Antitachycardia pacing in patients with implantable cardioverter-defibrillators: inverse circadian variation of therapy success and acceleration

We analyzed spontaneous ventricular tachycardias treated by antitachycardia pacing during long-term follow-up in 138 recipients of an implantable cardioverter-defibrillator. An inverse circadian variation of the antitachycardia pacing termination and acceleration rates with the worst antitachycardia pacing success during the time period with the highest episode frequency (morning hours) was demonstrated.     

Preimplant atrial defibrillation testing with a temporary catheter in sheep

Prior to implantation of an atrial defibrillator, its effectiveness should be tested in each patient. A new catheter design for temporary use with electrodes for atrial defibrillation, electrogram sensing, and pacing was tested in this study. Atrial defibrillation thresholds defined using this temporary catheter were compared to the ones defined by catheters intended for chronic use with an implantable atrial defibrillator. Atrial defibrillation threshold was determined in six sheep using both types of catheters. Each animal was subjected to studies on 2 consecutive days. On the first day, shocks were applied between two of the temporary catheters. On the following day, permanent leads were inserted and atrial defibrillation threshold was redetermined. In both cases, defibrillation electrodes were positioned in the same heart location with one electrode in the distal coronary sinus and the second electrode in the right atrium. Atrial defibrillation threshold was obtained using 10 V increments or decrements to determine the lowest shock intensity needed to defibrillate the atria. Threshold was defined as the shock intensity at which 20 shock percent success was at or between 15% and 85%. Statistical analysis showed no significant difference (P < 0.05) between atrial defibrillation threshold energy (0.53 J vs 0.55 J), voltage (122 V vs 120 V) or current (2.2 A vs 2.6 A) measured with the temporary catheters and the permanent leads, respectively. These data indicate that temporary catheters can be used for efficacy testing prior to implant of an atrial defibrillator, and that they predict atrial defibrillation threshold adequately for chronic leads.     

Early results of AV sequential pacing on left ventricular outflow obstruction after Senning procedure

Dual chamber pacing was shown to decrease left ventricular outflow tract (LVOT) obstruction in patients with hypertrophic cardiomyopathy 30 years ago. We report early results of AV sequential pacing from the LV apex in a patient with transposition of the great arteries who is post-Senning procedure. LVOT obstruction resulted from septal deviation and systolic anterior motion of the mitral valve. Pacing was indicated for sinus node dysfunction. AV sequential pacing with a short optimal AV interval of 60 ms demonstrated a 45% reduction in the degree of LVOT obstruction. This article suggests that LVOT obstruction after the Senning procedure can be palliated by asynchronous septal contraction induced by AV sequential pacing, even if the activation is from LV apex, and avoid or postpone surgery in selected situations.     

Cardiac pacing in Canada in 1998: working towards optimal pacing therapy. Canadian Working Group on Cardiac Pacing

The Canadian Working Group on Cardiac Pacing (CWGCP) was formed in 1996 with the primary goal of promoting optimal pacing therapy in Canada. In 1997, the CWGCP conducted a survey of pacing practices across Canada. Ninety-two of 125 implanting programs (74%) responded. Implant rates vary by province--from 39 per 100,00 population in Ontario to 63 per 100,000 population in Nova Scotia and Prince Edward Island. Variations in regional implant rates persist even after correcting for the age of the population. Physiological pacing was used for 35% of all implants in Canada in 1996/97. There were marked differences across Canada in the mode of pacing selected. In western Canada, 39.5% of pacing systems implanted were physiological compared with 18.2% in Atlantic Canada and 29% in Quebec. There were also differences in follow-up practices. Approximately 40% of centres follow patients with single chamber pacemakers annually, whereas most other centres still follow these patients every six months. Economic constraints, the size of pacing programs and the involvement of committed pacing physicians are factors that may influence the regional differences in cardiac pacing across Canada.     

