Evaluation of atrial thrombus formation and atrial appendage function in patients with pacemaker by transesophageal echocardiography

BACKGROUND: Physiologic pacing is claimed to be superior to ventricular pacing in as much as it entails lower risk of atrial fibrillation, stroke, and atrial remodeling. There are few data on the relation between atrioventricular (AV) synchrony and atrial clot formation. Utilizing transesophageal echocardiography (TEE), this study sought to evaluate the effect of AV synchrony loss on left atrial physiology, atrial stasis, and clot formation. METHODS: We conducted a cross-sectional study on patients with both AV and ventricular pacing with left ventricular ejection fraction (LVEF) >30%. TEE enabled us to explore atrial and pacing leads thrombi and measure left atrial appendage (LAA) flow velocity. RESULTS: A total 72 patients (mean age, 65 +/- 11.7) were enrolled in the study. The pacing mode was VVI in 53% and AV sequential in 47% of patients. LVEF (mean +/- SD; %) was 53.3 +/- 6.2% in ventricular pacing mode and 52.2 +/- 6.6 in physiologic pacing mode. Thrombus formation on pacing lead (<10 mm in 97% of patients) was observed in 32% of all the patients (23% in patients with AV sequential pacing mode and 39% with VVI mode). Left atrial appendage flow velocity (LAA-FV) was significantly higher among the patients with AV sequential pacing mode (49.44 +/- 18 cm/s vs 40.94 +/- 19.4 cm/s, P value = 0.02). LAA-FV >40 cm/s was detected in 60% of the patients, 60% of whom were in physiologic mode. Left atrial size was significantly larger among the patients with VVI pacing mode (42.3 +/- 2.3 mm vs 37.79 +/- 4.5 mm, P = 0.001). Multivariate analysis showed no relation between LAA-FV and age, hypertension, diabetes mellitus, left atrial size, and left ventricular function. Only one patient had right atrial clot. There was no thrombus in the ventricles and atrial appendage. CONCLUSION: Long-term loss of AV synchrony induced by VVI pacing is associated with the impairment of LAA contraction. Thrombus formation in the LAA is not increased by VVI pacing in patients with relatively good left ventricular (LV) function and sinus rhythm.     

Single versus dual chamber pacing in the young: noninvasive comparative evaluation of cardiac function

The advantages of atrial synchrony over asynchronous ventricular pacing remain unclear in the young, chronically right ventricular (RV) - paced patient. This is in contrast to the older patient with inherent diastolic dysfunction who has been shown to benefit from atrial synchrony with dual chamber (DDD,R/VDD), over single chamber rate response (VVI,R) ventricular pacing. The goal of this study was to noninvasively assess cardiac function in a group of young, RV-paced patients before and after establishment of atrial synchrony. Echocardiographic data were retrospectively analyzed from 10 patients with congenital or acquired complete AV block, who were VVI,R paced for 10.2 +/- 2 years (mean age at study 19.2 +/- 8.9 years), and were subsequently converted to DDD,R/VDD pacing (mean age at study 20.7 +/- 9.5 years). Paired t-test analysis of left ventricular (LV) systolic and diastolic function during VVI,R versus DDD,R/VDD pacing did not result in any short-term difference in LV short axis fractional area of change or FAC (53% +/- 7.5% vs 56.8% +/- 8.7%) or mitral maximal velocity (E) normalized to mitral flow velocity time integral (VTI) (5.2/s +/- 1.5 vs 4.4/s +/- 1.5). A decrease in mitral flow E/A ratio was observed after short-term DDD,R/VDD pacing (2.2 +/- 0.5 vs 1.9 +/- 0.3). Atrial synchronous dual chamber pacing in young patients with complete AV block does not lead to any appreciable early change in global LV function over single-site RV pacing. Therefore, early establishment of atrial synchrony in the young asymptomatic VVI,R-paced patient with normal intrinsic ventricular function may not be warranted.     

Complex dysrhythmias in infants and children.

