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Biomedical subjects

R Yee

Publications and source records attributed to R Yee.

At least 199 records · Page 11Linked to original sources
PubMed1990

Utility of low energy test shocks for estimation of cardiac and electrode impedance with implantable defibrillators.

We assessed the value and safety of using a low voltage test shock to predict cardiac and electrode impedance during subsequent high voltage, transvenous, sequential pulse shocks. Two transvenous defibrillation catheters were inserted in 15 patients undergoing electrophysiology study for the evaluation of ventricular tachycardia/fibrillation. A sequential pulse test shock at stored voltage of 50 or 100 volts was delivered during sinus rhythm and high voltage therapeutic shocks were delivered during induced ventricular tachycardia/fibrillation. The test shocks were well tolerated and caused only minimal discomfort. Peak delivered voltage for each pulse of the test shock ranged from 34 to 116 volts (mean 62 +/- 27) and for each pulse of the therapeutic shocks from 186 to 778 volts (mean 435 +/- 146). There was a very strong relationship between the impedance of the test and the mean impedance of the therapeutic shocks (R = 0.89, P less than 0.001). The mean impedance of the test shock was slightly greater than the mean impedance of the test shock as slightly greater than the mean impedance of the therapeutic shocks (mean 90 +/- 24 ohms compared to 77 +/- 16 ohms, P less than 0.001), with a maximum difference between test and therapeutic shock impedances of 39 ohms (mean difference 8.4 +/- 10.3 ohms). There was a significant inverse relationship between impedance and peak current (R = -0.49, P = 0.001). Cardiac and electrode impedance during transvenous defibrillation can be predicted reliably and safely by a low voltage test shock. This technique provides a safe and simple method to ensure appropriate connections and electrode function for subsequent countershock therapies.

Adult↗
PubMed1990

Correlation between the ventricular electrogram amplitude in sinus rhythm and in ventricular fibrillation.

During testing of implantable defibrillators, ability to sense ventricular fibrillation is assessed by observing electrograms and the emitted ECG interpretation channel during induced ventricular fibrillation. We hypothesized that ventricular electrogram amplitude in sinus rhythm could be used to predict the ventricular electrogram amplitude in ventricular fibrillation and serve as a first approximation of the "safety margin" for sensing ventricular fibrillation. We compared the peak-to-peak epicardial ventricular electrogram during sinus rhythm and ventricular fibrillation in 12 patients undergoing defibrillator implantation. The ventricular electrogram was recorded with an integrated bipolar lead and filtered at 10-50 Hz. Ventricular fibrillation was induced by alternating current and the ventricular electrogram measured from cessation of alternating current to the first countershock. The mean ventricular electrogram amplitude in sinus rhythm was 15.3 +/- 5.4 mV (range 7.1-25.5) and in 37 episodes of ventricular fibrillation was 8.3 +/- 3.6 mV (range 2.1-16.3). There was a significant relationship between the mean ventricular electrogram amplitude in sinus rhythm and in ventricular fibrillation (R = 0.7, P less than 0.001). There was wide variation among individuals in the decrease in the mean ventricular electrogram amplitude during ventricular fibrillation, with the ratio of mean ventricular electrogram in sinus rhythm to mean ventricular electrogram in ventricular fibrillation ranging from 0.29 to 1.05 (mean 0.55 +/- 0.20). This suggests that up to a fourfold decrease may be expected in the mean ventricular electrogram amplitude during ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1990

Feasibility of long-term electrocardiographic monitoring with an implanted device for syncope diagnosis.

