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Biomedical subjects

R Yee

Publications and source records attributed to R Yee.

At least 127 records · Page 7Linked to original sources
PubMed1994

Radiofrequency catheter ablation of accessory pathways during entrainment of AV reentrant tachycardia.

Radiofrequency ablation of accessory pathways must sometimes be done during orthodromic atrioventricular reentrant tachycardia when manifest anterograde accessory pathway conduction is absent or retrograde fusion obscures accessory pathway location during ventricular pacing. Unfortunately, abrupt heart rate slowing upon radiofrequency induced termination of atrioventricular reentrant tachycardia often causes catheter dislodgment. We report our experience in circumventing this problem during radiofrequency ablation by using entrainment of atrioventricular reentrant tachycardia. The latter maintains retrograde activation pattern over the accessory pathway while preventing abrupt ventricular rate change. Eight patients (4 men and 4 women, mean age 37.3 +/- 17.9) with eleven left-sided accessory pathways were included. Ablation during entrainment was used as the first approach in three patients with concealed accessory pathways and one patient with a bidirectional accessory pathway. In another four patients, ablation during entrainment was used after technical difficulties in ablating during tachycardia. Only 1-3 radiofrequency applications were required to eliminate the accessory pathway using the entrainment technique. The catheter remained stable when accessory pathway conduction was interrupted by radiofrequency current. In conclusion, entrainment of atrioventricular reentrant tachycardia during radiofrequency application is useful for maintaining catheter position for accessory pathway ablation during atrioventricular reentrant tachycardia.

Adolescent↗
PubMed1994

Intraoperative mapping is not necessary for VT surgery.

Surgical ablation of ventricular tachycardia is generally guided by the results of pre- and intraoperative cardiac mapping. However, in certain situations intraoperative cardiac mapping may not be possible and, therefore, surgery has to be based on information obtained preoperatively. This raises the question whether intraoperative mapping is necessary for the success of this approach. We describe our experience with encircling endocardial cryoablation for ischemic VT and examine the contribution of intraoperative mapping for this procedure. Thirty-three patients with inducible VT refractory to medical therapy and a well defined anatomic scar were considered for surgery. All patients underwent baseline electrophysiology study and intraoperative mapping was attempted during normothermic cardiopulmonary bypass. In 14 patients, VT was inducible intraoperatively (Group 1) and surgical ablation was guided by this information, whereas in 19 patients, VT could not be mapped for various reasons (Group 2). Reasons for failure to obtain intraoperative map included noninducibility (3), nonsustained VT (8), polymorphic VT (4), VF (3), and incessant VT with hemodynamic collapse and cardiac arrest (1). The two groups did not differ with respect to age, location of myocardial infarction, or preoperative left ventricular ejection fraction. The operative procedures were similar in the two groups with respect to aortic cross clamp time, cardiopulmonary bypass time, number of cryoablation lesions, concomitant revascularization, aneurysmectomy, and ICD implantation. Encircling endocardial cryoablation was performed in 32 patients and one patient underwent partial right ventricular free wall disconnection (RV infarct). Thirteen patients underwent concomitant coronary artery bypass grafting (5 in Group 1 and 8 in group 2). One patient had prophylactic ICD patches (Group 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1994

The value of electrophysiologic testing in patients resuscitated from documented ventricular fibrillation.

INTRODUCTION: Electrophysiologic testing is performed in patients resuscitated from ventricular fibrillation (VF) on the assumption that sustained monomorphic ventricular tachycardia (VT) may be a precursor to VF, with the former amenable to assessment by serial drug testing. METHODS AND RESULTS: We assessed the usefulness of this strategy by analyzing clinical and electrophysiologic data of 42 survivors (29 men and 13 women; mean age 54 +/- 14 years) of VF without a reversible cause. All patients had VF documented on ECG and required defibrillation. Underlying heart diseases included coronary disease in 28, dilated cardiomyopathy in 3, arrhythmogenic right ventricular dysplasia in 1, and no apparent structural heart disease in 10 patients. Only 2 (4.7%) patients had a prior history of documented VT. The electrophysiologic study was performed 7 to 30 days after VF. Programmed stimulation at the right ventricular apex using at least two drive cycle lengths and up to three extrastimuli induced sustained monomorphic VT in 4 (9.5%), sustained polymorphic VT in 3 (7.1%), nonsustained monomorphic VT in 1 (2.3%), nonsustained polymorphic VT in 5 (11.9%), and VF in 13 (30.9%) patients. Two patients with documented prior VT and coronary disease had sustained VT induced during the electrophysiologic study. On the other hand, sustained monomorphic VT was induced in 53 of the 59 (90%) patients (45 men and 14 women; mean age 57 +/- 16 years) with clinically documented VT concurrently studied using the same stimulation protocol. CONCLUSION: We conclude that reproducible induction of sustained monomorphic VT in survivors of documented VF is uncommon. It may be more cost effective to proceed directly to treatment with implantable cardioverter defibrillators in these patients.