Dysrhythmias in infants and children are, in many ways, similar to those in adults, yet several important differences exist in their presentation and management. Complex dysrhythmias most frequently encountered in pediatrics include sinus node dysfunction, chaotic atrial rhythm, atrial flutter, supraventricular tachycardia (including Wolff-Parkinson-White syndrome and junctional ectopic tachycardia), complete atrioventricular block (congenital and acquired), and ventricular dysrhythmias (premature ventricular contractions and ventricular tachycardia). Newer approaches to the diagnosis and management of these dysrhythmias are addressed in this paper.     

Comparison of two strategies to reduce ventricular pacing in pacemaker patients

Background: Managed Ventricular Pacing (MVP) and Search AV+ (SAV+) are two pacing algorithms designed to reduce ventricular pacing. MVP promotes conduction by operating in AAI/R mode with backup ventricular pacing during atrioventricular block (AVB). SAV+ operates in DDD/R mode with a nominal AV extension of 290 ms during atrial sensing and 320 ms during atrial pacing. The reduction in ventricular pacing was compared with these two algorithms in pacemaker patients.
Methods: The EnRhythm and EnPulse clinical studies assessed the percentage of ventricular pacing (%VP) after 1 month. Each patient's AVB status was assigned using the following hierarchical categories: persistent third-degree AVB (p3AVB), episodic third-degree AVB (e3AVB), second-degree AVB (2AVB), first-degree AVB (1AVB), and no AVB (nAVB). The%VP was tabulated for each AVB status category.
Results: Data were available from 322 patients of whom 129 received DDD(R) pacing with the MVP algorithm activated and 193 patients with DDD(R) pacing and the SAV+ function activated, each for a month period. MVP resulted in a significantly lower median%VP than SAV+ in all AVB categories except for p3AVB: nAVB (0.3 vs 2.9, P < 0.0001), 1AVB (0.9% vs 80.6%, P < 0.0001), 2AVB (37.6 vs 99.3, P< 0.002), e3AVB (1.2 vs 42.2, P = 0.02), p3AVB (98.9 vs 100, P = 1.00).
Conclusion: MVP resulted in a greater reduction in%VP than SAV+ across all patient groups except persistent third-degree AV block. The greatest reduction in%VP was observed in patients with mildly impaired AV conduction.     

Modification of the DDD Pacing Mode to Prevent Junctional Reentry Tachycardia: Computer Modelling Experiments

This paper examines the possibility of using short atrioventricular (AV) delay dual chamber pacing to prevent junctional reentry tachycardia mediated by an accessory pathway or by an intra-AV nodal circuit. For this purpose, a clinically realistic computer simulation model of cardiac rhythm and heart-pacemaker interactions has been used. The computational experiments compared the actions of two pacemaker models: (A) a clinically realistic DDD mode operating with quasi-Wenckebach prolongation of the AV delay; and (B) a new modification of the DDD mode introducing independent counters for the atrial and ventricular refractory periods of the heart, and the possibility of instantaneous or shortly delayed atrial pacing triggered by a sensed or paced ventricular event. The pathological phenomena modelled in the experiments simulate different possibilities of tachycardia initiation. These disorders include: (1) single atrial premature beats (APBs), (2) salvos of APBs, (3) closely coupled pairs of APBs, (4) ventricular premature beats initiating an antidromic reentry tachycardia, and (5) ventricular ectopic beats initiating an AV nodal reentry tachycardia. The computational results prove that many possible mechanisms of initiation of junctional reentry tachycardia are beyond the prophylactic capabilities of current sophisticated DDD pacemakers (A). The results also show that the suggested pacing mode (B) improves anti-tachycardia prophylaxis even when responding to complex pathological episodes of the natural cardiac activity. Future development of the suggested mode (B) is discussed.     

