Three cases of hypotension and syncope with ventricular pacing: possible role of atrial reflexes

Bradyarrhythmias and Physiologic Pacing in the ICU

Bradyarrhythmias represent a common pathology in the intensive care unit (ICU) with etiologies of varying severity. Treatment has often been focused on correcting underlying causes and may require pacing for urgent hemodynamic support. In recent years, there has been interest in physiologic pacing modalities which avoid the dyssynchrony from right ventricular (RV) only pacing. Cardiac resynchronization therapy (CRT) through biventricular pacing is a well-established device-based electrical therapy in patients with wide QRS and heart failure. Recently, it has been shown that biventricular pacing may also be pursued for hemodynamic rescue in the ICU setting. Efforts to re-engage the conduction system with His bundle pacing or further downstream have also emerged as alternative means to deliver resynchronization, with early applications in the ICU now being reported. The goal of the review is to examine bradyarrhythmia causes and management in the ICU as well as investigate new approaches in physiologic pacing and their potential roles in critically ill patients.

Beta-sympathetic blockade with chronotropic compensation in the management of heart disease

This presentation briefly describes the sympathetic and parasympathetic control of the heart, particularly in relation to coronary vascular effects. Autonomic disturbances following myocardial infarction and their significance are discussed. The influence of the autonomic system in chronic coronary heart disease is considered, particularly in relation to the beneficial effects which may be obtained by the combined use of beta-blocking drugs and cardiac pacing. Nine anginal patients with spontaneous or drug-induced bradycardia received temporary pacing and 27 others had pacemakers implanted. Pain was well controlled in the former group. Long term pacing produced worth-while benefit in 67% of the patients followed for periods up to 6 months, the figure falling to 50% among those followed for 24 months. Eight of the 27 relapsed. Thus, correction of bradycardia by pacing often produced a beneficial long term effect. A second group of 14 patients with ventricular arrhythmias was treated with beta-blocking agents combined with pacing. So far, 10 of these 14 have had their arrhythmias controlled either by the initial or by a modified drug regime. The results indicate that among patients with chronic coronary artery disease, beta-blockade to minimize cardiac sympathetic activity, coupled with pacing to prevent loss of chronotrophic control, often represents an effective combination for the management of refractory angina or arrhythmias.

Sick sinus syndrome treated with permanent pacemaker in 109 patients. A follow-up study

During the last decade implantation of permanent pacemakers has become the treatment of choice for patients suffering from the sick sinus syndrome (SSS). We have followed up 112 SSS patients treated with permanent pacemakers in Haukeland Hospital in the period 1966--76. The pacemakers were later removed from three of the patients. In the remaining 109 patients the SSS was characterized by tachy-bradyarrhythmias (TBA) in 44 and bradyarrhythmias (BA) in 65. Before implantation, 68 patients had syncopes and 27 severe dizziness. After implantation, symptomatic improvement was apparent in 104 patients; only three still had syncopes. During the follow-up period (mean 34.4 months), 29 patients died (yearly mortality 9.3%). There was no significant difference in total mortality between patients with TBA and with BA. Concomitant disturbances in atrioventricular (AV) conduction occurred in 35.8% of the patients. Among 79 of 80 patients still alive, five had developed total AV block, 19 had stable atrial fibrillation, 12 of these were possibly pacemaker-independent (ventricular rate greater than 60/min). Systemic embolization was observed in 16 patients, more frequently in the TBA (12/44) than in the BA group (4/65) (p less than 0.001). It is concluded that permanent pacemakers have an excellent symptomatic effect in patients with SSS. The prognosis is mainly determined by the presence or absence of coronary heart disease and/or heart failure.

Pacemaker-Like Syndrome Complicating Slow Pathway Ablation for AV Nodal Reentrant Tachycardia

This case report describes pacemaker-like syndrome after successful slow pathway ablation for atrioventricular (AV) nodal reentrant tachycardia due to recurrence of single AV nodal echo beats during sinus rhythm. The resultant AV dyssynchrony was responsible for the symptom complex. Following ablation of retrograde ventriculoatrial conduction, the AV nodal echo beats were eliminated and the pacemaker-like syndrome resolved.

Choice of pacemakers in patients aged 75 years and older: ventricular pacing mode vs. dual-chamber pacing mode

Half of all pacemakers implanted in the United States are for patients aged 75 years and older. The expectations and needs of an older group are different from patients who are younger, yet it is only recently that different pacing mode benefits for elderly persons have been tested in clinical trials. Some of the results have been surprising and suggest new algorithms for management. Other issues are still on the threshold of investigation. These include pacing for heart failure in elderly patients and pacing combined with cardioverter-defibrillator implantation.

