Hemodynamic consequences of atrial and ventricular pacing in subjects with normal hearts

Atrial fibrillation and quality of life after pacemaker implantation for sick sinus syndrome: data from the Mode Selection Trial (MOST)

BACKGROUND

In the Mode Selection Trial (MOST) of 2,010 patients with sinus node dysfunction, dual-chamber-paced patients had less atrial fibrillation (AF) and heart failure and had slightly improved health-related quality of life (QOL) compared with rate modulated right ventricular-paced patients. Our objective was to assess the impact of AF on QOL within MOST.

METHODS

We analyzed serial QOL measures (Short Form-36, Specific Activity Scale, time trade-off) in 3 groups: (1) those without AF; (2) those with paroxysmal AF (PAF), but not chronic AF (CAF); and (3) those with CAF. We carried forward the last known QOL before crossover for all subsequent time points in patients randomized to rate modulated right ventricular pacing who crossed over to dual-chamber pacing for severe pacemaker syndrome.

RESULTS

Three hundred seventeen patients (15.8%) had AF in the year after implantation, 206 patients within 3 months (191 PAF, 15 CAF), and another 159 (124 PAF, 35 CAF) between 3 and 12 months. There were no significant differences among groups in individual Short Form-36 subscales or time trade-off scores at 12 months as compared with baseline or 3 months. Cardiovascular health status was better at 12 months as compared with baseline or 3 months in those without AF.

CONCLUSIONS

Atrial fibrillation after pacemaker implantation in elderly patients with sick sinus syndrome was not a major determinant of QOL. However, there was a trend toward better cardiovascular functional status in patients without AF.

Delay of onset of second degree pacemaker block by beta-blockade in patients with P-synchronous pacemakers

Second degree pacemaker block is a safety mechanism of the synchronous pacer at atrial rates above 120-130. The aim of the present study was to determine the work level at which pacemaker block occurred before and after beta-blockade. Seven patients (mean age 53 y.) were submitted to graded, submaximal exercise on a bicycle ergometer without drug and after 0.8 mg pindolol i.v. (6 pats.) or alprenolol orally (1 pat.). Pacemaker block developed at much higher total work after beta-blockade in 3 patients (5800 vs. 1900 kpm. p less than 0.0005), while 4 patients had to stop work due to exhaustion before pacemaker block occurred. Total work increased significantly after beta-blockade (p less than 0.005). Lack of a stable i.v. atrial electrode has delayed the extensive use of the synchronous pacemaker. The design of the generator, however, is not optimal block occurs is too low for a number of patients. beta-Blockade effectively delays the occurrence of pacemaker block and can be of therapeutic value. It is suggested that the P-synchronous pacer should be redesigned with a programmable basic rate (50-70 beats/min) and a programmable upper rate (130-180 beats/min) to ensure that the obvious physiologic advantages of the atrial triggered pacemaker can be maintained both at rest and during physical exercise.

Pacemaker implantation and quality of life in the Mode Selection Trial (MOST)

BACKGROUND

Dual-chamber pacemakers restore AV synchrony compared with ventricular pacemakers, but the effects on health-related quality of life (QOL) are uncertain.

OBJECTIVES

The purpose of this study was to assess the effect of pacemaker implantation, clinical factors, and pacing mode on QOL.

METHODS

The Mode Selection Trial (MOST) randomized 2,010 patients with sinus node dysfunction to rate-modulated right ventricular (VVIR) or dual-chamber (DDDR) pacing. A longitudinal analysis of serial QOL measures (Short Form-36 [SF-36], Specific Activity Scale, and time trade-off utility) was performed. In patients who crossed over from VVIR to DDDR because of severe pacemaker syndrome, the last known QOL prior to crossover was carried forward.

