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Chu-Pak Lau

Publications and source records attributed to Chu-Pak Lau.

At least 91 records · Page 5Linked to original sources
PubMed2003

Does sinus rhythm beget sinus rhythm? Effects of prompt cardioversion on the frequency and persistence of recurrent atrial fibrillation.

Recent clinical and experimental studies have demonstrated that atrial fibrillation (AF) alters the electrical and mechanical remodeling of the atrium, which subsequently promote the maintenance and recurrence of AF. If atrial remodeling can be prevented with prompt and repeated cardioversion, the likelihood of AF recurrence may be reduced. Recent clinical studies have demonstrated that the strategies of transesophageal echocardiography facilitated early cardioversion and early repeated cardioversion may be clinically valuable in some patients who have persistent AF and recurrence of arrhythmia after the initial cardioversion. Furthermore, the use an implantable atrial defibrillator (IAD) for early repeated device-based cardioversion to maintain sinus rhythm appears to be safe and clinically feasible. Early cardioversion by IAD reduces AF burden, reverses atrial remodeling and prevents subsequent AF recurrence in selected patients without structural heart disease implanted with this device, indicating possible "sinus rhythm begets sinus rhythm". Despite encouraging initial observations, further long-term clinical studies in a larger patient population are needed to confirm this finding. Furthermore, whether the use of IAD in the fully automatic mode to provide immediate termination of AF episodes could intensify the potential beneficial effect and the clinical efficacy of this approach in patients with structural heart disease needs to be evaluated.

Atrial Fibrillation↗
PubMed2003

Impedance cardiography for atrioventricular interval optimization during permanent left ventricular pacing.

Left ventricular (LV) pacing is increasingly used in the management of congestive heart failure. Optimization of the atrioventricular (AV) interval is essential to maximize the hemodynamic benefits of this therapy. Although Doppler echocardiography (echo) is the most widely used method, it is time-consuming, expensive, and operator-dependent. We examined the value of an impedance cardiography (IC)-based method of cardiac output (CO) measurement to optimize the AV interval in 5 men and 1 woman (mean age = 72 +/- 11 years) during permanent LV pacing with a 4.8 Fr unipolar coronary sinus pacing lead. Simultaneous measurements of CO by IC and echo were performed at AV intervals of 50, 80, 110, 150, 180, and 225 ms during DDD pacing at 85 beats/min. The optimal AV interval varied between 110 and 180 ms. In 5 of 6 patients (83%), the optimal AV interval by echo and IC was identical. While CO measurements were higher with IC than with echo (6.1 +/- 0.4 L/min vs 4.7 +/- 0.3 L/min, P < 0.05), CO measurements by IC and echo were closely correlated r = 0.67, P < 0.001). In conclusion, our initial experience suggests that IC is a reliable method of AV interval optimization during LV pacing. IC and echo measurements of CO during LV pacing were closely correlated.

Aged↗
PubMed2003

Regional left ventricle mechanical asynchrony in patients with heart disease and normal QRS duration: implication for biventricular pacing therapy.

LV electromechanical delay results in asynchronized contraction. However, it is not known if the presence of cardiac diseases without QRS prolongation may result in inter- or intraventricular asynchrony. This study investigated the occurrence of systolic mechanical delay in different regions of the LV in patients with underlying heart diseases and normal QRS duration. Tissue Doppler imaging (TDI) was performed in 141 patients (age 63.7 +/- 11.5 years) with underlying heart diseases (82% had ischemic heart disease) and 92 normal healthy volunteers (age 63.9 +/- 9.8 years) based on the four-basal and four-mid-segment model by apical views. Of these, 124 patients had normal QRS duration (< or = 120 ms) while 17 were prolonged due to LBBB or intraventricular conduction defect. Patients with normal QRS duration had significantly lower peak myocardial isovolumic contraction velocity (IVCM), sustained systolic velocity (SM), and prolonged time to peak IVCM and SM in almost all myocardial segments when compared to controls. The time to peak IVCM (basal lateral vs basal septal segment: 61.0 +/- 29.4 vs 53.3 +/- 24.1 ms, P < 0.005) and SM (basal lateral vs basal septal segment: 174 +/- 44 vs 154 +/- 36 ms, P < 0.001) was further delayed in the LV free-wall segments. Mechanical delay was also evident in the LV free-wall segments in patients with preserved or impaired systolic function, in patients with or without previous myocardial infarction, and in patients with prolonged QRS duration. Patients with prolonged QRS had a higher prevalence of LV free-wall delay of > 50 ms (47 vs 24%, chi-square = 4.6, P < 0.05). In conclusion, the presence of cardiac diseases was characterized by LV global mechanical delay; and, intraventricular asynchronized contraction characterized mostly by further mechanical delay in the free-wall region. These changes occur even in those with normal QRS duration.

