Analysis of the effects of atrial pacing on the timing of left ventricular pressure rise in normal conduction and left bundle branch block

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian Research Council. BACKGROUND/INTRODUCTION: The timing of left ventricular pressure rise (Td) relative to QRS-onset is associated with dispersion of regional work distribution and prolongs with dyssynchrony and dyssynergistic contractions. Td is short in normal conduction and shortening of Td can be achieved with effective biventricular pacing (BIVP). The effect of atrial pacing on Td is unknown and could be important for the interpretation of Td when utilized for cardiac resynchronization therapy. PURPOSE: We wanted to test the effects from atrial pacing (AP) compared to sinus rhythm (SR) on Td in animals with narrow QRS (nQRS) complexes and after the creation of LBBB. METHODS: 9 mongrel dogs were included in the study and handled according to ethics committee approved protocol/GLP. Pacing electrodes were placed epicardial on the left atrial appendage. Pressure was measured with a Micro-tip pressure sensor (Millar Inc.) in the LV and sampled at 1000Hz. LBBB was created with a retrograde placed 7F standard ablation catheter and confirmed by surface ECG and four endocardial electrodes. Td was measured from 10 consecutive beats. Mixed models were utilized for the repeated measurements. RESULTS: Analysis of the marginal means in pooled data showed that the average Td with AP was 96.7ms (95% CI: -195.7, 388.7), and in SR 96.5ms (95% CI: - 195.5, 389.0). The analysis with the Bonferroni correction for multiple comparisons revealed that the differences between pacing configurations were not statistically significant (p=0.80). The analysis revealed that AP on average lengthens Td by 0.3ms (95% confidence interval (CI): - 1.7, 2.2, p=0.8), compared to no pacing. The difference in Td in nQRS between AP and SR was 82.4ms (95% CI: 76.8, 88.1) and 82.1ms (95% CI: 76.4, 87.8) respectively (p=0.02) while the difference in Td in LBBB between AP and SR was 111.1ms (95% CI: 104.8, 117.4) and 110.9ms (95% CI: 104.581, 117.197) respectively (p=0.48). Standard deviation within 10 consecutive beats was 1.0ms (max 3.7ms, min 0.4ms, median 0.95ms), and AP did not influence Td measurement variability (p=0.53). CONCLUSION(S): We did not find any influence from atrial pacing in Td in this study. The significant difference between AP and SR in nQRS was extremely small and less than the sample interval of 1ms. The significance of this difference is attributed to the robustness of the Td measurement and does not represent a meaningful clinical significance. Td can be measured without being influenced by atrial pacing in both native conduction and with LBBB.