Rate adaptive atrial pacing in the bradycardia tachycardia syndrome

In 42 patients (26 men, 16 women; mean age 69 +/- 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval < or = 240 ms during sinus rhythm at rest. The interval between the atrial spike and the following Q wave (SQ) was measured in the supine position at rest with an AAI pacing rate of 5 beats/min above the sinus rate (SQ-R + 5), and at the end of exercise with 110 beats/min (SQ-E110). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol with the pacemakers being programmed to AAI with a fixed rate of 60 beats/min. Chronotropic incompetence was defined as peak exercise heart rate: (1) < 100 beats/min; (2) < 75% of the maximum predicted heart rate; or (3) the heart rate at half the maximum workload < 60 + 2 beats/min per mL O2/kg per minute (calculated O2 consumption). During exercise, one patient developed atrial fibrillation. Chronotropic incompetence was present in 71% (29/41) of the patients according to definition 2, and in 76% (31/41) according to definition 1 or 3. Ten out of 41 patients (24%) exhibited a second-degree AV block with atrial pacing at 110 beats/min at the end of exercise. Only 9 out of the remaining 31 patients (29%) showed a physiological adaptation of the SQ-E110, and 21 patients (68%) exhibited a paradoxical increase of the SQ interval with rapid atrial pacing at the end of exercise as compared to the SQ-R + 5. These observations indicate that the pacing system to be used in most patients paced and medicated for the bradycardia tachycardia syndrome should be dual chamber, and the option of rate adaptation should be considered.     

Prevention of recurrent atrial fibrillation with chronic dual-site right atrial pacing

OBJECTIVES: We investigated 1) the feasibility, safety and efficacy of multisite right atrial pacing for prevention of atrial fibrillation (AF); and 2) the ability of atrial pacing in single- and dual-site modes to increase arrhythmia-free intervals in patients with drug-refractory AF. BACKGROUND: We recently developed and applied a novel technique of dual-site right atrial pacing in an unselected group of consecutive patients with AF requiring demand pacing. A prospective crossover study design was used to evaluate single- and dual-site right atrial pacing modes. METHODS: The frequency of AF during the 3 months before pacemaker implantation was analyzed. Consecutive consenting patients underwent insertion of two atrial leads and one ventricular lead with a DDDR pulse generator. Patients were placed in a dual-site pacing mode for the first 3 months and subsequently mode switched to single site pacing for 3 months. Mode switching was repeated at 6-month intervals thereafter. RESULTS: Atrial pacing resulted in a marked decline in AF recurrences (p < 0.001). During dual-site pacing with an optimal drug regimen, there was no AF recurrence in any patient compared with five recurrences in 12 patients during single-site pacing (p = 0.03). The mean (+/-SD) arrhythmia-free interval before pacing (14 +/- 14 days) was prolonged with dual- (89 +/- 7 days, p < 0.0001) and single-site pacing (76 +/- 27 days, p < 0.0001). Symptomatic AF episodes showed a declining trend during dual- and single-site pacing compared with those during the preimplantation period (p = 0.10). Mean antiarrhythmic drug use for all classes declined from 4 +/- 1.9 drugs before implantation to 1.5 +/- 0.5 (p < 0.01) drugs after implantation. Twelve (80%) of 15 patients remained in atrial paced rhythm at 13 +/- 3 months. CONCLUSIONS: We conclude that multisite right atrial pacing is feasible, effective and safe for long-term application. Atrial pacing significantly prolongs arrhythmia-free intervals in patients with drug-refractory paroxysmal AF. Dual-site right atrial pacing may offer additional benefits and should be considered either as the primary mode or in patients unresponsive to single-site pacing.     