Cardiac Pacing, Artificial↗
PubMed2003

Dose-response relationship for successful internal atrial defibrillation.

The dose-response relationship for successful defibrillation has been determined in man for the ventricle but not for the atrium. The purpose of this study was to determine the dose-response relationship for internal atrial defibrillation in humans. Seventy-seven consecutive patients underwent internal atrial defibrillation for acute (n = 14) or chronic AF (n = 63). Shocks were delivered in 40-V increments between electrodes positioned in the coronary sinus and the right atrium until successful conversion or a maximum of 400 V was reached. The shock strength versus success of shock data were subjected to a Kaplan-Meier survival analysis combined with a nonparametric probability analysis to arrive at the dose-response relationship. Using this relationship, comparisons were made between acute and chronic AF and clinical relevant conversion percentages (20, 50, 80 and 95%) were estimated and were compared with the conventional mean threshold. There were significant dose-response relationships in both patients groups (P < 0.05). The Kaplan-Meier analysis comparing patients with chronic and acute AF showed significant differences in their dose-response relationships (P < 0.001). The estimated shock intensity for 95% conversion in patients with acute and chronic AF was 279 V (2.9 J) and 433 V (6.6 J), respectively (P < 0.001). The conventional mean defibrillation threshold in patients with acute (192 +/- 15 V. 1.4 +/- 0.2 J) and chronic AF (343 +/- 8 V, 4.4 +/- 0.2 J) predicted the 60% and 45% chance of successful conversion, respectively. In conclusion, this study demonstrates that single shock conversion data can be used to determine a dose-response relationship, which can be used to estimate the shock intensity required for specific successful atrial defibrillation efficacy and to compare different clinical factors that affect defibrillation efficacy.

Aged↗
PubMed2003

Effect of coronary sinus electrode on the optimal atrial defibrillation pathway for an atrioventricular defibrillator.

INTRODUCTION: Previous studies have demonstrated significant failure in converting atrial fibrillation (AF) using a conventional ventricular pathway. The aim of this study was to assess the benefit of incorporating a coronary sinus (CS) lead into the atrial defibrillation pathway in atrial defibrillation threshold (ADFT) reduction in patients with persistent AF. METHODS AND RESULTS: This study was a prospective, randomized assessment of shock configuration on ADFT in 18 patients undergoing elective internal cardioversion for persistent AF (mean AF duration: 8 +/- 9 months). The lead system included a dual-coil defibrillation lead (Endotak DSP, Guidant) with a distal right ventricular (RV) electrode and a proximal superior vena cava (SVC) electrode, a CS lead (Perimeter, Guidant), and a left pectoral cutaneous electrode (Can). In each patient, dual step-up ADFTs were determined for each of three vectors: (1) RV --> SVC+Can; (2) CS --> SVC+Can; and (3) RV --> CS+SVC+Can (group 1, n = 8) or RV+CS --> SVC+Can (group 2, n = 10), using R wave-synchronized biphasic shocks. Successful defibrillation was achieved in all patients without any ventricular proarrhythmia. ADFT of CS --> SVC+Can (11.8 +/- 5.6 J) was significantly lower than ADFT of RV --> SVC+Can (16.5 +/- 7.8 J, P = 0.021). ADFT of CS --> SVC+Can was similar to RV --> CS+SVC+Can (group 1: 12.0 +/- 6.5 J vs 17.4 +/- 4.8 J, P = 0.16), but it was significantly higher than RV+CS --> SVC+Can (group 2: 9.0 +/- 3.9 J vs 11.6 +/- 5.0 J, P = 0.049). CONCLUSION: Patients with persistent AF of substantial duration can be reliably cardioverted using a conventional implantable cardioverter defibrillator (ICD) lead set; however, the incorporation of a CS lead to the conventional ICD lead configuration significantly lowered ADFT. The optimal shock vector that incorporates a CS lead for atrial defibrillation requires future studies.

Aged↗
PubMed2003

Atrial tachycardia arising from an epicardial site with venous connection between the left superior pulmonary vein and superior vena cava.