Patients with infrequent recurrent syncope undiagnosed after extensive noninvasive and invasive testing pose a diagnostic and therapeutic dilemma. The purpose of this pilot study was to assess the feasibility of using an implanted, long-term monitor as an aid to diagnosis in these patients. This was done using commercially available pacemakers with monitoring functions. Sixteen patients (eight males and eight females), aged 59.7 +/- 17 years who had unexplained syncope despite a 12-lead electrocardiogram, repeated Holter monitoring, exercise testing, echocardiography, an electrophysiological study, and a tilt test (n = 6), were entered into the study. Patients had experienced a mean of 3.1 +/- 1 episodes of syncope in the 12 months prior to the study. All provided a history suggestive of Stokes-Adams attacks and were referred for consideration of pacemaker implantation. Two patients had ischemic heart disease and one patient had a long QT interval. Patients had an Intermedics Nova II or Medtronic Quintech DPG pulse generator capable of recording sensed and paced events implanted with a single right ventricular lead. Syncope or presyncope occurred in ten patients (62%) 4.9 +/- 4.2 months after pacemaker implantation. Bradycardia was detected in six patients and four patients had no arrhythmia. In addition to bradycardia, one patient also had tachycardia detected. Pacing therapy resulted in symptom relief in all six patients with syncope or presyncope due to bradycardia. Complications of pacemaker implantation (lead insulation failure) occurred in two patients. One of these patients subsequently had an infection of the generator pocket with associated systemic sepsis.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1990

Surgery for atrial tachycardia.

Atrial flutter is associated with a macro-reentrant loop including an area of slow conduction cryoablation of which prevents atrial flutter to occur. Three patients underwent such intervention. Atrial fibrillation is associated with multiple reentrant circuits (leading circle of Allessie) that requires a critical surface area to perpetuate. We have designed an operation, the corridor operation, which isolate the sinus node and the AV node within a small segment of atrial tissue, to restore the chronotropic function of the sinus node. Nine patients underwent the corridor operation at our institution. There were eight men and one woman. Five had incessant atrial fibrillation and four paroxysmal. One patient had associated mitral valve stenosis and one cardiomyopathy. There were no perioperative complications. Six patients had normal sinus node function postoperatively including all the four patients with documented normal sinus node function preoperatively. Three patients required implantation of an AAI pacemaker. Two patients had recurrence of atrial fibrillation within the corridor. Our experience suggests that the corridor operation should be restricted to patients with documented good sinus node function and without structural heart disease. Our experience with five patients with paroxysmal sinus node tachycardia has been disappointing. Only one patient had long-term success although better series have been published.

Adult↗
PubMed1990

Management of the patient with the Wolff-Parkinson-White syndrome.

Patients with ventricular preexcitation may have symptomatic arrhythmias (Wolff-Parkinson-White syndrome) which can range from life-threatening, to disabling symptoms or minimal symptoms. Individuals may also be entirely asymptomatic. A rational approach to the management of these individuals is therefore dependent on the clinical circumstances. This review discusses the value and limitations of some of the available noninvasive and invasive investigations which may contribute to the successful management of these patients. In general, investigations are useful for establishing the diagnosis, identifying those patients at risk from life-threatening arrhythmias and providing a rational basis for therapy. The available pharmacologic and nonpharmacologic therapeutic options are discussed.

Anti-Arrhythmia Agents↗
PubMed1990

Prognostic value of electrophysiology testing in asymptomatic patients with Wolff-Parkinson-White pattern.

The prognostic value of electrophysiology testing was studied in 75 asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern. All patients underwent electrophysiology testing at entry to the study and were followed up annually for a total of 348 patient-years (median, 4.3 years). There were 44 male and 31 female patients, and age at enrollment ranged from 7 to 77 years (mean, 34 +/- 14 years). The median effective refractory period of the accessory pathway was 293 msec (interquartile range, 280-310 msec), and the median shortest RR interval between preexcited beats during atrial fibrillation (SRR) [corrected] was 274 msec (240-320 msec). Twenty-three patients had an SRR of 250 msec or less and eight patients had a median shortest SRR interval of 200 msec or less. Twelve patients had inducible sustained reciprocating tachycardia, 10 patients had inducible nonsustained reciprocating tachycardia, and 23 patients had inducible sustained atrial fibrillation. Twenty patients (27%) lacked retrograde conduction over the accessory pathway. No patient died suddenly during a median follow-up of 4.3 years. Six patients (8%) became symptomatic with documented supraventricular tachycardia, of whom two underwent operative ablation of their accessory pathways. No patient with absent retrograde accessory pathway conduction during the electrophysiology study became symptomatic. Inducible sustained or nonsustained reciprocating tachycardia at electrophysiology study did not predict the development of subsequent symptomatic supraventricular tachycardia. Nine patients lost preexcitation during follow-up. Age at enrollment (relative risk/decade, 1.4; 95% confidence interval, 1.0-1.8) and anterograde accessory pathway refractory period (relative risk, 1.06/10 msec; 95% confidence interval, 1.0-1.12) were independent predictors of loss of preexcitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Identification of cystatin C, a cysteine proteinase inhibitor, as a major secretory product of human alveolar macrophages in vitro.

