Transient ischaemic attack in a young woman.
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Adenocarcinoma↗
Biomedical subjects
H F Tse
Publications and source records attributed to H F Tse.
From profound hypokalemia to fatal rhabdomyolysis after severe head injury.
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Accidents, Traffic↗
Radiofrequency catheter ablation of inappropriate sinus tachycardia guided by activation mapping.
OBJECTIVE: The purpose of this study was to evaluate the value of activation mapping for radiofrequency modification of the sinus node and the long-term success rate of the procedure in a series of patients with inappropriate sinus tachycardia. BACKGROUND: The results of radiofrequency ablation of inappropriate sinus tachycardia have been reported in only a small number of patients. METHODS: The subjects of this study were 29 consecutive drug-refractory patients who underwent catheter ablation of inappropriate sinus tachycardia. Target sites were selected by activation mapping during sinus tachycardia. RESULTS: The ablation procedure was successful acutely in reducing the baseline sinus rate to <90/min and the sinus rate during isoproterenol infusion by >20% in 22 of 29 patients (76%). In 13 of 22 patients (59%) with a successful acute outcome, successive applications of radiofrequency energy at the site of earliest endocardial activation resulted in a cranial-caudal migration of earliest endocardial activation from the high lateral right atrium, along with a step-wise reduction in heart rate. In the other nine patients (41%) with a successful acute outcome, the reduction in sinus rate occurred abruptly, unaccompanied by migration of the site of earliest activation. Symptoms due to inappropriate sinus tachycardia recurred at a mean of 4.4+/-; 3 months after the ablation procedure in 6 of 22 patients (27%). After additional procedures in three patients, symptoms of inappropriate sinus tachycardia ultimately were successfully eliminated over the long-term in 19 of 29 patients (66%). CONCLUSIONS: In conclusion, radiofrequency ablation is at best only modestly effective for managing patients with inappropriate sinus tachycardia. The two different responses of heart rate to radiofrequency ablation may reflect differences in the number and/or multicentricity of subsidiary sites of impulse generation within the sinus node and/or atrium in patients with inappropriate sinus tachycardia.
Action Potentials↗
Atrial pacing for suppression of early reinitiation of atrial fibrillation after successful internal cardioversion.
AIMS: To evaluate the efficacy of atrial pacing in the suppression of early reinitiation of atrial fibrillation after successful internal cardioversion. METHODS AND RESULTS: The efficacy of atrial pacing in suppressing early reinitiation of atrial fibrillation was studied in 12 of 45 (29%) patients with early reinitiation of atrial fibrillation after successful cardioversion. These patients were randomized to undergo either repeated defibrillation alone or repeated defibrillation followed by high right atrial pacing at 500 ms in a crossover fashion. In patients with persistent early reinitiation of atrial fibrillation despite atrial pacing at 500 ms and repeated defibrillation, atrial pacing at 300 ms was tested. Lastly, if early reinitiation of atrial fibrillation persisted, administration of intravenous sotalol (1.5 mg. kg(-1)) was tested. Atrial pacing at 500 ms after defibrillation prevented early reinitiation of atrial fibrillation in five of 12 (42%) patients, and was significantly more effective than repeated defibrillation (0/9 patients, 0%, P<0.05). During atrial pacing at 500 ms, the density of atrial premature depolarizations (APDs) was significantly decreased (2.4+/-2.4 APDs. min(-1)vs 16.4+/-9.8 APDs. min(-1), P<0. 05) and the coupling interval of atrial premature depolarization was significantly increased (420+/-32 ms vs 398+/-19 ms, P<0.05) as compared to no pacing. In the remaining seven (58%) patients, atrial pacing at 500 ms failed to prevent early reinitiation of atrial fibrillation, but significantly decreased the density of atrial premature depolarization (3.4+/-2.4 APDs. min(-1)vs 14.2+/-4.8 APDs. min(-1), P<0.05) and delayed the onset of early reinitiation of atrial fibrillation (33+/-17s vs 11+/-11 s, P<0.05). Atrial pacing at 300 ms decreased the coupling interval of atrial premature depolarization as compared to no pacing and during atrial pacing at 500 ms (P<0.05), but without early reinitiation of atrial fibrillation suppression. Administration of intravenous sotalol was effective in preventing early reinitiation of atrial fibrillation in five of seven (71%) patients where pacing failed to suppress early reinitiation of atrial fibrillation. CONCLUSION: The results of this study suggest that atrial pacing can be useful when combined with transvenous defibrillation in patients with early reinitiation of atrial fibrillation.