Effective use of a novel rate-smoothing algorithm in atrial fibrillation by ventricular pacing

BACKGROUND: It is still unknown whether a fast heart rate or an irregular ventricular response in atrial fibrillation causes tachycardiomyopathy. Reduction in the variability of RR intervals without an increase in heart rate might be an alternative treatment when antiarrhythmic drugs fail to control the irregularity accompanying atrial fibrillation. SUBJECTS AND METHODS: Eight patients underwent temporary right ventricular pacing, using a novel rate-smoothing algorithm prior to DC cardioversion or His bundle ablation. A rate-smoothing algorithm was utilized by right ventricular apical stimulation. Spontaneous and paced RR intervals during atrial fibrillation were quantified and processed for statistical analysis. RESULTS: The rate-smoothing algorithm resulted in a substantial reduction in the variance of the RR intervals (slow mode 73.1%, fast mode 40.0%) and RR range (slow mode 49.3%, fast mode 34.3%). In contrast to previous algorithms, the mean heart rate during pacing intervention in atrial fibrillation did not change significantly to the heart rate directly preceding the pacemaker intervention (+2%). CONCLUSIONS: This initial study of the novel rate-smoothing algorithm shows that pacing intervention is a relatively safe, rapid and reliable alternative therapy for controlling irregular ventricular rhythms due to atrial fibrillation. Incorporation of the algorithm in implantable pacemakers appears justified, but demands further prospective studies in patients to evaluate relief of symptoms and reduction of tachycardiomyopathy due to atrial fibrillation.     

Effect of flecainide on atrial and ventricular refractoriness and conduction in patients with normal left ventricle. Implications for possible antiarrhythmic and proarrhythmic mechanisms

We studied the effects of intravenous flecainide (2 mg.kg-1) on atrial and ventricular refractoriness and conduction during sinus rhythm, induced atrial fibrillation and atrial pacing at rates of 100, 120 and 150 ppm, in 14 patients with normal left ventricle. Flecainide caused a significant increase in QRS duration during sinus rhythm (mean +/- SD: 87.2 +/- 8.4 ms vs 102.8 +/- 9.1 ms, P < 0.001), atrial fibrillation (87.8 +/- 10.0 ms vs 108.8 +/- 13.7 ms, P < 0.001) and at all paced rates. The duration of the atrial electrogram was significantly increased during sinus rhythm (54.9 +/- 13.2 ms vs 64.8 +/- 16.6 ms, P = 0.003) and at all pacing rates. The PA interval was also significantly prolonged, as was the pacing stimulus-to-atrial-electrogram interval at all pacing rates. There was increased QRS duration and atrial electrogram prolongation at higher pacing rates. Atrial refractoriness was prolonged during sinus rhythm (216.4 +/- 28.2 vs 228.6 +/- 36.1, P = 0.02), but not during atrial pacing at any rate. The QT interval, but not the JT interval or ventricular refractoriness, was significantly prolonged during sinus rhythm and at all pacing rates. Flecainide slows atrial conduction in a use dependent manner and increases atrial refractoriness during sinus rhythm but not during faster atrial pacing, thus not displaying a use-dependent effect. QRS duration is prolonged in a use-dependent manner without a commensurate increase in ventricular refractoriness. In the presence of rapidly conducted atrial fibrillation, which was not found to be slowed by flecainide, this effect may constitute a proarrhythmic mechanism even in patients with no apparent myocardial abnormality.     

Atrial septal pacing: a method for pacing both atria simultaneously

By pacing both atria simultaneously, one could reliably predict and optimize left-sided AV timing without concern for IACT. With synchronous depolarization of the atria, reentrant arrhythmias might be suppressed. We studied four male patients (73 +/- 3 years) with paroxysmal atrial fibrillation and symptomatic bradyarrhythmias using TEE and fluoroscopy as guides; a standard active fixation screw-in lead (Medtronic model #4058) was attached to the interatrial septum and a standard tined lead was placed in the ventricle. The generators were Medtronic model 7960. The baseline ECG was compared to the paced ECG and the conduction time were measured to the high right atrium, distal coronary sinus and atrial septum in normal sinus rhythm, atrial septal pacing, and AAT pacing. On the surface ECG, no acceleration or delay in AV conduction was noted during AAI pacing from the interatrial septum as compared with normal sinus rhythm. The mean interatrial conduction time for all 4 patients was 106 +/- 2 ms; the interatrial conduction time measured during AAT pacing utilizing the atrial septal pacing lead was 97 +/- 4 ms (P = NS). During atrial septal pacing, the mean conduction time to the high right atrium was 53 +/- 2 ms. The mean conduction time to the lateral left atrium during atrial septal pacing, was likewise 53 +/- 2 ms. We conclude that it is possible to pace both atria simultaneously from a single site using a standard active fixation lead guided by TEE and fluoroscopy. Such a pacing system allows accurate timing of the left-sided AV delay.     

