Regional myocardial blood flow in patients with sick sinus syndrome randomized to long-term single chamber atrial or dual chamber pacing--effect of pacing mode and rate

[Upgrading to biventricular pacing: indications and procedural challenges]

Upgrading RV pacing systems to biventricular resynchronization modalities is a promising option for paced patients with worsening heart failure. The potentially favorable effect of upgrading has been demonstrated in several, non-randomized trials. Selection of eligible patients and technical aspects of the procedure are described. The most common procedure-related complications are reported.

The MINERVA study design and rationale: a controlled randomized trial to assess the clinical benefit of minimizing ventricular pacing in pacemaker patients with atrial tachyarrhythmias

BACKGROUND

Dual-chamber (DDD) pacing has generally been regarded as "physiologic pacing" and therefore expected to be superior to ventricular pacing. Major randomized trials have so far failed to demonstrate significant reductions in the incidences of mortality, stroke, and heart failure. It has been shown that unnecessary ventricular pacing in patients with sinus node dysfunction or only intermittent atrioventricular block is associated with ventricular desynchronization and increased risk of atrial tachyarrhythmias (ATA).

METHODS

The MINimizE Right Ventricular pacing to prevent Atrial fibrillation and heart failure (MINERVA) study is a prospective, multi-center, randomized, international, single-blind, controlled trial designed to determine whether physiologic pacing through the managed ventricular pacing (MVP) algorithm combined with preventive atrial pacing (PAP) and atrial antitachycardia pacing (ATP) is superior to standard DDD pacing in terms of 2-year reduction in death, permanent ATA, and cardiovascular hospitalizations. Patients with standard class I or II indications for permanent DDD pacing and history of ATA will receive a Medtronic EnRhythm implantable pacemaker (Medtronic, Minneapolis, MN). After a 1-month run-in period, patients will be randomized in a 1:1:1 manner to the DDD (control group, all OFF), the DDDRP (MVP + PAP + ATP ON), and the MVP group (only MVP ON). Up to 1,300 patients will be included in approximately 70 centers in Europe, the Middle East, and Asia.

CONCLUSIONS

The MINERVA study will make an important contribution to the management of patients with paroxysmal ATA and accepted indications for dual-chamber pacemaker implantation by determining whether physiologic pacing combined with PAP and ATP is superior to standard DDD pacing in terms of reduction of mortality, incidence of permanent ATA, and cardiovascular hospitalizations.

Early Detection of Regional Myocardial Dysfunction in Paced Children With Congenital Complete Atrioventricular Block

BACKGROUND

Right ventricular apical pacing leads to global left ventricular dysfunction. Assessment of regional myocardial function may allow for earlier detection of pacing-induced myocardial remodeling. The aim of this study was to evaluate regional myocardial function in paced children with congenital complete atrioventricular block (CCAVB).

METHODS

We investigated regional myocardial function using strain echocardiography and tissue velocity imaging in 10 paced children with CCAVB and in 14 age-matched healthy children. Echocardiograms of the paced children were obtained during intrinsic junctional rhythm.

RESULTS

All patients had normal biventricular size and global function. The time from R wave to peak regional strain rate and the time from R wave to peak regional myocardial tissue velocity were measured in nine segments. The differences between maximum and minimum values were used as a measure of contraction delay (dSR and dTV). Study group patients had significantly higher dSR and dTV values compared to the control group. Mean peak strain rates and peak tissue velocities obtained from same segments were significantly decreased in the study group compared to the control group. Regional dysfunction was more prominent in the areas of ventricular pacing. No significant correlation is found between the duration of pacing (2.5-18 years) and dSR, dTV, mean peak strain rates, or mean peak tissue velocities.

CONCLUSION

Pacing leads to regional myocardial dysfunction that can be detected with strain echocardiography and tissue velocity imaging during intrinsic junctional rhythm in children with CCAVB. Pacing-induced regional myocardial remodeling does not seem to progress with long-term right ventricular pacing in children with CCAVB.

Permanent and atrial-synchronized ventricular stimulation for clinically stable patients with normal or impaired left ventricular systolic function

BACKGROUND

Ventricular desynchronization imposed by permanent dual-chamber ventricular pacing (VDD) may compromise ventricular function.

METHODS

We investigated the impact of background VDD pacing on the right and left ventricular (LV) function on 129 clinically stable outpatients (mean age 69 +/- 10) implanted chronically with a dual-chamber pacemaker or an automatic defibrillator by using echocardiographic techniques including tissue doppler imaging (TDI) and color M-mode (CMM) examinations, and B-type natriuretic peptide (BNP) measurements. Patients were divided into two groups of normal (n = 65) or impaired (n = 64) LV systolic function (ejection fraction 63 +/- 6% and 38 +/- 10%, respectively) according to clinical and echocardiographic criteria. Each patient group included two subgroups on the basis of the underlying permanent and atrial-synchronized heart rhythm: either intrinsic ventricular activation (IVA) or VDD pacing.

RESULTS

The BNP levels (mean, 95% CI) of patients with impaired LV systolic function were approximately threefold higher than those of patients with normal LV systolic function [189 (145-245) pg/mL vs 65 (50-85) pg/mL, P < 0.0001], but did not differ between subgroups of patients with IVA vs VDD pacing. By two-way analysis of variance and analysis of covariance, and after adjustment for age and gender, significant VDD pacing effects were found in terms of lower E/A ratio (P < 0.05) and increased LV end-systolic volume (P < 0.05). VDD pacing did not significantly affect the BNP levels and the LV filling pressures, as determined by the E/Ea and E/Vp ratios.

CONCLUSIONS

Long-term VDD pacing may not be harmful in clinically stable patients with normal or moderately reduced LV systolic function.

Ventricular Function and Long-Term Pacing in Children with Congenital Complete Atrioventricular Block

OBJECTIVE

To determine the sequela of right ventricular pacing in children with congenital complete atrioventricular block.

BACKGROUND

Pacing is a well-accepted therapy for patients with congenital complete atrioventricular block. The long-term sequela of right ventricular pacing in this population has not been well described.

METHODS

We performed a cohort study on all patients with congenital complete atrioventricular block who underwent pacemaker implantation at our institution from 1972 to 2004. Patients with associated congenital heart disease or ventricular dysfunction prior to pacemaker implantation were excluded.

RESULTS

A total of 63 patients were included in the study. The median age at pacemaker implantation was 6.5 years, with an average follow-up of 9.9 years. The cumulative dysfunction free survival at 20 years was 92%. In total, four patients (6%) were noted to develop LV dysfunction an average of 15.1 years after pacemaker implantation. Of 30 patients who were paced for >10 years, only three (10%) developed echocardiographic evidence of LV dysfunction. Right ventricular apex pacing and prolonged QRS duration were found to be predictive of decreased long-term LV systolic function (P < 0.05).

CONCLUSIONS

Left ventricular dysfunction in patients with congenital complete atrioventricular block is a rare finding, even in those who have been paced for more than 10 years. Right ventricular apex pacing and prolonged QRS duration may be associated with decreased ventricular function over time. At this time, with such a low incidence of cardiac dysfunction, right ventricular pacing should be considered an acceptable first-line therapy in this population.

