Resynchronization therapy for congestive heart failure

Opinion statement Ventricular contraction is achieved by the coordinated electrical activation of the ventricles through the action of the cardiac conduction system. In the presence of left bundle branch block (LBBB) or interventricular conduction delay (IVCD), the ventricular contraction pattern is desynchronized and the stroke volume is reduced as a consequence. In patients with congestive heart failure (CHF) due to systolic dysfunction, the presence of LBBB or IVCD further degrades ventricular function, contributing directly to the severity of their CHF symptoms. Cardiac resynchronization therapy (CRT) through biventricular pacing relieves CHF symptoms and improves functional status in patients with medically refractory heart failure due to left ventricular systolic dysfunction and LBBB or IVCD. The benefits of CRT are due to improvement in the ventricular activation sequence, resulting in a more coordinated and efficient ventricular contraction. In addition to symptomatic benefits, available data support the hypothesis that CRT alters the natural history of CHF in patients with intraventricular conduction delay.     

QRS Axis and the Benefit of Cardiac Resynchronization Therapy in Patients with Mildly Symptomatic Heart Failure Enrolled in MADIT‐CRT

Cardiac Resynchronization Therapy and QRS Axis . Background: Mildly symptomatic heart failure (HF) patients derive substantial clinical benefit from cardiac resynchronization therapy with defibrillator (CRT‐D) as shown in MADIT‐CRT. The presence of QRS axis deviation may influence response to CRT‐D. The objective of this study was to determine whether QRS axis deviation will be associated with differential benefit from CRT‐D. Methods : Baseline electrocardiograms of 1,820 patients from MADIT‐CRT were evaluated for left axis deviation (LAD: quantitative QRS axis ‐30 to ‐90) or right axis deviation (RAD: QRS axis 90–180) in left bundle branch block (LBBB), right bundle branch block (RBBB), and nonspecific interventricular conduction delay QRS morphologies. The primary endpoints were the first occurrence of a HF event or death and the separate occurrence of all‐cause mortality as in MADIT‐CRT. Results: Among LBBB patients, those with LAD had a higher risk of primary events at 2 years than non‐LAD patients (20% vs 16%; P = 0.024). The same was observed among RBBB patients (20% vs 10%; P = 0.05) but not in IVCD patients (22% vs 23%; P = NS). RAD did not convey any increased risk of the primary combined endpoint in any QRS morphology subgroup. When analyzing the benefit of CRT‐D in the non‐LBBB subgroups, there was no significant difference in hazard ratios for CRT‐D versus ICD for either LAD or RAD. However, LBBB patients without LAD showed a trend toward greater benefit from CRT therapy than LBBB patients with LAD (HR for no LAD: 0.37, 95% CI: 0.26–0.53 and with LAD: 0.54, 95% CI: 0.36–0.79; P value for interaction = 0.18). Conclusions: LAD in non‐LBBB patients (RBBB or IVCD) is not associated with an increased benefit from CRT. In LBBB patients, those without LAD seem to benefit more from CRT‐D than those with LAD. (J Cardiovasc Electrophysiol, Vol. 24, pp. 442‐448, April 2013)     

Right and left ventricular activation sequence in patients with heart failure and right bundle branch block: a detailed analysis using three-dimensional non-fluoroscopic electroanatomic mapping system

Three-dimensional mapping in RBBB and heart failure. INTRODUCTION: Recently, right bundle branch block (RBBB) was proved to be an important predictor of mortality in heart failure (HF) patients as much as left bundle branch block (LBBB). We characterized endocardial right ventricular (RV) and left ventricular (LV) activation sequence in HF patients with RBBB using a three-dimensional non-fluoroscopic electroanatomic contact mapping system (3D-Map) in order to provide the electrophysiological background to understand whether these patients can benefit from cardiac resynchronization therapy (CRT). METHODS AND RESULTS: Using 3D-Map, RV and LV activation sequences were studied in 100 consecutive HF patients. Six of these patients presented with RBBB QRS morphology. The maps of these patients were analyzed and compared post hoc with those of the other 94 HF patients presenting with LBBB. Clinical and hemodynamic profile was significantly worse in RBBB group compared to LBBB. Patients with RBBB showed significantly longer time to RV breakthrough (P<0.001), longer activation times of RV anterior and lateral regions (P<0.001), and longer total RV endocardial activation time (P<0.02) compared to patients with LBBB. Time to LV breakthrough was significantly shorter in patients with RBBB (P<0.001), while total and regional LV endocardial activation times were not significantly different between the two groups. CONCLUSIONS: Degree of LV activation delay is similar between HF patients with LBBB and RBBB. Moreover, patients with RBBB have larger right-sided conduction delay compared to patients with LBBB. The assessment of these electrical abnormalities is important to understand the rationale for delivering CRT in HF patients with RBBB.     

