Implantable cardioverter defibrillators: therapy against Canada's leading killer.
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Arrhythmias, Cardiac↗
Biomedical subjects
Anthony S L Tang
Publications and source records attributed to Anthony S L Tang.
Human study of biatrial electrical coupling: determinants of endocardial septal activation and conduction over interatrial connections.
BACKGROUND: The relative contribution of the atrial septum and interatrial connections to biatrial activation is a fundamental concept of human cardiac electrophysiology that has yet to be fully characterized. The purpose of the present study was to determine how both atria are coupled electrically. METHODS AND RESULTS: Twenty patients (16 men; mean age 54+/-11years) with a history of symptomatic atrial fibrillation (AF) underwent simultaneous biatrial noncontact mapping before catheter ablation of AF. The multiple electrode array catheters were positioned, respectively, in the left atrium (LA; transseptally) and the right atrium (RA). In all but 2 patients, isopotential maps revealed that endocardial septal activations of the RA and LA were separate, independent, and asynchronous of each other. Interatrial conduction was related to the site of initial atrial depolarization, revealing conduction over Bachmann's bundle in all patients during sinus rhythm, high RA pacing, and pacing from the LA appendage. Pacing from the coronary sinus was associated with conduction over the interatrial connection at the level of the coronary sinus in all patients, and conduction over Bachmann's bundle also occurred in 5 (26%) of 19 patients. Interatrial conduction over the fossa ovalis occurred in only 2 (2%) of the 116 segments analyzed. CONCLUSIONS: Electrical coupling of the RA and LA in humans is predominantly provided by muscular connections at the level of Bachmann's bundle and the coronary sinus. The true septum (the fossa ovalis and its limbus) of the RA and LA is asynchronous and discordant, usually without contralateral conduction during sinus rhythm or atrial pacing.
Adult↗
Reverse atrial electrical remodelling following atrial defibrillation as determined by signal-averaged ECG.
BACKGROUND: Following successful cardioversion for atrial fibrillation (AF), the rate of early recurrence remains high. Analysis of the signal-averaged electrocardiogram of the P wave has been proposed as a noninvasive method of predicting those at risk of recurrence. PURPOSE: To determine the change in signal-averaged P wave duration (SAPWD) following cardioversion from AF, and to determine whether SAPWD is associated with the risk of recurrence. METHODS: SAPWD was determined in 76 patients immediately following successful electrical cardioversion and three days later. Patients were then followed clinically for one year. RESULTS: Recurrent AF was observed in 32 of 76 patients at 90 days following cardioversion. There was no difference in SAPWD immediately following cardioversion (158+/-28 ms versus 164+/-31 ms, P=NS) or three days following cardioversion (152+/-24 ms versus 158+/-36 ms, P=0.4) in patients with and without recurrent AF. There was, however, a significant decrease in the SAPWD during the first three days following cardioversion in the patients who remained in sinus rhythm (158+/-28 ms initially versus 152+/-24 ms on day three, P=0.009). Among the patients with recurrent AF, the decrease was smaller and not statistically significant (161+/-30 ms versus 158+/-36 ms, P=0.3). CONCLUSION: Shortening of the SAPWD occurs following atrial defibrillation in patients who maintain sinus rhythm at 90 days. This provides evidence for reverse atrial electrical remodelling and its association with the maintenance of sinus rhythm.
Atrial Fibrillation↗
Canadian Trial of Physiological Pacing: Effects of physiological pacing during long-term follow-up.
BACKGROUND: The Canadian Trial of Physiological Pacing (CTOPP) reported that the risk of stroke or cardiovascular death was similar between patients receiving ventricular versus physiological pacemakers at the end of the original follow-up period of 3 years. However, the occurrence of atrial fibrillation was significantly less frequent with physiological pacemakers. To assess a potential delayed benefit of physiological pacing, follow-up of patients in this study was extended to 6 years. METHODS AND RESULTS: A total of 1474 patients requiring a pacemaker for symptomatic bradycardia were randomized to receive ventricular and 1094 to physiological pacemakers. The primary outcome was stroke or cardiovascular death. The study was completed in July 1998, and follow-up was extended to July 2001. At a mean follow-up of 6.4 years, there was no difference between treatment groups in the primary outcome of cardiovascular death or stroke. There was no significant difference in total mortality or stroke between groups. There was a significantly lower rate of development of atrial fibrillation in the physiological group, with a relative risk reduction of 20.1% (CI, 5.4 to 32.5; P=0.009). CONCLUSIONS: The CTOPP extended study does not show a difference in cardiovascular death or stroke, or in total mortality, or in stroke between patients implanted with ventricular or physiological pacemakers over a mean follow-up of >6 years. However, there is a persistent significant reduction in the development of atrial fibrillation with physiological pacing.