We describe a case of atrial tachycardia originating from an epicardial site with a venous connection between the left superior pulmonary vein (LSPV) and superior vena cava (SVC). Initial endocardial mapping with multiple electrodes catheters demonstrated early endocardial activation at both the SVC and LSPV. However, radiofrequency applications at the SVC failed to terminate the atrial tachycardia. With three-dimensional electroanatomic mapping, the earliest endocardial activation was found to be in the left atrial appendage (LAA). However, radiofrequency energy applications at multiple sites in the LAA resulted in only transient termination of the tachycardia. A left atrial angiogram demonstrated a venous connection between the LSPV and SVC, overlying the LAA. An application of radiofrequency energy with a saline-irrigated ablation catheter delivered at the earliest activation site in the LAA terminated the tachycardia. The tachycardia did not recur during 18-month follow-up.

Abnormalities, Multiple↗
PubMed2003

Regression of left ventricular hypertrophy after treatment of hypertension: comparison of directed M-echocardiography with magnetic resonance imaging in quantification of serial mass changes.

BACKGROUND: This study sought to validate the reliability of serial echocardiographic measurements in detecting left ventricular (LV) hypertrophy regression by using magnetic resonance imaging (MRI) as a reference standard. METHODS AND RESULTS: We studied a small population (n = 20) of patients enrolled in the Prospective Randomized Enalapril Study Evaluating Regression of Ventricular Enlargement (PRESERVE) trial for evaluating LV hypertrophy regression. LV mass was measured by both echocardiography and MRI at baseline and after 1 year. As compared with baseline, systolic and diastolic blood pressures were significantly decreased after 1 year (all P <.05). Echocardiographic technique showed an overestimation of LV mass by 27.6 g at baseline (P =.005) and by 37.1 g after 1 year (P <.001), and there were wide 95% limits of agreement (+/-36.0 g at baseline; and +/-27.6 g after 1 year) when compared with MRI measurement. Significant changes of LV mass from baseline of -20 +/- 22 g (P<.01) and -29 +/- 19 g (P <.01) were detected by using echocardiography and MRI after 1 year, respectively (P =.02), and there were similarly wide limits of agreement for change in LV mass (+/-24.2 g). CONCLUSIONS: Despite the use of careful methodology, echocardiographic measurement of LV mass at a single time point or for serial studies resulted in significant variation in LV mass estimates from measurement using MRI.

Aged↗
PubMed2003

Electrophysiological effects of a single intravenous administration of ivabradine (S 16257) in adult patients with normal baseline electrophysiology.

INTRODUCTION: Ivabradine is a heart rate-lowering agent that selectively inhibits the pacemaker current, I(f), in the sinoatrial node. The objective of this study was to evaluate the effects of a single intravenous administration of ivabradine on cardiac electrophysiological parameters in patients with normal baseline electrophysiology. The safety profile of ivabradine was also investigated. STUDY DESIGN: This was an open-label, single-dose, non-controlled study conducted at one centre. Patients received a single dose of ivabradine (0.2 mg/kg) intravenously as a slow bolus over 15 seconds. Electrophysiological investigations, after catheter ablation for cardiac dysrhythmia, were performed at baseline and 30 minutes and 1 hour after drug administration. Electrode catheters were introduced and advanced to the right atrium, the bundle of His and the right ventricular apex of the heart. Electrophysiological parameters assessed included heart rate, QT interval, corrected QT interval (QTc), PR interval, sinoatrial conduction time, sinus node recovery time, and right atrial and ventricle refractory periods. Changes in electrophysiological parameters over time were assessed using one-way analysis of variance. In the case of a significant time effect, the Newman-Keuls procedure was used for comparison. PATIENTS: A total of 14 patients, 12 male and 2 female, aged 18-75 years were included in the study. The arrhythmia requiring catheter ablation was atrioventricular (AV) excitation in seven patients, paroxysmal supraventricular tachycardia in five patients, atrial fibrillation and flutter in one patient, and cardiac dysrhythmia in one patient. All patients had normal electrophysiology at baseline. RESULTS: Mean heart rate decreased significantly with ivabradine by 12.9 beats/min at 30 minutes and 14.1 beats/min at 1 hour. The mean QT interval increased but QTc showed no significant change from baseline. The PR and QRS intervals were unchanged. The right atrial and right ventricle refractory periods showed no significant change from baseline. The measured QT interval and the sinus node recovery time were increased. There were no clinically relevant changes in any other major electrophysiological parameters. Ivabradine was well tolerated and no serious adverse events occurred. CONCLUSION: A single intravenous dose of ivabradine had a significant heart rate-lowering effect, observed at 30 minutes and 1 hour after administration. Ivabradine did not prolong QTc or modify conductivity and refractoriness of the atrium, AV node, His-Purkinje system and ventricles, or repolarisation duration. These results confirm the action of ivabradine as a specific heart rate-lowering agent.