Effect of adenosine antagonism on metabolically mediated coronary vasodilation in humans

OBJECTIVES: This study was performed to assess the importance of adenosine in mediating metabolic coronary vasodilation during atrial pacing stress in humans. BACKGROUND: Numerous animal studies have examined the role of adenosine in the regulation of coronary blood flow, with inconsistent results. METHODS: The effect of the adenosine antagonist aminophylline (6 mg/kg body weight intravenously) on coronary functional hyperemia during rapid atrial pacing was determined in 12 patients. The extent of inhibition of adenosine vasodilation was assessed using graded intracoronary adenosine infusions before and after aminophylline administration in seven patients. Coronary blood flow changes were measured with a 3F intracoronary Doppler catheter. RESULTS: After aminophylline administration, the increase in coronary flow velocity during adenosine infusions was reduced from 84 +/- 48% (mean +/- SD) to 21 +/- 31% above control values (p < 0.001) at 10 micrograms/min and from 130 +/- 39% to 59 +/- 51% above control values (p < 0.001) at 40 micrograms/min. During rapid atrial pacing under control conditions, coronary blood flow velocity increased by 26 +/- 16%. The flow increment during paced tachycardia after aminophylline (23 +/- 10%) was unchanged from the control value, despite substantial antagonism of adenosine coronary dilation by aminophylline. CONCLUSIONS: These data suggest that adenosine does not play an important role in the regulation of coronary blood flow in response to rapid atrial pacing in humans.     

Effect of coupling interval and pacing cycle length on morphology of paced ventricular complexes. Implications for pace mapping

BACKGROUND: Ventricular pace mapping is performed by comparing the QRS morphology of ventricular paced complexes to that of a template arrhythmia, either a premature ventricular depolarization or a QRS complex during ventricular tachycardia. The objective of this study was to evaluate the effect of coupling interval and pacing cycle length on QRS morphology. METHODS AND RESULTS: The study population consisted of 20 patients (mean age, 38 +/- 16 years) undergoing a clinically indicated electrophysiology procedure. In the first 10 patients, the effect of coupling interval on the morphology of single paced ventricular complexes was evaluated visually and by signal processing techniques. Visually apparent differences in QRS morphology occurred in a mean of 4/12 electrocardiographic leads with a change in coupling interval of > or = 100 ms. In the next 10 patients, the QRS complex morphology during ventricular overdrive pacing at cycle lengths of 600 and 300 ms was found to differ significantly in a mean of 4/12 leads. The QRS morphology during overdrive pacing differed significantly from that of a single paced complex whenever the pacing cycle length differed from the coupling interval of the single paced complex by > 80 ms. CONCLUSIONS: The morphology of single paced QRS complexes may vary, depending on coupling interval, and the QRS morphology during overdrive pacing is affected by the pacing cycle length. During ventricular pace mapping, the coupling interval or cycle length of the template arrhythmia should be matched during pacing. If not, rate-dependent changes in QRS morphology that are independent of the pacing site may confound the results of pace mapping.     

A gastroesophageal electrode for atrial and ventricular pacing

Temporary transvenous cardiac pacing requires technical expertise and access to fluoroscopy. We have developed a gastroesophageal electrode capable of atrial and ventricular pacing. The flexible polythene gastroesophageal electrode is passed into the stomach under light sedation. Five ring electrodes, now positioned in the lower esophagus, are used for atrial pacing. A point source (cathode) on the distal tip of the electrode, now positioned in the gastric fundus, is used for ventricular pacing. Two configurations of atrial and ventricular pacing were compared: unipolar and bipolar. During unipolar ventricular pacing the indifferent electrode (anode) was a high impedance chest pad. For bipolar ventricular pacing the indifferent electrode was a ring electrodes placed 2 cm proximal to the tip. Unipolar atrial pacing was performed with 1 of 5 proximal ring electrodes acting as cathode ("cathodic") or as anode ("anodic") in conjunction with a chest pad. Bipolar atrial pacing was performed using combinations of 2 of 5 ring electrodes. Atrial capture was obtained in all 55 subjects attempted. When all electrode combinations were compared, atrial capture was significantly more frequent using the bipolar approach (153/210 bipolar, 65/210 unipolar; t = 7.37, P < 0.001). For unipolar atrial pacing, cathodic stimulation (from esophagus) was more successful than anodic stimulation (cathodic 62/105, anodic 20/105; t = 5.81, P < 0.001). In 43 subjects attempted unipolar ventricular pacing resulted in a higher frequency of capture than the bipolar approach (unipolar 41/43 (95.3%), bipolar 19/43 (44.2%); P < 0.001). In conclusion, atrial pacing was optimal using pairs of ring electrodes ("bipolar") while ventricular pacing was optimal using the distal electrode tip (cathode) in conjunction with a chest pad electrode ("unipolar"). This gastroesophageal electrode may be useful in the emergency management of acute bradyarrhythmias and for elective electrophysiological studies.     