RESULTS

Pacemaker implantation resulted in substantial improvement in almost all QOL measures. Subjects 75 years or older experienced significantly less improvement in functional status and physical component summary scores than did younger subjects. In longitudinal analyses of the effect of pacing mode on QOL, significant improvement in three SF-36 subscales was observed with DDDR pacing compared with VVIR pacing: role physical [62.8 points (95% confidence interval [CI] 60.2, 65.5) vs 56.4 (95% CI 53.7, 59.1)], role emotional [85.0 (95% CI 82.9, 87.0) vs 81.9 (95% CI 79.9, 84.0)], and vitality [51.8 (95% CI 50.3, 53.3) vs 49.3 (95% CI 47.8, 50.7)], but not in other SF-36 subscales, the Specific Activity Scale, or utilities. The gains in QOL were larger than the declines associated with 1 year of aging but smaller than those associated with heart failure.

CONCLUSION

Pacemaker implantation improved health-related QOL. The mode selected was associated with much smaller, but significant, improvements in several domains, particularly role physical function.

Ventricular pacing or dual-chamber pacing for sinus-node dysfunction

BACKGROUND

Dual-chamber (atrioventricular) and single-chamber (ventricular) pacing are alternative treatment approaches for sinus-node dysfunction that causes clinically significant bradycardia. However, it is unknown which type of pacing results in the better outcome.

METHODS

We randomly assigned a total of 2010 patients with sinus-node dysfunction to dual-chamber pacing (1014 patients) or ventricular pacing (996 patients) and followed them for a median of 33.1 months. The primary end point was death from any cause or nonfatal stroke. Secondary end points included the composite of death, stroke, or hospitalization for heart failure; atrial fibrillation; heart-failure score; the pacemaker syndrome; and the quality of life.

RESULTS

The incidence of the primary end point did not differ significantly between the dual-chamber group (21.5 percent) and the ventricular-paced group (23.0 percent, P=0.48). In patients assigned to dual-chamber pacing, the risk of atrial fibrillation was lower (hazard ratio, 0.79; 95 percent confidence interval, 0.66 to 0.94; P=0.008), and heart-failure scores were better (P<0.001). The differences in the rates of hospitalization for heart failure and of death, stroke, or hospitalization for heart failure were not significant in unadjusted analyses but became marginally significant in adjusted analyses. Dual-chamber pacing resulted in a small but measurable increase in the quality of life, as compared with ventricular pacing.

CONCLUSIONS

In sinus-node dysfunction, dual-chamber pacing does not improve stroke-free survival, as compared with ventricular pacing. However, dual-chamber pacing reduces the risk of atrial fibrillation, reduces signs and symptoms of heart failure, and slightly improves the quality of life. Overall, dual-chamber pacing offers significant improvement as compared with ventricular pacing.

Quality of life and clinical outcomes in elderly patients treated with ventricular pacing as compared with dual-chamber pacing. Pacemaker Selection in the Elderly Investigators

BACKGROUND

Standard clinical practice permits the use of either single-chamber ventricular pacemakers or dual-chamber pacemakers for most patients who require cardiac pacing. Ventricular pacemakers are less expensive, but dual-chamber pacemakers are believed to be more physiologic. However, it is not known whether either type of pacemaker results in superior clinical outcomes.

METHODS

The Pacemaker Selection in the Elderly study was a 30-month, single-blind, randomized, controlled comparison of ventricular pacing and dual-chamber pacing in 407 patients 65 years of age or older in 29 centers. Patients received a dual-chamber pacemaker that had been randomly programmed to either ventricular pacing or dual-chamber pacing. The primary end point was health-related quality of life as measured by the 36-item Medical Outcomes Study Short-Form General Health Survey.

RESULT

The average age of the patients was 76 years (range, 65 to 96), and 60 percent were men. Quality of life improved significantly after pacemaker implantation (P<0.001), but there were no differences between the two pacing modes in either the quality of life or prespecified clinical outcomes (including cardiovascular events or death). However, 53 patients assigned to ventricular pacing (26 percent) were crossed over to dual-chamber pacing because of symptoms related to the pacemaker syndrome. Patients with sinus-node dysfunction, but not those with atrioventricular block, had moderately better quality of life and cardiovascular functional status with dual-chamber pacing than with ventricular pacing. Trends of borderline statistical significance in clinical end points favoring dual-chamber pacing were observed in patients with sinus-node dysfunction, but not in those with atrioventricular block.