Intra- and interatrial conduction delay: implications for cardiac pacing

Atrial conduction disorders are frequent in elderly subjects and/or those with structural heart diseases, mainly mitral valve disease, hyperthrophic cardiomyopathies, and hypertension. The resultant electrophysiological and electromechanical abnormalities are associated with a higher risk of paroxysmal or persistent atrial tachyarrhythmias, either atrial fibrillation, typical or atypical flutter or other forms of atrial tachycardias. Such an association is not fortuitous because intra- and interatrial conduction abnormalities delays disrupt (spatial and temporal dispersion) electrical activation, thus promoting the initiation and perpetuation of reentrant circuits. Preventive therapeutic interventions induce variable, sometimes paradoxical effects as with the proarrhythmic effect of class I antiarrhythmic drugs. Similarly, atrial pacing may promote proarrhythmias or an antiarrhythmic effect according to the pacing site(s) and mode. Multisite atrial pacing was conceived to correct, as much as possible, abnormal activation induced by spontaneous intra- or interatrial conduction disorders or by single site atrial pacing, which are situations responsible for commonly refractory arrhythmias. Atrial electrical resynchronization can also be used to correct mechanical abnormalities like left heart AV dyssynchrony resulting from intraatrial conduction delays.

Characteristics of the acute rise of atrial natriuretic factor during ventricular pacing

BACKGROUND

Previous studies have shown that peripheral venous levels of atrial natriuretic factor (ANF) are elevated during ventricular pacing as a result of asynchrony of atrial and ventricular contraction. However, the pattern by which ANF rises following institution of ventricular pacing has not been fully established and its physiologic consequences are unclear.

METHODS

Eight ambulatory patients in stable condition with dual-chamber pacemakers were studied. The pacemaker was reprogrammed from the dual-chamber to the ventricular pacing mode for 3 h, during which serial measurements were made of BP, heart rate and rhythm, levels of ANF, and plasma renin activity (PRA).

RESULTS

ANF levels rose markedly but slowly following the onset of ventricular pacing, reaching levels as high as 694% of control. The rise occurred over the course of 120 min, at which time the average value for the group plateaued at 82.5 +/- 22.1 fmol/mL (mean +/- SEM) vs 25.3 +/- 4.5 fmol/mL at control (p < 0.01); there was, however, marked variability in individual responses. By contrast, levels of PRA remained remarkably stable. Average BP changes were small, although there was a trend in the later part of the study for systolic pressure to decrease.

CONCLUSIONS

ANF levels rise markedly but gradually after institution of ventricular pacing and, hence, acute pacing studies must account for this delay in their design. The physiologic importance of the rise in ANF should be evaluated further since the rise in peptide levels may be associated with a decrease in systolic BP.

Effect of P-wave timing during supraventricular tachycardia on the hemodynamic and sympathetic neural response

BACKGROUND

Previous studies have shown the importance of the timing of atrial and ventricular systole on the hemodynamic response during supraventricular tachycardia (SVT). However, the reflex changes in autonomic tone during SVT remain poorly understood.

METHODS AND RESULTS

Eleven patients with permanent dual-chamber pacemakers were enrolled in the study. Arterial blood pressure (BP), central venous pressure (CVP), and peripheral muscle sympathetic nerve activity (SNA) were recorded during DDD pacing at a rate of 175 bpm (cycle length 343 ms) with an atrioventricular (AV) interval of 30, 200 and 110 ms, simulating tachycardia with near-simultaneous atrial and ventricular systole, short-RP tachycardia (RP<PR), and long-RP tachycardia (RP>PR). Each pacing run was performed for 3 minutes separated by a 5-minute recovery period. All patients demonstrated an abrupt fall in BP, an increase in CVP, and an increase in SNA regardless of the AV interval. The decreases in SBP, DBP, and MAP and the increase in CVP were significantly less during long-RP tachycardia (AV interval 110 ms) than during the other 2 pacing modes (P:<0.05), and the increase in SNA in 7 of the 11 patients was significantly greater during closely coupled atrial and ventricular systole than during long-RP tachycardia (P:<0.05).

CONCLUSIONS

These data suggest that the superior maintenance of hemodynamic stability during long-RP tachycardia is accompanied by reduced sympathoexcitation, which is primarily mediated by the arterial baroreceptors, with a modest cardiopulmonary vasodepressor effect.

Plasma brain natriuretic peptide as a biochemical marker for atrioventricular sequence in patients with pacemakers

We hypothesized that plasma brain natriuretic peptide, like plasma atrial natriuretic peptide, may reflect hemodynamic changes elicited by different cardiac pacing modes. The aim of this study was to investigate whether plasma brain natriuretic peptide could be influenced by different pacing modes or electrical stimulation. The subjects consisted of 164 patients with permanent pacemakers (52 VVI, 30 AAI, 82 DDD pacemakers) and unimpaired heart function. Patients with atrial fibrillation or spontaneous beats were excluded. Plasma atrial natriuretic peptide and brain natriuretic peptide levels were measured at a rate of 70 beats/min after 45 minutes in the supine position. Under ECG monitoring, the pacing mode was switched from DDD to VVI in 12 patients and from DDD to AAI in 4 patients with a dual chamber pacemaker. Plasma atrial natriuretic peptide and brain natriuretic peptide levels were also measured 30 minutes, 60 minutes, and 1 week after mode switching. Plasma atrial natriuretic peptide and brain natriuretic peptide levels were significantly higher in the nonphysiological pacing group than in the physiological pacing group, whereas these values were similar in the DDD and AAI pacing groups. One week after switching from DDD to VVI, plasma atrial natriuretic peptide and brain natriuretic peptide levels were significantly increased, however no significant changes were observed after switching to AAI. Based on a multivariate regression analysis of noninvasive clinical parameters, only a low plasma brain natriuretic peptide was significantly correlated with physiological pacing. We conclude that: (1) plasma brain natriuretic peptide, like atrial natriuretic peptide, is influenced by the pacing mode, but is not influenced by electrical stimulation; and (2) low plasma brain natriuretic peptide is important in relation to physiological pacing.