Diminished left ventricular dyssynchrony and impact of resynchronization in failing hearts with right versus left bundle branch block.

OBJECTIVES: We compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB). BACKGROUND: Cardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown. METHODS: Dogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively. RESULTS: Left bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dt(max)]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 +/- 0.03 vs. 0.58 +/- 0.09 for LBBB, p < 0.04; CURE 0-->1 is dyssynchronous-->synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 +/- 1.1% vs. 29.5 +/- 5.0% increase in dP/dt(max), p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function. CONCLUSIONS: Less mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay.     

QRS waveform of ventricular extrasystoles and their differentiation from aberrant conduction

Horizontal and frontal plane QRS loops of patients in sinus rhythm with uniform ventricular extrasystoles were constructed from digitised Frank orthogonal electrocardiogram. In 4 patients ventricular extrasystoles were indistinguishable from right bundle-branch complexes, and in another 4 from left bundle-branch complexes. In 25 patients ventricular extrasystoles showed an initial delay (greater than or equal to 20 msec) of the QRS, followed by an R loop, which in 13 patients resembled LBBB complexes, and 12 patients resembled RBBB complexes with an anterior clockwise loop in the horizontal plane. However, the frontal plane loop was often atypical of either RBBB or LBBB. In 51 patients ventricular extraplane loop was often atypical of either RBBB or LBBB. In 51 patients ventricular extrasystoles and an initial delay which was prolonged into the efferent limb of the QRS loop with acceleration of the afferent limb and/or the QRS loop was directed anteriorly, inferiorly and to the left. Conventional recordings of these extrasystoles usually showed an initial slow upstroke (or downstroke) of the QRS resembling a delta wave. It is suggested that extrasystoles resembling bundle-branch complexes arise close to the main bundle branches but that the other extrasystoles arise at the Purkinje-myocardial junction. Identification and differentiation of ventricular extrasystoles from aberrant conduction is aided by vectorcardiography.     

Comment on "Defining left bundle branch block in the era of cardiac resynchronization therapy"

Cardiac resynchronization therapy (CRT) has emerged as an attractive intervention to improve left ventricular mechanical function by changing the sequence of electrical activation. Unfortunately, many patients receiving CRT do not benefit but are subjected to device complications and costs. Thus, there is a need for better selection criteria. Current criteria for CRT eligibility include a QRS duration >120 ms. However, QRS morphology is not considered, although it can indicate the cause of delayed conduction. Recent studies have suggested that only patients with left bundle branch block (LBBB) benefit from CRT, and not patients with right bundle branch block or nonspecific intraventricular conduction delay. The authors review the pathophysiologic and clinical evidence supporting why only patients with complete LBBB benefit from CRT. Furthermore, they review how the threshold of 120 ms to define LBBB was derived subjectively at a time when criteria for LBBB and right bundle branch block were mistakenly reversed. Three key studies over the past 65 years have suggested that 1/3 of patients diagnosed with LBBB by conventional electrocardiographic criteria may not have true complete LBBB, but likely have a combination of left ventricular hypertrophy and left anterior fascicular block. On the basis of additional insights from computer simulations, the investigators propose stricter criteria for complete LBBB that include a QRS duration >140 ms for men and >130 ms for women, along with mid-QRS notching or slurring in >2 contiguous leads. Further studies are needed to reinvestigate the electrocardiographic criteria for complete LBBB and the implications of these criteria for selecting patients for CRT.     

