Hemodynamic and symptomatic consequences of ventricular pacing

After implantation of a ventricular demand pacemaker (VVI), occasional patients continue to have dizziness, syncope, or near syncope ("pacemaker syndrome"). To identify patients in whom VVI pacing may have deleterious effects, we compared cuff blood pressure responses to VVI pacing with blood pressure responses to atrioventricular sequential pacing (DVI) or sinus rhythm in 50 consecutive patients. Patients with intact ventriculoatrial conduction had a much greater decrease in systolic blood pressure with VVI pacing (24 +/- 11 mm Hg) than those with ventriculoatrial dissociation (-4 +/- 15 mm Hg) (P less than 0.005). Patients who were in heart failure had a lesser decrease in blood pressure with VVI pacing than did those without failure (P less than 0.05); 13 of the 14 heart failure patients lacked ventriculoatrial conduction. Ten patients had symptomatic dizziness after VVI pacing; the incidence of symptoms was higher in patients with ventriculoatrial conduction (9 of 23) than in those without ventriculoatrial conduction (1 of 27) (P less than 0.003). We conclude that the presence of intact ventriculoatrial conduction appears to be a crucial determinant of the hemodynamic response to VVI pacing, and its presence may identify patients who are at risk for "pacemaker syndrome."     

Assessment of the Work Capacity and Relationship Between Rate Response and Exercise Tolerance Associated With Activity-Sensing Rate-Responsive Ventricular Pacing

The relationship between rate response and exercise tolerance was studied by measuring the symptom-limited maximum treadmill time (MTT)both during fixed rate VVI pacing and during VVI + activity mode pacing (RRP) in 15 patients (mean age, 73 years) who had received rate-responsive ventricular pacemakers. Their indications were atrioventricular block, sino-atrial block, and atrial fibrillation with slow ventricular response. Basic rate was programmed to 60 ppm in both pacing modes; rate response and activity threshold were programmed to 5 and medium, respectively. The order in which the two pacing modes were tested was randomly determined. The MTT was, on average, 29% longer in RRP than in VVI mode with a mean of 12 minutes in VVI and 14.8 minutes in RRP (p less than 0.001). For the subgroup of eight patients with paced-only rhythm the average increase in MTT was 38% with a mean of 9.5 minutes in VVI and 12.8 minutes in RRP (p less than 0.01). Seven patients who showed episodes of spontaneous rhythm, increased their average MTT by 17% (mean in VVI, 14.9 minutes; in RRP, 17.1 minutes; p less than 0.02). During RRP, a significant positive correlation existed between MTT and the increase in heart rate (N = 15; r = 0.83; p less than 0.001). In 12 patients with paced-only rhythm, the pacing rate remained at the programmed basic rate when the patients were lying, sitting, and standing and increased to 86 +/- 4 ppm during casual walking, and to 101 +/- 4 ppm during jumping up and down with the pacemaker programmed to the above-mentioned parameters. The maximum pacing rate during jumping corresponded with the maximum pacing rates measured from Holter recordings during normal daily activities.     

Efficacy and Safety of Rate Responsive Pacing in Patients with Coronary Artery Disease and Angina Pectoris

The present study included 17 patients with angina pectoris and coronary artery disease in whom a rate responsive ventricular pacemaker (Medtronic Activitrax) had been implanted. All patients had an exclusively paced rhythm. Single blinded, random, cross-over treadmill tests in the rate responsive pacing mode (VVIR) and in the fixed-rate demand mode (VVI) were performed, with an interval of 4-6 weeks. Mean exercise duration increased by 25% during VVIR pacing. Maximal heart rate increased significantly during VVIR compared to VVI pacing (VVI = 74 +/- 2 bpm, VVIR = 116 +/- 8 bpm, P less than 0.001) as did the rate-pressure product (VVI = 10.850 +/- 1,124, VVIR = 16.628 +/- 2,110, P less than 0.001). Despite improved performance, the number of anginal attacks per week and the nitroglycerin consumption did not show a significant difference between the two pacing modes. It is concluded that rate responsive pacing is beneficial and safe in patients with angina pectoris and coronary artery disease.     