Adult↗
PubMed1994

Fatigue phenomenon in accessory pathways.

Fatigue phenomenon is transient failure of conduction following a period of repetitive excitation. Fatigue in accessory pathways is uncommon, and its electrophysiologic characteristics and clinical implications are unknown. Among the 215 patients who underwent electrophysiology studies from July 1992 to December 1993, 4 (2%) were found to exhibit fatigue over accessory pathways. The accessory pathway was posteroseptal in three patients and right free wall in one patient. The mean anterograde effective refractory period of the accessory pathway was 295 +/- 26 msec (range 270 to 330, basic drive cycle length 600 msec). Three patients had neither retrograde accessory pathway conduction nor inducible tachycardia even with infusion of isoproterenol. The fatigue phenomenon was observed after both atrial and ventricular stimulation in three patients and only after ventricular stimulation in one patient. Fatigue was dependent on duration more than rate of stimulation. We conclude that pathways exhibiting fatigue have a low margin of safety for conduction and are unlikely to be clinically problematic.

Adolescent↗
PubMed1994

Shortening of fast pathway refractoriness after slow pathway ablation. Effects of autonomic blockade.

BACKGROUND: Shortening of the anterograde effective refractory period (ERP) of the fast pathway has been reported after radiofrequency ablation of the slow pathway. We hypothesized that ERP shortening may be related to autonomic changes, possibly catecholamine release, as a result of ablation. METHODS AND RESULTS: To test this, 10 consecutive patients with atrioventricular node reentry undergoing slow pathway ablation were given autonomic blockade before the ablation procedure. This was achieved by atropine 0.03 mg/kg and propranolol 0.15 mg/kg IV supplemented by half the initial dose after ablation and before the final study. A control group of 10 patients underwent the protocol without autonomic blockade. Before ablation, autonomic blockade did not alter the ERP of either the fast pathway (295 +/- 22 versus 298 +/- 26 milliseconds) or the slow pathway (264 +/- 36 versus 269 +/- 38 milliseconds). Autonomic blockade obscured dual pathway physiology in 2 patients and brought it out in another 2 without dual pathway physiology initially. Slow pathway ablation shortened the ERP of the fast pathway for the group as a whole (331.5 +/- 54 versus 305.5 +/- 60 milliseconds, mean +/- SD, n = 20, P < .04). There was no difference in degree of ERP shortening in control patients (23.5 +/- 58 milliseconds) or autonomic blockade patients (25.5 +/- 52 milliseconds). CONCLUSIONS: These data suggest that shortening of the ERP of the fast pathway after slow pathway ablation is not mediated by autonomic changes.

Adult↗
PubMed1994

Mechanism of 'inappropriate' sinus tachycardia. Role of sympathovagal balance.