Direct conversion of atrial flutter to sinus rhythm with low-output, short-duration transesophageal atrial pacing

BACKGROUND AND HYPOTHESIS: Transesophageal atrial pacing (TAP) is useful for terminating paroxysmal non-self terminating atrial flutter (PAF); however, high output pacing of long stimulus duration causes severe symptoms such as chest pain. The objective of this study was to investigate the effect of low-output, short-duration TAP on the conversion of PAF. METHODS: We applied low-output (within 15 mA with a pulse duration of 10 ms), short-duration (within 4 s) TAP in 31 patients (50 +/- 19 years) with PAF. Transesophageal pacing was delivered with 10 pulses of burst pacing at intervals that were 20 ms shorter than those of the flutter wave length. When the conversion was unsuccessful, we delivered 20 pulses of burst pacing. RESULTS: Sixteen patients (52%) were converted directly to sinus rhythm and 12 (38%) to atrial fibrillation. Transesophageal pacing was ineffective in 3 (10%) patients. The duration of atrial flutter, maximum flutter wave amplitude, effective pacing intervals, underlying heart diseases, and cardiac function were not different between patients who had direct conversion to sinus rhythm and those converted to atrial fibrillation. The patients who had direct conversion to sinus rhythm had longer flutter wave cycle lengths than those converted to atrial fibrillation (248 vs. 221 ms, p < 0.005). No patient had complications and complained of any symptoms. CONCLUSION: Low-output, short-duration TAP was useful to convert PAF directly to sinus rhythm without side effects.     

Effects of right ventricular pacing on ventriculoatrial conduction and systemic venous responses in sick sinus patients

This study was designed to assess the ventriculoatrial (VA) conduction and systemic venous responses to right ventricular pacing at different pacing rates and the feasibility of identifying patients prone to pacemaker syndrome by means of a Doppler and two-dimensional echocardiographic technique. Twenty-two sick sinus patients who received ventricular-demand permanent pacemakers constituted the study group. The proximal inferior vena cava (IVC) diameters were measured by two-dimensional echocardiography. Fourteen patients had VA conduction by preimplant electrophysiologic study or paced electrocardiogram (Group II), while the other 8 patients presented no VA conduction (Group I). Abnormal systolic retrograde flow in the hepatic vein following each paced beat could be demonstrated in those patients with VA conduction in the basal state. In the 8 patients without VA conduction, the IVC diameters were significantly increased during rapid right ventricular pacing in those with left ventricular dysfunction (n = 4) as compared with those with normal left ventricular function (n = 4) (% increment at 120 beats per minute.     

Prospective randomised trial of atrial versus ventricular pacing in sick-sinus syndrome