Long-Term Effects of Atrial Synchronous Ventricular Pacing on Systolic and Diastolic Ventricular Function in Patients with Normal Left Ventricular Ejection Fraction

BACKGROUND

Atrial synchronous right ventricular pacing (VP) may compromise ventricular function in patients undergoing pacemaker implantation for atrioventricular block. We assessed the usefulness of tissue Doppler imaging (TDI) and color M-mode echocardiography in evaluating patients with VP, and examined the long-term effects of VP on ventricular function by echocardiographic indices and B-type natriuretic peptide (BNP) measurements.

METHODS

We studied 60 clinically stable elderly dual-chamber pacemaker recipients (mean age: 74 +/- 9 years) who had normal left ventricular (LV) systolic function and on the long term the same cardiac rhythm, either intrinsic normal ventricular activation (IA) (n = 20), or VP (n = 40).

RESULTS

Paced patients, compared to patients with IA, had decreased stroke volume (p < 0.05) and a more depressed relaxation pattern, as indicated by decreased peak early mitral velocity (E)/peak atrial contraction velocity ratio and tissue Doppler imaging (TDI)-early transmitral diastolic velocity (Ea) measures (p < 0.05). Both groups presented similar BNP levels and LV filling pressures, as assessed by E/Ea and E/early diastolic transmitral flow propagation velocity. In VP patients, age (beta = 0.31), Ea (beta = -0.28) and E/Ea (beta = 0.32) emerged as independent predictors of BNP levels.

CONCLUSIONS

VP is associated with reduced LV systolic function and signs of impaired relaxation. Elevated BNP levels in elderly VP patients with normal ejection fraction may be predicted by TDI signs of LV diastolic dysfunction.

Pacing in adults with congenital heart disease

Adults with congenital heart disease constitute one of the fastest growing populations in cardiology. Pacing is an integral part of their therapy and may reduce their morbidity and mortality significantly. The current generation of pacemakers is more sophisticated and complex, and they are being utilized for indications other than conduction abnormalities, such as termination of tachycardia and improvement of heart failure. The complex anatomy and history of multiple previous surgeries in adults with congenital heart disease, however, pose many limitations and technical challenges related to the placement of a pacemaker. Unique and innovative approaches to endocardial lead placement and improved epicardial leads is making pacemaker implantation more feasible in these patients.

Upgrade to biventricular pacing in patients with pacing-induced heart failure: can resynchronization do the trick?

Dyssynchrony imposed on ventricular function by right ventricular (RV) apical pacing may lead in some cases to worsening or appearance of heart failure (HF) symptoms. This is a result of an altered pattern of activation, leading to several histological and functional adjustments of the left ventricle, including inhomogeneous thickening of the ventricular myocardium and myofibrillar disarray, fibrosis, disturbances in ion-handling protein expression, myocardial perfusion defects, alterations in sympathetic tone and mitral regurgitation. Studies of mid- and long-term effects of RV apical pacing on left ventricular (LV) function have demonstrated a progressive decline in ejection fraction and other indices of LV functional competence. Upgrading RV pacing systems to biventricular resynchronization modalities is a theoretically promising option for paced patients with worsening HF. The potentially favourable effect of upgrading on LV functional indices and patient clinical status has been demonstrated in few, non-randomized trials. Apart from the scantiness of existing clinical data, issues concerning technical aspects of the procedure and selection of eligible patients are raised. Is pacing-induced dyssynchrony equivalent to the indigenous dyssynchrony in unpaced patients with HF? What selection criteria should be applied in order to identify potential responders to cardiac resynchronization therapy in this patient population? Answers to these and more questions are still lacking.

Increased AAI mode pacing threshold after termination of atrial fibrillation by acute administration of disopyramide phosphate

AIMS

We studied changes in atrial pacing threshold after termination of atrial fibrillation (AF) by acute administration of disopyramide phosphate (DP) to elucidate the suitable setting for atrial pacing output before AF termination.

METHODS AND RESULTS

Four patients with sick sinus syndrome implanted with AAI mode pacemakers were examined. Disopyramide phosphate (2 mg/kg body weight) was injected intravenously for termination of a total of eight AF episodes. The maximal pacing threshold after AF termination (5.2+/-0.8 V at 0.45 ms) was significantly higher than that at baseline (1.3+/-0.2 V at 0.45 ms; P<0.01) and the average increment was 433+/-68%. During a period free from AF, an acute administration of DP did not increase the atrial pacing threshold and serum disopyramide levels were not toxic.

CONCLUSION

The increased atrial pacing threshold observed after AF termination cannot be explained by the action of DP alone. However, our results suggest that atrial pacing output should be set at the maximum value before DP is administered to induce AF termination in patients with AAI pacemaker-dependent bradyarrhythmias.

Prevention of ventricular desynchronization by permanent para-Hisian pacing after atrioventricular node ablation in chronic atrial fibrillation: a crossover, blinded, randomized study versus apical right ventricular pacing

OBJECTIVES

The aim of our study was to evaluate the feasibility, the safety, and hemodynamic improvements induced by permanent para-Hisian pacing in patients with chronic atrial fibrillation and narrow QRS who underwent atrioventricular (AV) node ablation.

BACKGROUND

Right ventricular apical pacing, inducing asynchronous ventricular contraction, may impair cardiac function; permanent para-Hisian pacing could preserve interventricular synchrony and improve left ventricular function.

METHODS

After AV node ablation, 16 patients were implanted with a dual-chamber pacemaker connected to a screw-in lead positioned in close proximity to the His bundle and to a right ventricular apical lead. Clinical and echocardiographic data were collected at baseline and after two randomized six-month periods (with para-Hisian and conventional pacing).

RESULTS

During para-Hisian pacing, the interventricular electromechanical delay improved as well (34 +/- 18 ms) as during right apical pacing (47 +/- 19 ms), p < 0.05. Para-Hisian pacing allowed an improvement in New York Heart Association functional class (1.75 +/- 0.4 vs. 2.33 +/- 0.6 at baseline and 2.5 +/- 0.4 during apical pacing, p < 0.05 for both), in quality-of-life score (16.2 +/- 8.7 vs. 32.5 +/- 15.0 at baseline, p < 0.05), and in the 6-min walk test (431 +/- 73 m vs. 378 +/- 60 m at baseline and 360 +/- 71 m during apical pacing, p < 0.5 for both). Mitral and tricuspid regurgitation improved during para-Hisian pacing (1.22 +/- 0.8 and 1.46 +/- 0.5 index, respectively, vs. 1.68 +/- 0.6 [p < 0.05] and 1.62 +/- 0.7 [p = NS] index at baseline, respectively), with a slight worsening during apical pacing (1.93 +/- 1 and 1.93 +/- 0.7 index, respectively, p < 0.05 for both).

CONCLUSIONS

Permanent para-Hisian pacing is feasible and safe. Compared with conventional right apical pacing, it allows an improvement in functional and hemodynamic parameters over long-term follow-up.

