生理性心脏起搏的选择及应用限制的探讨

１２１例安置生理性心脏起搏器的患者，完全性及高度房室传导阻滞４２例；病窦综合征７９例，其中窦性心动过缓、窦性停搏６０例、慢─快综合征１９例。安置ＤＤＤ起搏器４０例，２８例为心房变时性反应正常的完全性房室传导阻滞。安置ＡＡＩ、ＡＡＩＲ（变时性反应不良者选用）起搏器４９例。发生并发症１４例，均为采用心房电极起搏方式者。其中电极脱位３例、低感知４例、膈刺激现象及输出阻滞各２例、起搏器介导性心动过速３例，根据笔者的经验，对不同心律失常类型提出了选择生理性起搏方式的原则，并就其应用限制进行了讨论，强调全面评估病情是作出最佳选择的前提。     

Hemodynamic benefits of atrioventricular sequential pacing after cardiac surgery

The hemodynamic effects of atrioventricular (A-V) sequential pacing were assessed and compared with those of ventricular and of atrial pacing in 10 patients with and without heart block after cardiac surgery. Ventricular pacing alone was either hemodynamically detrimental or of no benefit in six of the eight patients who initially had sinus or accelerated junctional rhythms. Atrial pacing alone produced significant improvement in cardiac output in all patients who were not pacemaker-dependent. However, five of the eight patients with intact A-V conduction had further increases in cardiac output through A-V sequential pacing at shorter than intrinsic A-V intervals. Optimal A-V intervals for maximal cardiac output could be identified in all patients and varied widely. Significant changes in cardiac output occurred with relatively small deviations in the A-V interval. In selected patients after cardiac surgery, temporary A-V sequential pacing is a workable and valuable adjunctive form of hemodynamic support and is preferable to ventricular or atrial pacing.     

Sick sinus syndrome: strategies for reducing mortality.

The evolution of sick sinus syndrome is slow, and its clinical and electrocardiographic manifestations are intermittent. A-V and I-V conduction disturbances often arise, but incidence of defects with clinical consequences is too low. Death rate, when large groups are considered, is slightly higher than that of the general population of the same age and with similar pathologies. Mortality depends on concomitant pathologies, on the development of congestive heart failure, on the arterial thromboembolism and on the type of sinus disease. The use of ventricular pacemakers (VVI) did not reduce mortality. Atrial pacing (AAI) gives the auricles electrical stability preventing fibrillation and systemic embolism. The hemodynamic role of the auricles is also preserved. As a consequence, death rate is reduced when AAI is used. In cases with a-v conduction disturbances or with paroxysmal atrial fibrillation, dual chamber pacing (DDD) is preferable because it permits ventricular pacing to be continued even if a-v block or paroxysmal or chronic atrial fibrillation appears. When using ventricular pacing and in cases in which pacing is not considered, warfarin or aspirin can prevent strokes and systemic embolism. In bradycardia-tachycardia syndrome requiring treatment of arrhythmias dual chamber pacemaker must be implanted.     

心房起搏脉冲传导延迟患者AV问期的优化

目的探讨心房起搏至心房除极波时间延迟患者设置起搏的房室间期（PAV）的方法及远期心房起搏的有效性。方法分析2005年1月至2012年12月我院起搏器植入后发生心房起搏至心房除极波时间延迟≥lOOms的患者10例,病窦综合征（SSS）患者的房室间期设置为最大值,并最大限度开启房室问期滞后功能;对房室传导阻滞（AVB）患者设置PAV的值为：140～180ms＋心房起搏至心房除极波延迟时间,不开启AV滞后。结果经1个月至7年随访,5例SSS患者心室起搏比例〈10％,3例SSS患者心室起搏比例30％。50％,Holter显示心室起搏时为假性融合波,l例SSS患者及1例AVB患者为心室起搏心律,起搏比例〉99％,保证了房室问期的生理性。10例患者心房起搏阈值均〈1．5／0．4ms,未发生心房起搏阈值增高及失夺获。结论心房起搏至心房除极波时间延迟患者远期的心房起搏夺获是安全的;设置起搏器PAV间期要将心房起搏至心房除极波延迟时间计算其中,程控随访中应注意观察程控仪中监护图的心房波,房室传导阻滞患者可延长房室间期后观察心房波,部分患者因监护导联显示不清,需要通过12导联心电图进行观察,避免心房起搏至心房除极波延迟病例被遗漏．导致增加心室起搏及非生理性的房室间期。     