In patients with sick-sinus syndrome, single-chamber atrial pacing has been reported, in retrospective studies, to be associated with lower frequencies of atrial fibrillation, thromboembolism, heart failure, and mortality than ventricular pacing; although single-chamber ventricular pacing is most commonly used. We did a prospective randomised trial in 225 consecutive patients (142 women, 83 men; mean age 76 years) with the sick-sinus syndrome, randomised to atrial (n = 110) or ventricular (n = 115) pacing and followed for up to 5 years (mean 40 [SD 18] months). During follow-up, the frequency of atrial fibrillation was higher in the ventricular group, except at the first follow-up at 3 months. Thromboembolic events (stroke or peripheral arterial embolus) occurred in 20 patients in the ventricular group and in 6 patients in the atrial group (p = 0.0083). 25 patients died in the ventricular group compared with 21 in the atrial group (p = 0.74). Heart failure estimated by the New York Heart Association classification and by the daily doses of diuretics did not differ between the two groups. Atrioventricular block occurred in 2 patients in the atrial group. Patients with sick-sinus syndrome should be treated with atrial pacing rather than ventricular pacing because atrial pacing is associated with lower frequencies of atrial fibrillation, thromboembolic complications, and a low risk of atrioventricular block.     

Epinephrine facilitates cardiac fibrillation by shortening action potential refractoriness

Epinephrine released during ventricular tachycardia (VT) or early fibrillation (VF) appears to be instrumental in stabilizing fibrillation. However, mechanisms remain unclear. Effects of epinephrine on refractory period at normal sinus rates depend on basic cycle length, but effects at short cycle lengths, typical of VT/VF, are unknown. Therefore, the goal of this study was to determine whether epinephrine shortens action potential duration and refractoriness at these short cycle lengths. To simulate early VT/VF, myocardial cell aggregates (n = 35) were paced using field stimulation (5 ms rectangular waveform) at cycle lengths of 200, 180, 160 and 140 ms, which occur during in situ fibrillation: normal sinus rhythm was simulated by pacing at 600 and 400 ms intervals. Action potentials and excitation threshold were recorded with intracellular microelectrodes under control conditions, with 0.9 microM/l epinephrine, and with 0.9 microM/l epinephrine and 0.5 microM/l propranolol. At short cycle lengths, epinephrine significantly shortened action potential duration and refractoriness compared to control. At a cycle length of 160 ms, action potential duration was reduced by 14 ms at 60% repolarization (P < 0.0002) and stimulation threshold by 18% (P < 0.02). Epinephrine also allowed pacing at a cycle length of 140 ms, not achievable under control conditions. Because epinephrine decreases action potential duration at short cycle length in situ, re-entry wavefronts are less likely to encounter refractory tissue: fibrillation is more likely to occur and to remain stabilised. Reduction in action potential duration and excitation threshold were reversed by propranolol, suggesting that epinephrine effects are produced by beta-stimulation.     

Neuropsychological function in adults with attention-deficit hyperactivity disorder

Pacemaker therapy in patients with atrial fibrillation means the best current pacemaker therapy for patients with bradycardias with the aim to avoid the onset of atrial fibrillation and to establish DDD pacing despite of a history of atrial tachyarrhythmias. The newer application of pacing is the suppression of atrial arrhythmias in patients with medical refractory atrial tachyarrhythmias. Patients with slow ventricular rates and permanent atrial fibrillation should receive a VVI-pacemaker, if the bradycardias causes syncope, dizziness or a decrease of their exercise tolerance. In case of chronotropic incompetence the pacemaker should provide rate responsive pacing. Patients with sick sinus syndrome should receive an atrial (AAI) or dual-chamber (DDD) pacemaker, because patients with these in contrast to VVI-pacemakers develop less often atrial fibrillation and subsequent complications such as atrial thromboembolism. A dual-chamber or VDD-pacemaker--the latter connected to a VDD-single-lead--is indicated in patients with advanced AV-block. Atrial fibrillation occurs in 3 to 6% of the patients with no history of arrythmia and is, if pacemakers have no automatic mode switch, an often reason to program the devices to the VVI-pacing mode. Nowadays, most DDD(R)-pacemakers provide an automatic mode switch: During an atrial tachycardia the pacemaker switches to a VVI/VVIR mode and restores the initial DDD(R)-pacing mode with termination of the arrhythmia. In respect to the newer applications, one approach to prevent atrial tachyarrhythmias is permanent atrial pacing. As lower pacing rates of 80 to 90 ppm are usually needed and many patients hardly tolerate these pacing rates, new algorithms are under clinical investigation. Another approach is the simultaneous depolarization of the right and left atrium. Biatrial pacing is performed with one lead in the high right atrium and another lead in the coronary sinus. Another solution is bifocal atrial pacing with leads placed in the high right atrium and in the coronary sinus ostium. One effect of the new pacing techniques is to shorten interatrial conduction times. Therefore, biatrial pacing has become a therapy to prevent atrial arrhythmias deriving from delayed interatrial conduction times. As atrial reentry circuits seem to be important in atrial fibrillation, multisite atrial pacing is also performed in patients with medical refractory paroxysmal atrial fibrillation. Preliminary results suggest a more effective prevention of atrial fibrillation; nevertheless, these techniques should be still restricted to patients enrolled in clinical studies.     