CONCLUSION

The implantation of a permanent pacemaker improves health-related quality of life. However, the quality-of-life benefits associated with dual-chamber pacing as compared with ventricular pacing are observed principally in the subgroup of patients with sinus-node dysfunction.

Contribution of synchronized atrial systole to left ventricular contraction in the newborn pig heart

Synchronized atrial contraction may be much more important in the newborn, who has a faster heart rate and a less compliant ventricle, than in the adult. We therefore investigated the extent by which synchronized atrioventricular contraction contributes to cardiac output and cardiac work in a neonatal circulation, and whether this effect can be fully explained by the Starling mechanism. In neonatal piglets, left ventricular pressure and volume (conductance catheter) were measured during atrial and ventricular pacing. By manipulating preload during atrial pacing, end-systolic pressure and volume, stroke work, and dP/dtmax were compared at the same end-diastolic volume as indices of contractility. Finally, end-diastolic pressure-volume relationships were assessed to investigate the validity of using end-diastolic pressure as an indicator of preload. We found a significant contribution of synchronized atrial contraction; cardiac output increased 27% when pacing mode was switched form ventricular to atrial. The mechanism by which this was achieved is entirely the enhancement of ventricular filling and thus the Starling effect; contractility was unaffected by pacing mode. This large and important effect can be explained by slowed relaxation (compared with the adult ventricle), which impairs passive filling during the ventricular relaxation phase, and makes active filling during atrial contraction more important. In addition, we found that the use of end-diastolic pressure as an indicator of preload, instead of end-diastolic volume, leads to serious misinterpretations, due to not only the nonlinearity of this relationship, but also the possible shifts in this relationship with certain interventions.

Effect of pacing rate on regional left ventricular wall motion. Assessment by quantitative analysis of equilibrium radionuclide angiography

We evaluated the hemodynamic impact of right ventricular pacing at different stimulation frequencies. Fourteen patients with a right ventricular pacemaker (VVI pacing with retrograde P wave) but without clinical and electrocardiographic evidence of coronary artery disease underwent two equilibrium radionuclide angiographies: one under low heart rate (50/60 beats per minute) and the other under fast heart rate (90/100 beats per minute). Left ventricular global and sectorial ejection fractions, amplitude and phase images of first harmonic, and sectorial phases of left ventricle were analyzed. In twelve patients (84.7%), sectorial ejection fraction abnormalities in the left ventricular apicoseptal and inferoapical regions were observed under low heart rate, and worsened under fast heart rate, while new onset sectorial ejection fraction abnormalities under fast heart rate were observed in the other two patients with normal sectorial ejection fraction under low heart rate. Sectorial ejection fractions of left ventricular apicoseptal and inferoapical regions significantly changed between low and high heart rate (- 14.1 +/- 3.8%, p < 0.005; - 7.5 +/- 2.4%, p < 0.01 respectively). Left ventricular sectorial phases were abnormal in only two patients (14.3%) under low heart rate, and in twelve patients (84.7%) under fast heart rate. Our study confirms that left ventricular regional wall motion abnormalities during VVI pacing significantly worsen under fast heart rate in comparison to those under low heart rate.

Increased risk of progressive hemodynamic deterioration in advanced heart failure patients requiring permanent pacemakers

To determine the influence of long-term permanent pacing systems on survival in patients with severe left ventricular dysfunction, data from 557 consecutive patients hospitalized with advanced heart failure for cardiac transplant evaluation and discharged on medical therapy were reviewed. Permanent pacemakers were identified in 42 (8%) patients. One-year actuarial risk of death from heart failure or urgent transplantation in paced patients was higher (49%) than that of a control group, matched for the severity of heart failure (15%, p = 0.003). Sudden death did not differ between paced patients and controls.

