The effects of pacing-induced left bundle branch block on left ventricular systolic and diastolic performances

Delayed Time to Peak Velocity Is Useful for Detecting Severe Aortic Stenosis

BACKGROUND

Time to peak velocity (TPV) is an echocardiographic variable that can be easily measured and reflects a late peaking murmur, a classic physical finding suggesting severe aortic stenosis (AS). The aim of this study was to investigate the usefulness of TPV to evaluate AS severity.

METHODS AND RESULTS

This study included 700 AS patients, whose aortic valve area (AVA) was <1.5 cm2, and 200 control patients. The TPV was defined as the time from aortic valve opening to when the flow velocity across the aortic valve reaches its peak. AS severity was classified as follows: High gradient severe AS, mean pressure gradient ≥40 mm Hg and AVA index (AVAI) <0.6 cm2/m2; Low gradient severe AS, mean pressure gradient <40 mm Hg, AVAI <0.6 cm2/m2, and dimensionless index <0.25; moderate AS, mean pressure gradient <40 mm Hg, AVAI ≥0.6 cm2/m2. The area under the receiver operating characteristic curve of TPV to predict high gradient severe AS was 0.94 (95% CI: 0.92-0.97, P<0.001). TPV was significantly delayed in low gradient severe AS compared with moderate AS both in patients with preserved (102±13 ms versus 83±13 ms, P<0.001) and with reduced ejection fraction (110±18 ms versus 88±13 ms, P<0.001). Delayed TPV was associated with increased all-cause mortality or need for aortic valve replacement after adjustment for confounders (hazard ratio for first quartile, reference is fourth quartile: 7.31, 95% CI 4.26-12.53, P<0.001).

CONCLUSIONS

TPV is useful to evaluate AS severity and predict poor prognosis of AS patients.

Cardiomyopathy induced by artificial cardiac pacing: myth or reality sustained by evidence?

Implantable cardiac pacing systems are a safe and effective treatment for symptomatic irreversible bradycardia. Under the proper indications, cardiac pacing might bring significant clinical benefit. Evidences from literature state that the action of the artificial pacing system, mainly when the ventricular lead is located at the apex of the right ventricle, produces negative effects to cardiac structure (remodeling, dilatation) and function (dissinchrony). Patients with previously compromised left ventricular function would benefit the least with conventional right ventricle apical pacing, and are exposed to the risk of developing higher incidence of morbidity and mortality for heart failure. However, after almost 6 decades of cardiac pacing, just a reduced portion of patients in general would develop these alterations. In this context, there are not completely clear some issues related to cardiac pacing and the development of this cardiomyopathy. Causality relationships among QRS widening with a left bundle branch block morphology, contractility alterations within the left ventricle, and certain substrates or clinical (previous systolic dysfunction, structural heart disease, time from implant) or electrical conditions (QRS duration, percentage of ventricular stimulation) are still subjecte of debate. This review analyses contemporary data regarding this new entity, and discusses alternatives of how to use cardiac pacing in this context, emphasizing cardiac resynchronization therapy.

The deleterious consequences of right ventricular apical pacing: time to seek alternate site pacing

BACKGROUND

The purpose of this article is to critically review the data accumulated to date from studies evaluating the hemodynamic and clinical effects of right ventricular apical pacing during conventional permanent cardiac pacing. The data from studies comparing the effects of right ventricular apical pacing and alternate site ventricular pacing are also reviewed.

METHODS

We conducted a MEDLINE and journal search of English-language reports published in the last decade and searched relevant papers.