The pacemaker syndrome -- a matter of definition

Pacemaker syndrome is an iatrogenic disease that is often underdiagnosed. We propose that pacemaker syndrome represents the clinical consequences of suboptimal atrioventricular (AV) synchrony or AV dyssynchrony, regardless of the pacing mode. Clinicians implanting and programming pacemakers should attempt to optimize AV synchrony to prevent the occurrence of pacemaker syndrome.

Noninvasive beat-to-beat arterial blood pressure measurement during VVI and DDD pacing: relationship to symptomatic benefit from DDD pacing

To noninvasively assess the hemodynamic effects of VVI and DDD pacing modes we measured beat-to-beat arterial blood pressure during VVI and DDD pacing in 30 patients with complete heart block (CHB), using fingertip photoplethysmography. Of these patients, 15 undertook a double-blind cross-over comparison of the symptomatic effects of VVI versus DDD pacing to determine the relationship between blood pressure changes and the occurrence of symptoms suggestive of the pacemaker syndrome during ventricular pacing. Mean (SD) systolic blood pressure was 11.7 (15.4) mmHg lower during VVI pacing compared to DDD pacing (P < 0.0005). The mean (SD) beat-to-beat variability of systolic blood pressure was 5.20 (2.87%) in VVI mode versus 2.12 (1.07%) in DDD mode (P < 0.0000005). In comparison with DDD pacing, the excess of symptoms experienced by patients during VVI pacing did not correlate with the change in mean systolic blood pressure, but was significantly correlated with the increase in beat-to-beat systolic blood pressure variation during VVI pacing (r = 0.58, P = 0.024). We conclude that noninvasive measurement of fingertip arterial beat-to-beat blood pressure is a rapid and simple method of assessing the hemodynamic effect of VVI pacing. Beat-to-beat blood pressure variability was related to symptomatic intolerance of VVI pacing and may have potential utility as an aid to diagnosis or as a predictor of pacemaker syndrome.

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

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

Diagnosis of retrograde ventriculoatrial conduction by left atrial appendage Doppler flow analysis

We report a case of pacemaker syndrome where the diagnosis of retrograde ventriculoatrial conduction was made by Doppler analysis of left atrial appendage flow. Doppler analysis of left atrial appendage flow provides another noninvasive parameter to diagnose retrograde ventriculoatrial conduction.

Acute and chronic changes in atrial natriuretic factor induced by ventricular pacing: a self controlled clinical trial

A self controlled clinical trial was carried out to study the acute and chronic effects of ventricular pacing (VVI) on the atrial natriuretic factor (ANF). Eleven people were selected from a pool of 20 DDD paced patients. Pacemakers were programmed to the VVI mode for 1 month and their effectiveness tested by ECG at rest and after an effort test. AnF was measured by radioimmunoassay at baseline, after 15 minutes, and again 1 month after programming. The reliability of the radioimmunoassay was confirmed using the coefficients of variation between (12.5%) and within assay (9.7%). Data analysis was done using Wilcoxon's test. Our results showed that the onset of VVI pacing led to a sudden sharp rise in ANF in all patients (P < 0.0001). During VVI pacing, three patients were dropped from the study (2 were withdrawn because of symptoms and 1 voluntarily withdrew). After 1 month of VVI pacing, a significant increase of ANF above the baseline was observed (P < 0.05). The results showed that ventricular pacing led to an immediate rise in ANF and, that with long-term VVI pacing, there was an increase in ANF levels as well. The role of these findings in the pathophysiology of the pacemaker syndrome calls for further research.

A peculiar form of pacemaker syndrome in DDD pacing

This paper documents the occurrence of a peculiar form of PM syndrome despite the presence of DDD pacing. This occurred because the post atrial refractory period was set inappropriately. Our aim is to highlight the intriguing nature of the syndrome and the need to rule out a concealed form of PM syndrome every time an implanted patient suffers from unexplained and confounding symptoms.

Variability of left atrial bloodflow predicts intolerance of ventricular demand pacing and may cause pacemaker syndrome

Variability of left and right atrial and left ventricular bloodflow was studied using transthoracic and transesophageal Doppler echocardiography and related to pacemaker mode preference during everyday activity. Bloodflow variability was less at all sites during dual chamber pacing compared to single chamber pacing. However, in patients suffering from pacemaker syndrome and who prefer DDDR pacing, significantly increased variability of left atrial antegrade (but not retrograde) bloodflow during VVIR pacing compared to DDDR pacing was noted, which was not evident in patients tolerating VVIR mode pacing. This effect was not detected at any other site and suggests that adverse left atrial hemodynamics may result in intolerance to VVI/R mode pacing and might cause pacemaker syndrome.