Clinical Experience with a New Software-Based Antitachycardia Pacemaker for Recurrent Supraventricular and Ventricular Tachycardias

The Intermedics Intertach 262-12 tachycardia reversion pulse generator was implanted in 14 patients (six male, eight female, mean age at implantation 45 +/- 16 years) with recurrent symptomatic tachycardias. Six patients had atrioventricular (AV) nodal reentrant tachycardia, three patients had orthodromic tachycardia with Wolff-Parkinson-White syndrome, two had circus movement tachycardia via a concealed bypass tract, two had ventricular tachycardia, one patient had atrial flutter. Mean duration of symptoms before implantation was 8 +/- 4 years and mean number of antiarrhythmic drug trials was 3.5 +/- 1. The primary tachycardia response made consisted of autodecremental pacing in one patient, burst pacing in two patients, and adaptive scanning of the initial delay or burst cycle length in eleven patients. The secondary tachycardia response mode consisted of autodecremental pacing in four patients, burst pacing in three patients and burst scanning in four patients. Tachycardia response was automatic in all but one patient with ventricular tachycardia. During a follow-up period of 30.5 +/- 10.6 months, one patient with ventricular tachycardia died from a nonarrhythmic cause. Reinterventions were necessary due to electrode fracture in one patient and due to pacemaker software defect in another one. Two patients underwent surgical cure of their arrhythmia: one patient with atrial flutter and one patient with AV nodal reentry tachycardia, 24 months and 11 months postpacemaker implantation, respectively. Four patients required digitalis to prevent pacing induced atrial fibrillation. Other proarrhythmic effects were not encountered. The pacemaker proved to be a versatile system with reliable tachycardia detection and termination functions. It provided a valuable adjunctive therapy in these selected patients.     

Prospective Evaluation of Infrahisal Second-Degree AV Block Induced by Atrial Pacing in the Presence of Chronic Bundle Branch Block and Syncope

The value of nonfunctional infrahisal second-degree atrioventricular (AV) block induced by incremental atrial pacing was prospectively examined in 192 patients with chronic bundle branch block (BBB) and syncope. We compared 174 (91 %) patients with normal response to atrial pacing (Group I) to 18 (9%) patients with atrial pacing induced nonfunctional infrahisal second-degree AV block (Group II). Patients in group I had higher incidence of organic heart disease, ventricular tachycardia induction, and retrograde ventriculoatrial conduction (P < 0.001, P < 0.05, P < 0.01, respectively), while patients in group II had higher incidence of primary conduction disease and prolonged H-V intervals (P < 0.001, P < 0.01, and P < 0.001). During mean follow-up period of 65 ± 34 months for group I, and 68 ± 35 months for group II, a development of spontaneous second- or third-degree AV block was higher in group II (14/18 [78%]), than in group I (15/174 [9%]) (P < 0.001). The site of AV block was infrahisal in all patients in group II, and in 10 of 15 patients in group I. Because of the prophylactic pacing in all patients in group II, the incidence of sudden death was similar among the two groups, but patients in group I had higher incidence of cardiac death (P < 0.05). Conclusion: In patients with chronic BBB and syncope, a nonfunctional infrahisal AV block induced by incremental atrial pacing identified patients with particularly high risk of development of spontaneous infrahisal AV block. Therefore, permanent cardiac pacing is absolutely indicated in these patients.     

AAIR versus DDDR pacing in the bradycardia tachycardia syndrome: a prospective, randomized, double-blind, crossover trial

In 19 patients paced and medicated for bradycardia tachycardia syndrome (BTS), AAIR and DDDR pacing were compared with regard to quality of life (QoL), atrial tachyarrhythmia (AFib), exercise tolerance, and left ventricular (LV)function. Patients had a PQ interval < or = 240 ms during sinus rhythm, no second or third degree AV block, no bundle branch block, or bifascicular block. In DDDR mode, AV delay was optimized using the aortic time velocity integral. After 3 months, QoL was assessed by questionnaires, patients were investigated by 24-hour Holter, cardiopulmonary exercise testing (CPX) was performed, and LV function was determined by echocardiography. QoL was similar in all dimensions, except dizziness, showing a significantly lower prevalence in AAIR mode. The incidence of AFib was 12 episodes in 2 patients with AAIR versus 22 episodes in 7 patients with DDDR pacing (P = 0.072). In AAIR mode, 164 events of second and third degree AV block were detected in 7 patients (37%) with pauses between 1 and 4 seconds. During CPX, exercise duration and work load were higher in AAIR than in DDDR mode (423+/-127 vs 402+/-102 s and 103+/-31 vs 96+/-27 Watt, P < 0.05). Oxygen consumption (VO2), was similar in both modes. During echocardiography, only deceleration of early diastolic flow velocity and early diastolic closure rate of the anterior mitral valve leaflet were higher in DDD than in AAI pacing (5.16+/-1.35 vs 3.56+/-0.95 m/s2 and 69.2+/-23 vs 54.1+/-26 mm/s, P < 0.05). As preferred pacing mode, 11 patients chose DDDR, 8 patients chose AAIR. Hence, AAIR and DDDR pacing seem to be equally effective in BTS patients. In view of a considerable rate of high degree AV block during AAIR pacing, DDDR mode should be preferred for safety reasons.     