Exploring postinfarction reentrant ventricular tachycardia with entrainment mapping

Ventricular tachycardia late after myocardial infarction is usually due to reentry in the infarct region. These reentry circuits can be large, complex and difficult to define, impeding study in the electrophysiology laboratory and making catheter ablation difficult. Pacing through the electrodes of the mapping catheter provides a new approach to mapping. When pacing stimuli capture the effects on the tachycardia depend on the location of the pacing site relative to the reentry circuit. The effects observed allow identification of various portions of the reentry circuit, without the need for locating the entire circuit. Isthmuses where relatively small lesions produced by radiofrequency catheter ablation can interrupt reentry can often be identified. A classification that divides reentry circuits into one or more functional components helps to conceptualize the reentry circuit and predicts the likelihood that heating with radiofrequency current will terminate tachycardia. These methods are helping to define human reentry circuits.     

Caring for patients with an ICD

The internal cardioverter defibrillator corrects life-threatening arrhythmias by providing antitachycardia pacing, pacing for bradycardia, and cardioversion or defibrillation shocks. However, there is little warning that the device may fire, which can cause physical, social and psychological problems for the patient. Nurses caring for ICD patients in the community and in hospital need to know what it is like to live with this device, how it works and the implications for other treatments.     

Changes in pacing lead impedance over time predict lead failure

It has been suggested that a decrease in lead impedance may predict pacing lead failure, but there is limited prospective data about the relation of changes in lead impedance over time to lead performance. We monitored changes in lead impedance through implantable pulse generators with real-time telemetry data capability in 105 patients with Medtronic 4012 leads (n = 38) and Medtronic 4004 leads (n = 67). Pacing lead failure was documented by serial ambulatory electrocardiographic monitoring or intensified pacemaker clinic surveillance. A significant decrease in lead impedance was observed in patients with Medtronic 4012 and Medtronic 4004 leads with documented lead failure, whereas lead impedance remained stable over time in patients without documented lead failure. The sensitivity and specificity of a lead impedance decrease of > or =15% to predict lead failure were 69% and 70%, respectively. The sensitivity and specificity of a lead impedance decrease of > or =30% to predict lead failure were 36% and 90%, respectively. The positive and negative predictive values for a lead impedance decrease of > or =15% were 54% and 81%, respectively, and for a lead impedance decrease of > or = 30% were 65% and 73%, respectively. Thus, small decreases in lead impedance may identify failing leads. Serial measurement of pacing lead impedance over time is a useful tool to monitor pacing lead performance.     

Oculocerebrocutaneous syndrome: report of three additional cases and aetiological considerations

Atrial fibrillation (AF) has been recognized, with increasing concern, as a potentially disabling illness, occurring either as a symptom of many cardiac diseases or as an isolated disorder. It can independently contribute to mortality and morbidity and may have serious prognostic importance in acute or chronic cardiac disease. In patients with symptomatic drug refractory atrial fibrillation, ventricular rate control by atrioventricular nodal ablation or modification commonly results in pacemaker implantation. The concept of AF prevention by pacemaker therapy has been introduced in patients with bradycardia-tachycardia syndrome or vagally mediated bradycardia-dependent AF. In patients with sick sinus syndrome, atrial pacing has proved to be more effective than VVI pacing in maintaining the electrical stability of the atrium in long-term follow up. Recently, the development of new techniques of atrial pacing employing pacing at two atrial sites may improve the effectiveness of the AF prevention by pacemaker therapy. Dual-site right atrial pacing using overdrive stimulation activates simultaneously the high right atrium and the left atrium via the ostium of the coronary sinus. Two main mechanisms have been proposed to explain the favourable effect of this technique. One is the suppression of atrial premature beats initiating AF by the overdrive pacing. The second is the alteration of atrial activation pattern by preexcitation of the area of the coronary sinus ostium which permits earlier recovery of excitability in sites of atrial conduction delay. The combination of drug therapy and pacing is essential for effective AF control. We have hitherto studied 30 patients with single- and dual-site pacing. Single-site pacing was performed at the high right atrium or coronary sinus ostium. The dual-site pacing mode increased the arrhythmia-free intervals, decreased patients' arrhythmia-related symptoms and anti-arrhythmic drug use as compared to the period preceding institution of pacing and incrementally over conventional high right atrial pacing alone. A multicentre randomized trial, Dual-site Atrial Pacing for Prevention of Atrial Fibrillation (DAPPAF), evaluating three pacing modes (dual-site, single-site and support pacing), is now in progress.     