The major inhibitor of the cysteine class of proteinases found in human body fluids, such as spinal fluid, milk, and seminal plasma, is cystatin C. In this study we show that human bronchoalveolar fluid also contains cystatin C and examine cystatin C expression by alveolar macrophages in vitro. Immunoprecipitation of extracts of metabolically labeled cells and immunoblotting of cellular extracts and culture media show that cystatin C is synthesized as a 14 (+/- 0.5) kilodalton (kD) protein and that greater than 90% of the protein is released as the 14 kD product into the culture supernatant (26.5 +/- 6.8 ng per 10(6) cells per 24 h). Cystatin C is not one of the most abundant proteins secreted during the first 24 h in vitro, representing approximately 10 to 12% of the total protein released by normal nonsmoker macrophages. Alveolar macrophages obtained from cigarette smokers or nonsmoker macrophages exposed to zymosan in vitro released 10 to 55% less cystatin C than nonsmoker macrophages. We also assayed culture supernatants from macrophages of smokers and nonsmokers for functional cystatin C. Supernatants of nonsmoker macrophages inhibited cathepsin B-like amidolytic activity in a fluorometric assay at pH 5.5. The inhibition was blocked by adsorption with Sepharose-coupled cystatin C antibodies and the inhibitor subsequently recovered from the Sepharose beads. In contrast, supernatants from smoker macrophages had obvious cathepsin B-like activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchoalveolar Lavage Fluid↗
PubMed1990

Incidence and clinical significance of ST segment depression in supraventricular tachycardia.

To evaluate the clinical significance of ST segment depression observed during paroxysmal supraventricular tachycardia, the data of 100 patients who underwent electrophysiologic testing between 1981 and 1986 in the drug free state were reviewed. Twelve lead electrocardiograms were taken within 20 s of tachycardia induction. Patients with antidromic tachycardia, tachycardia using multiple accessory pathways or tachycardia associated with bundle branch aberration or concomitant electrolyte abnormalities were excluded from the study. Significant ST depression was defined as at least 0.1 mV horizontal or downsloping or 0.2 mV upsloping depression, measured 80 ms after the J point. ST segment changes were correlated with historical data and the results of exercise tests and radionuclide or coronary angiograms. There were 52 males and 48 females, aged 11 to 67 years (mean 32.8 +/- 13.2). Tachycardia was due to atrioventricular reentry via an overt or concealed accessory pathway in 85 patients, and atrioventricular nodal reentry in 15 patients. Significant ST depression was seen in 51 patients (aged 11 to 65 years). Thirty-three of 70 patients younger than 40 years old had significant ST depression. There was no relationship between the presence of significant ST depression and age, sex, mechanism or rate of tachycardia. Only three patients had significant coronary artery disease, and all manifested significant ST depression during tachycardia. Thus the specificity of this finding was 51% and the predictive value only 6%. In conclusion, ST segment changes observed during narrow QRS complex tachycardia are common, nonspecific and a poor predictor of underlying coronary artery disease.

Adolescent↗
PubMed1990

Initial clinical experience with the pacemaker-cardioverter-defibrillator.

