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Biomedical subjects

R Yee

Publications and source records attributed to R Yee.

At least 91 records · Page 5Linked to original sources
PubMed1996

Recurrent unexplained syncope: diagnostic and therapeutic approach.

Patients with syncope of unknown etiology may suffer from recurrent disability. Syncopal episodes are often too infrequent and unpredictable for detection with conventional ambulatory monitoring techniques. A symptom-rhythm correlation is a frequently unattainable gold standard in many patients. Clinicians must often rely on the results of laboratory testing to make an inferential determination of the etiology of spontaneous syncope. Electrophysiological testing has a role in patients with structural heart disease and suspected ventricular arrhythmias, but is negative in 14% to 70% of patients studied and has a limited role in patients without structural heart disease. The external loop recorder is an ambulatory device worn for weeks or even months that freezes the preceding rhythm strip after an episode of spontaneous syncope. This device is useful in patients with frequent symptoms but is hampered by lack of patient compliance and technical limitations. In the absence of a diagnosis after extensive testing, an empirical trial based on index of suspicion may be warranted. This may include implantation of a pacemaker for suspected bradycardia or empirical therapy directed at a tachycardia. Finally, recent reports of an insertable loop recorder suggest a high diagnostic yield with a broad spectrum of etiologies in patients with recurrent syncope in spite of negative noninvasive and electrophysiological testing. In the future, such a device may assume a prominent role in the investigation of syncope.

Electrocardiography, Ambulatory↗
PubMed1995

The etiology of syncope in patients with negative tilt table and electrophysiological testing.

BACKGROUND: Patients with syncope of unknown etiology after negative noninvasive and electrophysiological testing may suffer from recurrent disability. Syncopal episodes are often too infrequent and unpredictable for detection by conventional ambulatory monitoring techniques. METHODS AND RESULTS: A long-term subcutaneous monitoring device was implanted in patients with negative ambulatory monitoring, tilt table and electrophysiological testing to establish cardiac rhythm during spontaneous syncope. Sixteen patients aged 57 +/- 19 years with a mean of 8.4 +/- 4.4 previous episodes of syncope underwent device implantation. Fifteen patients (94%) had recurrent syncope 4.4 +/- 4.2 months after implantation. The remaining patient has not had recurrent syncope and continues to be followed. A diagnosis was obtained in every patient who had recurrent episode. Syncope was secondary to sinus arrest in 5, atrioventricular block in 2, ventricular tachycardia in 1, supraventricular tachycardia in 1, and nonarrhythmic in 6. Successful therapy was implemented in all 15 patients, without recurrence of syncope during 13.0 +/- 8.4 months of follow-up. CONCLUSIONS: Unexplained syncope in patients with negative investigations has a broad spectrum of etiologies, the most common of which is bradycardia. An implantable long-term monitoring device is useful for establishing a diagnosis when symptoms are recurrent but too infrequent for conventional monitoring techniques.

Bradycardia↗
PubMed1995

Long-term reproducibility of ventricular tachycardia induction in patients with implantable cardioverter/defibrillators. Serial noninvasive studies.

