ELECTROCARDIOGRAPHIC, VECTORCARDIOGRAPHIC AND BODY SURFACE POTENTIAL MAPPING ANALYSES OF PATIENTS WITH CONGESTIVE HEART FAILURE AND LEFT BUNDLE BRANCH BLOCK, TREATED WITH BIVENTRICULAR PACING

Pastore CA, Tobias NM, Kaiser E, Samesima N, Martinelli Fº M, Pedrosa A, Nishioka S, Siqueira S, Lourenço UR, Atanes LM, Ramires JAF
Heart Institute (InCor) of the University of São Paulo Medical School
Av. Dr. Enéas de Carvalho Aguiar, 44 – 05403-000 São Paulo, SP – Brazil

OBJECTIVE 

To study through the body surface potential mapping (BSPM), including the electrocardiogram (ECG) and the vectorcardiogram (VCG), the electrical activation of the heart of patients (pts) suffering from congestive heart failure (CHF) and left bundle branch block (LBBB) who have undergone implantation of a biventricular cardiac pacemaker.

MATERIALS / METHODS

We studied 13 male pts, mean age 61 years, suffering from idiopathic dilated cardiomyopathy and LBBB – 5 with Chagas’ disease, 4 with idiopathic dilated cardiomyopathy, 3 with coronary artery disease, 1 with hypertension, NYHA function classes III and IV, mean ejection fraction of 35.5%.

All pts had a biventricular cardiac pacemaker implanted (implantation undergone between 01 April, 2000 and 01 January, 2001), with electrodes placed in the apex of the right ventricle (RV) and in the lateral region of the left ventricle (LV).   

Electrocardiography, vectorcardiography and body surface potential mapping examinations were performed with a Fukuda Denshi equipment, with 87 leads placed, 59 on the anterior chest and 28 on the back, besides the classical leads studied in the standard ECG and VCG.

Three different situations were analyzed: 1) baseline (pacemaker off); 2) one-chamber pacing (apex of RV); 3) biventricular pacing.  Body surface isochrone maps of the QRST complexes were constructed from lines recorded every 1ms, taking the onset of the QRS as the zero time (t₀) and the offset of the T wave as the maximal time (t_max).  ECGs and VCGs measured the duration of QRS complexes before (1) and after  (3) implantation of biventricular pacemaker.  QRS axes were measured in the frontal and in the horizontal planes, in the three study situations.  The ejection fraction was clinically measured by echocardiography in situations (1) and (3).

RESULTS

Baseline ECG/VCG examinations in situation (1) demonstrated 8 patients with LBBB left axis deviation, 3 with right axis deviation, and 3 within the regular parameters (between –30° and +30°). 

Baseline QRS mean duration was 180.5ms, while the same was 158.8ms in situation (3), after biventricular pacing, a very significant difference (p<0.00003). 

Ejection fraction after biventricular pacemaker implantation was 38.4% (p = 0.0082).

Both in the ECG and in the VCG the baseline QRS axes were oriented upwardly and to the left in the frontal plane (mean –46.7°), and posteriorly and to the left (mean –78.8°) in the horizontal plane. After implantation of biventricular pacing (situation 3) the axes orientation in the frontal plane changed upwardly and to the right (mean –106.5°) and in the horizontal plane they shifted posteriorly and to the right (mean –105.8°). The unicameral (situation 2) stimulation did not show any significant change.

In the BSPM, the isochrone lines of electrical activation usually recorded from a patient with LBBB are oriented right to left, starting at the RV, slowly crossing the septum and finally recording the characteristically asynchronous delayed activation of the LV.  During the one-chamber activation of situation (2), apex of RV, we observed the activation starting at the left postero-lateral area, flowing anteriorly from left to right, and finally activating the lateral right area with a significant delay time.  When both electrodes, one in each ventricle (situation 3) were activated, the activation of both ventricles was seen to flow concomitantly from the inferior region upwardly and rightward, like two major wave fronts activating the two ventricles in a sequence of faster isochrone lines than those seen in the other two study situations, in a clearly synchronous action.

DISCUSSION

The decrease in the QRS duration, recorded by the ECG/VCG after implantation of biventricular pacing (from 180.5ms baseline to 158.8ms in situation 3), suggests a better ventricular synchronization.  Recordings during study situation 2 (unicameral pacing) did not show significant alteration of the QRS axis, however a significant change was seen in situation (3) when compared with baseline, showing the ventricular activation oriented upwardly and to the right, and capable of characterizing the presence of the biventricular pacemaker.

The body surface mapping of isochrone lines of QRST shows their direction and orientation every millisecond, characterizing the cardiac electrical activation wave front and confirming the electro and vectorcardiographic orientation.  Thereby it is possible to compare activation in the presence of LBBB (with a wide QRS and causing systolic and diastolic dysfunction due to the time elapsed since the activation begins in the RV, slowly crosses the septum and finally reaches the LV) with the activation generated by the biventricular pacemaker dual stimulation.  The comparison between three different activations, baseline, one-chamber stimulation and biventricular pacing, gave evidence of the latter showing a significant change in the electrical activation direction and orientation, flowing from the lower portion upwardly and to the right, starting at the areas stimulated by the electrodes and reaching the two ventricles concomitantly, with shorter duration than in a LBBB. 

Thus, the re-synchronization process observed through the ECG, VCG and Body Surface Potential Mapping bear witness to the improvement in contractility of the myocardium fostered by biventricular pacing, and defines the orientation of the electrical activation.  The improvement of the ejection fraction coefficient can be taken as additional evidence corroborating these findings.

CONCLUSION

ECG/VCG and BSPM are useful means to assess the ventricular activation after implantation of biventricular pacemaker in patients suffering from left bundle branch block and congestive heart failure, by defining patterns that can confirm the resynchronization of the ventricular chambers. Those instruments help to consider biventricular re-synchronization as an enthusiastic and promising therapeutic tool.