The implantation of a new multiprogrammable pacemaker-cardioverter-defibrillator is reported in four patients suffering from drug-refractory ventricular tachycardia or fibrillation. The generator (PCD 7215; Medtronic Inc) was interfaced to the epicardium by three countershock patch electrodes and one ventricular myocardial screw-in lead for sensing/pacing. The device employs separate rate detection criteria for ventricular tachycardia and ventricular fibrillation with automatic delivery of up to four therapies per episode. Therapeutic options include: antitachycardia burst or autodecremental pacing, synchronized cardioversion, defibrillation and ventricular demand pacing at 30 to 90 beats/min. Four men and one woman (ages 29 to 75 years) underwent intraoperative implant evaluation, and the device was implanted in the four men. Over a follow-up of 1.5 to 23 months, 161 spontaneous episodes of ventricular tachycardia and nine episodes meeting ventricular fibrillation criteria (cycle length less than 280 to 290 ms) were detected and treated by the device. Ramp pacing was initially employed to terminate 140 ventricular tachycardia episodes and was successful 88.5% of the time while 10 (7.2%) required low energy epicardial cardioversion (4 to 10 J). Six (4.3%) episodes terminated spontaneously prior to therapy delivery. All nine spontaneous episodes of ventricular fibrillation were defibrillated using 10 to 15 J. Two patients continue to do well with the device functioning reliably. The device was removed at the time of heart transplant in one patient, while another patient died suddenly from drug overdose. No other complications, device malfunctions or inappropriate therapy delivery have been observed. These early results demonstrate the potential usefulness of a programmable device which provides graded therapy for ventricular tachycardia with added defibrillation and bradycardia pacing capability.

Adult↗
PubMed1990

Effects of amiloride on pH regulation in canine cardiac Purkinje fibers.

Myocardial cells utilize membrane transport systems for proton extrusion as well as internal buffers to preserve pH homeostasis. Our laboratory had shown previously that amiloride (0.01-1.0 mM) causes a time- and dose-dependent increase in action potential duration, early after depolarizations and enhanced automaticity. Ion-selective microelectrode technique was used to evaluate whether the observed electrophysiologic effects of amiloride are linked to inhibition of Na/H exchange and subsequent inability of the myocardial cell to maintain steady-state intracellular pH (pHi), either under normal physiological conditions or in the presence of an imposed acid load. We analyzed different components of intracellular pH transients that occur in response to NH4Cl exposure and washout, which allowed us to quantitatively describe the effects of Na/H exchange inhibition in a multicellular preparation. Amiloride (0.01-1.0 mM) did not change the steady-state pHi, but did cause a dose-dependent increase in both the time for the pHi to reach a minimum value (time-to-peak) during washout of NH4Cl as well as in the absolute minimum value of pHi (peak acid). The effects of amiloride on pHi transients are rapidly reversible and antagonized by physiologic values of extracellular sodium activity. We conclude that Na/H exchange inhibition by amiloride does not cause intracellular acidosis under normal physiologic conditions, despite the dramatic changes in action potential characteristics. However, amiloride affected the time-to-peak and the peak acid value of the pHi transient during NH4Cl washout at concentrations that had no discernible effect on the overall time course of pHi recovery.

Acid-Base Equilibrium↗
PubMed1989

The diagnostic sensitivity of electrophysiologic testing in patients with syncope caused by transient bradycardia.

Although electrophysiologic testing accurately delineates abnormalities in patients with fixed cardiac-conduction defects, its sensitivity in identifying transient rhythm disturbances is unknown. We prospectively studied 21 patients who had electrocardiographically documented intermittent atrioventricular block (n = 13) or sinus pauses (n = 8) causing syncope, but whose cardiac rhythm had reverted to normal by the time of referral. There were 14 men and 7 women, with a mean age (+/- SD) of 63 +/- 13 years. Fourteen patients had organic heart disease, and 8 were taking cardioactive medications. Electrophysiologic testing was performed before the implantation of a permanent pacemaker. Only three of the eight patients with documented sinus pauses had abnormalities during their tests that suggested the correct diagnosis (sensitivity, 37.5 percent), including a prolonged sinus-node recovery time in one and carotid-sinus hypersensitivity in two. Three of the eight patients had abnormalities detected that were unrelated to syncope, including atrial flutter, dual atrioventricular nodal pathways, and sustained monomorphic ventricular tachycardia. Of the 13 patients with documented atrioventricular block, only 2 had abnormalities suggesting the correct diagnosis (sensitivity, 15.4 percent). Additional observations unrelated to syncope among these 13 patients included abnormal sinus-node function, atrial flutter, and atrial fibrillation causing hypotension. These preliminary observations suggest that a negative electrophysiologic test in a patient with a normal cardiac rhythm who has experienced syncope does not exclude a transient bradyarrhythmia as a cause of the syncope. Furthermore, electrophysiologic testing may sometimes reveal unrelated rhythm disturbances that may mistakenly be designated as the cause of the syncope.