BACKGROUND: Noninvasive electrophysiological studies (EPSs) can be performed in current implantable antitachycardia pacemaker/cardioverter/defibrillators (ICDs). Thus, these devices may be used as tools to study changes in the electrophysiological substrate and ventricular tachycardia characteristics over time. METHODS AND RESULTS: Fifty-five patients receiving an ICD for treatment of sustained ventricular tachyarrhythmias underwent serial EPSs after implantation of the ICD. Studies were performed before hospital discharge and 1, 3, 5, 9, 12, 18, 24, and 36 months after ICD implantation. Sustained monomorphic ventricular tachycardia (VT) was induced in 37 patients (group 1) at the predischarge EPS, whereas no sustained arrhythmia could be induced in 18 patients (group 2) at baseline. Group 1 patients underwent 165 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 72% of the follow-up EPSs, ventricular fibrillation (VF) was induced during 11% of follow-up EPSs, and no sustained VT or VF was induced during 17% of follow-up visits. Sustained VT was induced at every follow-up EPS in 23 patients (62%), whereas no sustained VT/VF could be induced at least once during follow-up in 14 patients (38%). Clinical or electrophysiological variables did not predict noninducibility during follow-up. However, the probability that a patient would experience spontaneous VT decreased significantly over time in patients in whom VT was not inducible during at least 1 follow-up EPS (P = .05). Group 2 patients underwent 86 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 22% of follow-up EPSs, VF was induced during 19% of follow-up EPSs, and no sustained VT/VF could be induced during 68% of follow-up EPSs. No sustained VT/VF could be induced during every follow-up EPS in 9 patients (50%), whereas sustained monomorphic VT was induced at least once during follow-up in 7 patients (34%). Persistent noninducibility of VT during follow-up was associated with low probability of occurrence of spontaneous VT (11%), whereas inducibility of VT at least once during follow-up was associated with the occurrence of spontaneous VT (89%, P = .003). CONCLUSIONS: Considerable variability of VT induction is observed over a lengthy period in patients presenting with sustained VT/VF. Persistent noninducibility of VT is associated with a reduced probability of spontaneous VT. These observations suggest that the substrates for inducible and spontaneous VT change in parallel over time.

Aged↗
PubMed1995

Effect of dual atrioventricular node pathways on atrioventricular reentrant tachycardia.

BACKGROUND: Dual atrioventricular (AV) node pathway physiology is frequently observed in patients with AV accessory pathways. METHODS AND RESULTS: To examine the implications of this, we identified 36 patients (19 men and 17 women; mean +/- SD age, 30 +/- 13 years) with both phenomena. The 36 patients had 48 accessory pathways. Twenty-seven patients had bidirectional and 9 had unidirectional accessory pathways. Of the 34 patients with inducible atrioventricular reentry, 17 used the slow and 11 used the fast anterograde AV node pathway exclusively during AV reentrant tachycardia, whereas 6 patients used both the fast and the slow AV node pathways. AV node reentrant tachycardia was inducible in addition to AV reentry in 7 patients. Both the cycle length and AH intervals were significantly longer during slow pathway-dependent (cycle length, 411 +/- 58 milliseconds [ms]; AH, 229 +/- 42 ms) than during fast pathway-dependent (cycle length, 322 +/- 40 ms; AH, 121 +/- 25 ms; P < .05) reentrant tachycardias. Two patients had only AV node reentrant tachycardia inducible despite the presence of the accessory pathway. Four patients with technically difficult accessory pathways were managed by AV node modification with slow pathway (3) or fast pathway (1) ablation. Three of them remained free of symptoms 7, 14, and 25 months after the procedure whereas 1 patient had recurrence of arrhythmia. CONCLUSIONS: AV reentrance with dual AV node pathways frequently depends exclusively on either the slow or the fast AV node pathway for clinical tachycardia. This may provide additional options for ablation in technically difficult cases when the accessory pathway is not otherwise problematic.

Adolescent↗
PubMed1995

Diagnostic accuracy of a low-dose isoproterenol head-up tilt protocol.

The rate of positive head-up tilt (HUT), specificity, and same-day reproducibility of an HUT at 60 degrees combined with a low-dose isoproterenol infusion was assessed in the following patients: 120 consecutive patients with recurrent unexplained syncope, 30 healthy patients in a control group, and 30 patients with documented syncope not related to a vasodepressor reaction. HUT was positive in 61% (73 of 120) of patients with unexplained syncope. The false-positive rate in both the control and documented syncope groups was 6.6%. The mean isoproterenol dose infused was 1.4 +/- 0.5 microgram/min, 1.3 +/- 0.4 micrograms/min, 1.3 +/- 0.5 microgram/min, respectively (p = NS). HUT was positive during the drug free stage in 30 (25%) of 120 patients, and isoproterenol infusion was necessary in the remaining 43 (36%) patients. Immediate reproducibility was assessed in 75 patients, and HUT response was reproduced in 37 (82%) of 45 patients with a baseline positive HUT and in 28 (93%) of 30 patients with a baseline negative response. Overall, "sensitivity," specificity, and reproducibility were 61%, 93%, and 86%, respectively. Clinical variables that increased the probability of a positive outcome were age < or = 50 years and two or more syncopal episodes in the preceding 6 months in the absence of structural heart disease. These data support the use of an HUT protocol with low-dose isoproterenol infusion for the assessment of patients with recurrent syncope.