Short AV interval VDD pacing does not prevent tilt induced vasovagal syncope in patients with cardioinhibitory vasovagal syndrome

Eleven subjects (mean age 50 years, range 33-71 years), who had previously received permanent dual chamber pacemakers for cardioinhibitory vasovagal syncope, underwent paired Westminster protocol tilt tests, one with short AV delay VDD pacing and one without pacing, to test the hypothesis that continuous ventricular pacing would prevent the cardiac initiation of vasovagal syncope. Nine (82%) of the paced tilts produced positive vasovagal outcomes compared with seven (64%) of the unpaced tilts. No important differences in the heart rate or blood pressure behavior during tilt or the time to positive vasovagal outcomes were observed between the paired tilts. There was more accelerated syncope/presyncope once symptoms had developed during the paced tilts of subjects in whom both study tilts were positive, although this did not reach statistical significance (P = 0.054). This study shows that atrial synchronous ventricular pacing does not prevent the initiation, or progression, of tilt induced vasovagal syncope in predisposed subjects.

"AV nodal" reentry: Part II: AV nodal, AV junctional, or atrionodal reentry?

The classical model of "atrioventricular (AV) nodal" reentrant tachycardia suggests that the reentrant circuit is entirely within the compact AV node and that AV nodal tissue is present proximal and distal to the circuit. Recent evidence from mapping studies and from examination of the effects of curative procedures, however, suggests that the upper end of the circuit uses perinodal atrial or transitional tissue. Moreover, the anatomical substrate of dual "AV nodal" pathways is likely to be the multiple connections between compact AV node and atrium rather than discrete intranodal pathways. The antegrade slow pathway appears to be situated at the posteroinferior approaches to the AV node in the region between the coronary sinus orifice and the tricuspid annulus. The retrograde fast pathway appears to be situated in the anterior atrionodal connections at the apex of Koch's triangle, close to the His bundle. The lower turnaround point of the circuit is likely to be within the AV node.

Incidence and predictors of syncope in paced patients with sick sinus syndrome

In spite of a normal pacemaker function, syncope still occurs in some patients with sick sinus syndrome (SSS). Causes often remain unknown. To identify predictors and etiologies of this bothersome symptom, we studied 507 patients who received atrial, ventricular, and dual-chamber pacemakers for SSS. During a mean follow-up of 62 +/- 38 months, actuarial incidence of syncope was 3% at 1 year, 8% at 5 years, and 13% at 10 years. Causes were vasovagal (18%), orthostatic hypotension (25.5%), rapid atrial tachyarrhythmias (11.5%), ventricular tachycardia (5%), acute myocardial ischemia (2.5%), and pacemaker/lead malfunction (6.5%). In 13 patients (29.5%), syncope remained unexplained. The only preimplant predictor for syncope was syncope as primary indication for pacemaker implant. Electrocardiographic correlation with bradycardia was not a predictor of relief of syncope during the follow-up.

IN CONCLUSION

(1) syncope in paced patients with SSS has multiple etiologies and may be multifactorial; (2) the only predictor of syncope after pacemaker implant is the occurrence of preimplant syncope as the main indication for pacing; (3) extensive Holter monitoring is not useful to document bradycardiac origin of syncope nor to predict its recurrence; (4) SSS probably overlaps with other entities such as autonomic dysfunction, vasovagal syncope, carotid sinus hypersensitivity, and venous pooling, which would provide an explanation for recurrent syncope in patients with normal pacemaker function.

Should a VVIR Pacemaker Increase the Heart Rate with Standing?

To assess the usefulness of incorporating a posture sensor into a ventricular inhibited rate modulated pacemaker, the hemodynamic effects of increasing the ventricular pacing rate with standing were studied in 15 pacemaker dependent patients aged 55 +/- 3.5 years. In a randomized cross-over design, the pacing rate remained at 70 or was increased to 100 beats/min immediately prior to standing. Blood pressure was monitored continuously and forearm blood flow was measured by venous occlusion plethysmography. There was no difference in supine blood pressure (117 +/- 4/63 +/- 3 compared to 118 +/- 5/64 +/- 4 mmHg) or forearm blood flow (2.88 +/- 0.36 vs 2.94 +/- 0.32 mL/100 mL/min) before the 70 or 100 pacing rate intervention. With standing, blood pressure fell to an equivalent degree at the two pacing rates (fall in mean blood pressure at 70 beats/min 6 +/- 4 and at 100 beats/min 8 +/- 2 mmHg, P = 0.7). After 1 minute of standing differences in blood pressure were similar, but after 2.5 minutes of standing the increase in mean blood pressure was less at 70 than at 100 beats/min (increase from control 28 +/- 2 compared to 36 +/- 3 mmHg, P = 0.002). Forearm blood flow decreased after standing for 1 and 2.5 minutes but there was no difference between the 70 and 100 pacing rates (fall in forearm blood flow at 2.5 minutes 0.50 +/- 0.24 and 0.59 +/- 0.25 mL/100 mL/cm2).(ABSTRACT TRUNCATED AT 250 WORDS)

"Subclinical" pacemaker syndrome: a randomised study of symptom free patients with ventricular demand (VVI) pacemakers upgraded to dual chamber devices

OBJECTIVE

To determine whether symptom free patients with single chamber pacemakers benefit from dual chamber pacing.

DESIGN

A randomised double blind crossover comparison of ventricular demand (VVI), dual chamber demand (DDI), and dual chamber universal (DDD) modes after upgrading from a VVI device.

SETTING

Cardiology outpatient department.

PATIENTS

Sixteen patients aged 41-84 years who were symptom free during VVI mode pacing for three or more years.

INTERVENTION

Pacemaker upgrade during routine generator change.