Aged↗
PubMed1989

Surgical alternatives for supraventricular tachycardias.

Since Sealy's pioneering surgical intervention for Wolff-Parkinson-White syndrome, surgical electrophysiologic interventions have been developed for all supraventricular arrhythmias. The surgical rationales are based on the site of origin of the arrhythmic mechanism and the associated pathology that characterizes the "arrhythmogenic substrate." The Wolff-Parkinson-White syndrome is characterized by an accessory atrioventricular (AV) connection distinct from the AV node-His bundle system. It is associated with AV reentrant tachycardia or atrial fibrillation, or both, with fast ventricular responses through the accessory pathway. The current surgical management involves ablation of the accessory pathway using either an endocardial or an epicardial approach. Surgical ablation is associated with high efficiency and low morbidity. Epicardial dissection of the accessory pathway on the beating heart has helped to localize variant accessory pathways associated with Coumel's tachycardia or the Mahaim fiber. AV nodal reentrant tachycardia can be cured using direct AV nodal dissection (or perinodal cryoablation). Atrial flutter can be interrupted by cryoablation of the arrhythmogenic substrate located in the coronary sinus orifice region. The chronotropic atrial function, abolished by incessant or paroxysmal idiopathic atrial fibrillation, can be restored using the corridor operation (sinus node-AV node insulation). The success of surgical intervention in atrial tachycardias is uncertain, but it may be an option in selected patients with resistant atrial tachycardias.

Adolescent↗
PubMed1989

Operative therapy of atrioventricular node reentry and results of an anatomically guided procedure.

Operative therapy for atrioventricular (AV) node reentrant tachycardia consisting of dissection guided by anatomic landmarks is described. Of the 21 patients studied, 17 had the common type ("slow-fast") and 4 had the uncommon type ("fast-slow") of AV node reentry. Under normothermic cardio-pulmonary bypass, perinodal dissection was performed guided by anatomic landmarks: the atrial membranous septum, posterior superior process of the left ventricle, tendon of Todaro and os of the coronary sinus. There were no deaths or major complications. Seven to 10 days postoperatively, all patients had normal AV conduction except for one who continued to have AV node Wenckebach-type block. Postoperatively, the shortest cycle length capable of 1:1 conduction over the AV node changed from 323 +/- 66 to 421 +/- 90 ms (p less than 0.0001) anterogradely and from 330 +/- 86 to 449 +/- 164 ms (p = 0.004) retrogradely. Anterograde effective refractory period of the AV node prolonged from 264 +/- 49 to 358 +/- 107 ms (p = 0.012). Discontinuous AV conduction curves were no longer seen in 14 of 17 patients and 5 patients lost retrograde conduction. During follow-up (14.8 +/- 8.2 months), 19 patients have been free of arrhythmia without medication. Two patients required a second operation for recurrent tachycardia with success. No patient required a permanent pacemaker. These data show that operative therapy of AV node reentrant tachycardia can be guided by anatomic landmarks. Successful cure of tachycardia with perinodal dissection while preserving AV node conduction supports the view that the reentrant circuit is, at least in part, perinodal.

Adolescent↗
PubMed1989

Longitudinal electrophysiologic assessment of asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern.