Adolescent↗
PubMed2003

Advances in antithrombin therapy for ST-elevation myocardial infarction.

Thrombin is a pivotal molecule in acute myocardial infarction (MI) because of its extensive procoagulant and prothrombotic actions. Antithrombin therapy is an important component of the pharmacotherapy for acute MI. The standard agent used in clinical practice, unfractionated heparin (UFH), is associated with the disadvantages of variable anticoagulant effect, inability to inhibit clot-bound thrombin, neutralization by platelet factor 4, and the propensity to cause thrombocytopenic complications. Novel thrombin inhibitors have been developed to overcome these disadvantages. Although possessing the property of inhibiting both fluid-phase and clot-bound thrombin, the direct thrombin inhibitor hirudin has been shown to give marginal benefits over UFH as adjunct to fibrinolysis in ST-elevation MI. Bivalirudin, another direct thrombin inhibitor, is able to reduce reinfarction in patients treated with streptokinase and is a new anticoagulant treatment option in this setting. The pharmacokinetic characteristics of better availability, longer half-life, and dose-independent clearance together with the ability of inhibiting both thrombin generation and activity make the low-molecular-weight heparins (LMWHs) an attractive alternative to UFH. The favorable benefit/risk profile of the LMWHs as adjunct to different generations of fibrinolytic agents is setting the stage for larger clinical trials to confirm their role as the antithrombin agent of choice for STEMI.

Anticoagulants↗
PubMed2002

Electrophysiologic actions of dl-sotalol in patients with persistent atrial fibrillation.

OBJECTIVES: We sought to determine the electrophysiologic actions of sotalol in the remodeled atrium of humans. BACKGROUND: In experimental studies, sotalol has limited class III action in the electrically remodeled atrium and did not prevent atrial fibrillation (AF) induction. METHODS: We determined the effective refractory periods (ERPs) at three pacing cycle lengths (400, 500, and 600 ms) in the high right atrium (HRA) and distal coronary sinus (DCS) before and after intravenous infusion of dl-sotalol in 10 patients with persistent AF who underwent internal cardioversion. The same protocols were performed in 10 control subjects in sinus rhythm. RESULTS: In the HRA and DCS, the atrial ERPs at different drive cycle lengths were significantly shorter in patients with AF than in control subjects (p < 0.05). In patients with AF, the atrial ERP's adaptation to rate was nearly normal in the HRA, but was poor in the DCS. In both groups, dl-sotalol significantly increased the atrial ERPs at both the HRA and DCS, as compared with baseline (p < 0.05). However, the prolongation of atrial ERPs was significantly less at a drive cycle length of 600 ms in patients with AF versus control subjects (p < 0.05). After infusion of dl-sotalol, the atrial ERP's adaptation to rate at both the HRA and DCS was poor in patients with AF, and AF was still easily inducible in the majority of them, but not in control subjects. CONCLUSIONS: The results of the present study demonstrate that the electrophysiologic actions of dl-sotalol are significantly attenuated in the chronically remodeled human atrium, and these changes might represent a probable explanation for the low efficacy of dl-sotalol to prevent early AF recurrence after electrical cardioversion.

Aged↗
PubMed2002

Internal cardioversion of chronic atrial fibrillation during percutaneous mitral commissurotomy: insight into reversal of chronic stretch-induced atrial remodeling.