RESULTS

Although intraventricular conduction delay in the form of left bundle branch block (LBBB) has traditionally been viewed as an electrophysiologic abnormality, it has now become abundantly clear that it has profound hemodynamic effects due to ventricular dyssynchrony, especially in patients with heart failure. These deleterious effects can be significantly ameliorated by cardiac resynchronization therapy effected by biventricular or left ventricular pacing. However, not only is spontaneous LBBB harmful, but the iatrogenic variety produced by right ventricular apical pacing in patients with permanent pacemakers may be equally deleterious. In this review new evidence from recent studies is presented, which strongly suggests a harmful effect of our long-standing practice of producing an iatrogenic LBBB by conventional right ventricular apical pacing in patients receiving permanent pacemakers. This emerging strong new evidence about the adverse hemodynamic and clinical effects of right ventricular apical pacing would dictate a reassessment of our traditional approach to permanent cardiac pacing and direct our attention to alternate sites of pacing, such as the left ventricle and/or the right ventricular outflow tract or septum, if not for all patients, at least for those with left ventricular dysfunction. Indeed, current convincing data on alternate site ventricular pacing are encouraging and this approach should be actively pursued and further investigated in future studies.

CONCLUSIONS

Not only is spontaneous permanent LBBB harmful to our patients, but the iatrogenic variety produced by right ventricular apical pacing during conventional permanent pacing may also be deleterious to some patients. The compelling evidence presented herein cannot be ignored; it may dictate a change of attitude toward right ventricular apical pacing directing our attention to alternate sites of ventricular pacing and avoidance of the right ventricular apex.

Biventricular versus conventional right ventricular stimulation for patients with standard pacing indication and left ventricular dysfunction: the Homburg Biventricular Pacing Evaluation (HOBIPACE)

OBJECTIVES

The Homburg Biventricular Pacing Evaluation (HOBIPACE) is the first randomized controlled study that compares the biventricular (BV) pacing approach with conventional right ventricular (RV) pacing in patients with left ventricular (LV) dysfunction and a standard indication for antibradycardia pacing in the ventricle.

BACKGROUND

In patients with LV dysfunction and atrioventricular block, conventional RV pacing may yield a detrimental effect on LV function.

METHODS

Thirty patients with standard indication for permanent ventricular pacing and LV dysfunction defined by an LV end-diastolic diameter > or =60 mm and an ejection fraction < or =40% were included. Using a prospective, randomized crossover design, three months of RV pacing were compared with three months of BV pacing with regard to LV function, N-terminal pro-B-type natriuretic peptide (NT-proBNP) serum concentration, exercise capacity, and quality of life.

RESULTS

When compared with RV pacing, BV stimulation reduced LV end-diastolic (-9.0%, p = 0.022) and end-systolic volumes (-16.9%, p < 0.001), NT-proBNP level (-31.0%, p < 0.002), and the Minnesota Living with Heart Failure score (-18.9%, p = 0.01). Left ventricular ejection fraction (+22.1%), peak oxygen consumption (+12.0%), oxygen uptake at the ventilatory threshold (+12.5%), and peak circulatory power (+21.0%) were higher (p < 0.0002) with BV pacing. The benefit of BV over RV pacing was similar for patients with (n = 9) and without (n = 21) atrial fibrillation. Right ventricular function was not affected by BV pacing.

CONCLUSIONS

In patients with LV dysfunction who need permanent ventricular pacing support, BV stimulation is superior to conventional RV pacing with regard to LV function, quality of life, and maximal as well as submaximal exercise capacity.

Comparison of acute changes in left ventricular volume, systolic and diastolic functions, and intraventricular synchronicity after biventricular and right ventricular pacing for heart failure

BACKGROUND

Biventricular pacing (BiV) therapy has recently been shown to improve systolic function and cause reverse remodeling in patients with advanced heart failure with electromechanical delay. In these patients, the benefit of right ventricular (RV)-based pacing was controversial. We compared the acute changes in systolic and diastolic function, left ventricular (LV) volume, and intraventricular synchronicity in BiV pacing, RV pacing, and without pacing (No) by means of echocardiography and tissue Doppler imaging (TDI).

METHODS

TDI was performed in 33 patients with heart failure after undergoing pacemaker implantation, when the device was randomized to BiV, RV, and no pacing modes.