Functional correlation of molecular electronic properties with potency of synthetic carbinolamine antimalarial agents

Dual chamber rate responsive pacing incorporating a mode switching option is increasingly used in patients with chronic paroxysmal atrial fibrillation and high degree AV block. Single-lead VDDR pacemakers have rarely used for this indication. The purpose of this study was to determine their reliability of atrial sensing during atrial fibrillation, the percentage of atrial synchronous ventricular pacing, and the behavior of the sinus rate outside the phases of atrial fibrillation. We studied ten patients with a single-lead VDDR pacemaker implanted for this indication. Follow-up visits were performed at predischarge and after 1, 3, 6, 12, 18, and 24 months. During the mean follow-up period of 18.9 +/- 6.9 months, the atrial sensing thresholds in sinus rhythm remained stable. Atrial synchronous ventricular stimulation was achieved in 68.7 +/- 31.2% (median 82.5%) of the whole follow-up time. All patients showed an adequate atrial rate response during sinus rhythm. Atrial fibrillation was detected by the pacemakers in 24.0 +/- 29.8% of time. In 3 of 10 patients the duration of atrial fibrillation showed a steady increase from visit to visit. The sensed amplitudes of atrial fibrillation ranged from 0.1-1.0 mV. A programmed atrial sensitivity of 0.1 mV was necessary to achieve complete sensing of atrial fibrillation. None of the patients experienced tachycardias with optimized pacemaker programming. Single-lead VDDR pacing incorporating a mode-switching option is useful in patients with high degree AV block and paroxysmal atrial fibrillation, since it provides atrial synchronous ventricular pacing in more than two-thirds of follow-up time. In a subgroup of patients, a progressive increase of the time during atrial fibrillation was demonstrated. A reliable detection of paroxysmal atrial fibrillation requires the programming of the atrial sensitivity to its most sensitive value.     

Incidence and significance of ventricular tachycardia and fibrillation in the absence of hypotension or heart failure in acute myocardial infarction treated with recombinant tissue-type plasminogen activator: results from the Thrombolysis in Myocardial Infarction (TIMI) Phase II trial

OBJECTIVES: The purpose of this study was to determine the incidence of ventricular tachycardia and fibrillation without hypotension or heart failure after treatment with recombinant tissue-type plasminogen activator (rt-PA), anatomic correlates of their development, the effect of immediate intravenous metoprolol on their occurrence and the outcome of patients with these arrhythmias. BACKGROUND: Malignant arrhythmias after thrombolytic therapy have been reported to occur as a result of coronary reperfusion, which is associated with reduced mortality in patients receiving thrombolytic therapy. METHODS: We analyzed data from 2,546 patients in the Thrombolysis in Myocardial Infarction (TIMI) Phase II trial without congestive heart failure or hypotension during the 1st 24 h after study entry. Forty-nine patients (1.9%) developed sustained ventricular tachycardia or ventricular fibrillation within 24 h of study entry (group 1), and 2,497 patients (98.1%) did not (group 2). RESULTS: Baseline characteristics and admission laboratory values were similar in the two groups. In patients undergoing protocol angiography 18 to 48 h after rt-PA, the infarct-related artery was patient in a greater percent of group 2 patients (87% [1,015 of 1,169]) than group 1 patients (68% [15 of 22], p = 0.01), although angiography was performed less frequently in group 1 than in group 2. More group 1 than group 2 patients died within 21 days (20.4%) (1.6%, p < 0.001). For patients surviving to 21 days, there was no difference in mortality between patients in the two groups in the following year. CONCLUSIONS: Ventricular tachycardia and fibrillation are not markers for reperfusion after thrombolytic therapy. These arrhythmias are associated with occlusion, not patency, of the infarct-related artery. Early mortality is increased in patients who develop ventricular tachycardia and fibrillation, even in the absence of congestive heart failure and hypotension.     