Adult↗
Efficacy and tolerability of continuous overdrive atrial pacing in atrial fibrillation.
Overdrive right atrial pacing has been used to prevent atrial fibrillation, but its efficacy in atrial fibrillation prevention and the patient tolerability and quality of life during high rate pacing remain uncertain. The objective of this study was to test the effects of a consistent atrial pacing algorithm that automatically paced the atrium at 30 ms shorter than the sinus P-P interval for atrial fibrillation prevention. Fifteen patients with sick sinus syndrome implanted with a Thera DR (model 7940 or 7960, Medtronic Inc.) were randomly programmed to rate adaptive dual chamber pacing (DDDR) or DDDR + consistent atrial pacing mode, each for an 8-week study period. The efficacy of consistent atrial pacing was assessed by the number of automatic mode switching and the number of premature atrial complexes. Symptoms and quality of life were assessed by the SF-36 quality of life questionnaire and an atrial fibrillation symptom checklist. The percentage of atrial pacing increased from 57 +/- 32% to 86 +/- 28%. Overall, there was no significant difference in the number of automatic mode switching episodes between DDDR and DDDR + consistent atrial pacing (47 +/- 90 vs 42 +/- 87, P > 0.05), but a significant reduction in premature atrial complexes by 74.7% (P < 0.001). There was no undue increase in atrial rate by the DDDR + consistent atrial pacing mode versus DDDR (63 +/- 13 vs 70 +/- 7 bpm). There was no significant difference in quality of life scores and symptom severity on frequency between the two modes of pacing, but a trend towards a lower frequency of symptoms in the DDDR + consistent atrial pacing mode compared with baseline (29.5 +/- 10.2 vs 25.1 +/- 9.7, P = 0.07). An algorithm that provides consistent atrial overdrive pacing can suppress atrial fibrillation triggering premature atrial complexes without the need to increase the overall atrial rate compared with conventional pacing. The algorithm appears to be well-tolerated, but further studies are needed to address the clinical impact of this atrial fibrillation prevention algorithm.
Aged↗
A comparative study on the behavior of three different automatic mode switching dual chamber pacemakers to intracardiac recordings of clinical atrial fibrillation.
Automatic mode switching (AMS) allows patients with dual chamber pacemakers who develop paroxysmal AF to have a controlled ventricular rate. The aim of this study was to (1) compare the rate-controlled behavior of three AMS algorithms in response to AF, in terms of speed and stability of response and resynchronization to sinus rhythm, and (2) compare the influence of pacemaker programming on optimal mode switching. We studied 17 patients (12 men, 5 women; mean age 59 +/- 15 years) who developed AF during electrophysiological study. Unfiltered bipolar atrial electrograms during sinus rhythm and AF were recorded onto high fidelity tapes and replayed into the atrial port of three dual chamber pacemakers with different mode switching algorithms (Thera, Marathon, Meta). The Thera pacemaker uses rate smoothing, and mode switches occur when mean sensed atrial rate exceeds the predefined AMS rate (MR). Marathon mode switches after a programmable number of consecutive rapid atrial events (NR). Meta DDDR monitors the atrial rate by a counter for atrial cycles faster than the programmed AMS rate. It increases or decreases the counter if the atrial cycle length is shorter or longer than the programmed AMS interval, respectively. Mode switch occurs when the AF detection criteria are met (CR). A total of 260 rhythms were studied. NR was significantly faster than MR and CR (latency 2.5 +/- 3 s vs 26 +/- 7 s vs 15 +/- 22 s, respectively, P < 0.0001). During sustained AF, MR resulted in the most stable and regular ventricular rhythm compared to NR or CR. In CR, ventricular rate oscillated between AMS and atrial tracking (cycle length variations: 44 +/- 2 s vs 346 +/- 109 s vs 672 +/- 84 s, P < 0.05). At resumption of sinus rhythm, MR resynchronized after 143 +/- 22 s versus 3.4 +/- 0.7 s for NR and 5.9 +/- 1.1 s for CR, resulting in long periods of AV dissociation when a VVI/VVIR mode is used after AMS. Programming of atrial refractory periods did not affect AMS response, although the speed of AMS onset can be adjusted by programming of onset criteria in the Meta DDDR. AMS algorithms differ in their ability to handle recorded clinical atrial arrhythmias. The rapid-responding algorithm exhibits rate instability, whereas slow responding algorithm shows a long delay in response and risk of AV dissociation. Thus different instrumentation of AMS may have clinical implications in patients with dual chamber pacemakers who develop AF.
