Effect of coronary occlusion and reperfusion on local electrical resistivity of myocardium in dogs

Effects of coronary artery disease in patients with permanent left bundle branch area pacing: A retrospective study

Aims

Myocardial ischemia can affect traditional right ventricular (RV) pacing parameters, but it is unclear whether coronary artery disease (CAD) impact the pacing parameters and electrophysiological characteristics of left bundle branch area pacing (LBBaP) as a physiological pacing representative.

Methods

Patients who underwent coronary angiography (CAG) after/before the LBBaP procedure and underwent percutaneous coronary intervention after LBBaP procedure were divided into CAD group and Non-CAD group according to visual CAG. Pacing parameters and electrophysiological characteristics were recorded at LBBaP implantation. Multivariate logistic regression analysis was implemented to evaluate the association between CAD and higher capture threshold. Sensitivity analyses were conducted to verify result stability.

Results

A total of 176 patients met inclusion criteria (115 Non-CAD patients and 61 CAD patients) with a mean age of 71.1 ± 9.0 years. Compared with the Non-CAD patients, CAD patients had the higher capture threshold (0.67 ± 0.22 V vs. 0.82 ± 0.28 V, P < 0.001) and lower R-wave amplitude (12.5 ± 4.8 mV vs. 10.1 ± 2.7 mV, P = 0.001). Moreover, CAD was independently associated with higher capture threshold (adjusted Odds ratio (OR) 3.418, 95% confidence interval (CI): 1.621-7.206, P = 0.001), which was further validated through sensitivity analyses.

Conclusion

Patients without CAD might have safer pacing parameters in the LBBaP procedure. Besides, CAD might be the risk factor of capture threshold increase during permanent LBBaP implantation.

Long-term performance of right ventricular pacing leads: risk factors associated with permanent right ventricular pacing threshold increase

Purpose

Right ventricular pacing threshold (RVPT) may rise over time accompanied by the increased use of implantable cardiac pacemakers. However, risk factors for permanent RVPT increase are not fully clarified in patients without definite lead fracture and dislodgment. We aimed to evaluate the long-term performance of RV pacing leads and identify risk factors associated with the occurrence of permanent RVPT increase in this population.

Methods

Patients with first implantation of cardiac pacemakers from January 2008 to June 2016 were consecutively enrolled. Follow-up for RVPT increase was until December 2017. The clinical data, specific data on the pacemaker implantation, and routine follow-up were retrieved.

Results

During a follow-up duration of 5.4 ± 2.1 years, permanent RVPT increase (except lead fracture and dislodgment) was found in 8.4% (87/1033) patients. Patients with permanent RVPT increase had higher prevalence of myocardial infarction (MI), diabetes, and the use of amiodarone. The risk factors independently associated with permanent RVPT increase were MI (HR = 1.094, 95% CI 1.014–1.180, p = 0.031), diabetes (HR = 2.804, 95% CI 1.064–3.775, p = 0.003). MI patients with RVPT increase had higher prevalence of multivessel disease and atrioventricular block. Diabetic patients with RVPT increase exhibited higher serum fasting blood glucose (FBG) and hemoglobin A1c (HbA1c) levels, which were correlated with the maximum RVPT (p < 0.001).

Conclusions

Our data showed that permanent RVPT increases (except lead fracture and dislodgement) during long-term follow-up after pacemaker implantation. The likely risk factors predisposing to chronic permanent RVPT increase are MI and diabetes with higher FBG and HbA1c levels.

High-density epicardial mapping during current injection and ventricular activation in rat hearts

The purpose of this study is to report new methods for manufacturing precision electrode arrays for recording high-resolution potential distributions from epicardial surfaces of small-animal hearts. Electrode arrays of 64 leads (8 x 8) and 121 leads (11 x 11) were constructed with a tulle substrate to which insulated, fine silver wires (60-micrometer diameter) were attached by knots at mesh node intervals of 540 x 720 micrometers. Insulation was removed at the tips of the knots. Potential distributions and waveforms were recorded from saline solutions and rat heart epicardium during ventricular paced beats and during passive current injection in the diastolic interval. Electrical responses obtained from rat epicardium compared favorably with those observed in studies of larger-animal hearts, which used arrays having greater electrode spacing, and revealed the effects of myocardial anisotropy. Epicardial potentials measured early after stimulation in the region surrounding the pacing site were interpreted in terms of potentials generated by an equivalent quadrupolar source. We conclude that electrode arrays for epicardial mapping of small hearts can be constructed with sufficient ease and precision to allow detailed study of fiber structure and electrophysiology in these hearts in normal and pathological conditions.

Dependence of anisotropic myocardial electrical resistivity on cardiac phase and excitation frequency

Knowledge of myocardial electrical resistivity is of interest because passive electrical properties govern the electrotonic spread of current through the myocardium and influence the shape and velocity of the excitation wave. In addition, measurements of myocardial resistivity may provide information about tissue structure and components. The aim of the present study was to determine the excitation frequency dependence and the changes during the cardiac cycle of anisotropic myocardial electrical resistivity. Longitudinal and transverse myocardial resistivity were measured using an epicardial sensor in four open-chest dogs with excitation frequencies in the range of 5-60 kHz. Mean longitudinal resistivity gradually decreased from 313 +/- 49 omega.cm at 5 kHz to 212 +/- 32 omega.cm at 60 kHz, transverse resistivity decreased from 487 +/- 49 to 378 +/- 53 omega.cm. To analyze the phasic changes, we compared mean resistivity (averaged over the full cardiac cycle) with resistivity during four cardiac phases: pre-ejection, ejection, early diastole and late diastole. Longitudinal resistivity was significantly higher during the ejection phase (+9.6 +/- 4.1 omega.cm) and lower during late diastole (-6.9 +/- 2.9 omega.cm). Transverse resistivity was significantly higher during late diastole (+4.0 +/- 2.3 omega.m). The values during the other cardiac phases were not significantly different from mean resistivity. The phasic changes in longitudinal and transverse resistivity during the cardiac cycle were independent of the excitation frequency. We speculate that these changes are related to geometrical changes, especially to changes in myocardial blood volume.