Long-term evaluation of a new single lead VDD pacemaker]

Since June 1988 we have implanted 36 VDD pacemakers with single lead catheter which has floating differential sensing (Phymos). The patients were affected by 2nd and 3rd degree AV block with normal sinus node function. The reliability of the pacing system was assessed acutely and after 1 and 3 months and then every six months with ECG, Holter 24 hours monitoring, exercise stress test and nifedipine test. Two patients died during the follow-up period and two had atrial fibrillation. In the remaining patients an AV synchronization between 95 and 100% was demonstrated.     

Predictors of loss of atrioventricular synchrony in single lead VDD pacing

Objective—To evaluate maintenance of proper VDD function, defined as persistence of sinus rhythm with atrial synchronous ventricular pacing, and to define factors predicting failure of the VDD mode in patients with atrioventricular (AV) block and normal sinus function.
Design—Observational study in 86 consecutive patients (mean (SD) age 74 (12) years; 38 women, 48 men) with single lead VDD pacing systems (Intermedics Unity, n = 66, Medtronic Thera VDD, n = 20), implanted for high degree AV block with documented normal sinus node. Pacemaker function was assessed by event counters, telemetric measurements, and Holter recordings. Demographic, radiological, and pacing variables were correlated with loss of proper VDD function.
Results—During a mean (SD) follow up of 10 (10) months (range 1-37), sinus rhythm and atrial triggered ventricular pacing were maintained in 70 of 86 patients (81%). Atrial undersensing was observed in nine patients, lead migration in two, atrial fibrillation in three, and symptomatic sinus bradycardia in two. Univariate predictors of loss of proper VDD function were: low position of the atrial dipole relative to the carina ( 6 cm; p < 0.01) during fluoroscopy; and maximum programmable atrial sensitivity of the pacemaker (p = 0.03). In a multivariate analysis, only dipole position remained predictive of outcome (p < 0.02). Not predictive were sex, age, symptoms before pacemaker implantation, cardiothoracic ratio or dilatation of individual heart chambers on chest x ray, side of device implant, and P wave amplitude at implant.
Conclusions—To maintain proper VDD function in the long term, a low anatomical dipole position relative to the carina should be avoided. Electrical guidance of dipole positioning does not seem to influence long term outcome.

Keywords: VDD pacing;  atrioventricular synchrony;  arrhythmias     

老年人单导管DDD、VDD起搏系统的临床应用

目的：观察老年人单导管双腔起搏器（DDD）和心房感知型起搏器（VDD）起搏系统的临床应用。方法：18例老年人采用锁骨下静脉穿刺法植入单导管DDD和VDD起搏器,并在植入后1周,3－6月分别做动态心电图（Holter）观察,随访时间6月－4年。结果：18例患者均成功植入单导管DDD和VDD起搏系统。Holter检查显示：VDD和DDD起搏器的工作模式大多为VAT,房室同步起搏率达95％以上。结论：单导管DDD和VDD起搏系统安装简单,无心房电极脱位等优点,尤其适用于老年患者。     

单根电极导管VDD起搏系统的临床应用和随访

对１３例窦房结功能正常的高度房室传导阻滞患者植入单根电极导管ＶＤＤ起搏系统，并进行随访观察。结果显示：术中所测Ａ波平均振幅为２．４±１．４ｍＶ；随访期间（平均１１±４．９个月）Ａ波感知阈值无显著性变化（Ｐ＞０．０５），房室同步起搏率保持在１００％，无心房感知不良、肌电干扰和起搏器介导性心动过速等并发症。表明单电极导管ＶＤＤ起搏系统具有植入简便和房室同步功能稳定的特点，是高度房室传导阻滞伴窦房结功能正常者的理想治疗方法。     

The implantation of VDD pacemakers with a single electrode--a comparative study. The experience of the last 5 years]