BACKGROUND: "Inappropriate" sinus tachycardia (IST) is an uncommon and poorly defined atrial tachycardia characterized by inappropriate tachycardia and exaggerated acceleration of heart rate with "normal" P wave. The mechanism of this tachycardia is unknown. The purpose of the present study was to determine the role of autonomic balance in the genesis of IST. METHODS AND RESULTS: Six female patients aged 23 to 38 years with IST and 10 age- and sex-matched control subjects were assessed with the following autonomic function tests: (1) sympathovagal balance to the sinus node assessed by calculating the LF/HF (low frequency/high frequency) ratio using power spectral analysis both in the supine position and after 10 minutes of head-up tilt to 60 degrees, (2) cardiovagal reflex assessed by cold face test (CFT), (3) beta-adrenergic sensitivity as determined by calculating isoproterenol dose-response curves and isoproterenol chronotropic dose 25 (CD25), and (4) intrinsic heart rate (IHR) assessed after autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg administered as an intravenous bolus. No significant differences in the LF/HF ratio both in the supine position (2.8 +/- 0.3 versus 2.6 +/- 0.4) and during upright tilt (8.7 +/- 1.3 versus 8.5 +/- 0.5) were observed between control subjects and IST patients. Cardiovagal response to CFT was markedly depressed in all patients (6.3% IST patients versus 24.2% control subjects, P < .001). beta-Adrenergic hypersensitivity to isoproterenol was noted in all patients (mean CD25, 0.29 +/- 0.10 microgram IST patients versus 1.27 +/- 0.4 microgram control subjects; P < .001), and high IHR was noted in all cases. The patients were treated with high doses of beta-blockers with adequate short-term control. Radiofrequency catheter ablation of the sinus node area was performed in one drug-refractory patient. CONCLUSIONS: These findings suggest that the mechanism leading to IST is related to a primary sinus node abnormality characterized by a high IHR, depressed efferent cardiovagal reflex, and beta-adrenergic hypersensitivity.

Adrenergic beta-Antagonists↗
PubMed1994

A length of stay study of the dually entitled Medicare and Medicaid population: challenges for managed competition.

Length of stay (LOS) differences were not observed between the dually entitled and other Medicare stroke patients when complexity of disease was considered. LOS for dually entitled heart failure patients was 33.2 percent longer than other Medicare heart failures and were equally likely to be in the extreme DRG subclass. Patients with extreme heart failure stayed 15.5 days longer than those with mild heart failure. LOS differences (+4.5 days) were observed between the dually entitled and other Medicare heart failures when complexity of disease was considered. Within these two DRGs, incremental health care needs for dually entitled equalled 10 percent of the hospital's total Medicare days associated with stroke and heart failure.

Black or African American↗
PubMed1994

Complications of radiofrequency catheter ablation: a review.

Radiofrequency catheter ablation has revolutionized the management of patients with supraventricular tachycardias. Although initial reports were very favourable, it is becoming apparent that radiofrequency catheter ablation may lead to some potentially serious complications. Complication rate for accessory pathway ablation ranges from 1.8 to 4% and the risk of atrioventricular (AV) block for 'AV nodal modification' ranges from 1.3 to 8%. It is likely that complications are underreported and the true incidence may be higher. Some of these complications are probably related to operator experience or the volume of ablations performed at the centre, but other complications, such as systemic embolism, may be sporadic and unrelated to experience or volume. Although radiofrequency catheter ablation has emerged as an excellent therapeutic tool, the potential complications and limitations should be recognized.

Catheter Ablation↗
PubMed1994

The inefficacy of intravenous propafenone for rate control in atrial fibrillation.

The antiarrhythmic agent propafenone has been reported to prolong atrioventricular node conduction and may be suitable for rate control in atrial fibrillation (AF). To evaluate this, 10 patients (seven men and three women aged 29 to 67 years, mean +/- SD 48 +/- 14) were given intravenous propafenone during AF in both the supine and upright positions. Intracardiac catheters measured local electrograms from the high right atrium and right ventricular apex during AF. Atrial rate, ventricular rate and blood pressure were recorded in the control state and after head-up tilt with these measurements repeated after propafenone 1.5 mg/kg was infused over 5 mins. Four of 10 patients reverted to sinus rhythm. Propafenone increased the mean ventricular cycle length (496 +/- 147 versus 556 +/- 152 ms, P = 0.1), although this did not reach significance. In contrast, propafenone markedly increased the mean atrial cycle length (136 +/- 35 versus 226 +/- 39, P < 0.001). The mean ventricular cycle length reverted to baseline after tilt (447 +/- 103 ms) while the mean atrial cycle length decreased but not to baseline levels (170 +/- 21 ms). The authors conclude that intravenous propafenone is generally inadequate for rate control in AF, especially in the upright position.

Adult↗
PubMed1993

A prospective randomized comparison of autodecremental pacing to burst pacing in device therapy for chronic ventricular tachycardia secondary to coronary artery disease.