Duration of the atrial QT (QTa) under normal conditions and its values in atrial damage

Atrial QT(QTa) was measured in lead II, in right thoracic leads V4R, V3R and V1 as well as in five direct atrial unipolar leads in 40 dogs. Atrial damage of right or left atrium was provoked by infiltration of 96 degree alcohol in 30 dogs Premature right atrial beats were induced till one was blocked and A-V block was provoked in 10 other normal dogs as well as in those with right atrial damage. Control QTa was observed to include the terminal QRS notch and the proximal irregularity on ventricular ST interval that was better seen in direct leads with sinus rhythm and confirmed later in A-V block and blocked atrial premature beats. It was concluded that normal corrected QTa (QTac) can be obtained by QTac = 0.32 2 square root P-P +/- 0.02. In atrial damage the value increases beyond + 0.04 inclusive + 0.013 with the greater values in the right atrial unipolar. This formula allow us to recognize normal or abnormal QTac duration and to be acquainted that the terminal notch of QRS is produced by the final forces of atrial recoviry in some cases as well as to determine the position of vulnerable atrial period on the ST ventricular segment with and without atrial damage.     

Device-based therapies for atrial fibrillation

Optional statement Ablation of the atrioventricular conduction system and pacemaker implantation is the preferred procedure for patients with atrial fibrillation (AF) in whom a rate control strategy has been selected but in whom rate-controlling medications are intolerable or ineffective. Selection of standard right ventricular (RV) pacing versus biventricular pacing is individualized, based on the degree and etiology of left ventricular dysfunction. Atrial-based pacing is clearly preferable to ventricular-based pacing in patients with sick sinus syndrome, because it leads to a reduction in the development of AF. Emerging evidence indicates that excess RV pacing is deleterious, increasing AF, heart failure, and possibly mortality. Therefore, physiologic pacing with minimization of RV pacing is desirable. Atrial pacing algorithms that increase the frequency of atrial pacing have shown modest efficacy in the prevention of AF. Use of atrial pacing algorithms is reasonable for patients with a history of AF and standard bradycardia indications for permanent pacing in whom maintenance of sinus rhythm is desirable. Studies assessing novel and multiple site atrial pacing therapies have mixed results, without compelling evidence of clinically important benefit. The exceptions are biatrial and right atrial overdrive pacing immediately after cardiac surgery. Several studies have shown effective suppression of postoperative AF with their use. Device therapy (eg, atrial antitachycardia pacing and defibrillation) for the termination of AF is effective in reducing arrhythmia burden. However, improvement in clinically relevant end points is not established and indications are not clearly defined. If a patient lacks an indication for an implantable cardioverter-defibrillator, we do not offer atrial defibrillation as a treatment option. Atrial arrhythmias may be better prevented by programming to avoid ventricular pacing than by specific atrial interventions.     

Atrial alternans: Experimental echocardiographic and hemodynamic demonstration during programmed pacing

Simultaneous hemodynamic and echocardiographic recordings were used to demonstrate mechanical atrial alternans during programmed atrioventricular (A-V) pacing in five open chest dogs. Each animal was studied in two stages, first with the A-V conduction system intact (phase I) and later after the experimental induction of complete A-V block (phase II). Atrial alternans was demonstrated during rapid atrial stimulation at cycle lengths ranging from 250 to 120 ms. During phase I, rapid atrial pacing resulted in complex combinations of variable A-V conduction disturbances with superimposed atrial and ventricular alternans. During phase II, atrial alternans could be observed during a programmed prolonged pause in ventricular activity. It is anticipated that this method will facilitate recognition of atrial alternans in various clinical situations and shed further light on its possible hemodynamic significance.     

Dual-site atrial pacing for atrial fibrillation in patients without bradycardia.