OBJECTIVE: To compare the epidemiological characteristics and immediate results of all first single lead VDD pacemaker (PM) implantations with those of an equal number of dual chamber DDD PM, implanted during a 5-year period in a tertiary-care hospital. POPULATION AND METHODS: A total of 41 patients (pts) (25 males, mean age of 69.0 +/- 11.8 years) underwent a VDD PM implantation, from 30-11-92 to 15-9-97. This group was compared with an equal number of patients (28 males, mean age of 69.9 +/- 7.31 years) with a DDD PM implanted in the same period, selected by a criterion of immediate temporal proximity of procedure. For each patient we collected the clinical and electrocardiographic (ECG) indications for PM implantation, parameters of atrial (AS) and ventricular (VS) sensing and ventricular pacing (VP), X-ray exposure time (XRT) and complications. RESULTS: In the VDD group, 46.3% of the patients had syncope, 51.2% had complete AV block on the ECG, and 14.6% were PM-dependent. Analyzed procedure-related parameters were as follows: P-wave amplitude: 2.1 +/- 0.6 V; AS threshold: 1.2 +/- 0.7 V; R-wave amplitude: 9.1 +/- 3.3 V; VS threshold: 7.0 +/- 2.0 V; VP thresholds: 0.68 +/- 0.24 mA, 0.43 +/- 0.12 V (for a spike duration of 0.5 ms); ventricular impedance: 644.9 +/- 132.0 ohm; XRT; 7' 43" +/- 8' 23". There were two minor complications, for an incidence of 4.9% (one local hematoma and a vagal reaction). In the DDD group the clinical and ECG characteristics were similar, but there was a 22.0% prevalence of sinus-node dysfunction, VS 0% in the VDD group). The P-wave amplitude and AS threshold were significantly (p < 0.005) better (2.8 +/- 0.9 V and 2.8 +/- 0.9 V respectively). The other parameters were similar to those of the VDD group. CONCLUSIONS: The immediate results of VDD PM implantation are good and comparable with those of DDD PM, although with worse acute AS parameters.     

Development of sinus node disease in patients with AV block: implications for single lead VDD pacing

OBJECTIVE: To investigate the incidence of sinus node disease after pacemaker implantation for exclusive atrioventricular (AV) block. DESIGN: 441 patients were followed after VDD (n = 219) or DDD pacemaker (n = 222) implantation for AV block over a mean period of 37 months. Sinus node disease and atrial arrhythmias had been excluded by Holter monitoring and treadmill exercise preoperatively in 286 patients (group A). In 155 patients with complete AV block, a sinus rate above 70 beats/min was required for inclusion in the study (group B). Holter monitoring and treadmill exercise were performed two weeks, three months, and every six months after implantation. Sinus bradycardia below 40 beats/min, sinoatrial block, sinus arrest, or subnormal increase of heart rate during treadmill exercise were defined as sinus node dysfunction. RESULTS: Cumulative incidence of sinus node disease was 0.65% per year without differences between groups. Clinical indicators of sinus node dysfunction were sinus bradycardia below 40 beats/min in six patients (1.4%), intermittent sinoatrial block in two (0.5%), and chronotropic incompetence in five patients (1.1%). Only one of these patients (0.2%) was symptomatic. Cumulative incidence of atrial fibrillation was 2.0% per year, independent of the method used for the assessment of sinus node function and of the implanted device. CONCLUSIONS: In patients undergoing pacemaker implantation for isolated AV block, sinus node syndrome rarely occurs during follow up. Thus single lead VDD pacing can safely be performed in these patients.     

Adjustment of double-chamber pacemakers in VDD mode by measurement of thoracic electric bio-impedance]

An optimal atrioventricular interval (AVI) was sought in 6 patients with a double chamber pacemaker by an non-invasive technique: measurement of stroke volume by thoracic bioimpedance. This method proved to be easy and reliable in practice when there was only one pacing spike (VDD mode). It confirmed the existence of a variable optimal AVI according to individual patients: 250 ms (3 patients), 200-250 ms (1 patient), 150 ms (1 patient), 75-100 ms (1 patient). The value of optimal AVI is unpredictable since it depends upon individual electrophysiological and hemodynamic parameters. In a patient with severe mitral incompetence, Echo-Doppler provided evidence of end-diastolic ventriculo-atrial regurgitation at middle and long AVI, while a short AVI enabled elimination of end-diastolic regurgitation and a 15.45 per cent improvement in stroke volume. In two patients with a long optimal AVI (250 ms), a programmed short AVI (75 ms) paradoxically appeared to be more favourable than a middle AVI (150 ms).     