Contribution of Atrioventricular Synchrony to Left Ventricular Systolic Function in a Closed-Chest Canine Model of Complete Heart Block: Implications for Single-Chamber Rate-Variable Cardiac Pacing

This study assessed the impact of atrioventricular (AV) synchrony on characteristics of left ventricular (LV) systolic function during ventricular pacing over a wide heart rate range in a conscious closed-chest canine model of complete AV block. Ten healthy adult dogs underwent thoracotomy during which complete AV block was created by formaldehyde injection, and paired ultrasonic sonomicrometers were positioned on the LV anterior-posterior minor axis. Following recovery from surgery, peak and end-diastolic LV transmural pressure, maximum dP/dt, stroke work, end-diastolic minor axis dimension, and maximum velocity of shortening, were quantitated at heart rates of 80, 100, 120, 140, and 160 beats per minute (bpm) during both ventricular pacing alone and AV sequential pacing with increasing AV intervals (0, 50, 100, 150, 200, 250, and 300 ms). Over the heart rate range tested, parameters of LV systolic function did not differ significantly during ventricular pacing with or without AV synchrony. For example, during ventricular pacing alone maximum LV dP/dt varied from 2110 +/- 70 mmHg/s to 2463 +/- 567 mmHg/s, a range essentially identical to that observed in the presence of AV synchrony. On the other hand, although the impact on LV performance of varying AV interval from 0 to 300 ms was small, differences tended to become more pronounced at higher pacing rates. At 80 bpm, neither stroke work nor maximum LV dP/dt were affected by change in AV interval, while at heart rates greater than or equal to 120 bpm both stroke work and LV dP/dt tended to maximize at AV intervals of 50 and 100 ms and thereafter declined.(ABSTRACT TRUNCATED AT 250 WORDS)     

AV conduction with atrial rate adaptive pacing in the bradycardia tachycardia syndrome

AV conduction with atrial rate adaptive pacing (AAIR) during exercise was investigated in 43 patients (28 men, 15 female, mean age 68 +/- 7 years) who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome (BTS). 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 (R) with maximum AAI pacing rate (Fmax) achieved below the Wenckebach point (SQ-R-Fmax). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol, and AAI pacing rate was increased stepwise by programming load-adapted increments. Seven patients showed intrinsic rhythm during exercise. In those 36 patients who were atrially paced throughout ergometry (E), SQ was measured with 70 beats/min on the lowest CAEP stage (SQ-E-70) and with Fmax at maximum work load (SQ-E-Fmax). During exercise, no second-degree AV block was observed, but 28 of 36 patients (78%) showed a nonphysiological increase of the SQ interval, and the average SQ-E-Fmax was significantly longer than SQ-E-70 (250 +/- 31 versus 228 +/- 32 ms, P < 0.01). There was only a weak correlation between SQ-R-Fmax and SQ-E-Fmax (r = 0.35824, P < 0.05). When Fmax obtained during exercise was kept during recovery, 14 patients (39%) developed a second-degree AV block between 15 and 240 seconds after ergometry, 8 patients within 90 seconds. Patients who had exhibited a P on T wave in the ECG with Fmax at the end of exercise (11 of 36 patients) were reevaluated by Doppler echocardiography. Using the same exercise protocol and identical, load-adapted rate increments, only 3 of 11 patients showed premature mitral valve closure. It is concluded that patients paced and medicated for BTS are prone to a nonphysiological prolongation of AV conduction with AAIR pacing during and after exercise. As this risk can hardly be predicted by rapid atrial pacing at rest, the pacing system should be dual chamber in this subset of patients. This especially applies to the patients in whom mechanical AV timing is affected by the conduction delay.     