Defining left bundle branch block in the era of cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) has emerged as an attractive intervention to improve left ventricular mechanical function by changing the sequence of electrical activation. Unfortunately, many patients receiving CRT do not benefit but are subjected to device complications and costs. Thus, there is a need for better selection criteria. Current criteria for CRT eligibility include a QRS duration ≥ 120 ms. However, QRS morphology is not considered, although it can indicate the cause of delayed conduction. Recent studies have suggested that only patients with left bundle branch block (LBBB) benefit from CRT, and not patients with right bundle branch block or nonspecific intraventricular conduction delay. The authors review the pathophysiologic and clinical evidence supporting why only patients with complete LBBB benefit from CRT. Furthermore, they review how the threshold of 120 ms to define LBBB was derived subjectively at a time when criteria for LBBB and right bundle branch block were mistakenly reversed. Three key studies over the past 65 years have suggested that 1/3 of patients diagnosed with LBBB by conventional electrocardiographic criteria may not have true complete LBBB, but likely have a combination of left ventricular hypertrophy and left anterior fascicular block. On the basis of additional insights from computer simulations, the investigators propose stricter criteria for complete LBBB that include a QRS duration ≥ 140 ms for men and ≥ 130 ms for women, along with mid-QRS notching or slurring in ≥ 2 contiguous leads. Further studies are needed to reinvestigate the electrocardiographic criteria for complete LBBB and the implications of these criteria for selecting patients for CRT.     

Conduction system abnormalities in patients with obstructive hypertrophic cardiomyopathy following septal reduction interventions

We observed the impact of percutaneous transluminal septal myocardial ablation (PTSMA) and myectomy on the conduction system in patients with obstructive hypertrophic cardiomyopathy (HC). Septal reduction intervention is capable of eliminating the left ventricular outflow tract obstruction in patients with obstructive HC; however, conduction system abnormalities are frequent consequences of these procedures. A standard 12-lead electrocardiogram and Doppler echocardiogram were obtained in 204 patients who underwent PTSMA (n = 70) or myectomy (n = 134) before and at average of 3 months after intervention. Of 146 patients who had normal conduction systems before intervention, the duration of the QRS complex was significantly prolonged from 98 +/- 15 to 130 +/- 25 ms (p <0.0001), with right bundle branch block (RBBB) developing in 62% patients after PTSMA, and from 100 +/- 13 to 154 +/- 20 ms (p <0.0001), with left bundle branch block (LBBB) developing in 93% patients after myectomy. No significant difference in the QRS duration was found in the remaining 58 patients who had preexisting conduction abnormalities after intervention. In 174 patients without a preexisting permanent pacemaker, a pacemaker was implanted in 22% versus 13% of patients who underwent PTSMA (overall and without preexisting conduction block, respectively) and 10% versus 2% of patients with myectomy. The duration of baseline QRS was an independent predictor for the requirement of a permanent pacemaker (p <0.0001). Thus, RBBB often develops after PTSMA and LBBB is very frequently produced by myectomy. A possible requirement of a permanent pacemaker should always be considered before intervention when patients have preexisting RBBB or LBBB.     

QRS duration does not predict occurrence of ventricular tachyarrhythmias in patients with implanted cardioverter-defibrillators

OBJECTIVES: The aim of this study was to determine whether QRS duration (QRSd) correlates with occurrence of ventricular arrhythmia in patients with coronary disease (CAD) receiving implantable cardioverter-defibrillators (ICDs). BACKGROUND: A QRSd measured on a standard electrocardiograph (ECG) correlates with total mortality risk in CAD patients at high risk for sudden death; however, the relationship between QRSd and risk of ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) is unclear. METHODS: PainFREE Rx II was a randomized trial, comparing efficacy of antitachycardia pacing versus shock therapy for VT/VF in patients receiving ICDs. We retrospectively correlated the QRSd and specific ECG conduction abnormalities on the 12-lead ECG at study entry with occurrence of VT/VF in 431 patients with CAD enrolled in the trial. RESULTS: The QRSd was < or =120 ms in 291 of 431 (68%) patients. Left bundle branch block (LBBB) was present in 65 patients, right bundle branch block (RBBB) in 48 patients, and nonspecific intraventricular conduction delay (IVCD) was present in 124 patients. Over 12 months' follow-up, VT/VF occurred in 95 (22%) patients (22% of patients with QRSd < or =120 ms vs. 23% of patients with QRSd >120 ms, p = NS). Patients with LBBB were less likely to experience at least one VT/VF episode than patients with QRSd <120 ms. Patients with RBBB and nonspecific IVCD did not differ from patients with narrow QRS complexes with regard to occurrence of tachycardias. CONCLUSIONS: The QRSd and ECG conduction abnormalities are not useful to predict ICD benefit in patients having the characteristics of our study population. The utility of QRSd to predict VT/VF events in patients with CAD requires further prospective evaluation.     