Adult↗
Atrial fibrillation induction and determination of atrial vulnerable period using very low energy synchronized biatrial shock in normal subjects and in patients with atrial fibrillation.
The atrial vulnerable periods (AVP) for shock induction of atrial fibrillation (AF) in humans have not been clearly defined. Furthermore, the safety and efficacy of using low energy biatrial shock delivered transvenously for AF induction are unknown. We tested the safety and efficacy of using very low energy biatrial shocks, delivered between the right atrium and the coronary sinus for AF induction and used this technique to characterize the AVP in nine controls and nine patients with AF. Thirty-volt and 60-V 3/3-ms biphasic shocks were delivered, starting from 50 ms before the atrial effective refractory period with 20-ms increments until the end of the QRS interval to determine the AVP front, AVP end, and the AVP duration. Successful AF induction could be achieved in eight (89%) of the nine controls and in nine (100%) of the nine patients with AF without any complication. In patients with AF, the AVP front started significantly earlier within the QRS complex, and the AVP duration and the AVP duration/QRS percent ratios were also significantly greater as compared to controls. Furthermore, a higher induction shock energy in patients with AF was associated with an increase in AF inducibility and significantly increased the AVP duration and AVP duration/QRS percent ratio as compared to the controls. This study demonstrated the safe and efficacy of delivering a very low energy biatrial shock during the AVP within the R wave for AF induction. The characteristics of AVP in patients with AF were significantly different from normal subjects.
Adult↗
Is automatic mode switching effective for atrial arrhythmias occurring at different rates? A study of the efficacy of automatic mode and rate switching to simulated atrial arrhythmias by chest wall stimulation.
Automatic mode switching (AMS) is a useful means to avoid rapid ventricular response during atrial fibrillation (AF), but AMS cannot occur if the detected atrial rate during AF is below the mode switching criteria. This may be the result of antiarrhythmic medications, or when the atrial events fall within the atrial blanking period, or if the atrial amplitudes during AF are too small to be sensed. We hypothesize that the addition of an automatic rate switching (ARS) algorithm may complement AMS response during AF with different detected atrial rates. We studied the Marathon DDDR pacemaker (Model 294-09, Intermedics Inc.) with the AMS and ARS algorithms that are independently programmable but can also operate in combination. AF sensed above the AMS rate (160 beats/min) will lead to VDIR pacing, whereas AF below AMS rate will be tracked at an interim rate as dictate by the ARS, at a ventricular response that is 20 beats/min above the sensor indicated rate. Atrial tachyarrhythmias were simulated by chest wall stimulation (CWS). CWS was applied to 33 patients (16 men, 17 women, mean age 69 +/- 11 years) with a Marathon DDDR pacemaker using an external pacer to simulate AF occurring at two rate levels: above the AMS rate (programmed at 160 beats/min) at 180 beats/min and below the AMS rate at 120 beats/min. The maximum, minimum, and mean ventricular rates during CWS in DDDR mode with AMS alone, ARS alone, and their combination were compared. During CWS at 120 beats/min, the AMS plus ARS setting showed a mean ventricular rate of 79 +/- 3 beats/min and 124 +/- 14 beats/min in the AMS setting alone (P < 0.01). With CWS at 180 beats/min, the mean ventricular rate in the AMS plus ARS setting compared to the AMS setting alone was not significantly different. However, the variation in ventricular pacing rate was 7 +/- 14 beats/min in the AMS plus ARS setting and 40 +/- 42 beats/min in the AMS setting (P < 0.05). In conclusion, AMS is effective for simulated atrial tachyarrhythmias sensed above the AMS rate. Combined AMS with ARS is useful to handle simulated atrial tachyarrhythmia at a slower rate and to avoid rate fluctuation during AMS. There is also a possibility that this can be applied to the naturally occurring atrial tachyarrhythmias.