Effect of right ventricular apex pacing on the Tei index and brain natriuretic peptide in patients with a dual-chamber pacemaker

BACKGROUND: Asynchronous electrical activation induced by right ventricular apex (RVA) pacing can cause various abnormalities in left ventricular (LV) function, particularly in the context of severe LV dysfunction or structural heart disease. However, the effect of RVA pacing in patients with normal LV and right ventricular (RV) function has not been fully elucidated. The aim of this study was to characterize the effects of RVA pacing on LV and RV function by assessing isovolumic contraction time and isovolumic relaxation time divided by ejection time (Tei index) and by assessing changes in plasma brain natriuretic peptide (BNP). METHODS: Doppler echocardiographic study and BNP measurements were performed at follow-up (mean intervals from pacemaker implantation, 44+/-75 months) in 76 patients with dual chamber pacemakers (sick sinus syndrome, n=30; atrioventricular block, n=46) without structural heart disease. Patients were classified based on frequency of RVA pacing, as determined by 24-hour ambulatory electrocardiogram (ECG) that was recorded just before echocardiographic study: pacing group, n=46 patients with RVA pacing>or=50% of the time, percentage of ventricular paced 100+/-2%; sensing group, n=30, patients with RVA pacing<50% of the time, percentage of ventricular paced 3+/-6%. RESULTS: There was no significant difference in mean heart rate derived from 24-hour ambulatory ECG recordings when comparing the two groups (66+/-11 bpm vs 69+/-8 bpm). LV Tei index was significantly higher in pacing group than in sensing group (0.67+/-0.17 vs 0.45+/-0.09, P<0.0001), and the RV Tei index was significantly higher in pacing group than in sensing group (0.34+/-0.19 vs 0.25+/-0.09, P=0.011). Furthermore, BNP levels were significantly higher in pacing group than in sensing group (40+/-47 pg/mL vs 18+/-11 pg/mL, P=0.017). With the exception of LV diastolic dimension (49+/-5 mm vs 45+/-5 mm, P=0.012), there were no significant differences in other echocardiographic parameters, including left atrium (LA) diameter (35+/-8 mm vs 34+/-5 mm), LA volume (51+/-27 cm3 vs 40+/-21 cm3), LV systolic dimension (30+/-6 mm vs 29+/-7 mm), or ejection fraction (66+/-9% vs 63+/-11%), when comparing the two groups. CONCLUSIONS: These findings suggest that the increase of LV and RV Tei index, LVDd, and BNP are highly correlated with the frequency of the RVA pacing in patients with dual chamber pacemakers.     

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.     

Maintenance of Atrioventricular Sequence After His-Bundle Ablation for Paroxysmal Supraventricular Rhythm Disorders: A Unique Use of the Fallback Mode in Dual Chamber Pacemakers

The usual mode of controlling ventricular rate after His-bundle ablation is placement of a ventricular demand rate responsive pacemaker. Atrioventricular synchrony is therefore lost in individuals whose atrial rhythm disturbances are paroxysmal. Thirty-seven His ablations were performed at this institution, since January of 1983, for atrial rhythm disturbances that were not suppressible with medical therapy alone. Of those, ten patients were identified whose atrial rhythm disturbances were intermittent and who would otherwise benefit by having proper atrioventricular sequence during sinus rhythm. These patients underwent placement of a dual chamber pacemaker system having a fallback mode. At a mean follow-up period of 17 +/- 11 months, eight patients continued to maintain proper atrioventricular sequence with ventricular pacing tracking atrial activation during sinus rhythm. Supraventricular tachyarrhythmic attacks were associated with attainment of the programmed upper rate limit at which time the fallback mode was activated and the pacemaker automatically converted to a ventricular demand (VVI) mode. Restoration of normal sinus rhythm was associated with restoration of proper atrioventricular sequence. Two patients have developed chronic atrial fibrillation and their pacemakers continue to function in the fallback mode as VVI devices. In conclusion, intermittent supraventricular tachyarrhythmias which are resistant to drug therapy can be treated with His ablation and dual chamber pacing utilizing special pacemaker features such as the fallback mode.     