Although most asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern have a good prognosis, some die suddenly. The mechanism of sudden death is usually ventricular fibrillation, which is triggered by atrial fibrillation with a rapid ventricular response rate. Electrophysiologic testing has been proposed to identify asymptomatic patients who may be at risk for sudden death. Meaningful application of such testing requires a knowledge of whether the electrophysiologic measurements are reproducible over time. Consequently, we performed electrophysiologic studies on two occasions at least 36 months apart (mean +/- SD, 54.7 +/- 14) in 29 asymptomatic patients with the pattern. Twenty-seven patients remained asymptomatic, and sustained supraventricular tachycardia developed in two during the follow-up period. Nine patients (31 percent) lost the capacity for preexcitation and anterograde conduction over the accessory pathway, which produces the Wolff-Parkinson-White pattern. The others had little change in measurements of conduction over the accessory pathway. Patients who lost conduction over the accessory pathway tended to be older (mean +/- SD, 50 +/- 18 vs. 39 +/- 11 years; P = 0.06) than patients who retained preexcitation, and they had longer anterograde effective refractory periods at the first assessment (414 +/- 158 vs. 295 +/- 27 msec; P = 0.003). We conclude that a considerable number of asymptomatic patients with the Wolff-Parkinson-White pattern lose their capacity for anterograde conduction over the accessory pathway. This loss of capacity probably contributes to the low mortality among asymptomatic patients.

Atrial Fibrillation↗
PubMed1989

Results of operative therapy in the permanent form of junctional reciprocating tachycardia.

To assess the results of operative therapy for permanent junctional reciprocating tachycardia, a type of incessant tachycardia, the clinical and electrophysiologic data of 8 such patients referred for management of tachycardia were reviewed. The duration of incessant tachycardia was 14 +/- 10 years (range 2 to 30). The heart rate at rest during tachycardia ranged from 120 to 150 beats/min. Four of 8 patients had cardiomegaly or depressed ejection fraction (16 +/- 10%, range 5 to 27) at presentation and, of these, 2 had symptoms of congestive heart failure. Exertional dyspnea despite normal left ventricular function was noted in 1 patient, 2 had chronic palpitations and 3 were asymptomatic. Electrophysiologic data confirmed the presence of a posteroseptal pathway with atrioventricular node-like properties conducting slowly in the retrograde direction only. Seven patients underwent successful surgical ablation of the accessory pathway. Hypothermic cardiopulmonary bypass was used in 2 and a closed heart technique without cardiopulmonary bypass in the other 5. Three of 4 patients with reduced left ventricular function showed an improvement in ejection fraction to 34 +/- 20% (range 16 to 63) after control of dysrhythmia. Three patients had no evidence of cardiomegaly despite equivalent periods of incessant tachycardia. Another patient with normal left ventricular function despite incessant tachycardia for over 30 years underwent spontaneous remission to sinus rhythm and did not undergo surgery. These data suggest that permanent junctional reciprocating tachycardia has a variable presentation and that congestive heart failure is not an infrequent presenting symptom. The substrate is invariably an accessory atrioventricular pathway with a long conduction time and decremental properties conducting only in the retrograde direction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Usefulness of isoproterenol during atrial fibrillation in evaluation of asymptomatic Wolff-Parkinson-White pattern.

The asymptomatic individual with a Wolff-Parkinson-White (WPW) pattern is considered at risk for ventricular fibrillation if a rapid ventricular response (shortest RR interval less than or equal to 250 ms) is observed during induced atrial fibrillation (AF) in the laboratory. It has been suggested that isoproterenol administration during AF may more accurately define the patient at risk. Consequently, the effect of isoproterenol on ventricular response during AF was studied in 21 asymptomatic individuals with WPW pattern to assess the potential of isoproterenol to identify patients at risk for sudden death. An electrophysiologic study that included elective induction of AF was performed. The shortest and mean RR intervals between 2 consecutive preexcited and normal QRS complexes, the average RR interval and the proportion of preexcited QRS complexes were measured in the control state and after bolus injections of isoproterenol (0.5, 1.0, 2.0 and 4.0 micrograms) during AF. Both atrioventricular nodal and accessory pathway conductions were enhanced proportional to isoproterenol dose. Isoproterenol had a greater effect on the atrioventricular node, as reflected by significantly greater changes in the shortest RR between normal complexes (339 +/- 70 vs 255 +/- 21 ms, mean +/- standard deviation, p less than 0.001) than the shortest RR between preexcited complexes (264 +/- 39 vs 219 +/- 34 ms, p less than 0.001) and a decrease in percentage of preexcited complexes (65 +/- 37 vs 50 +/- 33%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