MAIN OUTCOME MEASURES

Change in subjective (general health perception, symptoms) and objective (clinical assessment, treadmill exercise, and radiological and echocardiographic indices) results between pacing modes before and after upgrading.

RESULTS

75% preferred DDD, 68% found VVI least acceptable with 12% expressing no preference. Perceived general well-being and exercise capacity (p less than 0.01) and treadmill times (p less than 0.05) were improved in DDD mode but VVI and DDI modes were similar. Clinical, echocardiographic, radiological, and electrophysiological indices confirmed the absence of overt pacemaker syndrome, although mitral and tricuspid regurgitation was greatest in VVI mode (p less than 0.01).

CONCLUSIONS

Most patients who were satisfied with long term pacing in VVI mode benefited from upgrading to DDD mode pacing suggesting the existence of "subclinical" pacemaker syndrome in up to 75% of such patients. The DDI mode offered little subjective or objective benefit over VVI mode in this population and should be reserved for patients with paroxysmal atrial arrhythmias. VVI mode pacing should be used only for patients with very intermittent symptomatic bradycardia or atrial fibrillation with a good chronotropic response during exercise.

An analysis of symptoms in patients with permanent ventricular pacemakers

The prevalence and severity of symptoms of the "pacemaker syndrome" were investigated in 64 patients with VVI pacemakers and compared, in the same patients, to a series of control symptoms, unrelated to pacemaker function. Symptoms were also compared in patient groups unlikely to have the "pacemaker syndrome" (atrial fibrillation), most likely to have such symptoms (retrograde atrial activation) and in an intermediate group (competitive paced and sinus rhythms). There was a linear relationship between the frequency and severity of "pacemaker" symptoms and control questions in all groups and no preponderance of "pacemaker" symptoms in any group. The study provides an estimate of the number and severity of symptoms in patients with VVI pacemakers, demonstrates the non-specificity of the "pacemaker syndrome" and shows no evidence of a sub-clinical "pacemaker syndrome" in the patients observed.

The pacemaker syndrome: old and new causes

The pacemaker syndrome refers to symptoms and signs in the pacemaker patient caused by inadequate timing of atrial and ventricular contractions. The lack of normal atrioventricular synchrony may result in decreased cardiac output and venous "cannon A waves." A sudden increase in atrial pressure at the onset of asynchrony may elicit a systemic hypotensive reflex response. A wide range of symptoms can be observed. The pacemaker syndrome is encountered in a significant number of patients with ventricular (VVI) pacemakers, mostly when 1:1 retrograde ventriculoatrial conduction is present. The risk of occurrence of the pacemaker syndrome is minimized if pacemaker systems are used which restore or maintain the normal atrioventricular contraction sequence. Hence, in sinus node disease, atrial stimulation with or without ventricular stimulation should be employed, while in high-grade atrioventricular block dual-chamber pacing is recommended. The pacemaker syndrome is not restricted to the VVI stimulation mode. It can be seen, though rarely, in atrial and dual-chamber pacing, and an awareness of these new causes is necessary. An established pacemaker syndrome can often be counteracted by adjusting the pulse generator function.

VVIR or DDD(R): does it matter?

A continuing emphasis on cost effectiveness in health care may require that we use more expensive pacing systems only in situations where there is clear medical and scientific evidence of increased efficacy. Although dual-chamber and/or sensor-based, rate-modulating pacing systems are electronically no less reliable, they are part of a more complex pacing system. The requirement for two leads, one of which must maintain both pacing and sensing in the atrium, will inevitably impact the cost and reliability of such systems compared with a single-chamber ventricular system. Yet, there is clear evidence that AV synchrony is important at rest, particularly in patients susceptible to pacemaker syndrome, and there is mounting evidence that AV synchrony during exercise is beneficial independent of rate response. Finally, and perhaps most important, there is the suggestion that patient longevity may be extended by using pacing systems that preserve AV synchrony and/or minimize ventricular pacing.

Transcutaneous cardiac pacing: evaluation of cardiac activation

The effects of transcutaneous cardiac pacing (TCP) on cardiac activation were evaluated by endocavitary recording (HRA, RVA) in eight patients, in order to test the possibility to obtain a simultaneous atrial and ventricular stimulation. The transcutaneous pacemaker used was the Pace Aid 52 (pacing rate 50-160 ppm, current output 10-150 mA, pulse width 20 sec). The two skin electrodes (surface area 50 cm2) were placed on the chest in anteroposterior position. Ventricular capture was observed in all patients (threshold = 74 +/- 14 mA), simultaneous atrial capture was obtained in only four cases (threshold = 138 +/- 25 mA). In conclusion, our data show that four-chamber simultaneous stimulation by TCP is possible, but only with pacing energies much higher than those usually required to capture the ventricle. The ability of TCP to simultaneously pace the atria and ventricles, though not relevant in the emergency cardiac stimulation for symptomatic severe bradyarrhythmias, could be useful in the treatment of reentrant supraventricular tachycardias.

