A different cardiac resynchronization therapy technique might be needed in some patients with nonspecific intraventricular conduction disturbance pattern.

BACKGROUND: Current cardiac resynchronization therapy (CRT), devised to eliminate dyssynchrony in left bundle branch block (LBBB), works by pacing the latest activated left ventricular site (LALVS). We hypothesized that patients with nonspecific intraventricular conduction disturbance (NICD) pattern respond less favorably to CRT, because their LALVS is far away from that in LBBB. METHODS: By measuring the amplitude and polarity of secondary ST-segment alterations in two optional frontal and horizontal surface electrocardiogram (ECG) leads and using a software, we determined the resultant 3D spatial secondary ST vector, which is directed 180o away from the LALVS, in 110 patients with LBBB pattern and 77 patients with NICD pattern and heart failure. To validate the ECG method, we also estimated the LALVS by echocardiography using 3D parametric imaging and 2D speckle tracking in 22 LBBB patients and 20 NICD patients. Patients with NICD pattern were subdivided according to their non-overlapping frontal plane resultant secondary ST vector ranges to the NICD-1 subgroup (n = 44) and the NICD-2 subgroup (n = 33). RESULTS: Based on the software determined coordinates of the resultant 3D spatial secondary ST vector directed 180o away from the LALVS, the LALVSs were located leftward, posterosuperior in the LBBB group, slightly left, superior in the NICD-1 subgroup, and slightly left, posteroinferior in the NICD-2 subgroup. The LALVS determined by ECG and echocardiography matched in all patients, except two. CONCLUSIONS: In the NICD-2 subgroup, a remote LALVS was found from that in LBBB pattern, which might explain the high non-response rate of the NICD pattern to the current CRT technique.

The role of electrocardiography in the elaboration of a new paradigm in cardiac resynchronization therapy for patients with nonspecific intraventricular conduction disturbance.

Cardiac resynchronization therapy (CRT) is associated with a favorable outcome only in patients with left bundle branch block (LBBB) pattern and in patients with a QRS duration > 150 ms, in patients with non-LBBB pattern with a QRS duration of 120-150 ms usually is not beneficial. After adjusting for QRS duration, QRS morphology was no longer a determinant of the clinical response to CRT. In contrast to the mainstream view, we hypothesized that the unfavorable CRT outcome in patients with non-LBBB and a QRS duration of 120-150 ms is not due to the QRS morphology itself, but to less dyssynchrony and unfavorable patient characteristics in this subgroup, such as more ischemic etiology and greater prevalence of male patients compared with patients with LBBB pattern. Further, the current CRT technique is devised to eliminate the dyssynchrony present in patients with LBBB pattern and inappropriate to eliminate the dyssynchrony in patients with non-LBBB pattern. We also hypothesized that electrocardiography may also provide information about the presence of interventricular and left intraventricular dyssynchrony and the approximate location of the latest activated left ventricular (LV) region. To this end, we devised new ECG criteria to estimate interventricular and LV intraventricular dyssynchrony and the approximate location of the latest activated LV region. Our preliminary data demonstrated that the latest activated LV region in patients with nonspecific intraventricular conduction disturbance (NICD) pattern might be at a remote site from that present in patients with LBBB pattern, which might necessitate the invention of a novel CRT technique for patients with NICD pattern. The application of the new interventricular and LV intraventricular dyssynchrony ECG criteria and a potential novel CRT technique might decrease the currently high nonresponder rate in patients with NICD pattern.