An unusual bundle-branch block

We report a case of right bundle-branch block (RBBB) showing a QRS configuration typical for left bundle-branch block (LBBB) in leads V(5) and V(6). The QRS axis was at +90 degrees, and the QRS duration was 0.14 second. There were wide S waves in leads I and aVL, suggesting at first glance an RBBB, but the QRS morphology in the inferior leads (monophasic R wave with secondary ST-T changes) was more consistent with an LBBB. Lead V(1) suggested an RBBB, whereas leads V(5) and V(6) showed a monophasic R wave as in LBBB; moreover, a negative T wave, typical of LBBB, was present in lead V(5). Placement of the electrodes of leads V(4), V(5), and V(6) 2 intercostal spaces above restored in these leads a QRS configuration suggestive of RBBB. The diagnostic problem was mainly caused by the inferior direction of the QRS axis. Because the electrode of V(6) is normally placed below the electrical center of the heart, namely, on a plane that is not orthogonal to the sagittal plane, a vector directed mainly inferiorly and slightly to the right does not project on the negative part but on the positive of the lead line. For this reason, the S waves normally observed in the left precordial leads with RBBB disappear. The superior displacement of the electrodes "normalizes" the plane upon which the lead lines lie, thereby restoring the expected QRS configuration.     

Mechanically-induced intraventricular block caused by a right-heart floating catheter--frequency and electrophysiologic findings

During the course of 2,434 right heart catheterizations with 2,019 floating 3F Grandjean catheters and 415 5F Swan-Ganz catheters we observed 7 patients (0.3%) with catheter-induced infranodal conduction impairment: right bundle branch block (RBBB) in 3 patients, left anterior fascicular block (LAFB) and subsequent RBBB in 1 patient, and complete heart block in 3 patients with pre-existing left bundle branch block (LBBB). There was no apparent difference regarding the incidence of blocks between the two types of catheters. Three patients (one with LAFB + RBBB and two with LBBB) underwent electrophysiologic studies. All three patients exhibited a prolongation of the HV-interval due to coexisting pathologic changes of the right bundle. LBBB patterns disappeared during distal His bundle pacing in two patients, indicating a proximal site of block and suggesting incomplete involvement of the right bundle. Additional mechanical trauma, probably in this region, produced the blocks. Thus, use of balloon tipped or flexible catheters does not provide complete protection against transient lesions of the conduction system.     

Cardiac resynchronization therapy in patients with right bundle branch block: analysis of pooled data from the MIRACLE and Contak CD trials.

BACKGROUND: Clinical trials of cardiac resynchronization therapy (CRT) have not included many patients with right bundle branch block (RBBB). OBJECTIVES: We pooled data from two randomized controlled trials of CRT (Multicenter InSync Randomized Clinical Evaluation [MIRACLE] and Contak CD) in order to assess outcomes of patients with RBBB. METHODS: A total of 61 patients with RBBB were identified, 34 of whom were randomized to the CRT group and 27 to the control group. The data from these patients were entered into a new database and analyzed. RESULTS: Baseline demographics were not different between the two groups (mean age 65.5 +/- 11.3 years vs 69.5 +/- 9.6 years; male gender 91% vs 85%; patients with coronary disease 76.5% vs 88%; QRS duration 167 ms vs 164 ms; all P = NS). Outcome variables (New York Heart Association [NYHA] class, 6-minute hall walk distance, peak oxygen consumption (VO2), Minnesota Living with Heart Failure quality-of-life scores, left ventricular ejection fraction, and norepinephrine levels) were analyzed at randomization, 3 months, and 6 months. CONCLUSIONS: (1) With the exception of NYHA class, patients with RBBB as the qualifying wide QRS did not derive significant benefit from CRT in any of the other parameters studied at 3 or 6 months. (2) RBBB patients who received active CRT showed significant improvements in NYHA class by 6 months and trends toward improvement in 6-minute walk distance, quality-of-life scores, and norepinephrine levels. However, control patients also showed significant improvement in NYHA class by 6 months but showed no improvement in objective measurements (VO2, 6-minute walk distance, left ventricular ejection fraction, and norepinephrine levels), consistent with a placebo effect. Analysis of a larger cohort of patients with RBBB undergoing CRT may demonstrate significant benefit, but the current analysis does not support the use of CRT in patients with RBBB.     