Left atrial size and wall motion in patients with permanent ventricular and atrial pacing

It is well known that during permanent ventricular pacing atrial arrhythmias and embolic complications occur much more frequently in comparison to permanent atrial or sequential pacing. Hemodynamic disturbances caused by ventriculoatrial conduction (VAC) are thought to be responsible for those complications. The aim of this study was to compare the left atrial size and its wall motion in three groups of patients with sick sinus syndrome. Group 1: 58 patients with VVI pacing and VAC observed (22 males, 36 females, aged 31-86, mean 62.3). Group 2: 43 patients with primary AAI pacing (13 males, 30 females, aged 27-74, mean 57.8). Group 3: 13 patients with AAI or DDD replacing the primary VVI mode due to pacemaker syndrome and/or heart failure, all with VAC present during VVI pacing (7 males, 6 females, aged 26-80, mean 59.8). Two-dimensional/M-mode echocardiography was performed in all these patients. In group 1 mean diastolic as well as mean systolic atrial diameters were significantly greater (P less than 0.005) and wall motion significantly smaller (P less than 0.005) in comparison to the other groups. Left atrial wall motion amounted to only 7.4% of the mean diastolic diameter in this group. Mean left atrial diastolic and systolic diameters and wall motion in patients with pacemakers preserving atrioventricular synchrony (group 2 and group 3) were almost identical and wall motion amounted to about 22% of the diastolic diameter in both these groups. We conclude that ventriculoatrial conduction leads to significant enlargement of left atrium and to the atrial wall-motion decrease. This predisposes to arrhythmias and embolic complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences between atrial single chamber pacing (AAI) and ventricular single chamber pacing (VVI) with respect to prognosis and antiarrhythmic effect in patients with sick sinus syndrome

Several studies suggest different effects of atrial (AAI) and ventricular single chamber pacing (VVI) for sick sinus syndrome with respect to the suppression of atrial tachycardias and to the prognosis. With this aspect in mind, we studied 222 patients with sick sinus syndrome, 110 of whom had been supplied with AAI systems, and 112 with VVI systems, in the period from January 1978 to December 1986. The mean observation period was 53 +/- 28 months. The cumulative 5-year survival rate was not significantly different in the two groups. After subgroups with comparable underlying diseases had been differentiated, patients with coronary heart disease showed a significantly higher survival rate (P less than 0.05) under AAI pacing, and the same was shown for patients with no underlying heart disease (P less than 0.02). The incidence of chronic atrial fibrillation was 6% in the AAI group and 19% in the VVI group. Patients with preexisting atrial tachyarrhythmias showed the lowest incidence of chronic atrial fibrillation under AAI pacing. Under VVI pacing this incidence was a function of the basic rate of the pacemaker systems. In conclusion, the pacing mode seems to have a prognostic importance in spite of all methodological difficulties. A suppressive effect of AAI pacing on atrial dysrhythmias can also be assumed.

True incidence of pacemaker syndrome

Although the purported incidence of pacemaker syndrome according to the literature is only 5%-15%, this is based on a series of patients with VVI pacing. Increasing numbers of studies are being reported in which patients prefer the dual chamber mode despite little benefit being demonstrated on objective testing, suggesting that pacemaker syndrome may be more common than is generally reported. This study was designed to evaluate the reported symptoms in a series of patients programmed to both the VVI and one or more dual chamber modes. Forty unselected patients with dual chamber pacemakers were entered into a blind, randomized trial comparing the symptoms associated with VVI pacing to those associated with dual chamber pacing. Patients were randomized to either VVI or dual chamber pacing. At the end of 1 week, questionnaires rating 16 different symptoms were completed. Blood pressure, LV function, presence of ventriculoatrial conduction, and ability to override the pacemaker were evaluated. The pacemaker was then programmed to the other mode. Overall, 12 of 16 symptoms were significantly worse in the VVI as compared to dual chamber mode. The most highly significant (P less than 0.005) were shortness of breath, dizziness, fatigue, pulsations in the neck or abdomen, cough, and apprehension. Pacemaker syndrome was clinically recognized in 83% of patients paced in the VVI mode with 65% of patients experiencing moderate to severe symptoms. There were no readily identified clinical, hemodynamic, or electrophysiological parameters that predicted which patients would develop pacemaker syndrome. Thus, when patients have an opportunity to experience both pacing modes in close proximity to one another, there is a high incidence of pacemaker syndrome in the VVI mode.

Pacemaker syndrome evaluated by cardiopulmonary exercise testing

Two patients who presented with dyspnea on effort, persisting after insertion of a fixed rate ventricular demand pacemaker (VVI) for sick sinus syndrome, were evaluated by cardiopulmonary exercise testing. During VVI pacing a heightened ventilatory response to exercise and a fluctuation of ventilation occurred. The high ventilatory equivalent for CO2 throughout exercise with VVI pacing suggests that the patients had ventilation-perfusion mismatching due to an increase in the pulmonary capillary wedge pressure caused by 1:1 ventriculoatrial conduction. Rate responsive ventricular (VVIR) pacing associated with intact 1:1 ventriculoatrial conduction exaggerated the exertional dyspnea, while rate responsive atrial (AAIR) pacing improved the ventilatory response to exercise. We suggest that a heightened ventilatory response to exercise due to ventilation-perfusion mismatching may be an important factor causing the pacemaker syndrome, and that cardiopulmonary exercise testing is useful in identifying the exercise-induced symptoms with ventricular pacing.