RESULTS

Systolic function was only improved during BiV pacing, but not during RV pacing. This included ejection fraction (No vs RV vs BiV = 24% +/- 12% vs 25% +/- 10% vs 30% +/- 14%, P =.02 vs No), +dp/dt (P =.01), myocardial performance index (P =.01), and isovolumic contraction time (P =.03). Mitral regurgitation was only reduced during BiV pacing (P =.02). LV early diastolic function was depressed in both RV and BiV pacing, as detected by transmitral flow (97 +/- 34 vs 80 +/- 34 vs 82 +/- 32 cm/s, both P < or =.005) and TDI (mean myocardial early diastolic velocity of 6 basal segments, 3.3 +/- 1.7 vs 2.6 +/- 1.0 vs 2.6 +/- 1.0 cm/s, both P =.01). The LV end-diastolic (187 +/- 86 vs 177 +/- 84 vs 166 +/- 79, P =.003) and end-systolic (146 +/- 77 vs 138 +/- 79 vs 122 +/- 69, P =.003) volumes were only decreased during BiV pacing. For systolic synchronicity, a significant delay in peak systolic contraction in the lateral over the septal wall (171 +/- 37 vs 217 +/- 46 ms, P =.004) was revealed by TDI when there was no pacing. This was abolished by BiV pacing, in which septal contraction was delayed (195 +/- 38 vs 201 +/- 53 ms, P = not significant). However, RV pacing restored the lateral wall delay, and systolic asynchrony reappeared (190 +/- 40 vs 227 +/- 56 ms, P =.01). Diastolic asynchrony between the septal and lateral walls was not evident in these patients and was not affected by either pacing mode.

CONCLUSION

Only BiV pacing, but not RV pacing, improves systolic function, and reduces mitral regurgitation and LV volumes in patients with heart failure and electromechanical delay. This is attributed to the improvement of systolic synchronicity. Diastolic synchronicity was unaffected, whereas early diastolic function could be jeopardized, by either pacing mode.

Regional left ventricle mechanical asynchrony in patients with heart disease and normal QRS duration: implication for biventricular pacing therapy

LV electromechanical delay results in asynchronized contraction. However, it is not known if the presence of cardiac diseases without QRS prolongation may result in inter- or intraventricular asynchrony. This study investigated the occurrence of systolic mechanical delay in different regions of the LV in patients with underlying heart diseases and normal QRS duration. Tissue Doppler imaging (TDI) was performed in 141 patients (age 63.7 +/- 11.5 years) with underlying heart diseases (82% had ischemic heart disease) and 92 normal healthy volunteers (age 63.9 +/- 9.8 years) based on the four-basal and four-mid-segment model by apical views. Of these, 124 patients had normal QRS duration (< or = 120 ms) while 17 were prolonged due to LBBB or intraventricular conduction defect. Patients with normal QRS duration had significantly lower peak myocardial isovolumic contraction velocity (IVCM), sustained systolic velocity (SM), and prolonged time to peak IVCM and SM in almost all myocardial segments when compared to controls. The time to peak IVCM (basal lateral vs basal septal segment: 61.0 +/- 29.4 vs 53.3 +/- 24.1 ms, P < 0.005) and SM (basal lateral vs basal septal segment: 174 +/- 44 vs 154 +/- 36 ms, P < 0.001) was further delayed in the LV free-wall segments. Mechanical delay was also evident in the LV free-wall segments in patients with preserved or impaired systolic function, in patients with or without previous myocardial infarction, and in patients with prolonged QRS duration. Patients with prolonged QRS had a higher prevalence of LV free-wall delay of > 50 ms (47 vs 24%, chi-square = 4.6, P < 0.05). In conclusion, the presence of cardiac diseases was characterized by LV global mechanical delay; and, intraventricular asynchronized contraction characterized mostly by further mechanical delay in the free-wall region. These changes occur even in those with normal QRS duration.

Prolonged QRS duration (QRS >/=170 ms) and left axis deviation in the presence of left bundle branch block: A marker of poor left ventricular systolic function?