Natural history of sinus node disease treated with atrial pacing in 213 patients: implications for selection of stimulation mode

OBJECTIVES

This study was designed to analyze the incidence and determinants of complications and long-term survival in sinus node disease treated with atrial pacing.

BACKGROUND

Knowledge of the natural history of sinus node disease treated with different pacing modes is imperfect, and controversy exists regarding the optimal pacemaker therapy.

METHODS

A consecutive series of 213 patients with sinus node disease initially treated with atrial pacing was studied for a median follow-up period of 60 months. The end points studied were permanent atrial fibrillation, high grade atrioventricular (AV) block, P wave undersensing, pacing mode change, reoperation and death. Several prognostic factors were evaluated statistically and the survival rate was compared with that of a matched general population.

RESULTS

The incidence rate of permanent atrial fibrillation during follow-up was 7% (1.4%/year). The risk of this arrhythmia increased substantially with age greater than or equal to 70 years at pacemaker implantation. Only 2 of the 15 patients who developed permanent atrial fibrillation required ventricular pacing. High grade AV block occurred in 8.5% (1.8%/year) and its incidence was much greater in patients with complete bundle branch block or bifascicular block (35%) than in patients without such conduction disturbances (6%). A change to ventricular or dual-chamber stimulation was necessary in 14% of all patients, primarily because of early lead dislodgment or high grade AV block. Surgical intervention with maintenance of atrial pacing was required in 7% of patients. The survival rates of 97% at 1 year, 89% at 5 years and 72% at 10 years did not differ significantly from those of a matched general population.

CONCLUSIONS

In sinus node disease, atrial pacing can be successfully applied during long-term follow-up. Patients with complete bundle branch or bifascicular block in addition to sinus node disease should initially receive a dual-chamber pacemaker, but routine application of dual-chamber stimulation does not appear to be warranted.

Effect of atrioventricular synchrony on stroke volume during ventricular tachycardia in man

The hemodynamic consequences of atrioventricular (AV) synchrony during ventricular tachycardia were evaluated during cardiac electrophysiologic testing. The relationship between stroke volume and the AV interval was investigated on a beat-by-beat basis in six patients during induced monomorphic ventricular tachycardia. Stroke volume was calculated either (1) in the right ventricle using impedance catheter method (four patients) or (2) in the left ventricle using Doppler measurement of aortic blood velocity (two patients). The impedance catheter method underestimated stroke volume by a factor of 4.2 +/- 2.4 compared with the thermodilution cardiac output method. However, there was a highly linear relationship between both methods for computing stroke volume (r greater than 0.9). Five patients had complete AV dissociation during ventricular tachycardia, and different AV intervals spanned the entire tachycardia cycle lengths. Largest stroke volumes were associated with optimal AV intervals within 120 and 230 msec, resulting in a 97 +/- 59% increase in stroke volume over ventricular tachycardia cycles not associated with atrial activity. Customized atrial pacing during ventricular tachycardia may provide a valuable means for artificially establishing the hemodynamically optimal AV interval and eliminating the ventricular tachycardia cycles not preceded by atrial activity.

Thoracocardiography. Part 1: Noninvasive measurement of changes in stroke volume comparisons to thermodilution

The thoracocardiograph (TCG) is a new noninvasive monitoring device that measures cardiac oscillations transmitted to the external surface of the thorax. It consists of 2.5 cm in height, elastic inductive plethysmographic transducers placed transversely in the proximity of the xiphoid process to provide changes in cross-sectional area on a transverse plane across the minor ventricular axis. Cardiac oscillations synchronous with each heart beat are extracted from the respiratory signal during breathing with an ensemble-averaging technique using the electrocardiograph as a trigger pulse. The average cardiac waveform at locations near the xiphoid process in normal humans has the appearance of a ventricular volume curve. The latter is also found in the majority of patients with heart disease although in some, outward (dyskinetic) rather than inward motion during systole occurs at one or more locations of the TCG transducers. As in echocardiography, such findings are consistent with ischemic or scarred myocardium invalidating computation of changes in stroke volume from such sites. In anesthetized dogs and critically ill patients with normal ventricular wall motion, changes in TCG derived ventricular volume waveform amplitudes agreed well with changes of thermodilution estimates of stroke volume during atrial pacing and fluid loading in the dogs on the one hand and with application of extrinsic positive end-expiratory pressure (PEEP) in patients on the other hand. Thoracocardiography has the potential for noninvasive, continuous monitoring of stroke volume and cardiac output as well as for detection of ischemic or scarred myocardium.