Cost-effectiveness of dual-chamber pacemaker therapy: does single lead VDD pacing reduce treatment costs of atrioventricular block?

AIMS: Implantation of single-lead VDD pacemakers is an established alternative to DDD pacing in patients with atrioventricular block. This study compares the long-term costs of both systems. METHODS AND RESULTS: Three hundred and sixty patients with atrioventricular block received VDD or DDD pacemakers in alternating order. Primary costs of implantation included: devices, leads and operation material, surgeons, nurses, medical technicians, and hospitalization. The mean cost of an uncomplicated DDD pacemaker implantation was defined as 1000 virtual cost-units (CU). Costs of pacemaker related complications or re-operations as well as upgrades from VDD to DDD devices were considered secondary costs and assessed during a mean follow-up period of 42+/-15 months. Pacing efficacy was assessed by event-free survival with maintained atrioventricular synchronized pacing mode. Costs of pacemaker devices were not different (639+/-26 CU in VDD vs 641+/-32 CU in DDD, ns). However, due to lower costs of lead hardware (102+/-10 CU in VDD vs 133+/-14 CU in DDD, P<0.001) and shorter implantation procedures (44.3+/-5.1 min vs 74.4+/-13.5 min, P<0.001), costs of an uncomplicated implantation were 8.9% lower in the VDD group (911+/-35 CU vs 1000+/-39 CU, P<0.001). A smaller complication rate in the VDD group led to a 16.1% reduction of secondary costs (26+/-17 CU year(-1)vs 31+/- 25 CU year(-1), P=0.024). Event-free survival did not differ between groups (83.4% in VDD vs 84.9% in DDD, ns). CONCLUSION: Use of single-lead VDD pacemakers achieves significant reduction of implantation and follow-up costs without loss of therapeutic efficacy compared to conventional DDD systems.     

Haemodynamic advantage with single chamber rate responsive pacemakers over dual chamber pacemakers during exercise in chronotropic incompetence.

Sequential cardiac chamber activation and chronotropic response are amongst the important determinants of cardiac performance. This study compared VVIR mode with DDD and VVI mode to assess the contribution of these two factors in the determination of cardiac performance during exercise. Ten patients with a mean age of 68 +/- 5 years were studied during 1988-90, who had complete heart block and sinus node dysfunction with a mean LV ejection fraction of 51.5 +/- 6.25%. Five patients had DDD pacemakers and the rest had VVIR pacemakers. Patients were exercised first in VVI mode followed by either DDD or VVIR mode. Exercise duration, maximum rate pressure product, exercise capacity and cardiac output were measured with graded treadmill test in Bruce protocol. There was remarkable increase in the exercise duration (P < 0.001) and the maximum rate pressure product (P < 0.001) in patients with VVIR as compared to DDD and VVI mode. In DDD mode, as compared to VVI mode, this increase was less remarkable, though statistically significant (P < 0.005). Therefore, it is concluded that patients with chronotropic incompetence as well as complete heart block do better during dynamic exercise when they have VVIR mode compared to VVI or DDD mode.     