BACKGROUND

Left bundle branch block (LBBB) is commonly associated with structural heart disease and left ventricular dysfunction. We propose that the QRS duration and degree of left-axis deviation (LAD) identify significant left ventricular systolic dysfunction in patients with LBBB.

METHODS

In this prospective study the ejection fraction (EF) of 300 consecutive patients with LBBB was evaluated by echocardiography. The relationship between QRS duration and LAD (axis between -30 degrees and -90 degrees ) and EF were derived.

RESULTS

There was no significant difference in age, sex, presence of ischemic or nonischemic cardiomyopathy and valvular heart disease, and EF among the patients with or without LAD. The EF of patients with QRS >/=170 milliseconds with LAD (n = 20) and without LAD (n = 18) was 25% +/- 16% and 23% +/- 13%, respectively (P =.71). The mean EF (24% +/- 10%) of the patients with a QRS duration of >/=170 milliseconds (n = 38) was significantly lower than the mean EF (36% +/- 16%) of the patients with a QRS duration of <170 milliseconds (n = 262, P <.015). The QRS duration also had a significant (P <.001) inverse correlation with EF (R = 0.37, adjusted R (2) = 0.13, SE of estimate = 16.21). However, the QRS axis was not significantly correlated with EF and did not have added predictive value.

CONCLUSIONS

The QRS duration has a significant inverse relationship with EF and prolongation of QRS duration (>/=170 milliseconds) in the presence of LBBB is a marker of significant left ventricular systolic dysfunction. The presence of LAD in LBBB does not signify a further decrease in EF.

Left ventricular and biventricular pacing in congestive heart failure

Dual-chamber pacing improved hemodynamics acutely in a subset of patients with left ventricular (LV) dysfunction but conveyed no long-term symptomatic benefit in most. More recently, LV pacing and biventricular (multisite) pacing have been used to improve systolic contractility by altering the electrical and mechanical ventricular activation sequence in patients with severe congestive heart failure (CHF) and intraventricular conduction delay or left bundle branch block (LBBB). Intraventricular conduction delay and LBBB cause dyssynchronous right ventricular and LV contraction and worsen LV dysfunction in cardiomyopathies. Both LV and biventricular cardiac pacing are thought to improve cardiac function in this situation by effecting a more coordinated and efficient ventricular contraction. Short-term hemodynamic studies have shown improvement in LV systolic function, which seems more pronounced with monoventricular LV pacing than with biventricular pacing. Recent clinical studies in limited numbers of patients suggest long-term clinical benefit of biventricular pacing in patients with severe CHF symptoms. Continuing and future studies will demonstrate whether and in which patients LV and biventricular pacing are permanently effective and equivalent and which pacing site within the LV produces the most beneficial hemodynamic results.

Electrical and hemodynamic correlates of the maximal rate of pressure increase in the human left ventricle

BACKGROUND

The rate of left ventricular (LV) pressure increase (LV + dP/dt) may be related to QRS duration, as well as to a number of hemodynamic parameters.

METHODS AND RESULTS

We studied the relation between basal LV + dP/dt and QRS duration in 43 patients with normal LV function and 81 patients with heart failure undergoing diagnostic catheterization. We also examined the relationship between LV + dP/dt and heart rate, as well as measures of both LV preload and afterload. In patients with normal LV function, there was a strong relationship between basal LV + dP/dt and resting heart rate, whereas the relationship with QRS duration was of borderline significance. In patients with heart failure, the relationship with heart rate was lost; however, LV systolic pressure, QRS duration, and LV end-diastolic pressure all made significant contributions to a model predicting LV + dP/dt.

CONCLUSIONS

These data show a strong relationship between resting heart rate and LV + dP/dt in the healthy human LV. In patients with heart failure, the relationship with heart rate is not maintained; however, there is a systematic relationship between LV + dP/dt and both the time-course of the electrical activation and measures of LV loading conditions.