Adult↗
PubMed1995

Propofol has no direct effect on sinoatrial node function or on normal atrioventricular and accessory pathway conduction in Wolff-Parkinson-White syndrome during alfentanil/midazolam anesthesia.

BACKGROUND: Propofol has been implicated as causing intraoperative bradyarrhythmias. Furthermore, the effects of propofol on the electrophysiologic properties of the sinoatrial (SA) node and on normal atrioventricular (AV) and accessory pathways in patients with Wolff-Parkinson-White syndrome are unknown. Therefore, this study examined the effects of propofol on the cardiac electrophysiologic properties in humans to determine whether propofol promotes bradyarrhythmias and its suitability as an anesthetic agent in patients undergoing ablative procedures. METHODS: Twelve patients with Wolff-Parkinson-White syndrome undergoing radiofrequency catheter ablation were studied. Anesthesia was induced with alfentanil (50 micrograms/kg), midazolam (0.15 mg/kg), and vecuronium (20 mg) and maintained with alfentanil (2 micrograms.kg-1.min-1) and midazolam (1-2 mg, every 15 min, as needed). A electrophysiologic study was performed consisting of measurement of the effective refractory period of the right atrium, AV node, and accessory pathway and the shortest cycle length of the AV node and accessory pathway during antegrade stimulation plus the effective refractory period of the right ventricle and accessory pathway and the shortest cycle length of the accessory pathway during retrograde stimulation. Determinants of SA node function including sinus node recovery time, corrected sinus node recovery time, and SA conduction time; intraatrial conduction time and atrial-His interval also were measured. Reciprocating tachycardia was induced by rapid right atrial or ventricular pacing, and the cycle length and atrial-His, His-ventricular, and ventriculoatrial intervals were measured. Alfentanil/midazolam was then discontinued. Propofol was administered (bolus 2 mg/kg + 120 micrograms.kg-1.min-1), and the electrophysiologic measurements were repeated. RESULTS: Propofol caused a statistically significant but clinically unimportant prolongation of the right atrial refractory period. The effective refractory periods of the AV node, right ventricle, and accessory pathway, as well as the shortest cycle length, were not affected. Parameters of SA node function and intraatrial conduction also were not affected. Sustained reciprocating tachycardia was inducible in 8 of 12 patients, and propofol had no effect on its electrophysiologic properties. All accessory pathways were successfully identified and ablated. CONCLUSIONS: Propofol has no clinically significant effect on the electrophysiologic expression of the accessory pathway and the refractoriness of the normal AV conduction system. In addition, propofol has no direct effect on SA node activity or intraatrial conduction; therefore, it does not directly induce bradyarrhythmias. It is thus a suitable agent for use in patients undergoing ablative procedures who require either a neuroleptic or general anesthetic.

Adolescent↗
PubMed1995

High voltage shock induced cellular electrophysiological effects: transient refractoriness and bimodal changes in action potential duration.

The cellular electrophysiological effects of defibrillation shocks on the myocardium during ventricular fibrillation are not clear. The present study investigated the effects of high voltage shocks on membrane potentials of isolated guinea pig and pig papillary muscles during rapid activations simulating ventricular fibrillation. High voltage shocks induced an action potential with a prolonged duration, followed by a transient refractory state. Subsequent action potentials following this refractory state had shortened durations. The duration of the transient refractory state varied in proportion to shock intensity and stimulation rate, whether the shock was biphasic or monophasic. Shock induced prolonged depolarization was not a consistent finding and mainly observed with slow stimulation rates. In conclusion, high voltage shocks induce bimodal changes of the action potential duration associated with a transient refractory state during rapid activation. The rate dependency of this refractory state suggests that the duration of the shock induced refractory state may be longer in the fibrillating than the normal beating heart, and may contribute to successful defibrillation.