A prospective randomized repeat-crossover comparison of antitachycardia pacing with low-energy cardioversion

BACKGROUND: Multiprogrammable antiarrhythmia devices can treat monomorphic ventricular tachycardia (VT) with autodecremental overdrive pacing and/or with low-energy cardioversion. These two methods provide the opportunity to decrease patient discomfort typically experienced with high-energy pulses. Although both therapies are known to be effective, controversy persists over their relative safety and efficacy. METHODS AND RESULTS: The purpose of this study was to examine the safety and efficacy of autodecremental overdrive pacing and low-energy cardioversion in reproducibly terminating monomorphic VT in 24 patients with multiprogrammable antiarrhythmia devices. The protocol required that identical ECG morphology VT be reproducibly induced four times to assess the outcome of antitachycardia pacing and cardioversion twice for each patient in a randomized fashion. Each episode of VT was induced via the implanted device. Autodecremental overdrive pacing initially began with seven stimuli at 97% of the VT cycle length, decrementing by 10 msec per stimulus to a minimum coupling interval of 200 msec. If ineffective, autodecremental overdrive pacing was allowed to iterate three more times for a total of four pacing interventions. With each iteration, one stimulus was added to the pacing train. Similarly, with low-energy cardioversion, up to four therapeutic attempts were made, beginning with a 0.2-J pulse. If ineffective, pulse energy was increased to 0.4, 1.0, and finally 2.0 J. All interventions were automatic without human interference. VT (cycle length, 306 +/- 42 msec) was repeatedly terminated in 15 of 24 patients (63%) by autodecremental overdrive pacing and in 18 of 24 patients (75%) by low-energy cardioversion (p = 0.53). Eight of the 24 patients (33%) had their VT terminated repeatedly by both therapies. VT accelerated to faster VT or ventricular fibrillation by autodecremental overdrive pacing in four of 24 patients (17%) and by low-energy cardioversion in five of 24 (21%) (p = 0.88). Only one of the 24 patients (4%) accelerated with both therapies. No patient was unaffected by either therapy. CONCLUSIONS: In the manner programmed, autodecremental overdrive pacing and low-energy cardioversion have similar efficacy and acceleration rates. Response to one therapy does not predict response to the other.     

The 1992 ethics code: boon or bane?

Discusses the 1992 version of the American Psychological Association (APA) Ethical Principles of Psychologists and Code of Conduct that marks the first major revision since 1981. It has a table of contents that facilitates location of standards about specific topics and it is the 1st code to be divided into 2 sections. These include a set of principles that are aspirational, representing the professional ideals, and a set of enforceable standards that are intended to be used as compelling rules. The most controversial standard pertains to sexual relationships with former psychotherapy clients. Standards related to other topics for the first time, such as the practice of forensic psychology and bartering, distinguish the 1992 APA code from its predecessors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ventricular tachycardia during follow-up in patients resuscitated from ventricular fibrillation: experience from stored electrograms of implantable cardioverter-defibrillators