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.

Atrial natriuretic peptide levels reflect hemodynamic changes under pacemaker stimulation

Pacemaker stimulation influences plasma levels of atrial natriuretic peptide (ANP). This study evaluated in individuals without impaired myocardial function whether a consecutive increase of pacing rates results in reduced alteration of plasma ANP levels mirroring a putative decrease of atrial contribution to cardiac output. In nine resting patients with DDD pacemakers, absolute and relative ANP plasma levels were determined under DDD (175 msec AV delay) and VVI pacing at a pacing rate of 72, 82, 92, and 113 beats/min. When pacing rates were consecutively increased, higher plasma ANP concentrations were measured. However, the differences in relative ANP levels were nearly identical. Therefore, it seems likely that the atrial contribution to cardiac output at high pacing rates is less important than at lower frequencies, at least when the overall myocardial function is not impaired.

Importance of heart rate response during exercise in patients using atrioventricular synchronous and ventricular pacemakers

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

Comparison of the effects of right atrial, right ventricular apex and atrioventricular sequential pacing on myocardial oxygen consumption and cardiac efficiency: a laboratory investigation

As the impact of cardiac pacing on myocardial energetics has not yet been established, this laboratory investigation was undertaken to evaluate the effects of right atrial (AP), right ventricular apex (VP) and atrioventricular sequential pacing (AVP) on cardiac energetics in a closed-chest model. Ninety-two pacing interventions were performed in ten anesthetized mongrel dogs with normal loading conditions and contractile states. The energetic effects of pacing were assessed in terms of myocardial oxygen consumption (MVO2), its hemodynamic determinants and cardiac efficiency. Efficiency was calculated as the ratio of O2-equivalent of external cardiac work to MVO2, using standard definitions. In the first series of experiments 36 intra-individual comparisons were made between AP and VP at identical rates (95-210 beats/min). In the second series AVP was compared to VP in 10 intra-individual comparisons at identical rates (109-190 beats/min). MVO2 was lower (p less than 0.001) during AP (8.30 +/- 2.14 ml O2/min.100 g) compared to VP (10.16 +/- 3.15 ml O2/min.100 g) at the same rate (158 +/- 32 beats/min). Efficiency (p less than 0.001) was considerably higher during AP (21.6 +/- 5.7%) compared to VP (12.8 +/- 5.9%). During AVP, MVO2 (10.85 +/- 1.76 ml O2/min.100 g) was not significantly different from VP (10.57 +/- 1.34 ml O2/min.100 g) at the same rate (146 +/- 25 beats/min). Hemodynamics were superior with AVP compared to VP. Efficiency was significantly higher (p less than 0.01) with sequential (15.4 +/- 3.9%) as compared to ventricular pacing (12.0 +/- 3.2%). In conclusion, this study indicated that VP exerts disadvantageous effects on MVO2 and cardiac efficiency. AP has beneficial effects on cardiac energetics because it improves the relationship between mechanical performance of the heart and its energy requirements. AVP results in a higher efficiency than VP due to superior hemodynamics, despite MVO2 levels comparable to those of VP. The mechanism of energy waste with right ventricular apex pacing is probably related to an asynchronous contraction in the ventricular myocardium due to a nonphysiological spread of excitation.