Atrial Fibrillation↗
Improvement of apparently fixed pulmonary hypertension with cardiac resynchronization therapy.
Many patients with advanced heart failure are ineligible for cardiac transplantation because of fixed pulmonary arterial hypertension. Cardiac resynchronization therapy, by stimulating the right atrium, and right and left ventricles, is a new therapy that effectively palliates symptoms in patients with heart failure. Cardiac resynchronization therapy increases cardiac output and decreases pulmonary capillary wedge pressure, thus partially reversing hemodynamic abnormalities that lead to secondary pulmonary hypertension in many heart failure patients. We describe a patient whose previously fixed pulmonary hypertension improved to the point that she was once again considered eligible for cardiac transplantation.
Cardiac Pacing, Artificial↗
Left atrial vein pacing: a technique of biatrial pacing for the prevention of atrial fibrillation.
Biatrial pacing is a promising new therapy for drug refractory AF. This article reports two studies. First, an initial 14-patient experience with a novel technique for biatrial pacing. The authors attempted to pace from the LA vein branches of the proximal CS for LA stimulation. LA vein pacing would potentially offer the advantages of greater interatrial synchronization and possibly greater reduction in AF burden and also of lesser far-field R wave sensing and greater lead stability. Second, a postmortem series examining the number, size, and site of LA veins draining into the proximal CS is described. LA vein pacing was successful in 9 of 14 patients. LA vein electrode parameters have been stable during a median follow-up of 580 days. There were three early lead dislodgments but no other complications. In the second study, a postmortem analysis of 43 human hearts was performed. The study found that 38 (88.4%) of 43 hearts had at least one LA vein draining into the proximal 5 cm of the CS. In addition, 81.2% (33/43) had at least one vein greater than 4 Fr caliber. Thus, pacing in a greater proportion of patients might be achieved by the development and use of smaller (3, 4, and 5 Fr) electrodes. Furthermore, these smaller leads would obviously allow deeper advancement into the LA veins with the potential advantages of greater interatrial synchronization and lead stability and lesser far-field R wave sensing.
Aged↗
Atrial tracking paradox: is the dual chamber pacemaker working properly?
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Equipment Failure↗
Functional and echocardiographic improvement following multisite biventricular pacing for congestive heart failure.
BACKGROUND: Heart failure remains a major cause of morbidity and mortality despite advances in pharmacological treatment. Recently, multisite biventricular pacing has been used in the treatment of patients with heart failure. OBJECTIVES AND METHODS: The short and medium term effects of this treatment modality were assessed, and the association between baseline clinical characteristics and the positive response to treatment was investigated. Consecutive patients who received this treatment modality were included. They underwent comprehensive clinical and echocardiographic assessment including a 6 min walk at baseline, one month and three months. RESULTS: Between January 1998 and June 1999, 95 patients received multisite biventricular pacing therapy in the three participating hospitals. In 63 patients with complete three-month follow-ups, there were improvements from baseline to three-month follow-up in New York Heart Association heart failure (3.3 +/- 0.5 to 2.2 +/- 0.6, P<0.001) and 6 min walk (305 +/- 120 to 403 +/- 113 m, P<0.001). Significant salutary changes in echocardiographic measurements were also observed in left ventricular (LV) diastolic dimension, ejection fractions (EFs), interventricular contraction delay and severity of mitral regurgitation (MR). The 63 patients were categorized into responders (n=42) and nonresponders (n=21) based on the clinical response. Clinical characteristics were similar between the two groups. The responders had a more pronounced decrease in QRS width. An increase in LVEF and a reduction in LV diastolic dimension, interventricular mechanical delay and severity of MR were observed in the responders but not in the nonresponders. Furthermore, there was a positive association between the reduction in QRS width and the increase in LVEF. CONCLUSIONS: Cardiac resynchronization by means of multisite pacing appears to be a promising therapy in the treatment of heart failure. The salutary clinical response is associated with echocardiographic improvement.