A number of modes of antitachycardia pacing therapies are available in the newer generations of implantable cardioverter/defibrillators. The efficacy of synchronized burst overdrive pacing for the termination of induced and spontaneous monomorphic ventricular tachycardia (VT) was compared with synchronized autodecremental (ramp) pacing in 21 patients who received an implantable antitachycardia pacemaker/cardioverter/defibrillator for treatment of recurrent sustained monomorphic VT. Patients undergoing serial noninvasive VT induction studies after device implantation were prospectively randomized to receive trials of burst or ramp pacing therapies in a crossover study design. Antitachycardia pacing therapies were equally efficacious in treating induced VT (68% for ramp, 76% for burst pacing trials). The efficacy of ramp (93%) and burst (96%) pacing therapies was significantly higher in terminating spontaneously occurring episodes of VT than in terminating induced episodes (p = 0.001). The incidence of tachycardia acceleration was similar for both modes of pacing. The incidence of VT acceleration was lower for spontaneously occurring episodes of VT (0.01%) than for induced episodes of VT (6%, p < 0.01). Thus, antitachycardia pacing is an effective therapy for episodes of monomorphic VT, and the risk of accelerating VT to a hemodynamically unstable form is low. Antitachycardia pacing therapies are more effective against spontaneously occurring episodes than induced episodes of VT. Differences in tachycardia cycle length and duration may contribute to these effects.

Adult↗
PubMed1993

Junctional tachycardia: a useful marker during radiofrequency ablation for atrioventricular node reentrant tachycardia.

OBJECTIVES: The aim of this study was to evaluate junctional tachycardia as a useful marker during radiofrequency ablation for atrioventricular (AV) node reentrant tachycardia. BACKGROUND: Junctional tachycardia appears to be a response of the atrioventricular node to injury and is seen during both radiofrequency AV node ablation and slow and fast pathway ablation for AV node reentrant tachycardia. We hypothesized that junctional tachycardia heralding AV node block and that associated with slow or fast pathway ablation may have different characteristics that could be useful in preventing inadvertent AV block. METHODS: Characteristics of junctional tachycardia were examined after 59 radiofrequency ablation sessions in 53 consecutive patients with a mean age (+/- SD) of 41.6 +/- 16.5 years. Type 1 junctional tachycardia was followed by transient second- or third-degree AV block (n = 5) or permanent third-degree AV block (n = 1). Type 2 junctional tachycardia was followed by normal AV conduction (n = 53). RESULTS: Fifty-one patients had typical AV node reentrant tachycardia, and two patients had atypical tachycardia. Fast pathway ablation was attempted during 6 sessions and slow pathway ablation during 53 sessions. Patients underwent 15.3 +/- 10 radiofrequency applications, with a mean duration of 24 +/- 9.7 s. Junctional tachycardia was observed an average of 2.8 +/- 1.8 times per ablation session. Type 1 junctional tachycardia had a significantly faster rate than that of type 2 (cycle length 363 +/- 44 vs. 558 +/- 116, p < 0.001). In addition, type 1 junctional tachycardia was associated with predominantly ventriculoatrial block whereas type 2 was associated with predominantly 1:1 ventriculoatrial conduction (2 of 6 vs. 47 of 53 episodes, p < 0.05). CONCLUSIONS: We conclude that junctional tachycardia leading to AV block can be recognized by a faster junctional rate and ventriculoatrial block. This is a useful marker of impending AV block during slow and fast pathway ablation.

Adult↗
PubMed1993

Biphasic versus sequential pulse defibrillation: a direct comparison in humans.

It has been demonstrated recently that both biphasic and sequential pulse defibrillation shocks are superior to monophasic defibrillation shocks in animals and humans. There is little information directly comparing these two waveforms when pulse characteristics, subjects, and total electrode surface areas are kept constant. We determined the defibrillation threshold intraoperatively in 12 patients undergoing arrhythmia surgery, with the use of two or three patch electrodes (Medtronic 6891 and 6892), while keeping the electrode surface area constant. Patients were randomized in a crossover design for determinations of defibrillation threshold by means of biphasic and sequential pulse shocks. Leading-edge delivered current and delivered energy were significantly lower with sequential pulse shocks than with biphasic shocks (delivered energy means +/- SEM 3.6 +/- 0.7 joules vs 5.5 +/- 0.9 joules, respectively). We conclude that sequential pulse defibrillation with three defibrillating electrodes provides an important current delivery system not matched by biphasic shocks with two electrodes when subjects, waveform characteristics, and total electrode surface areas are kept constant.