Electrophysiologic significance of leftward qrs axis deviation in bifascicular and trifascicular blocks

Background: Intraventricular conduction disturbances determine complete impairment of impulse propagation along the right or left bundle branch or the two left fascicles. Hypothesis: This study was undertaken to investigate the electrophysiologic significance of QRS axis (QRSA) orientation in bifascicular and trifascicular blocks. Methods: A group of 76 subjects, 43 with right bundle-branch block (RBBB) and left anterior hemiblock (LAH) (Group A), and 33 with left bundle-branch block (LBBB) (Group B) was submitted to electrophysiologic evaluation. Results: In Group A, QRSA was inversely related only to intraventricular conduction, while in Group B, QRSA inversely related to infrahisal conduction times. A value of <60° was considered the cut-off point for determin-ing subjects with a considerable leftward QRSA deviation. Of the 27 Group A patients with a QRSA <-60°, 38.5% developed an infrahisal second-degree atrioventricular (AV) block during incremental atrial stimulation (IAS) in comparison with 11.1 % of those with QRSA >-60°. Of the 9 Group B patients with a QRSA <-60°, 44.4% exhibited severe impairment of infrahisal conduction at baseline and 66.6% developed an infrahisal second-degree AV block during IAS, whereas among the remaining 24 with a QRSA >60°, in only 8.3% were both infrahisal (HV1 and HV2) intervals dangerously prolonged, and 23.8% encountered an infrahisal second-degree AV block during IAS. In Group A, atrioventricular conduction time >200 ms exhibited a better predictive accuracy than QRSA <60° for the development of an infrahisal second-degree AV block during IAS, whereas the latter appeared the best noninvasive predictor in Group B with a slightly lesser predictive accuracy than HV >80 ms. Conclusion: The degree of leftward QRSA deviation seems to reflect the entity of intraventricular conduction delay in patients with RBBB + LAH, while it appears to be directly related to infrahisal conduction prolongation in those with LBBB.     

Intraventricular conduction disturbances: a review of prevalence, etiology, and progression for ten years within a stable population of Israeli adult males.

The ECG tracings of 5,204 working males aged 40 years and over, representing a random sample of Israeli civil service employees were reviewed, and 123 (2.36 per cent) displaying intraventricular conduction disturbances (IVCD) in the form of left anterior hemiblock (LAH), RBBB, RBBB + LAH and LBBB, were followed for a period of 10 years (1963 to 1973). While these patients were slightly older than the population they were derived from (53.5 versus 4938 years average age), there was no significant difference in ages between the various types of IVCD, but there was a marked increase in the frequency of all IVCD with age. Left anterior hemiblock constituted the most frequent IVCD (1.42 per cent), being twice as frequent as RBBB (0.65 per cent). The prevalence of RBBB + LAH was 0.17 per cent (7 per cent of all IVCD). To the best of our knowledge, this is the first time that the frequency of this condition has been assessed in an unselected male population.The vast majority of these ECG changes seem to be acquired. Ischemic heart disease (IHD) constituted the most frequent associated condition for all types of IVCD (28 per cent), its prevalence being similar (21 to 28 per cent) in LAH, RBBB and RBBB + LAH, but much higher in patients with LBBB (five of six patients). Hypertension (HT), not associated with IHD, was present in 24 patients and constituted the next most frequent factor (20 per cent). No definite etiology could be demonstrated in the remaining 64 patients (52 per cent), except for five (4 per cent of all IVCD and 0.1 per cent of the population studied) who displayed progressive IVCD and were considered to represent examples of a degenerative disease of the conduction system (DDCS). The latter confirms that monofascicular blocks (MFB) may represent an initial stage of DDCS.From the ECG point of view, 14 per cent of cases with MFB showed progression to bifascicular block (BFB) or complete heart block (CHB) within 10 years, regardless of etiology. This was more frequent in RBBB than in LAH (22.5 per cent versus 9.5 per cent). From the clinical point of view, the natural history of IVCD in patients with IHD parallels the natural history and prognosis of this disease. In contrast, the prognosis of IVCD in patients with isolated HT, or in asymptomatic subjects, was more benign even in patients reaching the stage of CHB. The natural history of DDCS began as RBBB or LAH in middle age or earlier and progressed to CHB through the stage of BFB. This process may last from a few years to a few decades; LBBB seems to be rarely if ever encountered in its course.     