Reduction of right ventricular pacing in patients with sinus node dysfunction using an enhanced search AV algorithm

BACKGROUND

Dual chamber pacing typically results in a high percentage of ventricular pacing. A number of studies have been conducted suggesting detrimental effects of ventricular desynchronization produced by long-term RV pacing. Pacemaker algorithms that extend the AV interval to uncover intrinsic AV conduction have been utilized to reduce ventricular pacing. These algorithms are often limited to AV intervals below 250 ms limiting the ventricular pacing reduction. We hypothesized that by allowing AV intervals to extend beyond 300 ms, a marked reduction in RV pacing can be achieved.

METHODS

A total of 30 patients (17 men, mean age 71 +/- 9) with standard Brady indications, and implanted with a Medtronic Kappa 700 pacemaker, were randomized to 2-week treatments with default Search AV (KSAV) parameters or Enhanced Search AV (ESAV) parameters. The Enhanced Search AV algorithm included the capability for continuous adjustment of AV delays and the ability to auto disable in patients with persistent AV block.

RESULTS

Among patients with intact AV conduction, percent VP was greater in KSAV versus ESAV (70 +/- 40% vs 19 +/- 28%, P < 0.001). In patients with persistent AV block, the algorithm suspended appropriately and there was no significant change in the percent VP between both arms of the study. In 18/22 patients, percent VP was reduced below 40%.

CONCLUSIONS

Substantial reduction in ventricular pacing can be achieved by allowing the AV interval parameters to extend beyond 300 ms using the ESAV algorithm. In patients with AV block, ESAV suspended and patients were paced at their nominal settings.

A New Paradigm for Physiologic Ventricular Pacing

Clinical trials in patients with pacemakers for sinus node dysfunction or atrioventricular block (AVB) and implantable cardioverter-defibrillators provide increasing evidence showing that desynchronization of ventricular electrical activation and contraction, induced by conventional right ventricular apex (RVA) pacing, is a serious threat for long-term cardiac morbidity and mortality. The risk of heart failure is increased even in hearts with initially normal pump function and in case of part-time ventricular pacing. These epidemiologic data fit with knowledge from decades of pathophysiological research, indicating that right ventricular (RV) pacing creates abnormal contraction, reduced pump function, hypertrophy, and ultrastructural abnormalities. This paper presents a new paradigm that aims to tailor ventricular pacing to the individual patient to achieve a way of pacing that is as physiologic as possible. In patients without AVB and no intraventricular conduction abnormalities, ventricular pacing should be avoided as much as possible, using atrial-based pacing. In patients with AVB, alternate single-site RV or left ventricular pacing or biventricular pacing may be superior to RVA pacing. Efforts to optimize the pacing mode or site should be greater in patients with a longer expected duration of pacing, poorer cardiac function, and larger mechanical asynchrony. Awareness of the problem of desynchronization should also lead to more regular monitoring of cardiac pump function and mechanical asynchrony in any patient with ventricular pacing.

N-terminal brain natriuretic peptide as a screening tool for heart failure in the pacemaker population

AIMS

Assessment of N-terminal brain natriuretic peptide (NT-BNP) as a screening tool for heart failure in patients with a permanent pacemaker.

METHODS AND RESULTS

Consecutive patients undergoing a routine permanent pacemaker assessment were enrolled. Patients underwent medical history and examination, echocardiography and blood sampling for NT-BNP. Analysis was performed on 261 patients (132 DDD, 121 VVI, eight others), mean age 73+/-12 years, range 34-99 years. Seventy two subjects (27%) had heart failure as defined by left ventricular ejection fraction (LVEF) <or=40% and symptoms of heart failure (NYHA class II, III, or IV). Screening with NT-BNP gave a sensitivity of 73% and specificity of 72% for detecting heart failure in all patients [area under the curve (AUC) 0.76, P<0.001, 95% CI 0.69-0.83]. This increased in subjects with a DDD type pacemaker (sensitivity 80%, specificity 66%, AUC=0.8, CI 0.7-0.90) and reduced in subjects with a VVI type pacemaker (sensitivity 66%, specificity 61%, AUC 0.68 CI 0.57-0.78).

CONCLUSION

Symptoms of heart failure are common in patients with pacemakers. Screening with NT-BNP is feasible and assists in the detection of important cardiac co-morbidity, particularly in patients with a DDD type pacemaker.

Pacemaker-related myocardial perfusion defects worsen during higher pacing rate and coronary flow augmentation

BACKGROUND

Asynchronous activation resulting from right ventricular apical (RVA) pacing can adversely affect left ventricular function and myocardial perfusion despite normal coronary arteries. This situation makes detection of coronary heart disease in paced patients difficult.

OBJECTIVES

The purpose of this study was to assess the distribution, extent, and severity of myocardial perfusion defects with RVA pacing at low and high rates and increased coronary blood flow with adenosine.

METHODS

Fourteen patients with permanent RVA pacing and angiographically normal coronary arteries underwent myocardial perfusion single-photon emission computed tomography at rest at low and high pacing rates and with pacing at low rates with adenosine. Data were analyzed semi-quantitatively using a 20-segment scoring model and coded using a four-point scoring system.

RESULTS

At rest, 23 (55%) of 42 coronary flow territories showed abnormal perfusion and 52 (19%) of 280 corresponding segments demonstrated abnormal perfusion; mean perfusion score was 0.22. After high-rate pacing, perfusion was abnormal in 31 (74%) of 42 flow territories and 122 (44%) of 280 segments; mean perfusion score was 0.67. Adenosine infusion resulted in 28 (67%) of 42 abnormal flow territories and 90 (32%) of 280 abnormal segments; mean perfusion score was 0.44. Perfusion defects were observed most often in close proximity to the origin of the pacing site.

CONCLUSION

RVA pacing results in myocardial perfusion defects. The false-positive findings are present at rest and more obvious with high-rate pacing than during adenosine infusion. Detection of coronary artery disease should be performed with caution in RVA paced patients because of the high number of perfusion defects observed in the absence of coronary artery disease.

The clinical implications of cumulative right ventricular pacing in the multicenter automatic defibrillator trial II

INTRODUCTION

This study was designed to assess whether right ventricular pacing in the implantable cardioverter defibrillator (ICD) arm of the Multicenter Automatic Defibrillator Implantation Trial (MADIT) II was associated with an unfavorable outcome.

METHODS AND RESULTS

Data on the number of ventricular paced beats were available in 567 (76%) of 742 MADIT II patients with ICDs. The number of ventricular paced beats over the total number of beats showed a bimodal distribution with patients being predominantly paced or nonpaced. Therefore, patients were dichotomized at 0-50% and 51-100% of cumulative pacing with median pacing rate 0.2% and 95.6%, respectively. Endpoints included new or worsening heart failure, appropriate ICD therapy for VT/VF, and the combined endpoint of heart failure or death. Clinical features associated with frequent ventricular pacing included age >or=65 years, advanced NYHA heart failure class, LVEF < 0.25, first degree AV and bundle branch block, and amiodarone use. During follow-up, 119 patients (21%) had new or worsened heart failure, 130 (23%) had new or worsened heart failure or death, and 142 (25%) had appropriate therapy for VT/VF. In comparison to patients with infrequent pacing, those with frequent pacing had significantly higher risk of new or worsened heart failure (hazard ratio = 1.93; P = 0.002) and VT/VF requiring ICD therapy (HR = 1.50; P = 0.02).