Effects of different atrial pacing modes on atrial electrophysiology: implicating the mechanism of biatrial pacing in prevention of atrial fibrillation

BACKGROUND: Multiple-site atrial pacing has been shown to prevent recurrence of atrial fibrillation. However, information about the mechanisms of different atrial pacing modes in prevention of atrial fibrillation was not clear. METHODS AND RESULTS: Forty-two patients without structural heart disease were classified into group 1 and group 2 according to absence or presence of clinical atrial fibrillation, respectively. Atrial conduction time and electrogram width of the right posterior interatrial septum (RPS) were measured during drive-train stimulation (S1) and early extrastimulation (S2). The locations of S1 were the high right atrium (HRA), distal coronary sinus (DCS), or both sites simultaneously. Effective refractory periods (ERPs) of the HRA and DCS were also determined during S1 stimulation at each site and during biatrial pacing. The ERPs were not different between single-site atrial pacing and biatrial pacing. In contrast, early S2 stimulation at the HRA caused greater atrial conduction delay and greater increment of electrogram width of the RPS in patients with a history of atrial fibrillation. Biatrial pacing significantly reduced the conduction delay and electrogram width of the RPS caused by HRA extrastimulation. In addition, in 17 group 2 patients, atrial fibrillation was induced by an early HRA S2 coupled to HRA pacing. However, with the same coupling interval of S2 at HRA, only 6 of them had the arrhythmia induced during biatrial pacing. Furthermore, conduction delay and increase of electrogram width caused by early S2 at the HRA were reduced by biatrial pacing only in patients whose arrhythmia induction was successfully prevented by biatrial pacing. CONCLUSIONS: Biatrial pacing reduced both the atrial conduction delay and increase of electrogram width at the RPS caused by early S2 at HRA, and these effects could prevent induction of atrial fibrillation.     

Single-chamber atrial pacing is better than single chamber ventricular pacing in patients with sick sinus syndrome. Results of long-term follow up in a prospective randomized study

In a study of 225 patients with sick sinus syndrome randomized to single chamber atrial pacing (n = 110) or ventricular pacing (n = 115), atrial pacing was associated with less atrial fibrillation and thromboembolism after 3.3 years follow-up. To determine whether this beneficial effect of atrial pacing is maintained at long-term, follow-up was extended. Follow-up visits were at 3 months, 12 months, and then once every year, and included physical examination, ECG, and pacemaker check-up. After 5.5 years follow-up, all-cause mortality, cardiovascular deaths, atrial fibrillation, thromboembolism, and heart failure were significantly less in the atrial group. AV block occurred in four patients in the atrial group. The beneficial effect of atrial pacing observed previously is enhanced substantially after extended follow-up. Patients with sick sinus syndrome should be treated with an atrial pacing system.     

Studies on digitalis. VII. Influence of nephrotic syndrome on protein binding, pharmacokinetics, and renal excretion of digitoxin and cardioactive metabolites

Serum protein binding of digitoxin was lower (p less than 0.05) in 7 patients with nephrotic syndrome (96.2%, SD 1.4) than in 51 control patients (97.3%, SD 0.5). Urine protein binding of digitoxin was 60.1% in the 6 nephrotic patients in whom it was determined. Simultaneous serum and urine measurements of digitoxin and cardioactive metabolites were performed in 5 patients after a single intravenous dose of 0.6 mg digitoxin. A modified 86Rb method was used. Mean T/2 of serum elimation was 4.8 days and 8.1 days in 5 control subjects (p less than 0.05). Serum concentrations 24 hr after the dose were lower in the nephrotic group (p less than 0.0025). The urine concentration T/2 with a mean value of 5.0 days was not significantly different from controls (7.2 days). The cumulative renal exeretion was higher in the nephrotic group (23.2% of dose) than in controls (15.8%) for 8 days. The excretion during one serum T/2 was the same in the two groups. Increased renal excretion thus explains the shortened serum T/2 in nephrotic patients. Preliminary data on the metabolic pattern of digitoxin and cardioactive metabolites in serum and urine suggested that drug metabolism may be changed in patients with nephrotic syndrome. As renal excretion is enhanced, patients with nephrotic syndrome will require higher doses of digitoxin. They should be maintained at lower than usual serum levels of total drug due apparent increased volume of distribution and hypoalbuminemia with consequent increased free drug fraction.     