Experiences with atrial pacing

The records of 187 patients with permanent atrial pacemakers implanted between 1970 and 1980 were studied retrospectively to define the indications, outcome and short- and long-term complications of single-chamber atrial pacing. Pacemakers were implanted in 145 (77%) patients with tachybrady syndrome, 35 (19%) with sinus bradycardia and 7 (4%) with ventricular arrhythmia. Intact atrioventricular (AV) conduction was defined as absence of second- or third-degree heart block with incremental atrial pacing to a heart rate of 120 beats/min before implantation. The average follow-up was 30 months, including 87 patients (46%) who were followed an average of 48 months. Four patients developed significant conduction disease requiring placement of a ventricular lead. Complications included 4 lead fractures (all coronary sinus leads), 10 dislodgments (9 coronary sinus, 1 tined atrial "J") and 6 threshold rises requiring repositioning of the lead. Eight dislodgments occurred within an average of 5.6 days. The average increase in threshold that required repositioning occurred at 14 days. The average lead fracture occurred at 25 months. Atrial pacing is safe and effective for patients with sinoatrial node disorder (sick sinus syndrome) and intact AV conduction. Progression to clinically significant AV block is uncommon. Complications occur early with coronary sinus leads and are less common with newer leads.

Maintenance of exercise stroke volume during ventricular versus atrial synchronous pacing: role of contractility

Although atrial synchronous and rate-responsive ventricular pacing have been compared, the importance of maintaining synchronized atrial systole in addition to rate responsiveness has been incompletely defined. That is, the effects of these two pacing modes on cardiac volumes and contractility have not been studied. Accordingly, 16 patients with normal ventricular function were studied while in the upright position and at rest with gated radionuclide ventriculography during both atrial synchronous and ventricular pacing. Twelve of these patients were also studied during low-level upright exercise (300 kilopond-meters). Rest and exercise ventricular pacing heart rates were matched to those recorded with synchronous pacing. Ventricular volumes were determined with a counts-based method. The ejection fraction and peak systolic pressure/end-systolic volumes or contractility between the two pacing modes. However, during exercise to identical heart rates, blood pressures, and workloads, although stroke volume was the same during exercise with atrial synchronous and ventricular pacing (78 +/- 13 vs 75 +/- 12 ml), end-diastolic and end-systolic volumes were lower with ventricular pacing than with atrial synchronous pacing (end-diastolic volume 101 +/- 13 vs 113 +/- 16 ml, p less than .001; end-systolic volume 26 +/- 4 vs 35 +/- 7 ml, p less than .001). Stroke volume during ventricular paced exercise was maintained at atrial synchronous pacing levels by means of increased contractility (ejection fraction of 74 +/- 4% during ventricular pacing vs 69 +/- 5% during atrial synchronous pacing, p = .002; peak systolic pressure/end-systolic volume ratio of 6.51 +/- 1 during ventricular pacing vs 4.85 +/- 1 during atrial synchronous pacing, p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ventricular pacing on left ventricular function assessed by radionuclide angiography

Radionuclide angiography was used to evaluate left ventricular contraction on and off ventricular pacing in 35 patients. Twenty patients had permanent rate-adjustable ventricular demand pacemakers whose rate could be programmed to below an underlying sinus rhythm. In these patients there was no difference in left ventricular ejection fraction on and off pacing whether or not heart failure was present (n = 7) or whether or not ventriculoatrial conduction (n = 10) developed during pacing. Eight of the 20 patients also underwent supine bicycle exercise, and rest and exercise ejection fraction values were not significantly different at a similar heart rate and workload when on and off pacing were compared. During pacing, there appeared to be abnormal motion in septal, apical, and inferior walls. In addition, dysynchrony developed, consisting of early right ventricular and anterobasal and posterobasal left ventricular motion with subsequent contraction of the apex. Conversion to atrioventricular pacing produced a clinical improvement in all seven patients with heart failure and reduced ejection fraction and also in one of the remaining 13 patients without heart failure. Fifteen other patients were studied early after cardiac surgery. Temporary ventricular epicardial pacing resulted in a significant increase in right and left atrial pressure and a significant reduction in stroke volume, end-diastolic volume, and end-systolic volume with no significant change in ejection fraction. Conversion from sinus rhythm to ventricular pacing produces a deterioration in cardiac performance and severe regional left ventricular wall motion abnormalities, but no significant change in ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of rate on left ventricular volumes and ejection fraction during chronic ventricular pacing