Aged↗
Effect of cardiac resynchronization on myocardial efficiency and regional oxidative metabolism.
BACKGROUND: Recent studies have demonstrated increased left ventricular contractility with cardiac resynchronization therapy (CRT) using atriobiventricular stimulation. This study evaluated the effect of CRT on myocardial oxidative metabolism and efficiency. METHODS AND RESULTS: Eight patients with New York Heart Association functional class III-IV congestive heart failure were studied during atrial pacing (control) and atriobiventricular stimulation at the same rate. The monoexponential clearance rate of [11C]acetate (k(mono)) was measured with positron emission tomography to assess myocardial oxidative metabolism in the left and right ventricles (LV and RV, respectively). Myocardial efficiency was measured using the work metabolic index (WMI). Stroke volume index improved by 10% (P=0.011) with CRT, although both global LV and RV k(mono) were unchanged compared with control. Septal k(mono) increased by 15% (P=0.04), and the septal/lateral wall k(mono) ratio increased by 22% (P=0.01). WMI increased by 13% (P=0.024) with CRT. CONCLUSIONS: CRT improves LV function without increasing global LV oxidative metabolism, resulting in improved myocardial efficiency. Oxidative metabolism of the interventricular septum increases relative to the lateral wall, which suggests successful resynchronization.
Heart↗
Prevalence and significance of lead-related thrombi in patients with implantable cardioverter defibrillators.
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Chi-Square Distribution↗
Effect of pacing mode on health-related quality of life in the Canadian Trial of Physiologic Pacing.
BACKGROUND: Both "physiologic" (dual-chamber or atrial only) or ventricular-pacing-only permanent pacemakers provide chronotropic competence, with unknown health-related quality of life (QOL) differences between these options. The QOL studies within the Canadian Trial of Physiologic Pacing were performed to assess whether QOL differences exist in patients randomized to these 2 pacing modes. METHODS: Two QOL protocols were performed: 1) a substudy of 269 patients with detailed QOL measures (The Medical Outcomes Study, Short-Form [SF-36], the Pacemaker Syndrome Scale, an activity scale, and a pacemaker-specific scale) at baseline and 6 months after implantation; and 2) a parent study assessment of QOL in 1721 patients with a 12-item QOL instrument package (SF-6, "ladder of life," and pacemaker syndrome scale) given 6 months after implantation only. RESULTS: In the substudy, pacing was associated with an average significant (P <.05) 0.36 SD unit improvement in QOL across all domains (SF-36: 38 +/- 9 to 41 +/- 11 for physical scores, 47 +/- 11 to 52 +/- 9 for mental health scores, both P <.001). Similar improvements were seen with the pacemaker-specific scales. There were no significant differences in the absolute or relative improvement in QOL between assigned pacing modes. The parent study similarly showed no differences in QOL between pacing modalities. Presyncope occurred in 31% of patients in the physiological pacing group, compared with 38% of the patients in the ventricular pacing group (P <.01). No other symptoms were different between the 2 groups. Pacemaker dependency, defined as an escape heart rate <50 beats per minute, did not influence the lack of difference in QOL scores between the 2 assigned pacing modes. CONCLUSION: In this largest randomized assessment of QOL in patients with pacemakers, with the instruments used, there was no significant health-related QOL difference seen between "physiologic" pacing and ventricular pacing.
Aged↗
Cardiac resynchronization therapy in advanced heart failure the multicenter InSync clinical study.