Development of a Rate Adaptive Pacemaker Based on the Maximum Rate-of-Rise of Right Ventricular Pressure (RV dP/dtmax)

The maximum rate of rise of right ventricular pressure (RV dP/dtmax) may change in response to physiological stress and thereby provide an appropriate parameter upon which to base rate adaptive pacing. Initial feasibility testing was carried out in six patients using externally closed loop rate adaptive pacing with a pressure sensing lead (Model 6220) and an investigational VVI pulse generator (Medtronic, Model 2451). During exercise, maximum positive RV dP/dtmax increased from 223 +/- 55 to 405 +/- 181 mmHg.sec.1 (P less than 0.05). Based on these results, rate adaptive pulse generators using maximum positive RV dP/dt were implanted in 12 patients (Medtronic, Model 2503). Exercise treadmill testing in the VVI mode resulted in heart rates ranging from 69 +/- 6 beats/min at rest to 79 +/- 14 beats/min (n = 12; P greater than 0.05). In contrast, VVIR mode pacing rates ranged from 71 +/- 11 beats/min to 115 +/- 24 beats/min (n = 17; P less than 0.05). Holter recording showed heart rates ranging from 51 +/- 6 to 110 +/- 22 beats/min during activities of normal daily living (n = 9; P less than 0.05). Passive postural tilt resulted in rates of 69 +/- 8 beats/min in the supine position increasing to 74 +/- 14 beats/min with 60 degrees upright tilt (n = 16; P greater than 0.05). With up to 5-year follow-up data, there have been no late failures of pacing but one lead showed insulation failure with over- and undersensing after 4.5 years. A number of deficiencies were identified in the prototypes leading to modifications of a subsequent generation of rate responsive pacemaker based on RV dP/dtmax. These initial data demonstrate that rate adaptive pacing based on RV dP/dtmax responds in a physiological manner. This rate responsive system is of particular interest as it is based on a beat-to-beat parameter of cardiac mechanical function.     

Importance of Heart Rate Response During Exercise in Patients Using Atrioventricular Synchronous and Ventricular Pacemakers

Atrioventricular synchronous pacing offers advantages over fixed-rate ventricular (VVI) pacing both at rest and during exercise. This study compared the hemodynamic effects at rest and exercise of ventricular pacing at a rate of 70 beats/min, ventricular pacing where the rate was increased during exercise and dual chamber pacing. Ten patients, age 63 +/- 8 years, with multiprogrammable DDD pacemakers were studied using supine bicycle radionuclide ventriculography. Radionuclide data during dual chamber pacing was acquired at rest and during a submaximal workload of 200-400 kpm/min. The pacemakers were then programmed to VVI pacing at a rate of 70 beats/min, and 1 week later, studies were repeated in the VVI mode at rest, during exercise at a rate of 70 beats/min, and during exercise with the VVI pacemaker programmed to a rate adapted to the DDD pacing exercise rate. At rest, the cardiac output was lower in the VVI compared with the AV sequential mode (4.1 +/- 1.1 vs 5.7 +/- 1.1 1/min, P less than 0.01). During exercise, the cardiac output increased from resting values in the DDD and VVI pacing modes, however cardiac output in the rate-adapted VVI mode was higher than in the VVI mode with the rate maintained at 70 beats/min (8.1 +/- 1.5 vs 6.3 +/- 1.1 1/min, P = 0.02). Three patients completed lower workloads with VVI pacing at 70 beats/min compared with AV synchronous pacing. At rest, AV sequential pacing was superior to VVI pacing, suggesting the importance of the atrial contribution to ventricular filling. With VVI pacing during exercise, cardiac output was improved with an increased pacemaker rate, suggesting that the heart rate response during exercise was the major determinant of the higher cardiac output.     

Comparative Functional Effects of Chronic Ventricular Demand and Atrial Synchronous Ventricular Inhibited Pacing

We compared the effects of chronic ventricular inhibited (VVI) and atrial synchronous ventricular inhibited (VDD) pacing on functional capacity in 8 patients with complete atrioventricular heart block. Permanent VDD (Medtronic #2409, ASVIP) pacemakers were implanted in four men and four women (age range 27-76 years, mean 58.9 +/- 18.4 years), and randomly assigned to a three-month period of VDD or VVI pacing in this single blinded, crossover study. Functional capacity was assessed by questionnaire, graded treadmill exercise testing and radionuclide angiocardiography prior to pacemaker implant and following each pacing period. Following 3 months of pacing in each of VVI and VDD pacing modes, maximum heart rate (83.4 +/- 14 vs 134.9 +/- 16.4 beats/min, p less than 0.001) and double product (147.5 +/- 58.3 vs 218.9 +/- 52.7, p less than .001) were greater with VDD pacing. Although exercise duration on treadmill exercise testing (5.3 +/- 2.9 vs 6.9 +/- 3.1 minutes, p less than 0.1) was greater in the VDD mode, the difference was not significant. Similarly, there was no significant difference in functional capacity as measured by questionnaire scores (50.1 +/- 8.4 vs 46.9 +/- 8.9, p less than 0.1) or in left ventricular ejection fraction for the two pacing modes (.54 vs .55, p less than .5). Only one patient reported a subjective improvement with physiologic (VDD) pacing, whereas the remaining patients stated no preference. We conclude that VDD pacing offers improved maximal cardiac work during exercise compared to VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Comparative Evaluation of a Minute Ventilation Sensing and Activity Sensing Adaptive-Rate Pacemakers During Daily Activities