Atrial pacing has been shown to delay the onset of atrial fibrillation (AF) when compared with ventricular pacing in patients with sick sinus syndrome. The role for pacing in the control of AF in patients without bradycardia is uncertain. We performed a randomized, crossover, single-blinded study in 22 patients (14 women, aged 63 +/- 10 years) with paroxysmal AF refractory to treatment with oral sotalol (202 +/- 68 mg/day) and no bradycardic indication for pacing. All patients received a dual-chamber pacemaker with 2 atrial pacing leads positioned at the high right atrium and coronary sinus ostium, respectively. Patients were randomized in a crossover fashion to be paced for 12 weeks, either with high right atrial (RA) pacing at 30 beats/min ("Off") or dual-site RA pacing with an overdrive algorithm that maintained atrial pacing at a rate slightly above the sinus rate ("On"). Treatment on resulted in a significantly higher percentage of atrial pacing and a reduction in atrial ectopic frequency than the treatment off period. The time to the first clinical AF recurrence was prolonged (15 +/- 17 to 50 +/- 35 days, p = 0.006), and total AF burden was reduced (45 +/- 34% vs 22 +/- 29%, p = 0.04) in the on-treatment phase. However, there was no difference in AF checklist symptom scores or overall quality-of-life measures. Dual-site RA pacing with continued sinus overdrive prolonged the time to AF recurrence and decreased AF burden in patients with paroxysmal AF. The absence of a major impact on symptom control suggests that pacing should be used as an adjunctive therapy with other treatment modalities for AF.     

Arterial thromboembolism in patients with sick sinus syndrome: prediction from pacing mode, atrial fibrillation, and echocardiographic findings

OBJECTIVE: To evaluate whether thromboembolism in sick sinus syndrome can be predicted by pacing mode, atrial fibrillation, or echocardiographic findings. METHODS: Patients were randomised to single chamber atrial (n = 110) or ventricular (n = 115) pacing. They were divided into subgroups with and without brady-tachy syndrome at time of randomisation. The occurrence of atrial fibrillation and thromboembolism during follow up were investigated and compared with echocardiographic findings. RESULTS: The annual risk of thromboembolism was 5.8% in patients with brady-tachy syndrome randomised to ventricular pacing, 3.2% in patients without brady-tachy syndrome randomised to ventricular pacing, 3% in patients with brady-tachy syndrome randomised to atrial pacing, and 1.5% in patients without brady-tachy syndrome randomised to atrial pacing. In atrial paced patients without brady-tachy syndrome at randomisation and without atrial fibrillation during follow up, the annual risk of thromboembolism was 1.4%. Left atrial size measured by M mode echocardiography was of no value in predicting thromboembolism. CONCLUSIONS: Arterial thromboembolism in patients with sick sinus syndrome is very common and is associated primarily with brady-tachy syndrome at randomisation and with ventricular pacing. The risk of thromboembolism is small in atrial paced patients in whom atrial fibrillation has never been documented.     

A case of sick sinus syndrome, considered to develop to atrial standstill

A 25 year old man was admitted to our hospital because of dizziness and bradycardia. Physical examination was normal except for an irregular pulse of 90 beats/min. Chest X-ray film showed no cardiomegaly and no pulmonary congestive changes. ECG showed 2:1 or 3:1 atrial flutter on admission. After atrial flutter was terminated spontaneously, ECG revealed absent P waves, a QRS interval of 0.10 seconds, and A-V junctional rhythm with irregular R-R interval ranging from 1.20 to 2.12 seconds. At times, cardiac arrest was noted. Esophageal electrocardiogram also failed to demonstrate atrial activity while A-V junctional rhythm continued. Mitral valve echocardiogram lacked A point, and then ? waves were absent in both the right atrial and pulmonary capillary pressure recordings. Transient atrial standstill was suspected from these findings, so that electrophysiological study was performed. Right atrial electrogram revealed complete absence of atrial activity. His bundle electrogram revealed H-V prolongation [80-83 msec]. Right atrial pacing was attempted at several atrial sites, including the high lateral, middle lateral, low lateral right atrium, and low right atrial septum. Atrial activity could be elicited with stimulus strength of 3 to 5 volts. These atrial pacing thresholds were mild or moderately higher than usual. After the cessation of atrial pacing at 90 beats for two minutes, the recovery time of the first beat prolonged to 8.46 second. We considered that this case was sick sinus syndrome in young adult which revealed generalized disturbance of conduction system including the atrial muscle, and would develop to atrial standstill in the near future.     