Diagnostic Value of Synchronized Transesophageal Atrial Pacing

Synchronized transesophageal atrial pacing (single and double extrastimuli) was used in 137 patients with various tachycardias inducible by atrial pacing during transesophageal electrophysiological study (EPS). This pacing mode in five patients initiated atrioventricular tachycardias with ipsilateral bundle branch block not seen when using other pacing modes. During the tachycardia, single or double extrastimuli caused ipsilateral bundle branch block disappearance in two patients with atrioventricular tachycardia, and changed AV activation ratio in one patient with atrioventricular junctional reentrant tachycardia. This pacing mode causes very little discomfort, what is important in children, and enhances diagnostic abilities of transesophageal EPS. So, this pacing mode should be used routinely as one of the steps of transesophageal EPS.     

Experience and Implantation Techniques with a New Single-Pass Lead VDD Pacing System

Thirty-six patients were implanted with a single-lead atrial-synchronous ventricular pacing (VDD) system at our center in the first and second phases of a clinical trial between October 1987 and December 1989. The clinical system comprised a pulse generator in conjunction with a pacing lead incorporating two diagonal atrial bipolar (DAB) electrodes designed to lie in the mid-to upper-right atrium and a distal tip electrode for ventricular pacing and sensing. Twenty five of the patients had complete heart block, ten had second-degree block, and one had AV nodal block. A modified Bruce protocol limiting treadmill speed to 1.7 miles per hour was used to establish sinus node competency as evidenced by sustained sinus rate increase in a more-or-less linear fashion. The mean acute P wave amplitude measured at implant was 1.66 mV +/- 1.04 SD; the mean P wave amplitude (minimum and maximum, both sitting and supine) for all patients at all follow-up (N = 420) was 1.54 mV +/- 0.9 SD. The follow-up interval for all patients ranged from a minimum of 13 days and a maximum of 762 days, with a mean of 261 +/- 206 days as of December 1, 1989. Four dislodgments of the ventricular electrode occurred with the more pliable of two passive fixation mechanisms used on the lead; atrial sensing remained intact at all times with both fixation systems. Changes in atrial sensing threshold were quite frequent during the early follow-up visits due to electrode movement in the right atrium; however, adequate ventricular tracking of the atrial rate was achieved in all cases once the threshold values were established initially, even though several patients required atrial sensing of 0.2 mV at some of the follow-up visits. Two patients presented with pacemaker-mediated tachycardia associated with retrograde conduction, which was resolved with reprogramming; they are presently maintaining atrial synchrony in the VDD mode. Successful single-lead VDD pacing with consistent P wave sensing has been achieved with this atrial rate responsive system.     

Twin AV node and induced supraventricular tachycardia in Fontan palliation patients

INTRODUCTION: The coexistence of two distinct atrioventricular (AV) nodes has been described in congenital heart disease requiring Fontan type palliation. The purpose of this study was to evaluate the occurrence of twin AV node according to anatomical subgroups, and to determine its relation to tachycardia. METHODS: From 2001 to 2003, we performed an electrophysiologic (EP) study upon 52 consecutive patients who had undergone cardiac catheterization after Fontan completion. Atrial pacing was performed at three or more different atrial sites. RESULTS: In 10/52 patients, two different QRS complexes were recorded at different pacing sites, suggesting twin AV node (9/20 in right isomerism, 1/8 discordance AV connections, 0/24 other complex anomalies). AV reciprocating tachycardia (AVRT), presumably involving two AV nodes and a connecting sling, was induced in 6 of 10 patients who had twin AV node (4/6 used posterior AV node as an antegrade limb, 2/6 used an anterior AV node as an antegrade limb). Heterotaxy syndrome (P < 0.001) and complete AV septal defect (P = 0.002) were found to be risk factors for twin AV node. Junctional tachycardia (JT; HR > 150/min) with either VA dissociation (7/9) or second degree VA block (2/9) were induced by pacing or isoproterenol infusion in 9/52 patients. CONCLUSION: JT induction was associated with a twin AV node (P = 0.04), or a history of early postoperative junctional ectopic tachycardia (P = 0.02). A complicated AV node conduction system such as twin AV node was frequent in heterotaxy syndrome. Both AVRT and JT with VA block may be important causes of tachyarrhythmia in this patient group.     