Most studies evaluating the rate response of adaptive-rate pacemakers have been based on treadmill or bicycle exercise. These studies disregard the fact that few pacemaker recipients voluntarily undertake such activities. The rate responses of nine patients (mean age 62 years, range 33-79 years) with implanted minute ventilation sensing (Meta) pacemakers were studied. The indications for pacing were complete heart block (seven patients), sick sinus syndrome (one patient), and five nodal disease (one patient). Significant improvement in maximum distance covered during a 12-minute walking test was observed in the rate adaptive compared to the VVI pacing mode (989 +/- 104 vs 921 +/- 90 m, P less than 0.02). The rate responses of this pacemaker during daily activities were recorded with telemetry during a variety of structured daily activities. The rate responses were also compared to those of an externally attached Activitrax pacemaker in each patient and to a group of ten age and sex matched volunteers. For less strenuous activities such as walking, descending stairs, washing, and bed making, both pacemakers achieved adequate rate responses compared to normal subjects. For more strenuous activities, the Activitrax pacemaker failed to achieve an adequate rate response. For example, the pacing rate achieved on ascending stairs was lower than that achieved on descending stairs (92 +/- 3 vs 102 +/- 3 bpm, P less than 0.02). The direction of rate responses was more appropriate for the Meta pacemaker. Similar to the normal subjects, the maximum rate was reached before the end of an activity with the Activitrax pacemaker.(ABSTRACT TRUNCATED AT 250 WORDS)     

QT Sensing Rate Responsive Pacing Compared to Fixed Rate Ventricular Inhibited Pacing: A Controlled Clinical Study

Eighteen patients, five women and 13 men, (mean age 70 +/- S.E.M. 2 years) treated with QT sensing rate responsive pacemakers due to symptomatic high degree AV block took part in a double-blind study, comparing the rate responsive (TX) mode with fixed rate ventricular inhibited (VVI) pacing. The pacemaker was blindly programmed to either mode in a cross-over design. During the 1 month period a daily diary of symptoms (chest pain, vertigo, dyspnea, and palpitations) was kept. At the end of each period, a mental stress test and an exercise test were performed. The patient rated the general well-being and stated a preference for one of the modes. In the TX mode the heart rate was significantly higher at the end of exercise compared with VVI (107 +/- 4 vs 73 +/- 3 bpm; P less than 0.001) and the exercise tolerance was improved by 9% (104 +/- 8 vs 96 +/- 7 W; P less than 0.01). The patients reported significantly less dyspnea and fatigue at comparable workloads with TX pacing. During the mental stress test the pacing rate increased by 10% in the TX mode (from 73 +/- 2 to 82 +/- 4 bpm; P less than 0.001). There was a physiological rate variability on 24-hour Holter monitoring. Ten patients reported a significant improvement in feeling of general well-being in the TX mode. Eleven patients preferred the TX mode, five patients could not distinguish between the modes and two patients preferred the VVI mode due to worsening of angina pectoris with TX pacing. This preference for the TX mode was significant (P less than 0.05). The results of this controlled study indicate that TX is preferable to VVI in most cases, but the worsening of angina pectoris in two of the patients and the occurrence of rapid rate oscillations in a third patient are factors that warrant some caution in selecting patients.     

