36 and 32 (89%) of 36 locations. Determination of the earliest site of ventricular activation with the continuous loop digital technique was superior to standard analog analysis in overall accuracy (p less than 0.02) and in intraobserver variability (p less than 0.004). After validation of this technique, 21 patients with 22 accessory AV connections with anterograde conduction were studied. The earliest site of mechanical activity was determined during sinus (10 patients) or atrial paced (11 patients) rhythms by two blinded observers and compared with electrophysiologic mapping and surface electrocardiograms. Digitally processed echocardiograms correctly localized the earliest site of ventricular activation in 18 of 22 connections and predicted an adjacent location in the remaining 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Pacemaker insertion for prehospital bradyasystolic cardiac arrest.

We investigated the use of transvenous (TV) and transmyocardial (TM) pacemakers in the emergency department (ED) in 54 adult patients (42 men and 12 women) with bradyasystolic cardiac arrest. Down time prior to cardiopulmonary resuscitation (CPR) was 4.8 +/- 4.3 minutes. Time in the ED prior to pacer insertion was 26.9 +/- 17.7 minutes. Electrical capture rate was 63%. Pulse developed in 5%. Only 1.2% were admitted, and none was discharged alive. There was no significant difference in capture rate for TV versus TM pacers or in capture rate whether the pacer was inserted early or late after ED arrival. We conclude that ED pacer insertion for such patients does not alter survival rates.

Adult↗
PubMedDate not supplied

False-negative findings in pericardial effusion using M-mode echocardiography.

M-mode echocardiography in a 3-year-old patient with suspected pericardial effusion was negative for the presence of an effusion. A subsequent 2-dimensional echocardiogram demonstrated a large effusion lateral to the right atrium and right ventricle. The reasons for the false-negative M-mode echocardiogram and a discussion of the literature are presented.

Child, Preschool↗