Liver transplantation and HBsAg-positive postnecrotic cirrhosis: adequate immunoprophylaxis and delta virus co-infection as the significant determinants of long-term prognosis

BACKGROUND/AIMS: The place of liver transplantation in hepatitis B viral (HBV)-related diseases remains controversial because of the high rate of reinfection. The aim of this study was to define the determinants of long-term prognosis after transplantation. METHODS: Fifty-eight patients were transplanted during the period February 1984-September 1996. Six patients died during the early (< 3 months) posttransplant period from causes unrelated to HBV infection. All 52 long-term (> 3 months) survivors were evaluated in relation to the mode of presentation, viral replication at time of transplantation, absence of hepatocellular cancer at time of transplantation and use of adequate immunoprophylaxis (IP). Adequate immunoprophylaxis, defined as maintenance of anti-HBs levels over 100 mUI/ml, was introduced in December 1989. Intention-to-treat IP analysis compared patients transplanted before and after this date. The median follow-up was 74 months (range 4 to 131). Forty-seven patients (90%) had a minimal follow-up of 3 years. RESULTS: Five-year actuarial survival rates of 58 patients and of 52 long-term survivors were 72 +/- 6% and 80 +/- 6%, respectively. Univariate analysis showed that delta co-infection (n = 25) significantly improved survival (p < 0.001) [96 +/- 4% vs 63 +/- 10% in HBV patients (n = 27) at 5 years] as did absence of hepatocellular cancer (n = 36) (p = 0.020) [89 +/- 5% vs 61 +/- 12% in 16 non-cancer patients]. IP, however, significantly influenced 5-year survival in the HBV-patient group (n = 17) (p = 0.001) [85 +/- 10% vs 30 +/- 14% in 10 patients without IP). Multivariate analysis selected delta co-infection (p = 0.002) and IP (p = 0.01) as the significant determinants of prognosis independently influencing survival. Uni- and multivariate analyses showed that survival without reinfection was significantly influenced by IP (p = 0.002) [73 +/- 8% (n = 31) versus 33 +/- 12% in 15 non-treated patients). CONCLUSIONS: Delta virus co-infection and immunoprophylaxis are the most important prognostic factors after transplantation for postnecrotic HBsAg-positive cirrhosis. Transplantation can be proposed as a therapeutic tool only if life-long adequate adjuvant therapy can be achieved. Under this condition good results can even be obtained if there is viral replication at the time of transplantation.     

Immediate and long-term atrial sensing stability in single-lead VDD pacing depends on right atrial dimensions.

AIMS: Single-pass VDD is a physiological stimulation mode which requires a single-lead with a floating dipole to detect the atrial signal. We investigated the impact of right heart dimensions on immediate and long-term atrial sensing stability in VDD systems to draw guidelines for optimal atrial sensitivity programming. METHODS: Forty-one patients (23 males, mean age 73 +/- 11 years) with II or III degree AV block and normal sinus node function received a Thera VDD Medtronic 8948 pulse generator with Medtronic 5032 lead. Atrial sensing was evaluated at pre-discharge and during 12-months follow-up in the supine and upright positions, during normal and forced breathing. Atrial sensing variability, quantified by a D value (mV), which represents the difference between the maximum and the minimum atrial electrogram amplitude obtained during the various activities, was analyzed and related to right heart dimensions measured at echocardiography. RESULTS: Long-term appropriate atrial sensing was obtained in 40/41 patients. P wave mean amplitude at pre-discharge, during every specific activity, was predictive of 12-month values. No atrial oversensing was observed. According to the right atrial dimension (RAD), patients with RAD > 38 mm had a sensing variability significantly higher than those with RAD < or = 34 mm (D=1 + 1 Vs D=0.4+/-0.5; P<0.05). A linear relationship between D and RAD dimensions was observed (r=0.47; P<0.005). According to the distance from the roof of the right atrium to the right ventricular apex (RAVD), patients with RAVD < 93 mm had D=1.1 +/- 1, while patients with RAVD > 93 mm had D=0.5 +/- 0.4; P<0.05); a inverse correlation between RAVD and D was highlighted (r=-0.43; P<0.01). Using a cluster analysis, the combination of RAD and RAVD identified a subgroup (RAD > 30 mm and RAVD < 80 mm) at high risk of loss of AV synchrony with 67% sensitivity and 80% specificity. Nevertheless, apart from heart dimensions, no patient showed an atrial signal amplitude lower than 0.3 mV. CONCLUSIONS: According to our data, in VDD single-lead systems the amplitude of the atrial signal is stable over time in every physical activity. High RAD and low RAVD values may select patients with poor atrial sensing stability. Anyway, taking into account that no atrial oversensing was observed, atrial sensitivity setting at the highest value should be recommended.     