OBJECTIVE: The purpose of this study was to use the electrogram storage capabilities of the implantable cardioverter-defibrillator (ICD) to categorize any arrhythmic event during follow-up in a group of patients who had survived an episode of ventricular fibrillation (VF) and to possibly identify clinical predictors of future arrhythmic events. BACKGROUND: Little is known about the electrophysiologic characteristics of ventricular arrhythmias recurring during follow-up in survivors of VF as the sole documented arrhythmia at the time of resuscitation. METHODS: Forty patients (58+/-10 years; 73% men; left ventricular ejection fraction 42+/-18%; 70% with coronary artery disease) who had survived an episode of VF and subsequently received an ICD capable of intracardiac electrogram recording and storage were followed for 23+/-11 months. In all patients, the arrhythmogenic substrate was investigated by means of programmed electrical stimulation (PES). RESULTS: Among the 40 patients, 41 episodes of ventricular arrhythmias were documented in 13 patients (33%): 36 episodes of ventricular tachycardias (VT) were recorded in 11 patients (28%) and 5 episodes of VF were recorded in the remaining 2 patients (5%). Age, gender, cardiac disease and left ventricular ejection fraction failed to distinguish between patients with clinical recurrences and patients without. The sensitivity, specificity and positive accuracy of PES were 29%, 63% and 46%, respectively, for prediction of ventricular arrhythmia recurrence; 45%, 70% and 36%, respectively, for prediction of VT; and 50%, 98% and 50%, respectively, for prediction of VF during follow-up. CONCLUSIONS: In survivors of VF receiving ICD therapy, VT is the most common ventricular arrhythmia recorded on device-incorporated electrograms during follow-up. This finding, associated with the relatively well-preserved ventricular function, may account for the ability of these patients to survive at time of the index arrhythmia; the use of antitachycardia pacing as a modality to treat arrhythmia recurrences may contribute to reduce the incidence of shock during follow-up in these patients.     

Mid-diastolic potential is related to the reentrant circuit in a patient with verapamil-sensitive idiopathic left ventricular tachycardia

We report a case of verapamil-sensitive idiopathic ventricular tachycardia in which a mid-diastolic potential (MDP) 45 msec preceding the Purkinje potential (P potential) was recorded. Pacing during the tachycardia caused concealed entrainment, and the stimulus-QRS interval was equal to the P potential-QRS interval. The interval between the last pacing stimulus and the next P potential (postpacing interval) was longer than the ventricular tachycardia cycle length, but the MDP was orthodromically activated. These findings suggest that the MDP was on the reentrant circuit and the P potential was not on the reentrant circuit, but a bystander.     

Evidence that atrial natriuretic peptide tissue extraction is not changed by large increases in its plasma levels induced by pacing in humans

Atrial natiurectic peptide (ANP) is a cardiac hormone with a very short plasma half-life, which plays an important role in a variety of clinical conditions associated with an increase in pressure and/or volume overload on the heart. The MCR of the hormone is considered to represent a stable parameter, reflecting the uptake and degradation rate of ANP by the periphery, only scarcely affected by rapid oscillations of circulating levels. To evaluate the extent to which MCR is affected by rapid and large variations of circulating levels of the hormone, we measured MCR in five patients with different degrees of myocardial function (from normal to severely impaired), in whom changes in ANP levels were induced by atrial and/or ventricular pacing. Cardiac output was simultaneously measured by thermodilution to calculate whole body extraction of ANP. During constant i.v. infusion of [125I]ANP, the hormone MCR was determined both under basal conditions (at tracer equilibration, 20-30 min after the start of infusion) and during atrial and ventricular pacing. Pacing maneuvers, begun 50 min after the start of infusion, induced a marked and rapid increase in endogenous plasma ANP values in all patients (on the average, 3,7-fold compared to basal values; range, 1.8-5.68), whereas corresponding values of [125I]ANP only minimally changed. The MCR of ANP (3.62 +/- 1.06 L/min, mean +/- SD) slightly decreased (by repeated measures ANOVA, P = 0.0458) during atrial and ventricular pacing procedures (3.35 +/- 1.03 and 3.15 +/- 0.74 L/min, respectively), reaching a mean value of 88.7 +/- 9.0% compared to basal. The small decrease in MCR could be almost completely ascribed to hemodynamic factors; indeed, basal cardiac output (5.76 +/- 1.70 L/min) was found, on the average, to be slightly decreased during atrial and ventricular pacing (5.28 +/- 1.46 and 5.16 +/- 1.33 L/min, respectively), and so whole body extraction of the hormone, measured before pacing (50.0 +/- 12%), remains stable throughout the study period (50.4 +/- 10.6% and 49.6 +/- 10% during atrial and ventricular pacing, respectively). Our findings demonstrate that degradative mechanisms involved in ANP clearance are not saturable at least for acute elevations of ANP plasma levels up to 3-5 times the basal level.     