CONCLUSIONS

Patients in MADIT II who were predominantly paced had a higher rate of new or worsened heart failure and were more likely to receive therapy for VT/VF. These results suggest the deleterious consequences of RV pacing, particularly in the setting of severe LV dysfunction.

Randomized pilot study of a new atrial-based minimal ventricular pacing mode in dual-chamber implantable cardioverter-defibrillators

OBJECTIVE

We hypothesized that a new minimal ventricular pacing mode (MVP) that provides AAI/R pacing with ventricular monitoring and back-up DDD/R pacing as needed during AV block (AVB) would significantly reduce cumulative percent ventricular pacing compared to DDD/R.

BACKGROUND

Conventional DDD/R mode often results in high cumulative percent ventricular pacing that may adversely affect ventricular function and increase risk of heart failure and atrial fibrillation.

METHODS

MVP was made operational in 30 patients with DDD/R implantable cardioverter-defibrillators (ICDs) and no history of AVB. Patients were randomized to one week each in DDD/R and MVP. Holter monitor recordings (ECG, intracardiac electrograms, and event markers) and device diagnostics were analyzed for cumulative % atrial paced (Cum%AP), cumulative percent ventricular pacing, and frequency and duration of DDD/R pacing back-up. Diaries were used to report symptoms.

RESULTS

Age of the study population was 61 years +/- 12 years and 83% were male. Baseline PR interval was 204 ms +/- 32 ms and programmed AV intervals (DDD/R) were 200 ms +/- 50 ms (paced)/167 ms +/- 54 ms (sensed). Cum%AP was similar between MVP and DDD/R (47.9 +/- 37 vs 46.3 +/- 36). Cumulative percent ventricular pacing was significantly lower in MVP vs DDD/R (3.79 +/- 16.3 vs 80.6 +/- 33.8, P < .0001). Back-up DDD/R pacing during MVP operation due to transient AVB occurred in 10% of patients (9.3 +/- 7.4 [range 1-15] episodes/patient-day, duration 39.7 minutes +/- 156 minutes). Fifteen percent of AV intervals during MVP operation exceeded 300 ms. No significant symptoms were reported during MVP operation.

CONCLUSIONS

MVP dramatically reduced cumulative percent ventricular pacing compared to DDD/R while maintaining AV synchrony and providing sensor-modulated atrial pacing support. Intermittent oscillations between MVP and DDD/R during transient AV block appeared safe and well tolerated.

Atrial Pacing Failure Following Termination of Atrial Fibrillation by Acute Administration of Disopyramide Phosphate

Atrial pacing failure occurred after termination of atrial fibrillation by acute administration of disopyramide phosphate in a 71-year-old woman implanted with an AAI pacemaker for sick sinus syndrome. The atrial pacing threshold showed an 810% increase; however, the serum concentration of disopyramide corresponded to therapeutic level. Infusion of the same dose of disopyramide phosphate used during the period of atrial pacing rhythm did not increase the atrial pacing threshold. In the present patient, we supposed that atrial pacing failure did not occur by the effect of disopyramide alone, but rather was a reciprocal action in response to atrial fibrillation.

Influence of Permanent Right Ventricular Pacing on Cardiorespiratory Exercise Parameters in Chronic Heart Failure Patients With Implanted Cardioverter Defibrillators

STUDY OBJECTIVES

Patients with chronic heart failure and implanted cardioverter-defibrillators (ICDs) may have a higher incidence of new-onset or worsening heart failure requiring hospitalization with dual-chamber ICDs compared with single-chamber ICDs.

DESIGN AND SETTING

The purpose of this study was to show the impact of permanent right ventricular (RV) pacing on exercise capacity and related cardiorespiratory parameters in patients with chronic heart failure and ICDs.

PATIENTS AND INTERVENTIONS

Seventeen patients with chronic heart failure and a dual-chamber ICD performed cardiopulmonary exercise testing (CPX) on 3 different days. After CPX 1, patients were randomized either to back-up pacing or permanent RV pacing. After 3 months, CPX 2 was performed and patients changed groups (crossover design); CPX 3 was performed after 3 additional months.

MEASUREMENTS AND RESULTS

Maximal values for workload (108 +/- 46 W vs 117 +/- 48 W, p < 0.01), oxygen uptake (Vo(2)) [21.0 +/- 5.3 mL/min/kg vs 22.5 +/- 6.4 mL/min/kg, p < 0.05], oxygen pulse (13 +/- 3.7 mL vs 14 +/- 4.0 mL, p < 0.05), and metabolic equivalent (6.0 +/- 1.5 vs 6.4 +/- 1.8, p < 0.05) were significantly lower with permanent RV pacing compared to back-up pacing. Workload, Vo(2), and oxygen pulse were significantly reduced at the ventilatory anaerobic threshold, while workload and Vo(2) were significantly lower at the respiratory compensation point. No differences were found for maximal heart rate, minute ventilation Ve, and respiratory exchange ratio. The Ve/carbon dioxide production slope was significantly steeper with permanent RV pacing compared to back-up pacing.

CONCLUSIONS

Permanent RV pacing significantly reduced maximal and submaximal measures of exercise. For patients with chronic heart failure and sufficient atrioventricular conduction, every effort should be made to minimize permanent right ventricular pacing.

Cost-effectiveness of dual-chamber pacing compared with ventricular pacing for sinus node dysfunction

BACKGROUND

Compared with single-chamber ventricular pacing, dual-chamber pacing can reduce adverse events and, as a result, improve quality of life in patients paced for sick sinus syndrome. It is not clear, however, how these benefits compare with the increased cost of dual-chamber pacemakers.

METHODS AND RESULTS

We used 4-year data from a 2010-patient, randomized trial to estimate the incremental cost-effectiveness of dual-chamber pacing compared with ventricular pacing and then projected these findings over the patients' lifetimes by using a Markov model that was calibrated to the first 5 years of in-trial data. To assess the stability of the findings, we performed 1000 bootstrap analyses and multiple sensitivity analyses. During the first 4 years of the trial, dual-chamber pacemakers increased quality-adjusted life expectancy by 0.013 year per subject at an incremental cost-effectiveness ratio of 53,000 dollars per quality-adjusted year of life gained. Over a lifetime, dual-chamber pacing was projected to increase quality-adjusted life expectancy by 0.14 year with an incremental cost-effectiveness ratio of approximately 6800 dollars per quality-adjusted year of life gained. In bootstrap analyses, dual-chamber pacing was cost-effective in 91.9% of simulations at a threshold of 50,000 dollars per quality-adjusted year of life and in 93.2% of simulations at a threshold of 100,000 dollars. Its cost-effectiveness ratio was also below this threshold in numerous sensitivity analyses that varied key estimates.

CONCLUSIONS

For patients with sick sinus syndrome requiring pacing, dual-chamber pacing increases quality-adjusted life expectancy at a cost that is generally considered acceptable.