右室高位间隔部与心尖部VVI起搏对心功能的影响

目的探讨高位间隔部(HRVS)与心尖部(RVA)起搏对心功能的影响。方法行VVI起搏并愿随访的患者104例,其中HRVS起搏54例,RVA起搏50例,分别于术前及术后1周、半年、1年及3年在同一起搏频率下(60次/分)用超声心动图测定左室射血分数(LVEF)、左室短轴缩短率、心输出量和监测脑钠肽(BNP)水平。结果HRVS起搏患者LVEF及BNP水平无明显改变;RVA起搏患者LVEF(术后半年、3年分别为0.60±0.15、0.54±0.16)降低及BNP(术后半年、3年分别为96.51±46.41 ng/L、168.33±49.37 ng/L)水平升高。结论 VVI HRVS起搏优于RVA起搏。     

Single-pass lead VDD pacing system in children and adolescents: report of twenty-four patients

The dual-chamber pacing systems allow for AV synchrony, but generally require the placement of two separate transvenous leads. Single-lead atrioventricular synchronous pacing system (VDD) using single-pass leads has been accepted as therapeutic alternative for atrioventricular block with normal sinus node function. The aim of this study is to evaluate clinical performance of single-pass lead VDD pacing systems in 24 consecutive patients in a ten-year period. The study group includes 17 (70.8%) male and 7 (28.8%) female patients.The mean age and mean weight during pacemaker implantation was 10.4 +/- 3.8 years (4-17 years) and 30 +/- I I kg (13.5-55 kg), respectively. The patients have been followed for 7-84 months (median 42 months). The percentage of atrial sensing-ventricular pacing changed from 75 to 99.9% at the last control. During the follow-up period, pacing mode was changed to VVIR due to complete loss of AV synchrony in five patients (21%). Four of them had underlying cardiac disease. In these patients loss of AV synchrony might be related to cardiac enlargement/abnormal cardiac anatomy or small atrial dipole-ventricular tip length. Despite the loss of AV synchrony in post surgical AV block or dilated cardiomyopathy, single-lead VDD pacing systems can be successfully used in children with complete AV block and normal sinus node function. Patients and lead selection should be taken into consideration for the maintenance of AV synchrony.     

Short- and long-term determinants of baroreceptor function in aged normotensive and spontaneously hypertensive rats

In a variety of animal models, baroreceptor resetting during chronic hypertension has been correlated to vessel wall hypertrophy and decreased distensibility. In one possible mechanism of chronic resetting, termed the splinting hypothesis here, it has been suggested that a stiffer vessel wall might increase the minimum pressure required for activation of these mechanoreceptors (pressure threshold) and decrease suprathreshold pressure sensitivity. Lower vessel distensibility would alter baroreceptor function by preventing equivalent pressures from producing equivalent vessel distensions and, thus, receptor distortions. Recent studies have also suggested that the pressure threshold is strongly influenced by the most recent (minutes) history of blood pressure exposure during a process termed rapid resetting. Hypertension and advanced aging are associated with distensibility changes. The present study examines pressure and equivalent mechanical response characteristics of aortic baroreceptors from aged normotensive Wistar-Kyoto and spontaneously hypertensive rats. An in vitro aortic arch-aortic nerve preparation was used to assess the discharge properties from a number of baroreceptors and the pressure-diameter relationship of each aorta. Both control and rapid resetting protocols were used to study the baroreceptor characteristics. Aged Wistar-Kyoto rats were normotensive and averaged 115 weeks of age. Aged spontaneously hypertensive rats had systolic tail pressures of 187 mm Hg and averaged 76 weeks of age. Although aortic distensibility of aged WKYs was much lower than previously found in younger animals, the pressure threshold was unchanged. Aged spontaneously hypertensive rat receptors were chronically reset in proportion to their blood pressure. Decreased distensibility did not alter the rapid resetting process. It is concluded that baroreceptor pressure sensitivity is more closely related to aortic distensibility under several conditions altering vessel stiffness, whereas, the pressure threshold may be regulated additionally by mechanisms independent of distensibility. The results are inconsistent with the splinting hypothesis.     