Hemodynamic effect of the ventricular pacing site in fetal lambs with complete atrioventricular block

Complete atrioventricular (AV) block in hydrops fetalis is associated with high mortality. Fetal ventricular pacing to restore ventricular rate can be an effective procedure, however, no fetal data has shown an appropriate epicardial ventricular pacing site. To evaluate the hemodynamic effect of right and left ventricular pacing in fetal lambs with complete AV block, a fetal complete AV block model was created. Aortic pressure, central venous pressure, and QRS duration were measured, and right and left ventricular output was estimated in seven fetal lambs. The uterus was opened under maternal anesthesia, and under local anesthesia, catheters were inserted into the fetal superior vena cava and ascending aorta through a neck incision. Pacing leads were then sutured onto the fetal right and left ventricular epicardium via a midline thoracotomy. Complete AV block was created by cryoablation of the AV node. Ventricular output was estimated using echocardiography by a transuterine approach. Fetal hemodynamics were observed before AV block creation (control), and after complete AV block creation with the right and left ventricular pacing set at 150/min. The right ventricular output was 320 +/- 66 mL/kg per minute at control, decreased to 243 +/- 65 mL/kg per minute during right ventricular pacing (P < 0.05), and was 254 +/- 61 mL/kg per minute during left ventricular pacing. The left ventricular output was 224 +/- 98 mL/kg per minute at control, 176 +/- 77 mL/kg minute during right ventricular pacing, and 178 +/- 67 mL/kg per minute during left ventricular pacing. Biventricular (combined ventricular) output was 544 +/- 134 mL/kg per minute at control, 419 +/- 114 mL/kg per minute during right ventricular pacing, and 432 +/- 100 mL/kg minute during left ventricular pacing. Systolic aortic pressure was 62.2 +/- 8.7 mmHg at control, 55.2 +/- 9.5 mmHg during right ventricular pacing, and 53.4 +/- 9.1 mmHg during left ventricular pacing. Central venous pressure (CVP) was 2.6 +/- 0.5 mmHg at control, 4.0 +/- 2.7 mmHg during right ventricular pacing, and 4.4 +/- 2.5 mmHg during left ventricular pacing. The QRS duration was 51 +/- 54 ms at control, but lengthened to 87 +/- 19 ms during right ventricular pacing and to 78 +/- 21 ms during left ventricular pacing (P < 0.05). In conclusion, the right ventricular output decreased during right ventricular pacing in fetal lambs with complete AV block, while it was preserved during the left ventricular pacing. Left ventricular pacing might be superior for treating hydropic fetuses with complete AV block.     

Invasive optimization of cardiac resynchronization therapy: role of sequential biventricular and left ventricular pacing