Aged↗
Failure of coronary sinus pacing in reducing local atrial conduction delay in patients with atrial fibrillation after successful internal cardioversion.
Recent studies suggested that distal coronary sinus (CS) pacing may prevent atrial fibrillation (AF) by reducing site dependent intraatrial conduction delay. The aim of this study was to investigate the effect of high right atrial (HRA) and distal CS pacing on local conduction delay in patients with AF. The study population consisted of 10 patients with persistent AF after transvenous atrial defibrillation and 10 control subjects. The local conduction delays along the anterolateral right atrium (RA), in the CS, and at the right atrial septum (RAS), and the incidence of AF in response to an atrial extrastimulus during HRA and distal CS pacing at a drive cycle length of 400, 500, and 600 ms were evaluated. In patients with AF, distal CS and HRA pacing are associated with more prominent and similar extent of conduction delay within the atria, without any significant difference in the dispersion of conduction delay and susceptibility to AF induction (70% vs 60%, P = 0.9). In normal controls, distal CS pacing reduces the conduction delay at the RAS and CS ostium and decreases the dispersion of conduction delay and the propensity for AF induction (0% vs 50%, P = 0.03) compared to HRA pacing. The pacing drive cycle length has no significant effect on conduction delay in patients with AF and normal controls (P > 0.05). Compared to normal controls, patients with AF have significantly longer conduction delay at the RAS and along the anterolateral RA during HRA and distal CS pacing. The result of this study demonstrates that the effect of HRA and distal CS pacing on the local atrial conduction delay in patients with and without AF differ significantly. These patients with AF may have more diffuse atrial anisotropy causing the changes in conduction, and pacing from distal CS in these patients dose not reduce the propensity for AF.
Atrial Fibrillation↗
Reversal of left ventricular remodeling by synchronous biventricular pacing in heart failure.
Synchronous biventricular pacing is a new nonpharmacological supplemental treatment of advanced heart failure associated with electromechanical conduction delay. However, the role of pacing on left ventricular remodeling is unknown. Eleven patients with New York Heart Association Class III to IV heart failure, a left ventricular ejection fraction < 35%, and a QRS duration > or = 140 ms received a biventricular dual chamber pacemaker. Serial echocardiography, 6-minute hall walk, and Minnesota Living with Heart Failure quality-of-life (QOL) questionnaire were performed before and after up to 3 months of pacing. At 3 months there was a significant increase in fractional shortening (P < 0.001), ejection fraction (P < 0.001), and cardiac output (P < 0.05). The left ventricular end-diastolic volume (245 +/- 70 vs 185 +/- 37 mL, P < 0.05), end-systolic volume (209 +/- 69 vs 140 +/- 44 mL P < 0.05), and mitral regurgitation were reduced (P < 0.05), and diastolic filling time was lengthened (P < 0.05). There were also improvements in heart failure symptoms, an increase in 6-minute walk distance, and a decrease in QOL scores. Synchronous biventricular pacing for 3 months was associated with hemodynamic improvements, reversal of left ventricular remodeling, and increase in left ventricular systolic function, and a decrease in secondary mitral regurgitation.
Cardiac Pacing, Artificial↗
Initial clinical experience with a new self-retaining left ventricular lead for permanent left ventricular pacing.
This study evaluated the performance of a new lead for permanent left ventricular (LV) pacing via the coronary sinus (CS) in four men and nine women (mean age = 71 +/- 13 years) with sick sinus syndrome. It consists of a 75-cm-long, 4.8-Fr, unipolar ventricular lead with a distal portion preshaped in an S curve to provide steerability and stability within the CS. Its efficacy and stability for permanent LV pacing were tested at implant, predischarge, and at 1, 3 and 6 months of follow-up. The lead was successfully implanted in 11/13 patients (85%) within a mean fluoroscopy time of 35 +/- 22 minutes. The final positions of the electrodes at the tip of the lead within venous tributaries of the CS were: (1) anterior (n = 2, 18%); (2) posterolateral (n = 5, 45%); and (3) the lateral (n = 4, 36%). Unsuccessful implants were due to unstable lead position (n = 1), or high pacing threshold (n = 1). There was no postprocedural lead dislodgment or significant changes in the R wave amplitude, LV pacing threshold and lead impedance up to 6 months of follow-up. In summary, this initial experience suggests that this new lead offers safe and reliable permanent LV pacing via the CS in the majority of patients and may be used in isolation or in conjunction with right ventricular pacing for biventricular synchronization.
