Accuracy considerations in catheter based estimation of left ventricular volume

Abstract

Cardiac volume estimation in the Left Ventricle from impedance or admittance measurement is subject to two major sources of error: parallel current pathways in surrounding tissues and a non uniform current density field. The accuracy of volume estimation can be enhanced by incorporating the complex electrical properties of myocardium to identify the muscle component in the measurement and by including the transient nature of the field non uniformity. Cardiac muscle is unique in that the permittivity is high enough at audio frequencies to make the muscle component of the signal identifiable in the imaginary part of an admittance measurement. The muscle contribution can thus be uniquely identified and removed from the combined muscle - blood measurement. In general, both error sources are transient and are best removed in real time as data are collected. This paper reviews error correction methods and establishes that the relative magnitudes of the error concerns are different in small and large hearts.

Validation of admittance computed left ventricular volumes against real‐time three‐dimensional echocardiography in the porcine heart

“…The traditional CC technology has been used in several small‐ and large‐animal models, as well in as human research studies, to derive instantaneous pressure–volume relations from the LV and to generate load‐independent parameters of contractility (Burkhoff et al 2005; Jegger et al 2006; Schmitt et al 2009; Read et al 2011). The original theory of CC was proposed by Baan and co‐workers and relates the measured conductance to blood volume as a linear relation (Baan et al 1984; Pearce et al 2010). Conductance catheterization, although popular in basic science laboratories and evolving into the clinical setting (Kasner et al 2007; Penicka et al 2010; Read et al 2011), is known to have several limitations owing to the following technical reasons.…”

“…The electrical field from the conductance catheter extends into the blood pool and surrounding tissue (myocardium). The conductance method fails to correct for this parallel admittance of the myocardium accurately (Baan et al 1984; Wei et al 2007; Pearce et al 2010), causing the measured blood volume to be increased erroneously, because the catheter would ‘see’ beyond the blood pool (Wei et al 2007). The hypertonic saline technique used in CC to correct for parallel conductance ( G p ) assumes a constant value for G p (Baan et al 1984).…”

Advancements in pressure–volume catheter technology – stress remodelling after infarction

“…These difficulties can be exacerbated in models of cardiac disease, such as postinfarction remodelling, where there can be substantial interanimal variation in the area at risk (Michael et al 1995; Salto‐Tellez et al 2004) and the resultant infarct size (Gorog et al 2003), and the affected LV wall can be thin and prone to rupture (Sane et al 2009). Despite the innovations in catheter miniaturization, analysis tools and the development of surgical approaches over the past two decades, reproducible measurement of rodent LV function still presents the researcher with barriers, mainly concerning accurate calibration of the conductance signal and the determination of the contribution of the myocardium to the conductance signal, parallel conductance ( G p ), using a bolus of hypertonic saline introduced into the left ventricle, which is not ideal because the administration of even small amounts of saline can have significant effects on haemodynamics and blood resistivity of the animal (Krenz, 2009; Wei & Shih, 2009; Pearce et al 2010).…”

“…Although this measurement removes the need to use hypertonic saline to calibrate the volume signal, it is dependent upon the structure of the myocardium, which in a disease model can be significantly altered (Bayat et al 2002; Porterfield et al 2009; Raghavan et al 2009; Pearce et al 2010). We aimed to assess how the thickness of the LV anterior wall alters these measures.…”

Cardiac Pressure-Volume Loop Analysis Using Conductance Catheters in Mice

“…The mathematical relationship between conductance and volume, described by Baan and colleagues, is that volume = 1/α; (ρ L 2 )( G − G p ), where α=uniform field correction factor, ρ=blood resistivity, L=distance between the electrodes, G =conductance and G p =non-blood conductance 9 . Of note, the uniform field correction factor in mice approaches 1.0 due to small chamber volumes 10 . Coupled with pressure transducers, the conductance catheter provides real time simultaneous pressure and volume data.…”