Postoperative hemodynamic improvement with paced linkage of the donor and recipient hearts following heterotopic cardiac transplantation

It has been shown that following heterotopic heart transplantation the recipient left ventricle ejects more effectively when it contracts out of phase with the donor left ventricle. However, this is rarely the situation, as the two hearts beat independently of one another and the denervated donor heart tends to beat faster than the recipient. In this study the hemodynamic effects of connecting the two hearts by an external temporary dual-chamber pacemaker were evaluated. The donor right ventricle was sensed and the recipient right atrium paced after a timed delay. The delay was adjusted so that recipient systole coincided with donor diastole. Eleven patients were studied in the first postoperative day. Pacing resulted in an improvement in cardiac output from 5.0 to 5.6 l/min (p = 0.003) and a reduction in pulmonary capillary wedge pressure from 16 to 12 mmHg (p = 0.0035). This was associated with a 35% reduction in inotrope requirements. It is concluded that sequential pacing of the two hearts is a useful adjunct to inotropic support in the postoperative period.     

定时方式控制在1580热轧机组上的应用

定时方式控制是轧制节奏控制（ＭＰＣ）模型的控制方式之一。其主要原理是以大侧压机作为轧线的制约条件，通过加热炉节奏和轧线节奏确定加热炉的最佳抽出节奏。通过该模型的应用，可以实现轧线和加热炉的协调，提高生产率。     

Prolongation of conduction time during premature stimulation in the human atrium is primarily caused by local stimulus response latency

BACKGROUND: Conventional clinical electrophysiological techniques cannot accurately differentiate between local stimulus response latency and propagation time of the atrial response. The purpose of this study was to identify and distinguish local stimulus response latency from impulse propagation time in the human right atrium during programmed electrical stimulation. METHODS: Pacing was performed from two atrial sites (high and low right atrium) in 19 patients, using monophasic action potential recording/pacing combination catheters (interelectrode distance < 2 mm). Local stimulus response latency (interval between stimulus artifact and upstroke of the local monophasic action potential), and propagation time (interval between local and remote monophasic action potential upstroke) were evaluated at a basic cycle length (S1-S1) of 600 ms and as a function of the extrastimulus proximity (interval between extrastimulus and effective refractory period). Data are presented as means +/- SEM. RESULTS: During basic stimulation, local latency was very small (3.8 +/- 1.7 ms). During premature extrastimulation (proximity < 70 ms), local latency increased progressively with decreasing coupling intervals. Prolongation of local latency was most pronounced during stimulation close to the effective refractory period with local stimulus response latency increasing to 18.3 +/- 1.4 ms (380 +/- 7.9%) at 10 ms proximity (P < 0.002) and to 27.9 +/- 3.7 ms (630 +/- 13.2%) at 5 ms proximity, respectively (P < 0.0001). The impulse propagation time between the stimulation site and the remote recording site was on average 54.5 +/- 14.3 ms during basic stimulation, and increased up to 62.1 +/- 13.5 ms (14.0 +/- 8.4%), which was not significant. CONCLUSIONS: The intra-atrial impulse propagation remained essentially unchanged during the entire range of premature stimulation. Local stimulus response latency was negligible and constant during late coupling intervals but increased dramatically when extrastimulation approached the preceding repolarization phase. This has the following clinical impact: first, local stimulus response latency during premature extrastimulation curbs the targeted atrial response interval second, local stimulus response latency, not propagation time, seems responsible for the greater functional than effective refractory period during electrical stimulation; third, local stimulus response latency should be considered in pace mapping for accurate comparison of conduction time before pacing with that during pacing.     