Temporary Overdriving Pacing as an Adjunct to Antiarrhythmic Drug Therapy for Electrical Storm in Acute Myocardial Infarction

A-55-year-old man with diabetes mellitus was admitted to hospital because of chest pain. He was diagnosed as anterior acute myocardial infarction and treated with stent placement. After 7 days, ventricular fibrillation occurred because of a subacute reocclusion and balloon angioplasty was performed. Despite reperfusion therapy, intraaortic balloon pumping, antiarrhythmic drugs and beta-blocker, ventricular tachycardia or fibrillation relapsed and cardioversion was performed 29 times during 32 h. Temporary overdrive atrioventricular sequential pacing was initiated and the malignant arrhythmia finally disappeared. Even after stoppage of 25 h overdride pacing, it never recurred. Temporary overdrive pacing is an easy and feasible therapy for a drug-resistant electrical storm associated with AMI and should be performed in the early stage.

Left ventricular function during and after right ventricular pacing

OBJECTIVES

The aim of this research was to evaluate right ventricular pacing effects on left ventricular function.

BACKGROUND

Right ventricular pacing alters the ventricular activation sequence and reduces left ventricular ejection fraction (EF). It is unclear whether the observed reduction in EF can be completely attributed to the alteration in activation sequence.

METHODS

Twelve subjects (eight women), mean age 68 +/- 12 years, with transvenous dual-chamber pacemakers, normal left ventricular function, and intact atrioventricular (AV) conduction were studied with serial-gated blood pool studies. Left ventricular EF was measured at a fixed rate after at least 1 week of atrial pacing only (baseline), during short-term (2 h) and mid-term (1 week) AV sequential pacing with a short AV delay, and after short- and mid-term AV pacing.

RESULTS

Baseline EF was 66.5 +/- 4.5%. Short-term AV pacing resulted in a decrease in EF to 60.3 +/- 5.2% (p < 0.0002). After one week of AV pacing, there was a further decline in EF to 52.9 +/- 8.3% (p < 0.0001). After cessation of mid-term pacing, EF was 57.3 +/- 5.9% (p < 0.0001 vs. baseline). A total of 2, 5, 8, and 24 h later, EF remained depressed (59% to 60%, p < 0.007). At 32 h, EF was 62.9 +/- 7.6% (p < 0.11 compared with baseline).

CONCLUSIONS

The abnormal activation sequence resulting from right ventricular pacing accounts for only part of the reduction in EF as mid-term pacing is associated with a lower EF than short-term pacing, and EF remains depressed after cessation of AV pacing. Changes in ventricular function induced by right ventricular pacing may account for some of its associated adverse effects.

Clinical Significance of Preserving Spontaneous QRS Wave in the Therapy of DDD Pacing for Sick Sinus Syndrome

The aim of this clinical crossover study was to elucidate the effects of atrioventricular (AV) synchronous pacing on cardiac function in patients with sick sinus syndrome (SSS). Thirty SSS patients, each with dual chamber pacemaker (DDD), were enrolled and divided into two groups based on echocardiographic findings. Group A (n = 16) had hypertensive heart disease (wall thickness 11 approximately 12 mm) or mitral or aortic regurgitation (Grade I or II). Group B (n = 14) had no organic heart disease. Three successive 3-month pacing periods were tested. For the first 3 months, long AV delay that achieved > 80% ventricular sensing was chosen. For the next 3 months, AV delay was abbreviated to achieve > 80% ventricular pacing at an optimal AV interval. For the final 3 months, the first setting was resumed. At the end of each period, M mode echocardiography, pulsed-Doppler study, and measurement of plasma brain natriuretic peptide (BNP) level were conducted. In both groups, echocardiographic parameters were not significantly changed during the evaluation. In group A, plasma BNP level was significantly higher at the end of the short AV delay period than at the long AV delay period (P = 0.009), while in group B it did not differ during each period. AV synchronous pacing (> 80% ventricular pacing) in the SSS patients with a DDD pacemaker implanted could increase the ventricular load, and it is better to preserve the spontaneous QRS with the DDD mode with prolonged AV delay in patients with mild hypertensive or valvular disease.

Right Ventricular Outflow Tract Placement of Defibrillation Leads:. Five Year Experience

Over a 5-year period, 112 patients (89 male/23 female, mean age 65 years) underwent right ventricular outflow tract (RVOT) placement of permanent active-fixation transvenous pacing/defibrillating leads. At implantation, the pacing threshold was 0.6 +/- 0.3 V at 0.5 ms pulse duration and R wave amplitude was 10.9 +/- 4.9 mV. The defibrillation threshold (DFT) of right-sided implants was 17.7 +/- 3.4 J while that of left-sided implants was 16.1 +/- 3.3 J. Patients were followed at 1 and 3 month postimplant and at six-month intervals thereafter. At mean follow-up of 22.5 +/- 17.5 months (range 1-47 months) there were no lead dislodgments, unsuccessful shock therapies, or failure to sense or pace for bradycardia or tachycardia. Death was not sudden in the 17 patients who died. We conclude that RVOT pacing-defibrillation lead implantation is safe, efficacious, and potentially attractive because preliminary evidence suggests that it may not be associated with the adverse hemodynamic effects of pacing at the right ventricular apex.

Dual chamber versus single chamber ventricular pacemakers for sick sinus syndrome and atrioventricular block

BACKGROUND

Dual chamber pacing or single chamber atrial pacing ('physiologic' pacing) is believed to have an advantage over single chamber ventricular pacing in that it resembles cardiac physiology more closely by maintaining atrioventricular (AV) synchrony and dominance of the sinus node, which in turn may reduce cardiovascular morbidity and mortality thus contributing to patient survival and quality of life. However, a significant proportion of pacemakers currently implanted are single chamber ventricular pacemakers.

OBJECTIVES

The objective of this review was to assess the short- and long-term clinical effectiveness of dual chamber pacemakers compared to single chamber ventricular pacemakers in adults with AV block, sick sinus syndrome or both. An additional objective was to assess separately any potential differences in effectiveness between dual chamber pacing and single chamber atrial pacing. The clinical effectiveness of single chamber atrial pacing versus single chamber ventricular pacing was not examined.

SEARCH STRATEGY

The Cochrane Controlled Trials Register (The Cochrane Library Issue 3, 2002), MEDLINE (1966 to 2002), EMBASE (1980 to 2002) and the Science Citation Index (1980 to 2002) were searched on 19th August 2002. Citation lists and web sites were checked and researchers in the field contacted.

SELECTION CRITERIA

Parallel group or crossover randomised controlled trials of at least 48 hours duration comparing dual chamber pacing and single chamber ventricular pacing, and investigating cardiovascular morbidity, mortality, patient related quality of life, exercise capacity and complication rates.

DATA COLLECTION AND ANALYSIS

Data was extracted onto pre-piloted data extraction forms. Quality assessment was undertaken using a checklist, with a sub-sample of quality data independently extracted by a second reviewer. Where appropriate data was available, meta-analysis was performed. Where meta-analysis was not possible, the number of studies showing a positive, neutral or negative direction of effect and statistical significance were simply counted.