BACKGROUND: recent short-term observations have shown an improvement in cardiac function and heart failure symptoms from atrio-biventricular pacing. This study was designed to assess the safety and feasibility of an atrio-biventricular transvenous pacing system, and examine the long-term effects of cardiac resynchronization in patients with advanced heart failure and ventricular conduction abnormalities. METHODS AND RESULTS: between August, 1997 and November, 1998, 103 patients received a cardiac resynchronization system (CRS) consisting of a pulse generator interfaced with an atrio-biventricular lead system, including a lead designed for left ventricular (LV) pacing via cardiac veins. Baseline evaluation included 12-lead electrocardiogram, estimation of New York Heart Association (NYHA) functional class, assessment of quality of life (QOL), and distance covered during a 6-min walk (6-MW). Detailed echocardiographic data were also collected in a subset of 46 patients. Measurements were repeated in all surviving patients at 1, 3, 6 and 12 months after implantation of the CRS. A single, self-limiting procedure-related complication occurred. Over a follow-up of 12 months, 21 patients died. The 12-month actuarial survival was 78% (CI 70-87%). Nine surviving patients were withdrawn from the study during long-term follow-up for miscellaneous reasons. At each point of follow-up, a significant shortening of QRS duration was measured. In addition, significant improvements were observed in mean NYHA functional class, 6-MW and QOL score. In the 46 patients with complete echocardiographic data, LV ejection fraction increased from 21.7+/-6.4% at baseline to 26.1+/-9.0% at last follow-up (P = 0.006), LV end diastolic dimension decreased from 72.7+/-9.2 to 71.6+/-9.1 mm (P = 0.233), interventricular mechanical delay decreased from 27.5+/-32.1 to 20.3+/-25.5 ms (P = 0.243), mitral regurgitation apical four-chamber area decreased from 7.66+/-5.5 to 6.69+/-5.9 cm(2) (P = 0.197), and left ventricular filling time increased from 363+/-127 to 408+/-111 ms (P = 0.002). CONCLUSIONS: long-term cardiac resynchronization can be safely and reliably achieved by transvenous atrial synchronized right and left ventricular pacing. These changes were accompanied by clinically relevant improvements in functional status and QOL, as well as a measurable increase in LV performance. The outcome of randomised controlled trials is awaited.
Aged↗
Fiberoptic balloon catheter ablation of pulmonary vein ostia in pigs using photonic energy delivery with Diode laser.
Circumferential lesions to the pulmonary vein (PV) ostia to cause conduction block at the junction of the PV and left atrium could offer a new approach during catheter ablation of patients with paroxysmal (focal) atrial fibrillation. Diode laser can deliver energy through diffusing or ring fiber tips. In three pigs weighing between 60 and 65 kg, transseptal puncture was performed and a fiberoptic balloon catheter with a collapsed profile of 10 Fr was advanced through a sheath under fluoroscopic guidance to the ostium of the right and left PVs. The balloon was inflated with a 3-cc mixture of D2O (deuterium oxide) and contrast to deliver circumferential lesions with a 15-mm diameter x 3-mm ring width of light. Applications consisted of 3.2 to 3.8 W/cm for 120 seconds; the animals were sacrificed 3 hours after ablation for pathological examination. Photonic energy was delivered successfully to the ostium of five of the five targeted PVs, and was well tolerated hemodynamically in each animal without ectopy. Gross inspection revealed endocardial lesions at the ostium of four of five PVs, confined to the atrium in each and circumferential in three of five PVs. Microscopically, transmural coagulation necrosis of the atrium was present at the ostium of three of five PVs, and extended into the myocardial sleeves of two PVs. Photonic energy delivery using a fiberoptic balloon catheter can create circumferential lesions to the PV ostia, suggesting that this new form of energy delivery may be therapeutically advantageous for pulmonary vein ablation with need to pursue chronic studies.
Animals↗
PRKAG2 cardiac syndrome: familial ventricular preexcitation, conduction system disease, and cardiac hypertrophy.
Genetic studies of families with inherited cardiac rhythm disturbances have established a molecular basis for ventricular arrhythmogenic disorders. Genes responsible for the long QT syndrome, Brugada syndrome, and polymorphic ventricular tachycardia have been identified. The elucidation of genetic defects responsible for more commonly occurring supraventricular rhythm disturbances have not been as forthcoming, with the exception of SCN5A mutations known to cause conduction system disease. Recently, we identified the genetic cause of a familial arrhythmogenic syndrome characterized by ventricular preexcitation and tachyarrhythmias (Wolff-Parkinson-White syndrome), progressive conduction system disease, and cardiac hypertrophy. The causative gene was shown to be the gamma-2 regulatory subunit (PRKAG2) of AMP-activated protein kinase. The role of AMP-activated protein kinase in the regulation of the glucose metabolic pathway in muscle suggests that genetic defects in PRKAG2 may induce a previously undescribed cardiac glycogenosis syndrome.
AMP-Activated Protein Kinases↗