Reliability of different temporary myocardial pacing leads

Temporary myocardial pacing leads are routinely used for diagnosis and treatment of postoperative arrhythmias following open-heart surgery. The intention of this study is to compare five different electrodes for reliability during the postoperative period. A standardised technique of implantation was used to place 147 ventricular and 81 atrial wire electrodes in 149 patients. During operation and then daily over the next ten days, the stimulation threshold, P- and R-wave sensing, and impedance were measured with a pacing system analyser to evaluate the reliability of the pacing and sensing function. Five measurements were taken at each time; the mean values were statistically analysed. The number of failures in pacing and sensing and the course of the tested parameters during the postoperative period were compared. As a result, bipolar pacing leads (Osypka TME 64a/66a) proved to be more reliable than unipolar wires (Ethicon HD 12S, Osypka TME 60/60a), particularly in atrial sensing. Also the Medtronic 6400/6500 showed good reliability for the ventricle, so that they can be recommended for VVI-mode pacing. In conclusion, for reliable function during the postoperative course up to 10 days a specially developed bipolar temporary pacemaker electrode can be recommended for both atrial and ventricular or sequential pacing.     

Sick sinus syndrome due to cardiac amyloidosis

In a patient suffering from cardiac amyloidosis a case of sick sinus syndrome, manifested by markedly prolonged recovery time of the sinus node, was documented by an atrial pacing study. The first A-V junctional escape interval was markedly prolonged following the termination of the atrial pacing, pointing to a coexisting A-V nodal dysfunction. The patient required a permanent artificial pacemaker implantation.     

INITIAL EXPERIENCE WITH PHYSIOLOGICAL PACING

Fifty patients, aged 23 to 88 years, with permanent rate-responsive dual chamber pacemakers were studied prospectively for 14.1 ± 11.4 (S.D.) months after implantation to assess the benefits and complications associated with this technique. In 12 patients the device replaced a ventricular demand pacemaker. Minor complications associated with implantation occurred in one case. Atrial leads required repositioning because of increase in threshold and/or problems of sensing in five cases and ventricular leads in five. There were two patients with symptomatic pacemaker-related arrhythmias necessitating reprogramming; one patient with pacemaker-mediated tachycardia and one with pacemaker autoinhibition. Seven patients have died; one suddenly and possibly related to a pacemaker-triggered arrhythmia. Of 43 living patients, five are now programmed to the ventricular demand mode; two with atrial fibrillation, one with failed atrial lead repositioning, one with persistent sinus tachycardia, and one because of angina pectoris. Thirty-six of the 43 living patients are asymptomatic and a further six are symptomatically improved. All 12 patients changed from ventricular demand pacing have less symptoms. Rate-responsive dual chamber pacing is safe and appears to improve symptoms in most cases. Complications are infrequent and usually easily overcome. This mode of pacing should be considered in all patients with normal sinoatrial function in whom a permanent pacemaker is indicated.     

Acute Evaluation of a Preformed Single-pass VDD/DDD Pacing Lead

The clinical utility of single lead, atrial synchronous, ventricular pacing (VDD), for patients with normal sinus function and heart block is well established. Atrial stimulation, unavailable in VDD systems presents a significant disadvantage. DDD pacing systems however, require the introduction and positioning of two separate leads. The acute human study discussed evaluated a modified version of a commercially available VDD lead with a preshaped lobe, capable of both sensing and pacing the right atrium. P waves and atrial stimulation thresholds were determined in five patients. The mean P-wave was 2.5 ± 1 millivolts. Atrial stimulation in the unipolar configuration was 1.6 ± 0.5 volts and 1.7 ± 0.9 volts in the bipolar configuration. These acute stimulation thresholds and sensing amplitudes were comparable to conventional DDD pacing systems. Therefore, single-lead DDD pacing may be feasible and warrants further study.     

Atrial pacing for sick sinus syndrome

Atrial pacing is the most physiological way to pace patients with sinus node disease, as it provides both AV synchrony and a normal ventricular activation pattern. Long-term studies comparing atrial and ventricular pacing imply that atrial pacing results in fewer cardiac complications and, possibly, reduced mortality. Ventricular pacing should thus, if possible, be avoided in patients with sinus node disease. The potential risk of impending high-grade AV block during atrial pacing is low, with an annual incidence around 1% if patients are selected appropriately. Approximately 40-50% of patients with sinus node disease show signs of chronotropic incompetence during physical exercise, and are thus candidates for atrial rate responsive pacing. A preoperative evaluation of candidates for atrial pacing should include long-term Holter/telemetry, exercise test, carotid sinus stimulation, and an electrophysiological study excluding significant AV conduction disturbances.     