The effects of ventricular pacing on left ventricular geometry, function, myocardial oxygen consumption, and efficiency of contraction in conscious dogs

The effects of ventricular pacing on left ventricular (LV) dynamic geometry, function, and myocardial oxygen consumption (MVO2) were measured in 12 conscious dogs using sonomicrometry, micromanometry, ultrasonic flow probes, and oximetry catheters during right atrial (A-) and right ventricular (V-) pacing at 150 beats/min. Systolic function was quantified using slopes (MW) and volume-intercepts (VW) of linear relationships between end-diastolic volume (EDV) and stroke work (SW) for data obtained during vena caval occlusion. V-pacing shifted SW-EDV relationships downward (MW decreased from 97 +/- 21 to 81 +/- 21 Kerg/mL) and to the right (VW increased from 14 +/- 11 to 20 +/- 12 mL) in comparison with A-pacing (P < 0.02). These functional changes correlated with altered contractile geometry manifest as early shortening in the septal free wall relative to anterior-posterior dimension (increased minor axis mid-wall eccentricity at end-diastole and begin-ejection). Steady-state LV power output decreased from 802 +/- 213 mW during A-pacing to 514 +/- 170 mW during V-pacing (P < 0.05), while MVO2 remained relatively unchanged during V-pacing (10 +/- 3 mL O2/min vs 11 +/- 3 mL O2/min during A-pacing, P = NS). As a result, overall LV efficiency decreased from 0.24 +/- 0.08 during A-pacing to 0.16 +/- 0.06 during V-pacing (P < 0.05). These data illustrate the impact of V-pacing on dynamic LV geometry and function, including impaired LV work output at all physiological levels of preload. Most importantly, the relationship between LV work output and MVO2 is depressed during V-pacing, emphasizing the interaction between LV mechanics and pump efficiency in intact subjects. As a result, measures taken to restore normal contractile geometry might improve LV efficiency and performance when V-pacing is necessary.

Left ventricular Doppler diastolic filling patterns in patients with isolated left bundle branch block

To evaluate the effect of isolated left bundle branch block (LBBB) on diastolic filling patterns, we evaluated 14 subjects with isolated LBBB and 16 age- and sex-matched healthy subjects with normal ventricular conduction by echocardiography. Maximum E-wave velocity, E/A ratio, deceleration time of E wave, and the slope of deceleration of the E wave were lower in subjects with LBBB compared with subjects with normal ventricular conduction. Doppler filling patterns were significantly altered in subjects with isolated LBBB.

Refractory Heart Failure: A Therapeutic Approach

Optimal “triple therapy” for patients with chronic congestive heart failure (CHF) includes diuretics, digoxin, and either angiotensin-converting enzyme inhibitors or hydralazine plus nitrates. Refractory CHF is defined as symptoms of CHF at rest or repeated exacerbations of CHF despite “optimal” triple-drug therapy. Most patients with refractory CHF require hemodynamic monitoring and treatment in the intensive care unit. If easily reversible causes of refractory CHF cannot be identified, then more aggressive medical and surgical interventions are necessary. The primary goal of intervention is to improve hemodynamics to palliate CHF symptoms and signs (i.e., dyspnea, fatigue, edema). Secondary goals include improved vital organ and tissue perfusion, discharge from the intensive care unit, and, in appropriate patients, bridge to cardiac transplantation. Medical interventions include inotropic resuscitation (e.g., adrenergic agents, phosphodiesterase inhibitors, allied nonglycoside inodilators), load resuscitation (e.g., afterload and preload reduction with nitroprusside or nitroglycerin; preload reduction with diuretics and diuretic facilitators, such as dopaminergic agents or ultrafiltration), and electrical resuscitation (e.g., prevention of sudden death, correction of new or rapid atrial fibrillation, or dual chamber pacing in the setting of relative prolongation of the PR interval and diastolic mitral/tricuspid regurgitation). Surgical interventions are temporizing (e.g., intra-aortic balloon pump and other mechanical assist devices) or definitive (e.g., coronary artery revascularization, valvular surgery, and cardiac transplantation). Although these interventions may improve immediate survival in the short term, only coronary artery revascularization and cardiac transplantation have been shown to improve long-term survival.