Modern electrodes with and without steroid: effects on stimulation current of cardiac pacemakers

The aim of the investigation was to test whether new leads without steroid, a meshwire tip leads (Ionyx 4180, CPI; n = 10) and a carbon tip lead (Facet ITP 13, Vitatron; n = 10), have electrical characteristics similar to a new steroid-eluting tip lead (CapSure SP 4023, Medtronic; n = 10) and their impact on the pacemaker's pacing current. Pacing thresholds, impedance, and R-wave amplitudes measured at implantation were similar for the three leads. One, 4 and 12 weeks after implantation both nonsteroid leads had significantly higher pacing thresholds at 0.1 and 0.3 ms pulse duration in comparison to the steroid lead (after 12 weeks at 0.3 ms steroid: 0.9 +/- 0.2 V, carbon: 2.1 +/- 0.5 V; meshwire: 1.5 +/- 0.5 V). This result was restricted to the carbon lead after 52 weeks. At 0.5 ms pulse duration higher pacing thresholds were obtained for the carbon lead (after 12 weeks at 0.5 ms; steroid: 0.8 V, carbon: 1.7 +/- 0.6 V; meshwire: 1.1 +/- 0.4 V). Impedance of the steroid lead was 531 +/- 61 ohms, 535 +/- 54 ohms, and 511 +/- 50 ohms, respectively, after 4, 12, and 52 weeks, whereas the carbon lead had significantly higher values with 652 +/- 84 ohms, 669 +/- 93 ohms, and 657 +/- 107 ohms, respectively. The impedance of the meshwired lead (4 weeks: 585 +/- 92 ohms; 12 weeks: 592 +/- 89 ohms; 52 weeks: 550 +/- 130 ohms) did not differ from the steroid lead.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-term efficacy of d/l sotalol in patients with sustained ventricular tachycardia refractory to class I antiarrhythmic drugs

The efficacy of d/l sotalol was investigated in 50 patients (43 men, seven women; 33 with coronary artery disease, 15 with dilated cardiomyopathy; ejection fraction 33 +/- 10%) with inducible sustained ventricular tachycardia. Before d/l sotalol a mean of 2 +/- 1 (1 to 4) class I antiarrhythmic drugs were ineffective. In 24 patients (48%) oral d/l sotalol (320 +/- 47 mg.day-1) prevented induction of the ventricular tachycardia; in 23 patients the ventricular tachycardia remained inducible (d/l sotalol 326 +/- 50 mg.day-1). The electrophysiological effects of d/l sotalol did not differ between patients in whom d/l sotalol prevented induction of ventricular tachycardia and those in whom the ventricular tachycardia remained inducible. In two patients, torsade des pointes developed after oral application of d/l sotalol; one patient suffered from severe hypotension even with 80 mg of sotalol per day. During long-term follow-up (27 +/- 12 months) 5/24 patients (21%) had a non-fatal recurrence of ventricular tachycardia (1 week to 21 months), one patient died suddenly and another from progressive heart failure. In patients in whom the ventricular tachycardia could be induced despite oral application of d/l sotalol, control of the ventricular tachyarrhythmia was attempted by the use of sotalol in combination with mexiletine (n = 2), amiodarone (n = 9), catheter ablation (n = 2), antitachycardia surgery (n = 1) or the implantation of an automatic cardioverter defibrillator (n = 12). Recurrence of ventricular tachycardia was observed in four patients without an implanted cardioverter defibrillator. Seven out of 12 patients with an implanted cardioverter defibrillator received appropriate shocks or successful antitachycardia pacing. Although no patient died suddenly, overall mortality was 17% in this group. It is concluded that d/l sotalol is highly effective in the suppression of sustained monomorphic ventricular tachycardia inducible by programmed electrical stimulation. However during a mean follow-up of 27 +/- 12 months a recurrence of ventricular tachycardia was seen in 21% of patients, and one patient died suddenly.     

Predictable and unpredictable shock stimulates gastric contractility and causes mucosal injury in rats.

The effects of tailshock on gastric contractility and lesions were investigated in rats exposed to 100 1-mA tailshocks while confined inside plastic tubes. A light preceded each shock in one group and was randomly presented with respect to shock in the other. Contractility of the corpus of the stomach was measured by means of chronically implanted extraluminal force transducers. Contractility was measured in 10-min blocks and analyzed by computer. Signaled (n?=?13) and unsignaled (n?=?17) shock stimulated high-amplitude gastric contractions in fasted rats, which continued for 2 hr after the shock session. Cumulative contractile activity (1.5-hr shock plus 2-hr rest) in shocked animals was twice that in restrained and unrestrained control animals (n?=?19, p?