BACKGROUND: Mechanoelectrical feedback caused by atrial dilatation plays an important role in atrial fibrillation (AF). To test the hypothesis that remodeling is reversible by reducing atrial stretch, we investigated electrophysiological changes after a reduction of left atrial (LA) pressure in patients undergoing percutaneous balloon mitral commissurotomy (PBMC). METHODS AND RESULTS: In 22 patients with chronic AF who were undergoing PBMC for mitral stenosis, internal cardioversion was successful in 19 patients (86%). Twelve patients with sinus rhythm acted as controls. Mean LA pressure was significantly reduced after PBMC (18.5+/-5.9 mm Hg versus 10.2+/-4.1 mm Hg; P<0.001). The effective refractory period (ERP), conduction delay (CD), and the index of heterogeneity (CoV) of the ERP and CD were compared. Changes in LA pressure were only significantly correlated with AF vulnerability (r=0.7; P=0.02) and CoV of CD (r=0.3; P=0.03). There were no significant changes in ERP and CD immediately after PBMC in the AF group. However, the overall CoV of ERP was reduced in the AF group after PBMC. There were homogenous, although not significant, increases in regional ERP in the control group immediately after PBMC. Atrial CD and CoV of CD were significantly reduced after PBMC in the control group; this was most prominent within the regions of the LA. CONCLUSIONS: AF vulnerability and CoV of CD correlated significantly with LA pressure. A homogenous increase in regional ERPs could be demonstrated in the control group after an immediate reduction of atrial stretch, whereas the recovery course of electrical remodeling was prolonged and heterogenous in the AF group. Regional conductions were irreversible in patients with preexisting AF.

Angioplasty, Balloon, Coronary↗
PubMed2002

New Bayesian discriminator for detection of atrial tachyarrhythmias.

BACKGROUND: Accurate, rapid detection of atrial tachyarrhythmias has important implications in the use of implantable devices for treatment of cardiac arrhythmia. Currently available detection algorithms for atrial tachyarrhythmias, which use the single-index method, have limited sensitivity and specificity. METHODS AND RESULTS: In this study, we evaluated the performance of a new Bayesian discriminator algorithm in the detection of atrial fibrillation (AF), atrial flutter (AFL), and sinus rhythm (SR). Bipolar recording of 364 rhythms (AF=156, AFL=88, SR=120) at the high right atrium were collected from 20 patients who underwent electrophysiological procedures. After initial signal processing, a column vector of 5 features for each rhythm were established, based on the regularity, rate, energy distribution, percent time of quiet interval, and baseline reaching of the rectified autocorrelation coefficient functions. Rhythm identification was obtained by use of Bayes decision rule and assumption of Gaussian distribution. For the new Bayesian discriminator, the overall sensitivity for detection of SR, AF, and AFL was 97%, 97%, and 94%, respectively; and the overall specificity for detection of SR, AF, and AFL was 98%, 98%, and 99%, respectively. The overall accuracy of detection of SR, AF, and AFL was 98%, 97% and 98%, respectively. Furthermore, sensitivity, specificity, and accuracy of this algorithm were not affected by a range of white Gaussian noises with different intensities. CONCLUSIONS: This new Bayesian discriminator algorithm, based on Bayes decision of multiple features of atrial electrograms, allows rapid on-line and accurate (98%) detection of AF with robust anti-noise performance.

Adolescent↗
PubMed2002

Tissue Doppler echocardiographic evidence of reverse remodeling and improved synchronicity by simultaneously delaying regional contraction after biventricular pacing therapy in heart failure.

BACKGROUND: Biventricular pacing has been proposed to improve symptoms and exercise capacity in patients with advanced heart failure and wide electrocardiographic wave complexes. This study investigated the effect of biventricular pacing on reverse remodeling and the underlying mechanisms. METHODS AND RESULTS: Twenty-five patients with NYHA class III to IV heart failure and electrocardiographic wave complex duration >140 ms receiving biventricular pacing therapy were assessed serially up to 3 months after pacing and when pacing was withheld for 4 weeks. Tissue Doppler echocardiography was performed using a 6-basal, 6-mid segmental model to assess the time to peak sustained systolic contraction (T(S)). There was significant improvement of ejection fraction, dP/dt, and myocardial performance index; decrease in mitral regurgitation, left ventricular (LV) end-diastolic (205+/-68 versus 168+/-67 mL, P<0.01) and end-systolic volume (162+/-54 versus 122+/-42 mL, P<0.01); and improved 6-minute hall-walk distance and quality of life score after pacing for 3 months. The mechanisms of benefits were as follows: (1) improved LV synchrony, as evident by homogeneous delay of T(S) to a timing close to the latest (usually the lateral) segment abolishing the intersegmental difference in T(S) and decreasing the standard deviation of T(S) within the left ventricle (37.7+/-10.9 versus 29.3+/-8.3 ms, P<0.05); (2) improved interventricular synchrony; and (3) shortened isovolumic contraction time (122+/-57 versus 82+/-36 ms, P<0.05) but increased diastolic filling time. These benefits are pacing dependent, because withholding the pacing resulted in varying speeds in the loss of cardiac improvements. CONCLUSIONS: Biventricular pacing reverses LV remodeling and improves cardiac function. Improvement of LV mechanical synchrony seems to be the predominant mechanism.

