Late Potentials and Ventricular Ectopy in Patients with and without Left Bundle Branch Block and Heart Failure

Y Peychev, Y Yotov, V Sirakova

Cardiology Clinic I, Univesity Hospital “St. Marina”, Medical University, Varna, Bulgaria

Correspondence: Y Peychev, Cardiology Clinic I, University Hospital “St. Marina”, Christo Smirnenski bld., 1, Varna 9010, Bulgaria.
E-mail: yavor_peychev@hotmail.com, phone +359 52 302933, fax +359 52 302933

1.  Introduction

The left bundle branch block (LBBB) is found in about 25% of patients with heart failure (HF) and is associated with an increased all-cause and sudden death mortality¹. Patients with LBBB are often excluded from signal averaged ECG (SAECG) performed in the time domain since firm criteria of abnormality have not yet been established². The exclusion of these patients is an important limitation of the technique. Another issue that remains under discussion is the relationship between the presence of late potentials (LP) and the severity of ventricular ectopy on ambulatory electrocardiograms in patients with HF. We hypothesized that by means of using specific criteria to define LP, it seems reasonable to include patients with LBBB in studies assessing the arrhythmia risk in patients with HF.

2.  Material and Methods

We investigated 41 males and 5 females with HF, 64±10 (43−79) years old, ejection fraction 30±7%, NYHA class 3,0±0,5 with 7 (15%) in class II and 39 (85%) in class III to IV. Each patient underwent SAECG with measurement of filtered QRS duration (QRSd), root mean square voltage of the terminal 40 ms of the filtered QRS (RMS), and the duration of the low amplitude signal below 40 μV (LAS). Abnormal values of these three variables were defined as QRSd > 120 ms, RMS < 20 μV, and LAS > 38 ms in the absence of LBBB³ and as QRSd > 145 ms, RMS < 17 μV, and LAS > 55 ms in the presence of LBBB⁴. Late potentials were defined by the presence of 2 abnormal criteria out of three. Twenty-four hour Holter ECG was performed in every patient. The severity of ventricular ectopy (VES) was determined according to Lown’s classification⁵.

3.  Results

We found LBBB in 9 (19.6%) patients. LP were registered in all patients with LBBB and in 10 (27%) patients without LBBB (p<0.05). Ventricular ectopy class III-V was found in 9 (100%) of patients with LBBB and in 28 (75.7%) of patients without LBBB (p<0.01). The addition of the 9 patients with LBBB to the group without LBBB, did not alter the incidence of class III-V VES among LP+ patients (80% vs. 89%, ns), neither the incidence of severe ventricular ectopy in the whole group (75,7% vs. 80,4%, ns) (table 1).

Table 5.    Arrhythmic events in patients with and without LBBB.

p₁ – before vs. after addition of patients with LBBB in LP + subgroup.

p₂ – before vs. after addition of patients with LBBB in the total group.

Values in parentheses indicate percentages.

4.  Discussion

The SAECG in the time domain is used for the detection of areas of slowed conduction. Such areas are identified as a substrate, potentially capable to support a reentrant circuit. In patients with bundle branch block the delay in ventricular activation probably interferes with the detection of late potentials. That is the reason why bundle branch block has been interpreted as an exclusion criterion for SAECG in most of the studies. On the other hand patients with bundle branch block are prone to increased risk of syncope, sudden death and severe ventricular arrhythmias⁶. Since bundle branch block is rather common in patients with heart failure it becomes obvious that the exclusion of these patients is an important limitation for any study. Several criteria for application and assessment of SAECG in patients with conduction defects have been proposed although none have been validated yet^2,4. Analysis of the SAECG data in our study, on the basis of such specific criteria (T. Buckingham et al), found significantly higher incidence of LP in the presence of LBBB. In many cases LBBB reflects an advanced heart disease, as it is in the setting of heart failure. In this case specific electrophysiological signs are often lost. In HF electrophysiological abnormalities reflect the varying contributions of both the processes of damage and repair and the reflex responses to the condition (myocardial stretch, cell slippage, fibrosis, hypertrophy, electrolytes, catecholamines, deficiency of gap junctions)⁷. The ambulatory ECG has been used for the risk stratification of sudden death in heart failure in previous works⁸. It identifies ventricular ectopic activity that may supply the trigger for initiating a reentry tachycardia. The combination of these two techniques may identify patients with HF and LBBB as a subgroup, prone to high risk for potentially lethal ventricular arrhythmias and sudden death.

5.  Conclusions

Patients with HF and LBBB have a high incidence of LP (suggesting arrhythmogenic substrate), as well as a high incidence of severe ventricular ectopy (suggesting possible trigger for development of ventricular arrhythmias). This may identify patients with HF and LBBB as a high risk subgroup for sudden cardiac death.

Using specific criteria (T. Buckingham et al) for a definition of late potentials in patients with LBBB, it seems possible to include these patients in studies assessing the arrhythmia risk in heart failure, as far as the analysis of the data, before and after inclusion of patients with LBBB, yielded similar findings.

References

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