BACKGROUND: Aim of this invasive study was to characterize and quantify changes in left ventricular (LV) systolic function due to sequential biventricular pacing (BV) as compared to right atrial triggered simultaneous BV (BV(0)), LV, and right ventricular (RV) pacing in patients with congestive heart failure (CHF). METHODS: In 22 CHF patients, all in sinus rhythm, temporary multisite pacing was performed prior to implantation of a permanent system. LV systolic function was evaluated invasively by the maximum rate of LV pressure increase (dP/dt(max)). Sequential BV pacing was performed with preactivation of either ventricle at 20-80 ms. RESULTS: In comparison to RV pacing, LV and BV(0) pacing increased dP/dt(max) by 33.9 +/- 19.3% and 34.0 +/- 22.6%, respectively (P < 0.001). In 9 patients, optimized sequential BV pacing further improved dP/dt(max) by 8.5 +/- 4.8% compared to BV(0) (range 3.3-17.1, P < 0.05). In 10 patients exhibiting a PR interval < or =200 ms, LV pacing was either superior (n = 6) or equal to BV(0) pacing (n = 4). In these 10 patients, LV pacing yielded a 7.4 +/- 8.0% higher dP/dt(max) than BV(0) pacing (P < 0.05). CONCLUSIONS: Using sequential BV pacing, generally with LV preactivation, moderate improvements in LV systolic function can be achieved in selected patients. Baseline PR interval may aid in the selection of the optimum cardiac resynchronization therapy (CRT) mode, favoring LV pacing in patients with a PR interval < or =200 ms.     

Evaluation of atrial conduction time at various sites of right atrial pacing and influence on atrioventricular delay optimization by surface electrocardiography

Cardiac function and electrical stability may be improved by programming of optimal AV delay in DDD pacing. This study tested the hypothesis if the global atrial conduction time at various pacing sites can be derived from the surface ECG to achieve an optimal electromechanical timing of the left heart. Data were obtained from 60 patients following dual chamber pacemaker implantation. Right atrial septal pacing was associated with significantly shorter atrial conduction time (P < 0.0005) and P wave duration (P < 0.005), compared to standard right atrial pacing sites at the right atrial appendage or at the right free wall. The last two pacing sites showed no significant difference. In a group of 31 patients with AV block, optimal AV delay was achieved by programming a delay of 100 ms from the end of the paced P wave to peak/nadir of the paced ventricular complex. Optimization of AV delay resulted in a relative increase of echocardiographic stroke volume (SV) (10.9 +/- 13.7%; 95% CI: 5.9-15.9%) when compared to nominal AV delay (170 ms). Optimized AV delay was highly variable (range 130-250 ms; mean 180 +/- 35 ms). The hemodynamic response was characterized by a weak significant relationship between SV increase and optimized AV delay (R2 = 0.196, R = 0.443, P = 0.047). The study validated that septal pacing is advantageous for atrial synchronization compared to conventional right atrial pacing. Tailoring the AV delay with respect to the surface ECG improved systolic function significantly and was superior to nominal AV delay settings in the majority of patients.     

Pacing Techniques in the Prophylaxis of Junctional Reentry Tachycardia

Atrial premature beats (APBs) which encounter sufficient AV delay may initiate junctional reentry tachycardia (JRT). This form of initiation may be prevented by rendering part of the reentry circuit refractory by artificial stimulation following an APB which would otherwise initiate JRT. Two such approaches have been suggested: preexcitation pacing, that is, ventricular stimulation with a short AV delay triggered by atrial depolarization; and preemptive pacing, which consists of early atrial stimulation coupled to the initiating APB. We compared these approaches and describe them as follows. Ten patients with JRT (six with atrioventricular reentry and four with AV nodal reentry) were studied. Against a background of regular atrial drive, the range of coupling intervals over which a stimulated APB initiated JHT (tachycardia initiation window) was determined (control). The tachycardia initiation window was also measured when a second atrial stimulus followed the initiating APB 20 ms after atrial recovery (preemptive pacing) or when a ventricular stimulus closely followed the initiating APB with an AV delay of 65 ms (preexcitation pacing). The tachycardia initiation window in response to an isolated APB was also assessed following regular AV pacing with a short (65 ms) AV delay (preconditioning pacing) and the effect of preexcitation pacing following the initiating APB was also assessed after a similar drive (combined preconditioning and preexcitation pacing). All protocols were performed at two basic drive cycle lengths. The results are arranged for the slow and fast drives, respectively, and were as follows: control initiating windows—49.5, 28.5 ms; preemptive pacing initiation windows—151, 38 ms; preexcitation pacing initiation windows—26, 23.5 ms; preconditioning pacing initiation windows—45.5, 35 ms; combined preconditioning and preexcitation pacing initiation windows—10.0, 2.5 ms. Whereas preemptive pacing tended to widen the tachycardia initiation windows (a proarrhythmic effect) the combination of preconditioning and preexcitation pacing considerably reduced the possibility of JRT initiation by an atrial premature beat.     