Resting left ventricular (LV) function was evaluated in 22 patients with permanent ventricular pacemakers. LV ejection fraction and volume indexes were determined by gated blood pool scintigraphy at ventricular pacing rates of 50-100 beats/min. In patients with a normal heart size, increases in pacing rates resulted in significant linear decreases in stroke volume index and ejection fraction. However, end-systolic volume index and cardiac index did not change. Patients with cardiomegaly appeared to respond differently. End-diastolic volume index decreased significantly as the pacing rate was increased from 50 to 100 beats/min. Ejection fraction was significantly reduced only at pacing rates of 90 and 100 beats/min. Mean cardiac index was highest at ventricular pacing rates of 70-90 beats/min. Increases in cardiac index, achieved by increasing the pacing rate, were maintained over a 4.3-month follow-up. Patients with underlying sinus rhythm had a 27% increase in cardiac output in association with an increase in ejection fraction from 55% to 62% when sinus rhythm was compared to ventricular pacing at a rate of 60 beats/min. These data suggest that patients with cardiomegaly have a narrow range of optimal pacing rates at rest.

Recent advances in programmable pacemakers. Consideration of advantages, longevity and future expectations

The important electrical characteristics of conventional ventricular demand pacemakers currently widely employed are unable to be altered by noninvasive means after their implantation. However, a number of domestic pacemaker manufacturers have started to introduce a new modality for atraumatic modulation of these devices, the fully programmable pacemaker system, whereby the several variables regulating pacemaker operation may be optimized on an individual basis according to need. Such programmable pacemaker functions which can be varied include rate, energy output, refractory period and sensing threshold. The indications, significance and mechanisms for control of the various function programming are delineated for physician understanding at the present time.

Symptomatic unilateral cannon "a" waves in a patient with a ventricular pacemaker

A 64-year-old woman was referred because of intermittent pulsations of the left side of the neck, face, and scalp that were first noticed after the insertion of a ventricular pacemaker. The pacemaker had been inserted because of symptomatic 2:1 atrioventricular block. Right cardiac catherization showed cannon "a" waves, and phlebographic studies revealed stenosis of the right innominate and internal jugular veins. The symptoms were abolished by conversion to an atrial synchronous pacing system. Comments are offered on the hemodynamic findings, the "pacemaking syndrome", and the use of atrial synchronous pacing.

Atrial pacing from the coronary vein. Ten-year experience in 50 patients with implanted pervenous pacemakers

During the past ten years, pervenous atrial pacemakers have been implanted in 50 patients (mean age 68 years, 60% males) using an electrode positioned in the coronary vein. The indications for atrial pacing were symptomatic sinus bradycardia (72%), atrial brady-tachy syndrome (20%), and recurrent tachyarrhythmias (8%). Atrial pacemakers have been implanted for a total of 1531 pacing months, average 31 months per patient, median 26 months and range 3-97 months. Effective atrial pacing has been achieved with Medtronic model 5818 and 6904 electrodes. Unipolar or bipolar atrial pacing has been equally effective, and commercially available Medtronic 5950, Cordis 162 and CPI 602 pulse generators have been utilized without difficulty. A total of 11 electrode related malpacing events occurred in the ten-year period with a malpacing event rate of 10% in the first pacing month, 1.1% per paced month during the next six months, and 0.25% per paced month thereafter. Life table analysis reveals that effective atrial pacing was achieved in 76% of the patients during a follow-up of more than five years. This experience substantiates the long-term safety and effectiveness of atrial pacing from the coronary vein using standard pacemaker electrodes and generators.