Action Potentials↗
PubMed1995

Catheter ablation of idiopathic left ventricular tachycardia.

Idiopathic left ventricular tachycardia (ILVT) characterized by right bundle branch block, left axis morphology, response to verapamil and inducibility from the atrium in patients without structural heart disease may represent a distinct clinical entity. We report our experience with catheter ablation of this uncommon arrhythmia using radiofrequency energy (RF) and/or direct current (DC) shocks. Six men and 2 women, aged 16-50 years (mean +/- SD, 32 +/- 13), had recurrent VT for 16 +/- 16 years with a mean frequency of 4 +/- 3 episodes/year. Three patients had syncope during VT. None had identifiable structural heart disease. Catheter ablation was guided by earliest endocardial activation, presence of a high frequency presystolic potential and/or pacemapping of the left ventricle. The left ventricle was accessed via a retrograde aortic approach in 6 patients, a transeptal approach in 1 patient, and a combined approach in the remaining patient. All patients had inducible right bundle branch block morphology, left axis VT with a mean cycle length (CL) of 361 +/- 61 ms. A presystolic potential preceding ventricular activation and the His potential during VT was identified in 4 patients. All ablation sites were identified in a relatively uniform location, in the inferoapical left ventricle. Noninducibility of VT was obtained with RF in 3 patients and with DC in 5 patients. In 1 patient, DC delivery after unsuccessful RF prevented further inducibility. Similarly, RF was successful in 1 patient in whom an initial DC attempt was ineffective. Mean total procedure time was 282 +/- 51 minutes and mean total fluoroscopy time was 40 +/- 15 minutes. There were no complications. One patient treated with DC shock had recurrence of VT during treadmill test the day after ablation and refused repeat ablation. During a mean follow-up of 17 +/- 13 months, no VT recurrences or other cardiovascular events occurred. In conclusion, catheter ablation in the inferoapical left ventricle is an effective treatment for this type of ILVT. RF energy can be safely complemented by low energy DC shocks when the former is ineffective.

Adult↗
PubMed1995

Inappropriate sinus tachycardia: evaluation and therapy.

Inappropriate sinus tachycardia is an ill-defined clinical syndrome characterized by an increased resting heart rate accompanied by an exaggerated response to exercise or stress. It is not associated with underlying structural heart disease. The mechanism may involve a primary abnormality of the sinus node demonstrating enhanced automaticity or, alternatively, a primary autonomic disturbance with increase sympathetic activity and enhanced sinus node beta-adrenergic sensitivity. The diagnosis of inappropriate sinus tachycardia is one of exclusion. It is most common in young females, with a disproportionate number employed in the health care field. Autonomic and electrophysiologic testing may be required in selected individuals to clarify the mechanism and rule out sinus node reentry or right atrial tachycardia. Therapy of inappropriate sinus tachycardia is empiric. Pharmacologic approaches include beta blockers or verapamil. Radiofrequency catheter ablation of the superior portion of the sinus node shows promise as a useful alternative in patients with refractory symptoms.

Adult↗
PubMed1995

Effect of isoproterenol on accessory pathways without overt retrograde conduction.