Electrophysiological Significance of QRS Alternans in Narrow QRS Tachycardia

To investigate the electrophysiological significance of QRS alternans during narrow QRS tachycardia, transesophageal atrial pacing and recording was performed in 24 patients with a history of paroxysmal supraventricular tachycardia. Standard electrocardiograms showed ventricular preexcitation in 15 patients and normal QRS pattern in nine patients. The ventriculoatrial interval during tachycardia, as defined by means of transesophageal electrogram, allowed tentative diagnosis of the tachycardia mechanism. A 12-lead ECG was recorded either during spontaneous or induced tachycardia, as well as during transesophageal atrial pacing at increasing rates. Electrical alternans occurred spontaneously in eight patients (33%, group A): five with accessory pathway reentry (mean VA: 136 +/- 43 msec), and three with AV nodal reentry (mean VA: 48.3 +/- 12 msec). Tachycardia rate ranged between 170 and 230 beats/min (mean 200.7 +/- 16). In two patients, alternation of the QRS occurred only in the presence of a heart rate exceeding 180 and 190 beats/min, respectively. The amplitude of QRS remained stable during tachycardia in 16 patients (67%, group B): 14 had accessory pathway reentry (mean VA: 137.5 +/- 32 msec), and two had AV nodal reentry (mean VA: 45 +/- 7 msec). In this group, the tachycardia rate ranged from 150 to 210 beats/min (mean 175 +/- 12). Incremental transesophageal atrial pacing up to rates equal to that of tachycardia was performed in five patients from group A and in five patients from group B. Electrical alternans could not be induced in both groups with pacing at progressively increasing rates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Permanent left atrial and left ventricular single-lead DDD pacing with a coronary sinus electrode

This report describes a patient with drug refractory severe chronic congestive heart failure, first-degree AV block, and wide QRS complexes of 175-ms duration with left bundle branch block who was successfully treated by a left-sided dual chamber pacemaker system using a single-lead coronary sinus electrode. Left atrial and ventricular signal amplitudes, left atrial and ventricular pacing thresholds were 2.5 mV, 13 mV, 1.8 V and 0.7 V (0.5 ms), respectively. Using DDD pacing with an optimal 120-ms AV delay the QRS duration decreased to 150 ms and the mitral filling pattern improved. Three months after implantation the patient's functional status improved from NYHA Class III-IV to Class II.     

Single Lead VDD Pacing: Multicenter Study

Optimal treatment for patients with AV block and normal sinoatrial node (SA) function entails atrial sensing and ventricular pacing (VDD mode). Single-lead VDD pacing preserves AV synchrony, precludes the need to insert two leads, and makes the implanter's work simpler and quicker. Our objectives were to verify the performance of the Thera(tm) VDD pacing system (Medtronic, Inc., Minneapolis, MN, USA), and evaluate the effectiveness of its atrial sensing and its ventricular sensing and pacing. In 165 patients, 150 adults (mean age 62 ± 18 years) and 15 children (mean age 7 ± 5 years) with 1°–3° AV block and normal SA node function, a Thera VDD system (Models 8948 or 8968) was implanted. Intraoperative ventricular electrical measurements were not significantly different from those of VVI pacemakers. The mean amplitude of the atrial signal during implantation was 4.1 ± 1.9 mV. Optimal atrial signals during implantation were usually obtained in the mid or lower part of the right atrium by using a special technique. Adequate atrial measurements remained stable throughout 24 months. There was no difference between serial measurements of atrial signal amplitudes at predischarge and during follow-up visits. Reposition of the lead was done in 2 patients (1.4%), and reprogramming to VVI in 7 patients: due to atrial fibrillation in 3 (1.8%) and due to atrial undersensing in 4 patients (2.4%). Thera VDD pacing is reliable and easy to manage with dependable atrial sensing and ventricular pacing. The survival rate of VDD pacing at 2 years was 96%.