Adverse effects of right ventricular pacing in a patient with aortic stenosis, Hemodynamic documentation and management

A patient with moderate aortic stenosis, left ventricular hypertrophy, and a permanent right ventricular pacemaker for a sick sinus node presented with hypotension, dizziness, and angina pectoris with paced beats. The hemodynamics of pacing were documented with non-invasive and invasive studies. The patient was successfully treated with a programmable generator and pacing at a lower rate. The neccessity of evaluating the effects of a temporary pacemaker before insertion of a permanent one and of a reevaluation of the hemodynamic status in the presence of unexplained cardiac failure in a patient with permanent pacemaker are emphasized in this case report.

Permanent pacing of the heart: 1952 to 1976

The theory and science of electrical pacing of the heart is scarcely 2 decades old, but developments in these areas have in a way revolutionized modern cardiology. This report, basically a review of the major developments during that time, describes the present state of the art, and calls attention to the many people who have brought us to this point. Results of a recent national survey reveal that about 156,000 patients in the United States are living with implanted pacemakers or about 1 in every 1,300 persons. The rate of new implants is 270/million each year, the highest in the world. The impact of such a volume is considerable, affecting industrial growth, federal legislation and control, insurance plans and a multitude of medical programs. New power sources, some touted to last a lifetime, will have a great impact but will not change the current state of the art materially because 30 percent or more of pacemaker operations are for problems other than routine battery exhaustion. The need for improvements in other pacemaker components is emphasized.

Experimental myocardial infarction. 8. Chronotropic augmentation of cardiac function in left ventricular failure of acute and healing stages in intact conscious dogs

The hemodynamic effects of tachycardia induced by atrial pacing were investigated in left ventricular failure of acute and healing experimental myocardial infarction in 20 intact, conscious dogs. Myocardial infarction was produced by gradual inflation of a balloon cuff device implanted around the left anterior descending coronary artery 10-15 days prior to the study. 1 hr after acute myocardial infarction, atrial pacing at a rate of 180 beats/min decreased left ventricular end-diastolic pressure from 19 to 8 mm Hg and left atrial pressure from 17 to 12 mm Hg, without change in cardiac output. In the healing phase of myocardial infarction 1 wk later, atrial pacing decreased left ventricular end-diastolic pressure from 17 to 9 mm Hg and increased the cardiac output by 37%. This was accompanied by evidence of peripheral vasodilation. In two dogs with healing anterior wall myocardial infarction, left ventricular failure was enhanced by partial occlusion of the circumflex coronary artery. Both the dogs developed pulmonary edema. Pacing improved left ventricular performance and relieved pulmonary edema in both animals. In six animals propranolol was given after acute infarction, and left ventricular function deteriorated further. However the pacing-induced augmentation of cardiac function was unaltered and, hence, is not mediated by sympathetics.The results show that the spontaneous heart rate in left ventricular failure of experimental canine myocardial infarction may be less than optimal and that maximal cardiac function may be achieved at higher heart rates.

Long-term pervenous atrial pacing

Long-term pervenous right atrial pacing has been used in five patients with intact atrioventricular (A-V) conduction for the treatment of refractory ventricular arrhythmias in two subjects and marked sinus bradycardia in three, two of whom also had paroxysmal supraventricular arrhythmias. The pervenous method was used to avoid a thoracotomy, and atrial pacing was chosen over ventricular pacing to preserve the normal A-V contraction sequence. Reliable atrial pacing was established in four cases, but one patient required ultimate conversion to a ventricular system because of irregular atrial capture. The most constant pacing was achieved by using a curved electrode with the tip positioned in the right atrial appendage.

The 'A' wave of the apex cardiogram in aortic valve disease and cardiomyopathy

Images

Atrial fibrillation produced by atrial stimulation

Twenty-six episodes of atrial fibrillation and flutter-fibrillation, each lasting less than 23 sec, were recorded in three normal subjects during atrial pacing studies. The cause of these atrial arrhythmias was determined to be the result of stimulation within the atrial vulnerable period.