Aged↗
PubMed2002

Heterogeneity of sodium current in atrial vs epicardial ventricular myocytes of adult guinea pig hearts.

The different sodium channel currents (I(Na)) were reported in myocardium, neuron, and skeletal muscles. To study whether I(Na) is homogeneous within the heart, we applied whole-cell voltage clamp technique to evaluate fast voltage-gated I(Na) in atrial and ventricular myocytes isolated from guinea pig heart. It was found that the density of inward I(Na) was 50% greater at -35 mV in atrial (-42.6+/-2.9 pA/pF) than in ventricular (-27.5+/-1.8 pA/pF, P<0.01) myocytes. The half activation and inactivation voltages (V(0.5)) of I(Na) in atrial myocytes were shifted 4.5+/-0.2 and 9.6+/-0.3 mV negative to those of ventricular myocytes. Time constants for I(Na) activation (tau(m)) and inactivation (tau(h)) were twice as rapid in atrial as in ventricular myocytes. The tau(m) and tau(h) were 0.34+/-0.03 and 1.36+/-0.07 ms for atrial myocytes, and 0.69+/-0.05 and 3.27+/-0.23 ms for ventricular myocytes, respectively. Recovery of I(Na) from inactivation was slower in atrial than in ventricular myocytes, whereas the development of resting state inactivation was more rapid in atrial (tau=67.5+/-4.3 ms) than in ventricular (152.8+/-7.5 ms, P<0.01) myocytes. The results reveal marked heterogeneity of I(Na) in the density and biophysical properties in atrial and ventricular myocytes, and the study suggests the potential possibility of tissue specific cardiac sodium channel isoforms.

Action Potentials↗
PubMed2002

Nonfluoroscopic magnetic electroanatomic mapping to facilitate focal pulmonary veins ablation for paroxysmal atrial fibrillation.

RF ablation of ectopic foci in the pulmonary veins (PVs) is a promising treatment for patients with paroxysmal AF. The aim of this study was to evaluate the feasibility of using nonfluoroscopic magnetic electroanatomic mapping of PV during spontaneous or induced ectopy to facilitate focal ablation procedure. The study included 35 patients with drug refractory paroxysmal AF who underwent focal RF ablation of the PV. In 10 (29%) patients, mapping and RF ablation procedures were performed using the nonfluoroscopic magnetic electroanatomic mapping system to enable automatic capture of the location and the timing of the ectopy. As a control, 25 patients underwent conventional endocardial activation mapping technique. There were no significant differences in the clinical characteristics between the two groups. Overall procedural duration was similar between them (199 +/- 52 vs 221 +/- 82 minutes, P > 0.05). However, the mean fluoroscopy time (25 +/- 6 vs 52 +/- 12 minutes, P = 0.01) and the mean number of RF applications (5 +/- 3 vs 12 +/- 9, P = 0.02) were significantly less in patients who underwent electroanatomic mapping. There were no significant differences between the two groups in the acute (90 vs 84%) and long-term success rate (60 vs 56%) after a mean follow-up of 12 +/- 9 months. In conclusion, RF ablation of ectopic foci using nonfluoroscopic magnetic electroanatomic mapping of PVs during spontaneous or induced ectopy is useful even in patients with a limited number of ectopy, and is associated with a similar success rate, but less fluoroscopy time and RF application compared to the conventional approach.

Adult↗
PubMed2002

Automatic mode switching of implantable pacemakers: I. Principles of instrumentation, clinical, and hemodynamic considerations.

Automatic mode switching (AMS) is now a programmable function in most contemporary dual chamber pacemakers. Atrial tachyarrhythmias are detected when the sensed atrial rate exceeds a "rate-cutoff," "running average," "sensor-based physiological" rate, or using "complex" detection algorithms. AMS algorithms differ in their atrial tachyarrhythmia detection method, sensitivity, and specificity and, thus, respond differently to atrial tachyarrhythmia in terms of speed to the AMS onset, rate stability of the response, and speed to resynchronize to sinus rhythm. AMS is hemodynamically beneficial, and most patients with atrial tachyarrhythmias are symptomatically better with an AMS algorithm in their pacemakers. New diagnostic capabilities of pacemaker especially stored electrograms not only allow programming of the AMS function, but enable quantification of atrial fibrillation burden that facilitate clinical management of patients with implantable devices who have concomitant atrial tachyarrhythmia.

Algorithms↗