Aged↗
Effects of different atrioventricular intervals during dual-site right atrial pacing on left atrial mechanical function.
Recent studies have suggested that dual-site right atrial (RA) pacing via the high RA and coronary sinus ostium (CSos) prevents atrial fibrillation (AF). However, the programming of the atrioventricular (AV) interval associated with optimal left atrial (LA) mechanical function during high RA and dual-site RA pacing has not been defined. LA mechanical function was studied by measuring transmitral pulsed Doppler echocardiographic peak A wave velocity and percent A wave filling, in six women and three men, 67 +/- 8 years of age, who had received dual-site RA pacemakers in a randomized study. Serial echocardiographic measurements were performed during high RA or dual-site RA pacing at 80 beats/min with AV intervals of 50, 100, 150, or 200 ms tested in random order. High RA and dual-site RA pacing at an AV interval of 50 ms were associated with significantly lower peak A wave velocity and percent A wave filling, compared to the other AV intervals (all P < 0.05). Compared with high RA pacing, dual-site RA pacing was associated with significantly higher peak A wave velocity (85 +/- 12 vs 72 +/- 17 cm/s, P = 0.04) and percent A wave filling (24 +/- 3 vs 20 +/- 4%, P = 0.02) at an AV interval of 100 ms, but a lower peak A wave velocity at an AV interval of 200 ms (77 +/- 10 vs 84 +/- 8 cm/s, P = 0.004). In conclusion, variations in the AV interval during atrial pacing have significant effects on LA function. As a consequence of altered atrial activation, the AV interval associated with optimal LA mechanical function during dual-site RA pacing was significantly shorter than that during RA pacing. This observation has important implications with respect to the programming of dual-site RA pacemakers implanted to prevent AF for hemodynamic purpose.
Aged↗
Automatic optimization of resting and exercise atrioventricular interval using a peak endocardial acceleration sensor: validation with Doppler echocardiography and direct cardiac output measurements.
Peak endocardial acceleration (PEA) measured by an implantable acceleration sensor inside the tip of a pacing lead reflects ventricular filling and myocardial contractility. The contribution of the plateau phase of PEA as an indicator of optimal ventricular filling, hence of the appropriate atrioventricular interval (AVI) at rest and during exercise, was studied in 12 patients (age 69 +/- 6 years) with complete AV block and a PEA sensing DDDR pacemakers (Living 1 Plus, Sorin Biomedica). At a mean resting heart rate of 79 +/- 15 beats/min, the mean AVI optimized by PEA versus Doppler echocardiography (echo) were identical (142 +/- 37 vs 146 +/- 26 ms, P = 0.59). During submaximal exercise at a mean heart rate of 134 +/- 6 beats/min, AVI optimized by PEA was 135 +/- 37 ms. Cardiac output at rest, measured by the CO2 rebreathing method, was comparable with AVI determined by echo versus PEA (4.3 +/- 2.9 and 3.7 +/- 2.4 L/min, respectively), and increased to the same extent (8.0 +/- 3.9 vs 8.3 +/- 5.2 L/min) during submaximal exercise. In patients with AV block, AVI automatically set by PEA was comparable with AVI manually optimized by Doppler echocardiography and was associated with comparable exercise induced hemodynamic changes.
Aged↗
Prevention of ventricular fibrillation by pacing in a man with Brugada syndrome.
The unique ECG appearance of Brugada syndrome is caused by failure of the dome of the action potential to develop. It occurs when the outward currents (mainly Ito) overwhelm the inward currents (mainly Ica) at the end of phase 1 of the action potential. Because Ito becomes less prominent at a faster rate, increased heart rate is associated with decreased ST segment elevation on ECG and probably decreased incidence of ventricular arrhythmia. We present the first report on prevention of ventricular fibrillation in a man with Brugada syndrome by overdrive pacing from his dual chamber implantable cardioverter defibrillator.