Comparison of Normal Sinus Rhythm and Pacing Rate in Children with Minute Ventilation Single Chamber Rate Adaptive Permanent Pacemakers

Rate adaptive pacemakers are used to achieve a better cardiac performance during exercise by increasing the heart rate and cardiac output. The ideal rate adaptive sensor should be able to mimic sinus node modulation under various degrees of exercise and other metabolic needs. Minute ventilation sensing has proven to be one of the most accurate sensor systems. In this study, alterations in sinus rhythm and pacing rates during daily life conditions in 11 children (median age 11 years, range 6–14 years) with minute ventilation single chamber pacemakers were investigated. Correlation of sinus rhythm with pacing rates was assessed. ECG records were obtained from 24–hour Holter monitoring. Average rates of five consecutive P waves and pace waves were determined every half hour. The average of the two values was then used to determine hourly rates. Correlation coefficients between the sinus rhythm and pacing rates were calculated. In nine patients, pacing rates correlated well to sinus rhythm (range 0.6793–0.9558. P < 0.001 and P < 0.05), whereas in two cases correlation was not sufficient (P > 0.05). Most of the patients, in whom rate response factor (RRF) measurements during peak exercise by treadmill with cnronotropic assessment exercise protocol were performed and pacemakers were programmed to these parameters, had more appropriate ventricular rates compared to spontaneous sinus rates. In these patients mean RRF value was 15.3 ± 2.7 (range 12–20, median 15). This study shows that during daily activities minute ventilation rate adaptive pacemakers can achieve pacing rates well correlated to sinus rhythm that reflects the physiological heart rate in children.     

Long-term complication rates in ventricular, single lead VDD, and dual chamber pacing

A higher incidence of pacemaker related complications has been reported in DDD systems as compared to VVI devices. The implantation of single lead VDD pacemakers might reduce the complication rate of physiological pacing in patients with AV block. In a retrospective study, the data records of 1,214 consecutive patients with pacemaker implantation for AV block between 1990 and 2001 (VVI 36.5%, DDD 32.9%, VDD 30.6%) were analyzed. Complications requiring surgical interventions were compared during a follow-up period of 64 +/- 31 months. Operation and fluoroscopic times were longer in DDD pacemaker implantation compared to VDD and VVI devices:58 +/- 23 versus 39 +/- 10 and 37 +/- 13 minutes (P<0.001), 9.2 +/- 5.2 versus 4.1 +/- 2.4 and 3.5 +/- 2.3 minutes, respectively. Differences remained significant after correction for covariates. In a multivariate Cox regression model, the corrected complication hazard of a DDD pacemaker implantation was increased by 3.9 (1.4-11.3) compared to VVI and increased by 2.3 (1.1-4.5) compared to VDD pacing. Higher complication rates in DDD pacing were mainly due to a higher incidence of early reoperation for atrial lead dysfunction, whereas the long-term complication rate was not different from VDD or VVI pacing. Early and long-term complication rates did not differ between VDD and VVI pacemaker systems. In conclusion, operation time and complication rates of physiological pacing are reduced by VDD pacemaker implantation achieving values comparable to VVI pacing. Thus, single lead VDD pacing can be recommended for patients with AV block.     

Clinical Experience with Sensolog 703: A New Activity Sensing Rate Responsive Pacemaker

Sensolog 703 is a new activity sensing rate responsive pacemaker which detects body vibration during physical exercise and uses the vibration as an indicator of the physiological need for a rate increase. This pacemaker was implanted in 11 patients with complete heart block and atrial arrhythmias. Their mean age was 58 (range 39-72) years. With appropriate rate response, exercise capacity, as assessed by the duration of graded treadmill exercise using the Bruce protocol, was significantly improved over the VVI pacing mode (mean +/- SEM, 462 +/- 52 s in the rate responsive mode and 368 +/- 34 s in the VVI mode, P less than 0.02). Cardiac output at peak exercise, as assessed by continuous wave Doppler sampling of aortic root blood flow, was also significantly increased compared to the resting value in both piecing modes. However, the increase was more marked when exercise was performed in the rate response mode (93 +/- 22% increase over resting cardiac output in the rate responsive mode and 57 +/- 13% increase in the VVI mode, P less than 0.05). The rate responses of this pacemaker were compared with those of a Medtronic Activitrax pacemaker. Although both pacemakers responded to an increase in walking speed, neither responded appropriately to walking up different gradients, In both cases, ascending and descending four flights of stairs resulted in similar pacing rates. There was no response to physiological activities with minimal body movements such as isometric exercise and the Valsalva maneuver. Technical problems were encountered in two implanted Sensolog pacemakers: one had spontaneous rate acceleration at rest immediately following implantation and one showed intermittent rate acceleration while the patient was at rest. Both units were programmed to the VVI mode. In conclusion, satisfactory rate response, improvement in exercise duration and increase in cardiac output were achieved with the Sensolog 703 pacemaker. However, as body vibration is not closely related to physiological needs, it has similar limitations in rate response as the Activitrax pacemaker.     