MAIN RESULTS

Five parallel and 26 crossover randomised controlled trials were identified. The quality of reporting was found to be poor. Pooled data from parallel studies shows a statistically non-significant preference for physiologic pacing (primarily dual chamber pacing) for the prevention of stroke, heart failure and mortality, and a statistically significant beneficial effect regarding the prevention of atrial fibrillation (odds ratio (OR) 0.79, 95% CI 0.68 to 0.93). Both parallel and crossover studies favour dual chamber pacing with regard to pacemaker syndrome (parallel: Peto OR 0.11, 95% CI 0.08 to 0.14; crossover: standardised mean difference (SMD) -0.74, 95% CI - 0.95 to -0.52). Pooled data from crossover studies shows a statistically significant trend towards dual chamber pacing being more favourable in terms of exercise capacity (SMD -0.24, 95% CI -0.03 to -0.45). No individual studies reported a significantly more favourable outcome with single chamber ventricular pacing.

REVIEWERS' CONCLUSIONS

This review shows a trend towards greater effectiveness with dual chamber pacing compared to single chamber ventricular pacing, which supports the current British Pacing and Electrophysiology Group's Guidelines regarding atrioventricular block. Additional randomised controlled trial evidence from ongoing trials in this area will further inform the debate.

An update on clinical trials in pacing: is dual chamber pacing better?

PURPOSE OF REVIEW

As pacemaker technology has increased in complexity and now offers a variety of additional capabilities, there is uncertainty as to which pacing mode offers more benefit-dual-chamber or single-chamber.

RECENT FINDINGS

Two large-scale randomized trials, the Canadian Trial of Physiologic Pacing and the Mode Selection Trial, demonstrated that dual-chamber pacing does not reduce the incidence of stroke or improve survival when compared with ventricular pacing. However, dual-chamber pacing does reduce the incidence of atrial fibrillation and in patients with sinus node dysfunction, reduces heart failure symptoms when compared with ventricular pacing. The modest results of these trials were unexpected when viewed in the context of the very favorable retrospective studies.

SUMMARY

A rethinking of the physiology of cardiac pacing has led to the concept that although atrioventricular synchrony supports an improvement in cardiac output and ventricular pressures, these favorable hemodynamics may be attenuated by ventricular dyssynchrony from right ventricular apical pacing. In patients with a reduced ejection fraction, this dyssynchrony may be especially detrimental. Two trials (DANPACE and SAVE-PACE) are currently underway that will clarify the clinical significance of reducing forced ventricular desynchronization. The results of these trials may direct pacemaker physicians away from the right ventricular apical lead toward a new imperative of atrioventricular and right ventricular-left ventricular synchrony.

Relation Between Abnormal Ventricular Impulse Conduction and Heart Failure

Ventricular pacing and left bundle branch block (LBBB) are two of the most common causes of asynchronous electrical activation of the ventricles. The sequence of activation is an important determinant of cardiac pump function. The sequence of activation during LBBB and during pacing at the conventional pacing site, the RV apex, is similar. In this article the literature on the effect of RV pacing and LBBB on regional and global LV pump function, on long-term adaptations (remodeling) and on their possible contribution to the development of heart failure is discussed. Evidence is increasing that asynchronous electrical activation contributes significantly to the development of heart failure.

Effect of right atrial overdrive pacing in the prevention of symptomatic paroxysmal atrial fibrillation: a multicenter randomized study, the PAF-PACE study

The aim of this study was to assess if right atrial overdrive pacing can suppress symptomatic episodes of paroxysmal atrial fibrillation (PAF) in patients without bradyarrhythmias. Forty-two patients with frequent and symptomatic PAF without other pacing indication had a pacemaker implanted after a 4-week run-in period, during which the frequency of symptomatic PAF episodes and the mean heart rate were objectively documented. Depending on the mean heart rate recorded during run-in, the pacemaker was programmed in random order to right atrial AAI pacing at 10-19 beats/min > mean heart rate (medium overdrive [MO]), at 20-29 beats/min > mean heart rate (high overdrive [HO]) and to no pacing (OAO mode) for 4-12 weeks each using a crossover design. In the 35 patients who completed the protocol, the number of symptomatic episodes of PAF (>30-second duration) per week was significantly lower during MO pacing (median 0.88, P = 0.001, n = 35) and during HO pacing (median 0.75, P = 0.002, n = 20) than during OAO (median 2.02 and 2.04, respectively). There was no difference between MO and HO pacing in the 20 patients paced at both rates (0.97 vs 0.75, P = 0.33). Seven patients did not complete the protocol due to persistent atrial fibrillation (n = 4), angina pectoris requiring surgery (n = 1), and unwillingness to continue the study due to improvement (n = 1) or worsening (n = 1) of symptoms during the study periods. Right atrial overdrive pacing can reduce the number of symptomatic PAF episodes in patients with frequent and drug refractory PAF but without bradyarrhythmias.

Left ventricular mechanics and myocardial blood flow following restoration of normal activation sequence in paced patients with long-term right ventricular apical stimulation

STUDY OBJECTIVES

Asynchronous ventricular activation, as induced by ventricular pacing, is known to affect left ventricular (LV) systolic and diastolic function and myocardial blood flow. However, it is not clear whether the long-term disturbances it causes are reversible after the restoration of the normal ventricular activation sequence.

DESIGN

In this study, we used the conductance catheter method and a Doppler guidewire to assess the changes in LV mechanics, and correspondingly in myocardial blood flow, after the restoration of the normal ventricular activation sequence in patients with long-term right ventricular apical pacing.

PATIENTS

Sixteen patients (mean [+/- SD] age, 61 +/- 11 years; 9 men) with right ventricular apical stimulation and complete ventricular pacing capture for a very long period were studied. In eight patients, we analyzed pressure-volume loops before and immediately after the restoration of the normal ventricular activation sequence, and in the remaining eight patients the myocardial blood flow and flow reserve were analyzed.

MEASUREMENTS AND RESULTS

End-systolic elastance (Ees) [5.503 +/- 0.6 vs 4.287 +/- 0.28 mm Hg/mL, respectively; p = 0.003] and its ratio to effective arterial elastance (1.63 +/- 0.51 vs 2.00 +/- 0.64, respectively; p = 0.009), which are indexes of systolic function and ventriculoarterial coupling, respectively, improved significantly after restoration of the normal ventricular activation sequence. Indexes of diastolic function and the predicted myocardial oxygen consumption (MO(2)) showed no clear change. Coronary flow in the dominant coronary artery increased significantly (46.55 +/- 14.12 vs 71.55 +/- 27.53 mL/min, respectively; p = 0.002), while the coronary flow reserve in the same artery decreased (3.5 +/- 1.0 vs 2.6 +/- 0.5, respectively; p = 0.008).

CONCLUSIONS

The restoration of a normal activation sequence after long-term ventricular asynchrony enhances acutely contractile function without affecting MO(2). These changes in LV function do not appear to have causal relationships with myocardial blood flow changes.

Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRS duration in a clinical trial of pacemaker therapy for sinus node dysfunction

BACKGROUND

Dual-chamber (DDDR) pacing preserves AV synchrony and may reduce heart failure (HF) and atrial fibrillation (AF) compared with ventricular (VVIR) pacing in sinus node dysfunction (SND). However, DDDR pacing often results in prolonged QRS durations (QRSd) as the result of right ventricular stimulation, and ventricular desynchronization may result. The effect of pacing-induced ventricular desynchronization in patients with normal baseline QRSd is unknown.

