Relationship between intracardiac impedance and left ventricular contractility in patients undergoing cardiac resynchronization therapy

Abstract

AimsCardiac resynchronization therapy (CRT) has dramatically improved the symptoms and prognosis of patients with heart failure in large randomized clinical trials. Optimization of device settings may maximize benefit on an individual basis, although the best method for this is not yet established. We evaluated the use of cardiogenic impedance measurements (derived from intracardiac impedance signals) in CRT device optimization, using invasive left ventricular (LV) dP/dtmax as the reference.Methods and resultsSeventeen patients underwent invasive haemodynamic assessment using a pressure wire placed in the LV cavity at the time of CRT device implantation. Intracardiac impedance measurements were made at different atrioventricular (AV) and interventricular (VV) delays and compared with LV dP/dtmax. We assessed the performance of patient-specific and generic impedance-based models in predicting acute haemodynamic response to CRT. In two patients, LV catheterization with the pressure wire was unsuccessful and in two patients LV lead delivery was unsuccessful; therefore, data were acquired for 13 out of 17 patients. Left ventricular dP/dtmax was 919 ± 182 mmHg/s at baseline and this increased acutely (by 24%) to 1121 ± 226 mmHg/s as a result of CRT. The patient-specific impedance-based model correctly predicted the optimal haemodynamic response (to within 5% points) for AV and VV delays in 90 and 92% of patients, respectively.ConclusionCardiogenic impedance measurements are capable of correctly identifying the maximum achievable LV dP/dtmax as measured by invasive haemodynamic assessment. This study suggests that cardiogenic impedance can potentially be used for CRT optimization and may have a role in ambulatory assessment of haemodynamics.

Impact of Acute Changes of Left Ventricular Contractility on the Transvalvular Impedance: Validation Study by Pressure-Volume Loop Analysis in Healthy Pigs

“…Pacing leads bearing just standard electrodes can be used to assess cardiac impedance [21] . Different electrode arrangements are proposed for impedance assessment [17] , [21] – [24] , namely the unipolar configuration (current is applied between the ventricular tip electrode and the device case and the corresponding voltage drop is measured at the same spots), the bipolar configuration (current is applied between two cardiac electrodes and the corresponding voltage drop is measured at the same spots), or different multipolar configurations (current is applied between two cardiac electrodes and the voltage drop is measured on another electrode pair). The transvalvular impedance (TVI) is a particular example of bipolar configuration, where the atrial pole is represented by the ring electrode placed in right atrium and the ventricular pole by either the tip or ring electrode of the right ventricular lead.…”

Assessing left ventricular systolic dysfunction after myocardial infarction: are ejection fraction and dP/dtmax complementary or redundant?

“…Another invasive indicator, the peak rate of the LV pressure systolic increase over time, calculated as maximum dP/dt (dP/dt max ), is a simple indicator of cardiac contractility (14,21,28). Numerous studies have used dP/dt max with convincing results (9,20,22,32,35); however, this index is known to be preload dependent (23, 31), and it is also affected by the heart rate (HR) (8, 37). Both EF and dP/dt max thus have advantages and limitations, and they are often reported simultaneously in studies while it is not clear if they are complementary or redundant.…”

New Cardiomechanic Pacing Lead Sensor Based on High Frequency Parameters: Experimental Studies in Sheep

“…Other companies like Biotronik (Berlin, Germany) and Medico (Milan, Italy), proposed impedance measurement as another way of assessing the ventricular contractility with an implanted device. [6][7][8][9] These methods are based on the assumption that the intracardiac impedance signals (cardiogenic impedances) depend on the blood volume contained in the cardiac chambers at any time, and that measuring of volumetric fluctuations within the heart during the cardiac cycle can be used to monitor cardiac contractility. The main limitation of this technique is that in some measurement configurations it reflects more the contractility of the right ventricle than of the left ventricle.…”