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

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

Differing effects of right ventricular pacing and left bundle branch block on left ventricular function

OBJECTIVE

To compare the different effects of right ventricular pacing and classic left bundle branch block on left ventricular function.

DESIGN

Retrospective and prospective study of 48 patients by electrocardiography, and M mode, cross sectional, and Doppler echocardiography.

SETTING

A tertiary cardiac referral centre.

PATIENTS

48 patients (age range 21 to 89 years, 15 women), 24 with a VVI pacemaker implanted and 24 with classic left bundle branch block. Functional mitral regurgitation was present in all those with right ventricular pacing and 22 of those with left bundle branch block.

RESULTS

Age, RR interval, and left ventricular size were similar in the two groups, as were conventional measurements of overall systolic function: shortening fraction and pre-ejection and aortic ejection times. In right ventricular pacing, however, QRS duration (p < 0.01) and electromechanical delay were much longer (p < 0.001), whereas the time intervals from onset of mitral regurgitation to aortic opening (contraction time) and from A 2 to the end of mitral regurgitation (relaxation time) were consistently shorter (p < 0.01) than corresponding values in patients with left bundle branch block. Reversed splitting of the second heart sound was much commoner in left bundle branch block (p < 0.02), and only these patients showed an early systolic ventricular septal contraction. Its onset followed the initial deflection of the QRS complex by 40(15) ms and preceded mitral regurgitation by a small but consistent interval of 10 ms (p < 0.01). The onset of posterior wall thickening was synchronous with the onset of mitral regurgitation in right ventricular pacing but much later (p < 0.01) in patients with left bundle branch block. The extent of incoordinate wall motion measure as relative dimension change during pre-ejection and isovolumic relaxation period was much greater (p < 0.01) in left bundle branch block. These major differences were not altered by left ventricular cavity size in either group, nor by the presence of previous left bundle branch block in patients who were subsequently paced.

CONCLUSIONS

The left ventricle seems to be activated much more rapidly with right ventricular pacing than with left bundle branch block. This applies even when left bundle branch block is present before pacing. Electromechanical delay, contraction and relaxation times, and extent of incoordinate ventricular wall motion differ strikingly between the two conditions. The use of right ventricular pacing as an experimental model of left bundle branch block in humans must be re-examined.

Clinical significance of QRS duration during ventricular pacing

To clarify the clinical significance of an abnormally prolonged paced QRS duration, we studied 114 patients who had undergone pacing for atrioventricular block (AVB). Patients were divided into two groups: group I consisted of 29 patients with at least one paced QRS duration greater than or equal to 180 msec during the follow-up period; group II consisted of 85 patients with paced QRS durations less than 180 msec. The clinical background, QRS complexes before pacing, and the echocardiographic findings were assessed. Males (P less than 0.05), those with H-V block (P less than 0.05) and a wider QRS complex of conducted and escape beats (both P less than 0.01) were dominant in group I. The incidence of underlying heart disease was greater in group I than in group II (83% vs 32%, P less than 0.01). Reduced left ventricular ejection fraction (LVEF) and increased left ventricular end-diastolic dimension (LVDd) were more prominent in group I than in group II (LVEF 0.49 +/- 0.17 vs 0.68 +/- 0.10, P less than 0.01, LVDd 57.1 +/- 7.9 mm vs 48.5 +/- 5.6 mm, P less than 0.01). The paced QRS duration correlated with LVEF (r = -0.61) and LVDd (r = 0.81). A paced QRS duration greater than or equal to 180 msec was sensitive and specific for a LVEF less than 0.5 (83.3% and 85.2%) and LVDd greater than or equal to 60 mm (100% and 81.4%). We conclude that patients with a prolonged paced QRS duration have more serious heart disease, and the paced QRS duration can be a useful indicator of impaired LV function.