Incidence and prognostic significance of intraventricular block in acute myocardial infarction.

In 404 consecutively admitted patients with their first myocardial infarction (MI), intraventricular block (IV) was a complication in 124 (31%). The following types of block were encountered: 21 (5%) had left bundle-branch block (LBBB), 73 (18%) left anterior hemiblock (LAH), 13 (3%) left posterior hemiblock (LPH); 7 (2%) right bundle-branch block (RBBB); 9 (2%) RBBB + LAH, and 1 (0.3%) RBBB + LPH. Patients with IV block at the time of admission did not develop total atrioventricular block more frequently in the acute phase of MI (0-30 days) or in the follow-up period (3-5 years) than patients without IV block. During the acute phase, only patients with RBBB with or without hemiblock showed significantly higher mortality than patients without IV blocks. The other types of IV block did not influence the short-term prognosis. Among patients who survived the acute phase, significantly lower long-term survival rates were found in patients with LBBB compared to patients without IV block, whereas the presence of LAH did not affect the long-term prognosis.     

Ischemia-associated intraventricular conduction disturbances during exercise testing as a predictor of proximal left anterior descending coronary artery disease

To determine the incidence and significance of transient intraventricular conduction abnormalities occurring in association with myocardial ischemia during exercise testing, the recordings of 2,200 consecutive exercise tests were reviewed. Ten patients (0.45%) were identified as having both ischemia and intraventricular conduction abnormalities that developed transiently during the exercise test. In all 10 patients both typical angina and electrocardiographic evidence of ischemia developed during exercise. Among the 10 patients, left anterior hemiblock developed in 4, left posterior hemiblock in 2, right bundle branch block (RBBB) in 2, RBBB with left axis deviation in 1, and left anterior hemiblock progressing to complete left bundle branch block (LBBB) in 1. All 10 patients had cardiac catheterization showing significant obstruction of the left anterior descending (LAD) coronary artery at or before the origin of the first septal branch. Eight patients were treated surgically and 2 medically, all with relief of ischemic symptoms. Nine of the 10 had repeat exercise stress testing without angina or electrocardiographic evidence of ischemia and without recurrence of the transient intraventricular conduction disturbance.It is concluded that the development of transient intraventricular conduction abnormalities associated with myocardial ischemia during exercise testing is an uncommon occurrence (0.45%). When such conduction disturbances do develop, the existence of significant disease in the proximal portion of the LAD coronary artery is strongly suggested. With control of myocardial ischemia, the transient conduction disturbances during exercise are ameliorated.     

Cardiac resynchronization therapy and other new approaches for the treatment of heart failure in the elderly

Approximately 15% to 20% of patients with systolic heart failure have a QRS duration greater than 120 ms, which is most commonly seen as left bundle-branch block (LBBB). In LBBB, the left ventricle is activated through the septum from the right ventricle, resulting in a significant delay between the onset of right (RV) and left ventricular (LV) contraction. In patients with LV dysfunction, ventricular dyssynchrony caused by LBBB places the already failing left ventricle at an additional mechanical disadvantage. Ventricular dyssynchrony appears to have a deleterious impact on the natural history of heart failure, as a wide QRS complex has been associated with increased mortality in patients experiencing heart failure. On the basis of these observations, investigators hypothesized that patients with LV dysfunction and delayed ventricular conduction would benefit from pacing at sites that achieve a more favorable contraction pattern, and correct interatrial and/or interventricular conduction delays to maintain optimal atrial-ventricular (AV) synchrony. Multiple clinical trials of cardiac resynchronization therapy have demonstrated that it is safe and effective, with patients achieving significant improvement in both clinical symptoms as well as multiple measures of functional status and exercise capacity. Moreover, it has reduced measures of morbidity and mortality in several studies. Thus, cardiac resynchronization therapy should be routinely offered to eligible patients experiencing heart failure.     