Efficacy of single lead VDD pacing in patients with impaired and normal left ventricular function

Atrial synchronous ventricular pacing seems to be the best pacing mode for patients with advanced AV block and impaired LV function. The long-term follow-up of single lead VDD pacing was studied in 33 patients with impaired LV function and compared to 42 patients with normal LV function. All patients received the same VDD lead and VDDR pacemaker. The lead model with 13-cm AV spacing between the atrial and ventricular electrode was implanted in 89% of the patients. Follow-ups were 1, 3, 6, and 12 months after implantation. The percentage of atrial sensing and the P wave amplitude were determined at each follow-up. Minimal P wave amplitude at implantation was 2.0 +/- 1.4 mV in patients with impaired and 1.7 +/- 0.9 mV with normal LV function (not significant). At the 12-month follow-up, 33 patients with normal and 23 patients with depressed LV function remained paced in the VDD mode. The remaining patients died in five (impaired LV function) and seven cases (normal LV function) or their pacemakers were programmed to the VVI/VVIR pacing mode in four (impaired LV function) and three cases (normal LV function). P wave amplitude did not differ in the two groups (e.g., at month 12: impaired: 1.17 +/- 0.42 mV; normal: 1.09 +/- 0.49 mV). The atrial sensitivity was programmed in most patients to sensitive settings with no differences between the two groups (e.g., at month 12: impaired: 0.13 +/- 0.06 mV; normal: 0.13 +/- 0.05 mV). The diagnostic counters indicated nearly permanent atrial sensing (e.g., at month 12: impaired: 99.3 +/- 2.2%; normal: 99.0 +/- 1.0 mV). In conclusions, single lead VDD pacing restored AV synchronous ventricular pacing in patients with normal and with impaired LV function indicating that it could be an alternative to DDD pacemakers, but not to dual-chamber pacing.     

速度向量成像评价DDD起搏前后心室收缩功能

目的 应用速度向量成像(velocity vector imaging,VVI)技术分析DDD起搏前后心室心肌运动速度、应变、应变率变化规律,初步探讨VVI技术的应用价值.方法 对17例DDD起搏患者于术前术后采用VVI技术检测心室各节段心肌收缩期纵向运动速度、应变、应变率和径向运动速度、环向应变及应变率,并比较术前术后差异.结果 术前术后左、右心室各室壁基底段、中间段、心尖段收缩期纵向峰值运动速度依次递减,基底段的速度最大,心尖段的速度最小;收缩期纵向应变、应变率在基底段、中间段及心尖段差异无统计学意义.左心室各室壁收缩期径向峰值运动速度、环向应变及应变率差异无统计学意义.右室后间隔与游离壁术前、术后平均峰值运动速度与应变率和术后平均应变均高于左室后间隔与侧壁,术后右室平均应变及应变率均高于左室.与术前相比,术后左室平均应变显著降低.结论 VVI技术能准确地定量评价DDD术前后节段性室壁功能及其变化.     

速度向量成像评价DDD起搏前后心室收缩功能

目的 应用速度向量成像(velocity vector imaging,VVI)技术分析DDD起搏前后心室心肌运动速度、应变、应变率变化规律,初步探讨VVI技术的应用价值.方法 对17例DDD起搏患者于术前术后采用VVI技术检测心室各节段心肌收缩期纵向运动速度、应变、应变率和径向运动速度、环向应变及应变率,并比较术前术后差异.结果 术前术后左、右心室各室壁基底段、中间段、心尖段收缩期纵向峰值运动速度依次递减,基底段的速度最大,心尖段的速度最小;收缩期纵向应变、应变率在基底段、中间段及心尖段差异无统计学意义.左心室各室壁收缩期径向峰值运动速度、环向应变及应变率差异无统计学意义.右室后间隔与游离壁术前、术后平均峰值运动速度与应变率和术后平均应变均高于左室后间隔与侧壁,术后右室平均应变及应变率均高于左室.与术前相比,术后左室平均应变显著降低.结论 VVI技术能准确地定量评价DDD术前后节段性室壁功能及其变化.     