METHODS AND RESULTS

Baseline QRSd was obtained from 12-lead ECGs before pacemaker implantation in MOST, a 2010-patient, 6-year, randomized trial of DDDR versus VVIR pacing in SND. Cumulative percent ventricular paced (Cum%VP) was determined from stored pacemaker data. Baseline QRSd <120 ms was observed in 1339 patients (707 DDDR, 632 VVIR). Cum%VP was greater in DDDR versus VVIR (90% versus 58%, P=0.001). Cox models demonstrated that the time-dependent covariate Cum%VP was a strong predictor of HF hospitalization in DDDR (hazard ratio [HR], 2.99 [95% CI, 1.15 to 7.75] for Cum%VP >40%) and VVIR (HR 2.56 [95% CI, 1.48 to 4.43] for Cum%VP >80%). The risk of AF increased linearly with Cum%VP from 0% to 85% in both groups (DDDR, HR 1.36 [95% CI, 1.09, 1.69]; VVIR, HR 1.21 [95% CI 1.02, 1.43], for each 25% increase in Cum%VP). Model results were unaffected by adjustment for known baseline predictors of HF hospitalization and AF.

CONCLUSIONS

Ventricular desynchronization imposed by ventricular pacing even when AV synchrony is preserved increases the risk of HF hospitalization and AF in SND with normal baseline QRSd.

Left ventricular septal and apex pacing for optimal pump function in canine hearts

OBJECTIVES

The goal of this study was to test the hypothesis that left ventricular (LV) pump function is optimal when pacing is performed at the LV near the sites where the impulses exit the Purkinje system.

BACKGROUND

Pacing at the conventional site, the right ventricular (RV) apex, adversely affects hemodynamics. During normal sinus rhythm (SR), electrical activation of the working myocardium starts at the LV septal endocardium and spreads from apex to base.

METHODS

Experiments were conducted in anesthetized open-chest dogs with normal ventricular conduction to investigate hemodynamic effects of pacing at various epicardial LV sites, the RV apex, and combinations of these sites (n = 11) and of RV and LV septal pacing (n = 8). The LV septal endocardium was reached via the RV by puncturing through the septum with a barbed electrode. Left ventricular systolic (LVdP/dtpos and stroke work) and diastolic (LVdP/dtneg and Tau) function were assessed using pressure-volume relations (conductance catheter technique).

RESULTS

Left ventricular systolic and diastolic function were highly dependent on the site of pacing, but not on QRS duration. Left ventricular function was maintained at SR level during LV septal, LV apex, and multisite pacing, was moderately depressed during pacing at epicardial LV free wall sites, and was most severely depressed during RV apex pacing. On average, RV septal pacing did not improve LV function, compared with RV apex pacing, but in each experiment one (variable) RV pacing site was found, which only moderately reduced LV function.

CONCLUSIONS

During ventricular pacing, LV pump function is maintained best (i.e., at SR level) when pacing at the LV septum or LV apex, potentially because pacing from these sites creates a physiological propagation of electrical conduction.

Management of arrhythmias in heart failure

Arrhythmias continue to contribute significantly to morbidity and mortality in heart failure. Implantable defibrillators have assumed an increasingly important role in preventing sudden death and are recommended for patients who have been resuscitated from cardiac arrest, have unexplained syncope, or exhibit inducible ventricular tachycardia in the setting of prior myocardial infarction. The extension of survival conferred by implantable defibrillators is likely to be limited in patients with advanced heart failure. Ongoing trials will help define the use of these devices in heart failure populations, in whom atrial fibrillation is common and rate control and anticoagulation are of major importance. Among pharmaceutical options, amiodarone and dofetilide are the major agents for maintenance of sinus rhythm. The complexity of coexistent heart failure and arrhythmia management warrants close collaboration between heart failure and arrhythmia specialists.

Regional myocardial perfusion during chronic biventricular pacing and after acute change of the pacing mode in patients with congestive heart failure and bundle branch block treated with an atrioventricular sequential biventricular pacemaker

BACKGROUND

Biventricular (BiV) pacing has been found to improve systolic function and exercise tolerance in patients with severe congestive heart failure and bundle branch block. The mechanisms behind this beneficial effect is still not sufficiently clarified.

AIM

To evaluate the regional myocardial perfusion (MP) during BiV pacing and after acute change of the pacing mode to conventional dual chamber (DDD) pacing, and single chamber atrial (AAI) pacing in patients with severe congestive heart failure and prolonged QRS width treated with chronic BiV pacing.

METHODS AND RESULTS

Fourteen patients (age 63+/-7 years, 13 male) were evaluated 13+/-7 months after implantation of a triple-chamber biventricular pacemaker. MP was quantified with 13N-labeled ammonia positron emission tomography during BiV pacing, DDD pacing, and AAI pacing. MP was assessed in the anterior, lateral, inferior, and septal regions, and the global mean MP was calculated. Clinical assessment was performed before pacemaker implantation and after at least 3 months of BiV pacing including a 6-min walk test (WT), New York Heart Association (NYHA) class functional score and echocardiography. Global mean MP (BiV: 0.65+/-0.20 vs. DDD: 0.65+/-0.21 vs. AAI: 0.65+/-0.18 mlg(-1)min(-1)) and MP in each of the four regions did not differ between the three pacing modes. The patients improved clinically during BiV pacing; 6 min WT increased (338+/-59 vs. 415+/-73 m, P<0.001), NYHA class score improved (class I/II/III/IV: 0/0/11/3 vs. 1/9/2/0, P<0.001), and left ventricular ejection fraction increased (21+/-5 vs. 29+/-8%, P=0.004).

CONCLUSION

No differences in regional MP are detectable after chronic BiV pacing when the pacing mode is changed acutely in patients with severe congestive heart failure and bundle branch block. This finding indicates, that the clinical improvement caused by BiV pacing is not associated with any increase in the MP and thereby oxygen demand.

[Clinical safety and efficacy of single-chamber atrial pacing in sick sinus syndrome: long-term follow-up]

INTRODUCTION AND OBJECTIVES

Although atrial pacing is a more physiological mode of stimulation in sinus node dysfunction, the pacing modes most often are used DDD and VVI. The aim of our study was to demonstrate that AAI/AAIR pacing is effective and safe by analyzing the complications and mortality of this pacing mode in a long-term follow-up study.

PATIENTS AND METHOD

Between 1982 and 2000 definitive AAI-mode pacemakers were implanted for sinus node dysfunction in mode AAI in 160 patients. We analyzed the clinical characteristics, evolution, and complications of the AAI pacing mode during a follow-up of 5.4 4.5 years.

RESULTS

The sample was made up of 104 women and 56 men with an average age of 72 12 years. During follow-up, it was necessary to change the pacing mode for symptomatic bradycardia in 11 patients (annual incidence 1.2%), which was caused by second or third-degree atrioventricular block in 7 patients (annual incidence 0.8%), and chronic atrial fibrillation with bradycardia in 4 patients (annual incidence 0.4%). During follow-up, atrial arrhythmias occurred in 32 patients (annual incidence 3.7%), stroke in 4 patients (annual incidence 0.4%), and 27 patients (annual incidence 3.1%) died.