Electrophysiologic properties of prenalterol

We assessed the electrophysiological properties of prenalterol, a new beta-selective agonist, in 10 patients with normal and 10 patients with delayed atrioventricular (A-V) conduction times. We evaluated sinus node function, A-V conduction times, refractory periods, atrial or ventricular arrhythmias, spontaneous or induced by the single extrastimulus technique during basal conditions, 5 minutes after a first dose of 20 micrograms/kg of prenalterol, and 5, 15 and 30 minutes after a second injection of the same dose. Prenalterol increased heart rate about 20%, with statistically significant shortening of right atrial refractory periods, A-V nodal functional and effective refractory periods and A-H interval in both groups after the first dose. In the 6 patients with sick sinus syndrome, prenalterol increased heart rate significantly and decreased maximum sinus node recovery time which reached a statistically significant value (P less than 0.05) 5 and 30 minutes after the second dose. At the highest dose, prenalterol seemed to increase the number of ventricular and/or atrial arrhythmias only in those patients with the arrhythmias before treatment. Prenalterol increases heart rate and decreases A-V node conduction times. The shortening of maximum sinus node recovery time in patients with the sick sinus syndrome, especially if confirmed after oral administration, could indicate a specific use of this drug in patients with sinus bradycardia or atrial fibrillation with a slow ventricular response.     

Double-counting of intracardiac electrogram during biatrial pacing.

BACKGROUND: Biatrial pacing has a significant problem with memory function that misinterprets normal sinus rhythm as atrial tachyarrhythmias and in addition estimation of the atrial pacing thresholds (biatrial and uniatrial pacing thresholds) is sometimes difficult because of small P waves. METHODS AND RESULTS: The intracardiac electrograms recorded by a pacemaker in 10 patients (age, 66.7+/-10.7 (SD) years) with implanted biatrial pacemakers were analyzed. Atrial sensing within the atrial refractory period after atrial pacing was counted in 6 of the 10 patients (timing of the double counting was 143+/-64 ms) when pacing failed in the left or right atrium. Atrial sensing within the atrial refractory period after atrial pacing disappeared when biatrial pacing was successfully performed. Atrial double-counts depend on interatrial conduction delay. The memory function of implanted pacemaker devices misinterpreted normal sinus rhythm as atrial tachyarrhythmias because of atrial double-counts. On the other hand, the biatrial pacing threshold was easily recognized using this phenomenon. CONCLUSIONS: The memory function of pacemaker devices is unreliable because of atrial double-counting during sinus rhythm in patients with biatrial pacing. However, the biatrial pacing threshold is easily checked using this phenomenon.     

Effects of verapamil on sinusal function and on atrioventricular conduction along normal and abnormal pathways, in patients with pre-existing troubles of excitation conduction (author's transl)]

Effects of verapamil (5 mg i.v.) on excitation conduction in 20 patients who already had a basic alteration (7 with ventricular pre-excitation syndrome) were studied by His electrogram, during spontaneous sinusal rhythm and atrial electrostimulation in increasing frequencies. In 4 cases, a test crossed with atropine was carried out. The effects of the drug on the effective refractory period of the A-V node and the anomalous tract in 3 patients with W.P.W. syndrome of Kent's bundle were studied. The effects were: no significant modifications in the sinusal frequency; increase in the corrected preautomatic pause only in cases with sick sinus node syndrome and serious basic compromise of the sinus node function; slowing down of A-V conduction in the supra-hisian area and increase of the effective refractory period of the A-V node; no modification of the intra-atrial conduction, or the under-hisian and intraventricular A-V conduction; uneven slowing down of conduction along the anomalous tract of the pre-excitation syndrome of the James bundle; modification of the effective refractory period of the anomalous tract of the Kent bundle type, variable from case to case. On the basis of the electrophysiological properties, the possibilities and limits of use of the drug in sick sinud node syndrome in the common supraventricular paroxymal tachycardias, in atrial fibrillation, atrial flutter and arrhythmias of the ventricular pre-excitation syndrome are emphasized.