Effect of 4 wk of deep water run training on running performance

The authors studied complications associated with intraventricular chemotherapy in patients with leptomeningeal metastases (LM). One hundred twenty consecutive patients with LM (71 females and 49 males) ranging in age from 10 to 72 years (median 42 years) were treated with involved-field radiotherapy and intraventricular chemotherapy using an Ommaya reservoir and intraventricular catheter system. The diagnosis of LM was determined by a combination of clinical presentation (114 patients); cerebrospinal fluid cytological studies (100); or neuroradiographic studies (42). Systemic tumor histological findings included breast (34 patients); non-Hodgkin's lymphoma (22); melanoma (16); primitive neuroectodermal tumors including medulloblastoma (10); glial neoplasms, leukemia, small cell lung, nonsmall cell lung, and colon (six each); prostate and kidney (three each); and gastric cancers (two). Sixteen patients, all with non-Hodgkin's lymphoma, also had acquired immune deficiency syndrome. Patients received one to four (median two) chemotherapeutic drugs and underwent a total of 1110 cycles of intraventricular chemotherapy (median 10). Intraventricular chemotherapy administration and diagnostic Ommaya reservoir punctures totaled 4400, with a median of 46 per patient. Complications included aseptic/chemical meningitis (52 patients); myelosuppression due to intraventricular chemotherapy (21); catheter-related infections (nine); unidirectional catheter obstruction (six); intraventricular catheter malpositioning (two); Ommaya reservoir exposure (two); leukoencephalopathy (two); and chemotherapy-related myelopathy (one). There were no treatment-related deaths; however, seven patients (6%) required additional surgery for either catheter repositioning (two) or reservoir removal (five). Seven patients with catheter-related infections were treated successfully with intraventricular and systemic antibiotic drugs, thereby preserving the Ommaya system. The authors conclude that Ommaya reservoirs are convenient and pharmacologically rational systems for administering intraventricular chemotherapy. Overall, serious complications requiring surgery are infrequent (6%) and most often secondary to catheter infections, Ommaya reservoir exposure, or initial catheter malpositioning. In the majority of instances, catheter infections may be managed medically, as may the most common complications of intraventricular chemotherapy including aseptic meningitis (43% of patients) and myelosuppression (18%).     

Basophilic differentiation of the human leukemia cell line KU812 upon treatment with interleukin-4

To assess the effect of right ventricular pacing on rate regularity during exercise and daily life activities, 16 patients with sinoatrial disease and chronic atrial fibrillation (AF) were studied. Incremental ventricular pacing was commenced at 40 beats/min until > 95% of ventricular pacing were achieved during supine, sitting, and standing. Thirteen patients also underwent randomized paired submaximal exercise tests in either a fixed rate mode. (VVI) or a ventricular rate stabilization (VRS) mode in which the pacing rate was set manually at 10 beats/min above the average AF rate during the last minute of each exercise stage. The pacing interval for rate regularization was shortest during standing (692 +/- 26 ms) compared with either supine or sitting (757 +/- 30 and 705 +/- 26 ms, respectively, P < 0.05). During exercise VRS pacing significantly increased the maximum rate (119 +/- 5.2 vs 106 +/- 4.2 ms, P < 0.05), percent of ventricular pacing (85% +/- 5% vs 23% +/- 7%, P < 0.05), rate regularity index (5.8% +/- 1.6% vs 13.4% +/- 1.9%, P < 0.05), and maximum level of oxygen consumption (12.4 +/- 0.5 vs 11.3 +/- 0.5 mL/kg, P < 0.05) compared with VVI pacing. There was no change in oxygen pulse or difference in symptom scores in this acute study between the two pacing modes. It is concluded that right ventricular pacing may significantly improve rate regularity and cardiopulmonary performance in patients with chronic AF. This may be incorporated in a pacing device for rate regularization of AF using an algorithm that is rate adaptive to postural and exercise stresses.