Rate-modulated pacing

The primary role of cardiac rate in adapting cardiac output to changing physiological needs has been more clearly recognized in recent years. Previously, the rate of cardiac stimulation had been determined either at pacemaker manufacture, by programming a single rate, or by sensing the atrium. More recently, sensing another physiological or nonphysiological function that changes in response to body need has become possible. Exercise changes blood oxygen saturation, central venous pH, central venous temperature, minute ventilation and respiratory rate, stroke volume, circulating catecholamines, QT interval, evoked endocardial response to a stimulus, and the mechanics of myocardial contraction. Some sensors respond to muscle work but not to intellectual effort or emotion. Pacemaker-based sensors of physiological function or activity allow a change in cardiac stimulation rate in response to need. Whichever sensor is used, increases in ventricular rate during exercise regularly produce a cardiac output response. Single-chamber, rate-modulated pacemakers in atrium or ventricle and dual-chamber devices are now implanted on a widespread basis. These drive the atrium, the ventricle, or both, sensing or pacing the atrium at a rate determined by the sensor.

Recurrent symptoms after ventricular pacing in unexplained syncope

We report clinical and hemodynamic data in two cases of recurrent syncope. Both patients received permanent demand ventricular pacing (VVI) for unexplained syncope. Both patients experienced recurrent syncope after pacemaker implantation. They later underwent 60 degrees head-up tilt testing, initially noninvasively and then with hemodynamic profile. A vasovagal response to tilt occurred with bradycardia and was complicated by the onset of ventricular pacing and retrograde atrioventricular conduction (RAVC) with hemodynamic deterioration and rapid reproduction of syncope. Limited intracardiac electrophysiological study (EPS) excluded atrioventricular (AV) conduction disease, sinus node disease, and carotid sinus syndrome, and confirmed RAVC. Both patients were upgraded to dual chamber pacing, DDI mode, with 50/80 rate hysteresis. One patient was asymptomatic at repeat tilt testing; the other experienced continued symptoms due to the vasodepressor component of vasovagal syncope. Cardiac pacing alone is ineffective treatment for this phenomenon, and no proven therapy is presently available. Ventricular pacing applied to patients with unexplained syncope may lead to an increase in or continuation of symptoms rather than an amelioration. There is a need for full investigation of such patients, which must include tilt testing, to allow for the most accurate diagnosis possible and guide the most appropriate therapy.

Developmental sequelae of fixed-rate ventricular pacing in the immature canine heart: an electrophysiologic, hemodynamic, and histopathologic evaluation

Permanent, fixed-rate ventricular pacing (VVI) is associated with hemodynamic deterioration in the adult with compromised myocardial function. The effects of this pacing mode on the intact, immature heart, however, are largely unknown. Twelve beagle puppies (age 3 to 4 months) were equally divided into paced and age-matched control groups. All underwent identical hemodynamic and electrophysiologic evaluations. Transepicardial atrioventricular block and pacemaker insertion were additionally carried out in the paced group. After 4 months of observation, repeat hemodynamic and electrophysiologic measurements followed by histopathologic examinations were done in all puppies. The paced group exhibited significant (p less than 0.05) elevations of right atrial and pulmonary artery pressures, alterations in sinus node function, and prolongation of ventricular refractory periods compared with the control group. Initiation of dysrhythmias by programmed electrical stimulation was observed only among the paced group of puppies. Histologic examination demonstrated myofibrillar cellular disarray, dystrophic calcifications, prominent subendocardial Purkinje cells, and an increase in variable-sized, disorganized mitochondria only in the paced specimens. These findings indicate that permanent, apically-initiated VVI pacing ultimately predisposes to adverse cellular changes associated with hemodynamic and electrophysiologic deterioration in the intact, developing immature canine heart.

Atrial natriuretic peptide during different pacing modes in a comparison with hemodynamic changes

The study investigates the response of atrial natriuretic peptide (ANP) to different cardiac pacing modes in comparison with hemodynamic changes. Ten patients underwent Swan-Ganz catheterization during pacemaker implant. Atrioventricular and ventricular pacing were performed consecutively at three pacing rate levels (80, 100, and 110 ppm). Blood samples were taken from the pulmonary artery for ANP determination, both basally and at the end of each pacing period. Concomitantly, mean pulmonary capillary wedge pressure (PCWP) and mean pulmonary artery pressure (PAP) were measured. Cardiac output (CO) was determined by thermodilution both basally and during the 110 ppm steps. During atrioventricular pacing, whereas no significant changes were observed for ANP, PCWP and PAP, CO increased significantly (P less than 0.0005). At the beginning of ventricular pacing hemodynamic parameters and ANP levels were comparable with those of baseline conditions. During subsequent ventricular pacing PCWP and ANP increased significantly at the 110 ppm rate step (P less than 0.05). PAP did not change significantly, whereas CO decreased in all cases (P less than 0.01). A positive correlation was observed between ANP and PCWP during ventricular (P less than 0.001), but not atrioventricular pacing. The results, while confirming the hemodynamic advantages of atrioventricular pacing, point to a major stimulation of ANP secretion during ventricular pacing. This fact, together with the observed drop in CO and the correlation between ANP and PCWP, suggest that the increase of ANP in ventricular pacing may be the expression of a compensatory mechanism to the hemodynamic disadvantages of atrioventricular asynchrony.