CONCLUSIONS

The AAI/AAIR pacing mode was safe and effective in sinus node dysfunction, with a low percentage of pacing changes required for progression to atrioventricular block, low incidence of atrial arrhythmias, stroke and low mortality during long term follow-up.

Functional abnormalities in patients with permanent right ventricular pacing: the effect of sites of electrical stimulation

OBJECTIVES

We sought to evaluate the long-term effects of alternative right ventricular pacing sites on myocardial function and perfusion.

BACKGROUND

Previous studies have demonstrated that asynchronous ventricular activation due to right ventricular apical (RVA) pacing alters regional myocardial perfusion and functions.

METHODS

We randomized 24 patients with complete atrioventricular block to undergo permanent ventricular stimulation either at the RVA (n = 12) or right ventricular outflow (RVOT) (n = 12). All patients underwent dipyridamole thallium myocardial scintigraphy and radionuclide ventriculography at 6 and 18 months after pacemaker implantation.

RESULTS

After pacing, the mean QRS duration was significantly longer during RVA pacing than during RVOT pacing (151 +/- 6 vs. 134 +/- 4 ms, p = 0.03). At six months, the incidence of myocardial perfusion defects (50% vs. 25%) and regional wall motion abnormalities (42% vs. 25%) and the left ventricular ejection fraction (LVEF) (55 +/- 3% vs. 55 +/- 1%) were similar during RVA pacing and RVOT pacing (p > 0.05). However, at 18 months, the incidence of myocardial perfusion defects (83% vs. 33%) and regional wall motion abnormalities (75% vs. 33%) were higher and LVEF (47 +/- 3 vs. 56 +/- 1%) was lower during RVA pacing than during RVOT pacing (all p < 0.05). Patients with RVA pacing had a significant increase in the incidence of myocardial perfusion defects (p < 0.05) and a decrease in LVEF (p < 0.01) between 6 and 18 months, but patients with RVOT pacing did not (p > 0.05).

CONCLUSIONS

This study demonstrates that preserved synchronous ventricular activation with RVOT pacing prevents the long-term deleterious effects of RVA pacing on myocardial perfusion and function in patients implanted with a permanent pacemaker.

Assessment of myocardial adrenergic innervation in patients with sick sinus syndrome: effect of asynchronous ventricular activation from ventricular apical stimulation

OBJECTIVE

To investigate ventricular sympathetic innervation in patients with sick sinus syndrome and to detect regional deterioration of adrenergic innervation caused by asynchronous ventricular activation from right ventricular pacing.

DESIGN

Prospective controlled study.

SETTING

Tertiary cardiac referral centre.

PATIENTS

22 patients with sick sinus syndrome and indications for permanent dual chamber pacing; 20 healthy individuals as controls.

INTERVENTIONS

All patients underwent myocardial imaging with planar and single photon emission computed tomography (SPECT) after an intravenous infusion of 5 mCi 123I-meta-iodobenzylguanidine (123I-MIBG) before and after pacemaker implantation. A SPECT thallium201 myocardial study was done during the same week as the 123I-MIBG study in all patients.

MAIN OUTCOME MEASURES

The heart to mediastinum (H/M) ratio and washout rate were calculated during the 123I-MIBG study to assess the global cardiac sympathetic activity; the aim of the SPECT study was to investigate the regional distribution of adrenergic innervation.

RESULTS

The H/M ratio was significantly smaller in the patients with sick sinus syndrome than in the controls (p < 0.001). In sick sinus syndrome there were regional adrenergic innervation defects, mostly in the inferior and apical walls. After a medium term pacing period, a redistribution of 123I-MIBG uptake was detected, with deterioration of adrenergic innervation in the inferior, apical, and posterior walls. The thallium201 myocardial perfusion study showed no change after three months of permanent pacing.

CONCLUSIONS

Patients with sick sinus syndrome have global and regional disturbances of the adrenergic innervation of the left ventricular myocardium. These seem to deteriorate as a result of asynchronous electrical activation. The clinical significance of this finding requires further investigation.

Relation between local myocardial growth and blood flow during chronic ventricular pacing

Several studies have shown that, per unit mass, myocardial blood flow (MBF) and oxygen consumption are similar in hypertrophic and non-hypertrophic ventricles. This observation may be explained by the degree of myocardial growth matching the increase in oxygen demand. Such matching may, however, not be perfect at the local level, because substantial heterogeneity of MBF exists within the ventricular wall. We investigated to what extent local growth and MBF are matched after redistribution of workload within the left ventricular (LV) wall. Redistribution of workload was established by ventricular pacing at physiological heart rate, which induces asynchronous activation and contraction. Local wall mass (2D-echocardiography) and MBF (fluorescent microspheres) were determined in the canine LV wall before (t=0) and after 6 months of normal sinus rhythm (SHAM group, n=5) or 6 months of pacing at the LV free wall (PACE group, n=8). During acute pacing MBF (ml/min/g) increased with increasing distance to the pacing site. Local relative MBF (rMBF, local MBF normalized to mean MBF in the LV wall) varied from 0.8 adjacent to the pacing site to 1.2 in remote regions. After 6 months of pacing these regional differences had disappeared, probably due to changes in wall mass, which increased with increasing distance to the pacing site (by up to 39+/-13%). In SHAM animals rMBF at t=0 correlated well with rMBF 6 months later (r=0.71). In PACE animals, however, this correlation was poor (r=0.33), because rMBF increased in regions close to the pacing site with initial rMBF<1 and rMBF decreased in regions remote from the pacing site with initial rMBF>1.

CONCLUSIONS

After redistribution of workload within the LV wall as induced by ventricular pacing, local load-regulated growth tends to equalize MBF distribution, but local adaptation of MBF also depends on initial MBF.

Management of arrhythmias in heart failure

Arrhythmias often complicate the management of heart failure and contribute to mortality and morbidity. Implantable cardioverter defibrillators are the best protection from death caused by ventricular arrhythmias, but their benefit will probably be less in heart failure populations than has been observed in trials that have not focused on heart failure populations. Implantable cardioverter defibrillators are first-line therapy for high-risk patients who have been resuscitated from sustained ventricular tachycardia or ventricular fibrillation, who have inducible ventricular tachycardia in the setting of previous myocardial infarction, or who have unexplained syncope. Amiodarone is the major pharmacologic option for treatment of symptomatic arrhythmias. In selecting therapy, the severity of heart failure and cause of heart failure are important considerations. Atrial fibrillation occurs with increasing frequency as the severity of heart failure increases. Anticoagulation and rate control are important. Attempted maintenance of sinus rhythm with amiodarone or dofetilide is a reasonable consideration for selected patients, although the benefit of treatment strategies that seek to maintain sinus rhythm has not been demonstrated. Ongoing trials will provide further guidance for arrhythmia management.

Implantable cardioverter defibrillators in heart failure

Implantable cardioverter defibrillators provide effective and reliable treatment of spontaneous VT and VF. These devices can be expected to decrease the risk for arrhythmic death in patients with heart failure but do not improve overall survival when death from severe pump dysfunction is imminent. Appropriate patient selection is a major aspect of arrhythmia management. Future devices will incorporate features that have the potential to reduce atrial arrhythmias, improve ventricular function, monitor hemodynamics, and prevent sudden arrhythmic death.