Adult↗
PubMed1993

Initiation of atrial fibrillation in the Wolff-Parkinson-White syndrome: the importance of the accessory pathway.

Atrial fibrillation in the Wolff-Parkinson-White syndrome may be related to microreentry in the accessory pathway. If such is the case, catheter ablation of the accessory pathway should eliminate atrial fibrillation. Among 95 patients undergoing catheter ablation, 20 had atrial fibrillation during standard electrophysiologic study (atrial vulnerability) before ablation. There were 16 women and four men with a mean age of 32 years. Before ablation six patients required electrical cardioversion. Thirty minutes after ablation, 11 continued to have inducible atrial fibrillation. Atrial fibrillation terminated spontaneously in every patient after ablation. A control group of 20 patients with accessory pathway ablation had no inducible atrial fibrillation before or after ablation. Catheter ablation had no effect on atrial properties including functional refractory period (227 +/- 37 vs 215 +/- 29 msec before versus after ablation, mean +/- SD) or wavelength (7.4 +/- 3.2 vs 7.2 +/- 2.7 before versus after ablation). These data suggest that an intact accessory pathway is not necessary for initiation of atrial fibrillation in most patients with Wolff-Parkinson-White syndrome. A rapid ventricular response over the accessory pathway may facilitate the perpetuation of atrial fibrillation in persons prone to this arrhythmia.

Adult↗
PubMed1993

Synergistic inhibition of the calcification of glutaraldehyde pretreated bovine pericardium in a rat subdermal model by FeCl3 and ethanehydroxydiphosphonate: preincubation and polymeric controlled release studies.

Calcification is a frequent cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde-pretreated porcine aortic valves or glutaraldehyde-pretreated bovine pericardium (GPBP). We investigated the hypothesis that ferric chloride (FeCl3) and sodium-ethanehydroxydiphosphonate (EHDP) may act synergistically to prevent bioprosthetic tissue calcification. Pre-incubations and controlled release systems were studied individually. FeCl3-EHDP polymeric controlled release matrices were formulated using silicone rubber and evaluated for in vitro release kinetics at pH 7.4 and 37 degrees C. The effects of Fe-EHDP synergism on GPBP calcification were investigated with 21 d subdermal implants in 3 wk-old male rats. Results demonstrated that levels of Fe3+ and EHDP uptake, measured in GPBP tissues pre-incubated first in an FeCl3 solution (10(-5) M) followed by an EHDP solution (0.1 M), were higher than in the reverse order of incubation. In the first series of rat implants, GPBP was pre-incubated in either FeCl3 or Na2EHDP solutions, or sequential pre-incubations of first FeCl3 and then Na2EHDP solutions, or the reverse. The inhibition of calcification was greatest when FeCl3 (first pre-incubation, 10(-5) M) was combined with Na2EHDP (second pre-incubation, 0.1 M) (1.78 +/- 0.2 micrograms of Ca2+/mg of dried tissue) compared with the other pre-incubation groups: EHDP (first pre-incubation) combined with FeCl3 (second pre-incubation) (21.7 +/- 6.4), FeCl3 solution alone at 10(-5) M (27.9 +/- 10.7), Na2EHDP solution alone at 0.1 M (52.3 +/- 11.9) and the control group (72.3 +/- 10.2). In a second series of implants, GPBP specimens were co-implanted with individual controlled release systems containing one of the following formulations (weight percentage in silicone rubber): 1% FeCl3, 20% CaEHDP, 20% protamine sulphate, 1% FeCl3-20% CaEHDP, and 1% FeCl3-20% protamine sulphate. The 1% FeCl3-20% CaEHDP silicone-rubber matrices were the most effective for inhibiting GPBP mineralization (13.7 +/- 3.0 micrograms Ca2+/mg of dried tissue) compared with non-drug silicone co-implant controls (74.7 +/- 5.58 micrograms Ca2+/mg of dried tissue) and other polymeric treatment groups (32.3 +/- 2.3-80.0 +/- 19.7). No adverse effects on bone or overall growth of any treatment protocols were noted. Thus, combinations of FeCl3 and EHDP, using either pre-incubations or polymeric controlled release, were synergistic for inhibiting GPBP calcification.

Animals↗