INTRODUCTION: Absence of overt retrograde accessory pathway conduction may be related to low resting sympathetic tone in patients with apparent unidirectional anterogradely conducting accessory pathways (UACAP). METHODS AND RESULTS: To test this hypothesis, we studied the effect of isoproterenol on accessory pathway function and tachycardia induction in 18 patients (12 men and 6 women, ages 34 +/- 16 years [mean +/- SD]) with UACAP. After baseline study in the drug-free state, electrphysiologic testing was repeated during infusion of isoproterenol (0.5 to 1.5 micrograms/min, titrated to increase heart rate by 20%). Isoproterenol shortened the anterograde effective refractory period (398 +/- 117 vs 305 +/- 63 msec; P < 0.01; basic drive cycle length 600 msec) of the accessory pathway. However, retrograde accessory pathway conduction and atrioventricular reentrant tachycardia were exposed in only 3 (17%) patients by isoproterenol infusion. All 3 patients with retrograde accessory pathway revealed after isoproterenol had clinically documented tachycardia (supraventricular tachycardia in 2, atrial fibrillation in 1) during exercise, while none of the patients with persistent absence of retrograde accessory pathway conduction had this symptom. CONCLUSIONS: We conclude that absence of overt retrograde conduction over accessory pathways may be related to low resting sympathetic tone in some individuals. Restoration of retrograde conduction with isoproterenol is unusual and most likely to be observed in patients with clinically documented paroxysmal supraventricular tachycardia related to exercise.

Accessory Nerve↗
PubMed1995

Changes in intraocular pressure during low dose intravenous sedation with propofol before cataract surgery.

AIMS: This study examined the effects on intraocular pressure, pulse rate, and blood pressure of low dose intravenous sedation with propofol. METHODS: Twenty adult patients who were scheduled to undergo cataract surgery were given a single intravenous bolus (0.98 (SEM 0.4) mg/kg) of propofol for sedation before administering the local anaesthetic for cataract surgery. A small intravenous dose of lignocaine was the only other anaesthetic or sedative agent given. The intraocular pressure in the non-surgery eye, the pulse rate, and the blood pressure were measured before and after propofol induction. RESULTS: Compared with the preinduction baseline, there was a 17% to 27% (from 16.2 (0.7) mm Hg to 11.8 (0.7) mm Hg) decrease in intraocular pressure after propofol induction. A significant decrease in intraocular pressure occurred within the first minute and was still evident at 7 minutes when the measurements were stopped. There was also a 7%-12% increase in pulse rate during the first 4 minutes, a 12% decrease in mean systolic blood pressure, and a 7% decrease in mean diastolic blood pressure from baseline after propofol induction. CONCLUSION: A single low dose bolus of propofol used for sedation before cataract surgery caused a moderate reduction in intraocular pressure with minimal, easily managed side effects.

Aged↗
PubMed1995

Surgical management of pseudotumor cerebri in pregnancy: case report.

Little has been written concerning the surgical treatment of pregnant patients with pseudotumor cerebri. We present four cases of pregnant women who underwent lumboperitoneal shunt placement during pregnancy for progressive visual loss despite maximal medical therapy. The intraperitoneal pressure measured during surgery was significantly less than the cerebrospinal fluid pressure. Three of the four women had marked improvement in their vision after shunting, and one required optic nerve sheath decompressions for improvement. All delivered healthy babies. Pseudotumor cerebri in pregnant patients with progressive visual loss despite medical therapy is surgically treatable, and normal deliveries are expected. Therapeutic abortion to limit progression of the disease is not indicated.

Adult↗
PubMed1995

Atypical retrograde atrial activation in 'typical' atrioventricular nodal reentrant tachycardia.

Atrioventricular nodal reentrant tachycardia (AVNRT) can be cured by radiofrequency catheter ablation by selective ablation of the slow or the fast pathway. Retrograde fast pathway ablation is performed anterosuperiorly at the apex of Koch's triangle, whereas slow pathway ablation is performed at the base of Koch's triangle near the coronary sinus ostium. A patient with otherwise typical slow-fast AVNRT who demonstrated earliest retrograde atrial activation at the proximal coronary sinus rather than the usual His bundle recording position is described. Loss of retrograde fast pathway conduction occurred after radiofrequency ablation at the base of Koch's triangle, suggesting an atypical location of the fast pathway. This supports recent evidence that the retrograde fast pathway may be located near the coronary sinus ostium in some patients with otherwise typical AVNRT.

Adult↗