PURPOSE: The ventriculophasic response (VR) refers to shortening of the atrial cycle length (PP-interval) during heart block that occurs when a QRS complex is interposed between P-waves. The purpose of this study was to determine if VR varied in relation to the width of the interposed QRS complexes
METHODS: We studied 16 patients with advanced heart block and chronically implanted pacemakers or defibrillators who had underlying escape rhythms. With devices temporarily programmed to VVI mode at 30 ppm the ECG and intracardiac electrograms were recorded at 50 mm/sec for 30 seconds. VR was computed for each P-P interval (A-A interval on the atrial electrogram) containing a QRS as the percent decrement in the P-P (A-A) interval with an interposed QRS compared to the preceding atrial interval with no QRS. For each patient we compared the average VR at the start of the recording, when interposed QRS complexes were paced, to the VR at the end of the recording when escape QRS complexes were present.
RESULTS: The mean VR associated with paced QRS complexes, was significantly less than the VR generated by escape complexes (1.90 ±1.60 % vs. 4.37±3.85 %, p=0.017). The QRS duration of paced complexes was significantly longer than escape complexes (158.75 ±33.04 vs. 117.50±30.87 msec, p<0.001).
CONCLUSIONS: Narrow ventricular escape beats generate a larger VR than paced QRS complexes, which are wider and would likely generate more ventricular dyssynchrony than narrow QRS complexes.
CLINICAL IMPLICATIONS: These findings suggest that the degree of ventricular synchrony associated with interposed QRS complexes during heart block may be an important determinant of the ventriculophasic response.
DISCLOSURE: The following authors have nothing to disclose: Razvan Dadu, Craig McPherson
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