Adult↗
Comparison of endocardial activation times at effective and ineffective ablation sites within the pulmonary veins.
INTRODUCTION: Recent studies demonstrated that atrial arrhythmias may be generated within pulmonary veins. The purpose of this study was to compare the endocardial activation times at effective and ineffective ablation sites during radiofrequency catheter ablation of arrhythmias initiated or generated within pulmonary veins. METHODS AND RESULTS: Twenty-one of 28 patients without structural heart disease underwent successful ablation of 23 arrhythmogenic foci within a pulmonary vein. Electrograms were recorded at 75 pulmonary venous sites and categorized into three groups: 23 successful ablation sites; 28 unsuccessful target sites within an arrhythmogenic pulmonary vein; and 24 sites within nonarrhythmogenic pulmonary veins. The endocardial activation time of premature depolarizations arising at successful target sites was significantly earlier than at other sites. During premature depolarizations, an endocardial activation time of -75 msec or earlier had a sensitivity of 83% and a specificity of 79% for identification of a successful ablation site. Endocardial activation times earlier than -100 msec were recorded only at successful ablation sites, and endocardial activation times later than -30 msec were recorded only at sites within nonarrhythmogenic pulmonary veins. The presence of a split potential during sinus rhythm or premature depolarizations was not a specific indicator of a successful ablation site. CONCLUSION: The endocardial activation times of premature depolarizations that arise within pulmonary veins and initiate atrial tachycardia/fibrillation are useful in identifying successful ablation sites.
Adult↗
Prevalence and significance of exit block during arrhythmias arising in pulmonary veins.
INTRODUCTION: Recent studies described the occurrence of conduction block within pulmonary veins. The purpose of this study was to evaluate the prevalence of exit block during arrhythmias that arise in pulmonary veins. METHODS AND RESULTS: Twenty-five patients with atrial tachycardia/fibrillation underwent successful ablation of 28 arrhythmogenic foci within a pulmonary vein. The prevalence of exit block in the pulmonary veins was determined in 28 arrhythmogenic pulmonary veins and 40 nonarrhythmogenic pulmonary veins. During isolated premature depolarizations, exit block in a pulmonary vein was observed at 50% of arrhythmogenic pulmonary vein sites and was never observed within pulmonary veins that did not generate a tachycardia (P < 0.01). During tachycardia, exit block from a pulmonary vein was observed in 61% of the arrhythmogenic pulmonary veins. The mean cycle length of the pulmonary vein tachycardias associated with exit block was significantly shorter than the cycle length of tachycardias that were not associated with exit block (163 +/- 32 vs 251 +/- 45 msec, P < 0.001). Exit block in two pulmonary veins during the same episode of tachycardia was observed in 3 of the 28 arrhythmogenic pulmonary veins (11%) in three different patients. Simultaneous recordings in the two pulmonary veins demonstrated bursts of tachycardia in both veins that were not synchronized. Radiofrequency catheter ablation of the arrhythmogenic site in one of the pulmonary veins eliminated spontaneous recurrences of tachycardia from the other pulmonary vein. CONCLUSION: Exit block from pulmonary veins is a common observation during tachycardias generated within pulmonary veins and indicates that an arrhythmogenic pulmonary vein has been identified. The occurrence of exit block in more than one pulmonary vein most likely is attributable to simultaneous tachycardias, one or both of which may be tachycardia induced and perpetuated by the other.
Adult↗
Images in cardiology: Three dimensional reconstruction of femoral pseudoaneurysm using contrast enhanced axial CT angiography.
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Aneurysm, False↗
Electrocardiographic predictors of successful ablation of tachycardia or bigeminy arising in the right ventricular outflow tract.
Among various electrocardiographic variables, the QRS duration in V2 was found to be the best discriminator of outcome in patients undergoing radiofrequency catheter ablation of the right ventricular outflow tract tachycardia and/or bigeminy. If the QRS duration is <160 ms in lead V2, the probability of successful ablation is lower than if the QRS duration is longer.
Adult↗