Coronary collateralization: determinants of adequate distal vessel filling after arterial occlusion

BACKGROUND: The protective effect of collateral vessels in coronary artery disease (CAD) is well established. Little is known, however, about factors that influence collateral formation. METHODS: We studied the coronary angiograms of 200 consecutive patients with single-vessel coronary artery occlusion. Patients were excluded if obstructive stenoses were present in other vessels or if prior revascularization had been undertaken. Collateral circulation to the occluded artery was graded as 'poor' (no or incomplete filling) or 'rich' (complete filling). Patient characteristics, including mode of presentation, medications and CAD risk factors, were assessed. RESULTS: Positive univariate correlates of rich collaterals included increasing age [odds ratio (OR) 1.03, P = 0.016], 'statin' use (OR 2.50, P = 0.005), nitrate use (OR 1.96, P = 0.034), calcium-channel blocker (CCB) use (OR 4.07, P < 0.001), presentation with stable angina (OR 2.34, P = 0.006), longer time since diagnosis of CAD (OR 1.12, P = 0.002) and history of hyperlipidemia (OR 3.55, P < 0.001). Significantly poorer collateralization was observed in the setting of acute myocardial infarction (MI) (OR 0.23, P < 0.001), diabetes mellitus (OR 0.33, P = 0.003), impaired left ventricular function (OR 0.64, P = 0.015) and occlusion of the left anterior descending coronary artery (LAD) (OR 0.28, P < 0.001). On multivariate analysis, rich collateralization was associated with hyperlipidemia (P = 0.003) and CCB use (P = 0.028). Independent predictors of poor collaterals were presence of diabetes (P < 0.001), LAD occlusion (P = 0.001) and presentation with acute MI (P = 0.017). CONCLUSION: Diabetes mellitus, occlusion of the LAD and presentation with acute MI are independently associated with poor distal vessel collateralization, whereas hyperlipidemia and use of CCBs are associated with rich collateralization. Factors determining coronary collateral formation may in turn influence outcomes after coronary artery occlusion.     

Mitral valve closure and left ventricular filling time in patients with VDD pacemakers. Assessment of the onset of left ventricular systole and the end of diastole.

The effect of mitral valve closure on left ventricular filling time and its relation to the onset of systole were assessed from mitral valve echocardiograms and simultaneous apex cardiograms in 21 normal subjects, 11 patients with left bundle branch block, and 19 patients with VDD pacemakers programmed for atrioventricular intervals of 50, 150, and 250 ms. The interval between the electrocardiograph Q wave and the apex cardiogram upstroke was similar in normal subjects and patients with left bundle branch block, but was significantly longer in patients with VDD pacemakers at all atrioventricular intervals. Similarly there was little difference in the time interval between the Q wave and mitral valve closure in normal individuals and patients with left bundle branch block but this was considerably delayed in VDD pacemaker patients with the atrioventricular interval set at 50 ms. With increasing atrioventricular intervals the mitral valve closed significantly earlier, whereas the onset of left ventricular systole and the timing of mitral valve opening remained unchanged. Thus as a result of earlier mitral valve closure left ventricular filling time decreased progressively as the atrioventricular interval was increased. Since the onset of left ventricular systole, with respect to left ventricular stimulation, is considerably delayed in VDD pacemaker patients a short atrioventricular interval is required in these patients to maintain the normal time relations between atrial and ventricular contraction and hence maximise left ventricular filling.