Pacemakers of the 1980s. An overview

Methods and devices for permanent cardiac pacing remained relatively stable for over two decades with use of the single-chamber ventricular demand (VVI) pacemaker. However, changes have occurred in the 1980s and are expected to continue with the availability of more advanced technology and with increasing knowledge about cardiac pacing. The physiologic benefit of the newer dual-chamber atrial synchronous (VDD) and fully automatic, universal (DDD) pacemakers over the VVI pacemaker in patients with permanent complete heart block and normal sinus node function has been established. These newer units not only reestablish atrioventricular synchrony but also are physiologically rate-responsive. The VDD pacemaker is expected to be phased out in favor of the DDD pacemaker. When the atrial rate or interval is lower than the lower rate limit, the VDD pacemaker functions as a VVI, whereas the DDD pacemaker functions as an atrioventricular sequential (DVI) pacemaker to maintain continuous atrioventricular synchrony. Contrary to general belief, patients with complete heart block and normal sinus node function may gain very little physiologic benefit, if any, from DVI pacing. The sinus node will compete with the pacemaker's atrial stimulation when the sinus rate is faster than the DVI pacemaker rate (which usually occurs during activity). Also, the ventricular pacing rate will not vary with physiologic change. The DVI and atrial demand (AAI) pacemakers have been used in some patients with sinus node dysfunction. Increasing exercise tolerance should not be expected in the majority of patients because they are not pacemaker-dependent during activity, ie, their heart rate is higher than the pacemaker rate. However, these pacemakers appear to help in eliminating pacemaker syndrome, which does not infrequently occur with VVI pacemakers. Patients with sinus node dysfunction but without atrioventricular block do not gain more physiologic benefit with a DDD than with a DVI pacemaker. Whether these patients have severe sinus node dysfunction all the time or adequate sinus node function most of the time during follow-up, the DDD pacemaker will function as a noncommitted DVI with atrial sensing (DDI). The early report of DVI pacemaker-induced atrial fibrillation during follow-up has been refuted by more recent works. If the DDD pacemaker is significantly more expensive than the DVI pacemaker, the latter type may be a good alternative for this condition.     

速度向量成像评价DDD起搏前后心室收缩功能

目的 应用速度向量成像(velocity vector imaging,VVI)技术分析DDD起搏前后心室心肌运动速度、应变、应变率变化规律,初步探讨VVI技术的应用价值.方法 对17例DDD起搏患者于术前术后采用VVI技术检测心室各节段心肌收缩期纵向运动速度、应变、应变率和径向运动速度、环向应变及应变率,并比较术前术后差异.结果 术前术后左、右心室各室壁基底段、中间段、心尖段收缩期纵向峰值运动速度依次递减,基底段的速度最大,心尖段的速度最小;收缩期纵向应变、应变率在基底段、中间段及心尖段差异无统计学意义.左心室各室壁收缩期径向峰值运动速度、环向应变及应变率差异无统计学意义.右室后间隔与游离壁术前、术后平均峰值运动速度与应变率和术后平均应变均高于左室后间隔与侧壁,术后右室平均应变及应变率均高于左室.与术前相比,术后左室平均应变显著降低.结论 VVI技术能准确地定量评价DDD术前后节段性室壁功能及其变化.     

速度向量成像评价DDD起搏前后心室收缩功能

目的 应用速度向量成像(velocity vector imaging,VVI)技术分析DDD起搏前后心室心肌运动速度、应变、应变率变化规律,初步探讨VVI技术的应用价值.方法 对17例DDD起搏患者于术前术后采用VVI技术检测心室各节段心肌收缩期纵向运动速度、应变、应变率和径向运动速度、环向应变及应变率,并比较术前术后差异.结果 术前术后左、右心室各室壁基底段、中间段、心尖段收缩期纵向峰值运动速度依次递减,基底段的速度最大,心尖段的速度最小;收缩期纵向应变、应变率在基底段、中间段及心尖段差异无统计学意义.左心室各室壁收缩期径向峰值运动速度、环向应变及应变率差异无统计学意义.右室后间隔与游离壁术前、术后平均峰值运动速度与应变率和术后平均应变均高于左室后间隔与侧壁,术后右室平均应变及应变率均高于左室.与术前相比,术后左室平均应变显著降低.结论 VVI技术能准确地定量评价DDD术前后节段性室壁功能及其变化.