New insights into pacemaker syndrome gained from hemodynamic, humoral and vascular responses during ventriculo-atrial pacing

Ventricular pacing is performed during programmed electrical stimulation and during normal functioning of single chamber (VVI or VVIR) pacemakers. In many patients, retrograde ventriculoatrial (V-A) conduction may occur and evoke hemodynamic and reflex neurohumoral responses, which are unique to this pacing mode. Accordingly, forearm blood flow, forearm vascular resistance, mean and phasic arterial pressure, cardiac output and plasma norepinephrine, epinephrine and dopamine were measured during atrial, ventricular and V-A pacing at a cycle length of 600 ms (100 beats/min) before and after regional alpha blockade with intraarterial phentolamine in 16 patients with a left ventricular ejection fraction greater than 35% and little or no symptoms of congestive heart failure. During V-A pacing, cardiac output decreased by 10%, whereas forearm vascular resistance increased from 52 +/- 7 to 70 +/- 9 U (p less than 0.001) and plasma norepinephrine increased from 183 +/- 27 to 232 +/- 27 pg/ml (p less than 0.01). Phentolamine nearly abolished the increase in forearm vascular resistance in response to V-A pacing (18 +/- 4.1 U before vs 5.8 +/- 1.5 U after, p less than 0.05). The change in forearm vascular resistance with V-A pacing correlated with systolic arterial pressure, but not with changes in mean arterial pressure, pulse pressure, cardiac output, mean or peak right atrial pressure, pulmonary artery or pulmonary capillary wedge pressure. These results suggest that forearm vascular resistance responses to V-A pacing are mediated mainly by alpha-adrenergic receptors, through the arterial baroreflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantification of the heart rate-independent vasodepressor component in carotid sinus syndrome

In 45 patients with carotid sinus syndrome, the heart rate-independent vasodepressor component under ventricular and av-sequential pacing of the heart was investigated both in supine and in standing patients. Under both forms of pacing, the carotid pressure determination has led to a marked lowering of systolic and diastolic arterial blood pressure which is significantly more pronounced under orthostasis. The blood pressure values reached both in supine and in standing patients are significantly higher under av-sequential pacing than under ventricular pacing. Accordingly, the proportion of symptomatic patients is less under av-sequential pacing in the supine position (17% versus 29%) and in standing (65% versus 83%). The heart rate-independent vasodepressor reaction is maximal on average between 11 s and 16 s after the beginning of the carotid pressure test and persists for 3 s to 7 s. The blood pressure reaches initial values again after 14 s to 20 s. To summarize, these data document that a clinically relevant heart rate-independent vasodepressor reaction is to be reckoned with in the majority of patients with carotid sinus syndrome. This shows a different time course than the vagally determined effect of the carotid sinus reflex on heart rate. Orthostasis intensifies the vasodepressor reaction so that the hemodynamically more favorable av-sequential pacing which is actually more favorable in hemodynamic terms cannot guarantee freedom from symptoms in the majority of patients in the upright standing position.

Influence of pacing mode and rate on peripheral levels of atrial natriuretic peptide (ANP)

The effect of acute modifications of pacing mode and rate on plasma ANP levels was evaluated. ANP was determined in ten resting patients with DDD pacemakers due to binodal disease or intermittent second-and third-degree AV block. At 82/minute pacing rate the ANP plasma levels (normal range 2 to 30 fmol/mL) corresponded to those under AAI (4.05 +/- 2.10 fmol/mL) and DDD (4.18 +/- 2.02 fmol/mL) pacing, but increased significantly (P 0.05) during VVI pacing (6.96 +/- 3.70 fmol/mL). Acceleration of DDD stimulation frequency from 82 to 113/minutes led to significant increase of ANP levels by the factor of three in all chosen AV delays. The lowest ANP plasma levels were measured at 175 msec AV delay under 82/minute pacing rate in DDD mode. Under 113/minutes the differences of ANP concentration after variations of AV delays were less pronounced. The influences of altered atrial pressure and tension on ANP release are discussed to account for changes in ANP plasma levels following different modes and rates of pacemaker stimulation.

Atrial inhibited pacing in the sick sinus node syndrome: clinical value and the demand for rate responsiveness

A consecutive series of 66 patients (males = 32; mean age +/- SD = 71 +/- 9 years) given atrial inhibited pacemakers for sick sinus nodes were followed to study the incidence of lead failures, chronic atrial tachyarrhythmias, and atrioventricular conduction disturbances. The need for rate responsive pacing was also assessed. Pre and postoperative investigation could include carotid sinus massage, Holter monitoring, exercise testing, and invasive electrophysiology. The mean follow-up time +/- SD was 32 +/- 29 months (median = 26 months). Three patients (5%) had their pacemakers replaced due to lead failures (loss of sensing = 2; exit block = 1). Two pacemakers (3%) were replaced after 5 and 22 months due to atrial fibrillation. Four patients (6%) received new pacemakers because of development of second-degree or complete atrioventricular block after 1, 6, 12, and 31 months, respectively. During exercise, most patients (76%) responded with an increase in sinus rate at least as marked as that achievable with the currently available rate responsive pacemakers. Assuming careful patient selection, atrial inhibited pacing is well suited for many patients with sinus node dysfunction and preserved atrioventricular conduction. There is a limited need for rate responsive pacemakers in these patients.