Quantitative and qualitative changes in the resting electrocardiograph after percutaneous transluminal septal myocardial ablation for the treatment of symptomatic obstructive hypertrophic cardiomyopathy

Percutaneous Transluminal Septal Myocardial Ablation (PTSMA) may reduce symptoms in patients with obstructive hypertrophic cardiomyopathy. Limited quantitative and qualitative data exists on the effects of PTSMA on the resting electrocardiograph. We report repolarisation and conduction abnormalities and incidence of arrhythmia post-PTSMA. Twelve-lead electrocardiographs from subjects without pre-procedural pacemakers who underwent successful procedures (37 procedures, mean age 61+/-14 years) were analysed for rhythm, heart rate, PR and QTc intervals, QRS duration and left or right bundle branch block (RBBB, LBBB). Four subjects developed permanent complete AV block, 19 subjects developed new RBBB and two subjects developed new LBBB pre-discharge. At a median follow-up of 34 (range 1-84) months, no new AV block, ventricular arrhythmias or deaths occurred. Post-PTSMA PR, QRS and QTc intervals lengthened (PR 180+/-33 ms, 204+/-40 ms, QRS 105+/-20 ms, 132+/-27 ms and QTc 454+/-32 ms, 491+/-37 ms (pre- and post-PTSMA respectively, all p=0.001). Predictors of permanent complete AV block included female gender (p=0.013), older age (p=0.013) and pre-existing LBBB (p<0.001). Atrio-ventricular and intra-ventricular conduction disturbances are common post-PTSMA. A pre-existing LBBB is a risk factor for the development of complete AV block and may merit prophylactic pacemaker insertion.     

Elektrotherapie der Herzinsuffizienz

Intracardiac conduction disturbances, mostly manifested as a left bundle branch block (LBBB), are common findings in cardiac failure and associated with a poor prognosis. LBBB is a marker of disease progression and also leads to worsened cardiac hemodynamics by dyssynchronous contraction that can accelerate progression of the underlying disease. Cardiac resynchronization therapy (CRT) can reduce the negative effects of these disturbances leading to improvement in hemodynamics and long-term improvement in cardiopulmonary exercise tolerance, reduction of left ventricular volumes and functional mitral regurgitation. Prospective multicenter studies, such as the CARE-HF and COMPANION trials have demonstrated reduced mortality with CRT or combined treatment with defibrillator capability (CRT-D). Thus, CRT has been adopted in the current guidelines of cardiology societies. Nevertheless, there are a number of open issues with CRT, such as the high number of non-responders or the value of CRT in patients with atrial fibrillation, narrow QRS complex and mild cardiac failure or asymptomatic left ventricular dysfunction. In addition, the question whether every CRT patient needs a device with defibrillating capabilities is not fully resolved, at least for patients with dilative cardiomyopathy.     

Bundle-branch block as a risk factor in noncardiac surgery

BACKGROUND: Despite extensive data examining perioperative risk in patients with coronary artery disease, little attention has been devoted to the implications of conduction system abnormalities. OBJECTIVE: To define the clinical significance of bundle-branch block (BBB) as a perioperative risk factor. METHODS: Retrospective, cohort-controlled study of all noncardiac, nonophthalmologic, adult patients with BBB seen in our preoperative evaluation center. Medical charts were reviewed for data regarding cardiovascular disease, surgical procedure, type of anesthesia, intravascular monitoring, and perioperative complications. RESULTS: Bundle-branch block was present in 455 patients. Right BBB (RBBB) was more common than left BBB (LBBB) (73.8% vs 26.2%). Three patients with LBBB and 1 patient with RBBB died; 1 patient had a supraventricular tachyarrhythmia. Three of the 4 deaths were sepsis related. There were 2 (0.4%) deaths in the control group. There was no difference in mortality between BBB and control groups (P = .32). Subgroup analysis suggested an increased risk for death in patients with LBBB vs controls (P = .06; odds ratio, 6.0; 95% confidence interval, 1.2-100.0) and vs RBBB (P = .06; odds ratio, 8.7; 95% confidence interval, 1.2-100.0). CONCLUSIONS: The presence of BBB is not associated with a high incidence of postoperative cardiac complications. Perioperative mortality is not increased in patients with RBBB and not directly attributable to cardiac complications in patients with LBBB. These data suggest that the presence of BBB does not significantly increase the likelihood of cardiac complications following surgery, but that patients with LBBB may not tolerate the stress of perioperative noncardiac complications.