Observations on Attenuation of Local Electrogram Amplitude and Circuit Impedance During Atrial Radiofrequency Ablation: An In vivo Investigation Using a Novel Direct Endocardial Visualization Catheter.

AIMS: To define the temporal characteristics of atrial lesion growth (lesion surface area), local electrogram amplitude attenuation, and circuit impedance decrement during in vivo radiofrequency (RF) ablation with direct endocardial visualization (DEV). METHODS AND RESULTS: A direct endocardial visualization catheter was used for real-time endoscopic visualization of atrial endocardial surface during RF ablation. Videos of lesion growth (surface area), circuit impedance, and local electrogram amplitude were recorded during ablation in 11 ovine. Fifty-two atrial ablations at 12 W, 14 W, and 16 W power for 30 seconds were analyzed. During 30-second RF ablation, the lesion matured (90% of final lesion dimension) in the first 23.0 ± 5.8 seconds. The local electrogram amplitude attenuation (80% decrement) and circuit impedance attenuation (20% decrement from initial) occurred 13.8 ± 8.2 seconds and 13.1 ± 7.9 seconds, respectively, before lesion maturity in a significant proportion of 30 second atrial ablations. CONCLUSION: The DEV observations suggest that in smooth atrial surface ablations with significant local electrogram and impedance decrement in the first 10 seconds, further extension of ablation for 10-15 seconds could deliver optimal surface dimensions; however, real-time measurement of depth was not possible.

Electrogram-gated radiofrequency ablations with duty cycle power delivery negate effects of ablation catheter motion.

BACKGROUND: Cardiac and respiratory movements cause catheter instability. Lateral catheter sliding over target endocardial surface can lead to poor tissue contact and unpredictable lesion formation. We describe a novel method of overcoming the effects of lateral catheter sliding movements using an electrogram-gated pulsed power ablation. METHODS AND RESULTS: All ablations were performed on a thermochromic gel myocardial phantom. Ablation settings were randomized to conventional (nongated) 30 W versus electrogram-gated at 20% duty cycle (30 W average power) at 0-, 3-, 6-, and 9-mm lateral sliding distances. Forty-eight radiofrequency ablations were performed. Deeper lesions were created in electrogram-gated versus conventional ablations at 3 mm (4.36±0.08 versus 4.05±0.17 mm; P=0.009), 6 mm (4.39±0.10 versus 3.44±0.15 mm; P<0.001), and 9 mm (4.41±0.06 versus 2.94±0.16 mm; P<<0.001) sliding distances. Electrogram-gated ablations created consistent lesions at a quicker rate of growth in depth when compared with conventional ablations (P<0.001). CONCLUSIONS: (1) Lesion depth decreases and length increases in conventional ablations with greater degrees of lateral catheter movements; (2) electrogram-gated pulsed radiofrequency delivery negated the effects from lateral catheter movement by creating consistently deeper lesions irrespective of the degree of catheter movement; and (3) target lesion depths were reached significantly faster in electrogram-gated than in conventional ablations.

Intramyocardial adiposity after myocardial infarction: new implications of a substrate for ventricular tachycardia.

BACKGROUND: Collagen has been attributed as the principal structural substrate of ventricular tachycardia (VT) after myocardial infarction (MI), even though adiposity of myocardium after MI is well recognized histologically. We investigated the effects of intramyocardial adiposity compared with collagen on electrophysiological properties, connexin43 expression, and VT induction after MI. METHODS AND RESULTS: Simultaneous left ventricular plunge-needle, noncontact mapping was performed in sheep without MI (MI-; n=5), with MI and inducible VT (MI+VT+; n=7), and with MI and no inducible VT (MI+VT-; n=8). Histological intramyocardial quantity of adipose and collagen and degree of discontinuity were coregistered with electrophysiological parameters (MI+; 290 specimens). Additional assessment of connexin43 expression was performed. Left ventricular scar contained a body mass-independent abundance of adipocytes (adipose:collagen=0.8). Increased adipose density and discontinuity contributed to a greater inverse correlation (r) with conduction velocity (r for adipose=0.39, r for discontinuity=0.45, r for collagen=0.26) and electrogram amplitude (r for adipose=0.73, r for contiguity=0.77, r for collagen=0.68) compared with collagen. Collagen density was similar between the MI+ groups (P>0.29). However, the MI+VT+ group demonstrated a significant (all P≤0.01) increase in adipose (8%) and discontinuity (qualitative) and decrease in conduction velocity (13%) and electrogram amplitude (21%) at MI borders compared with the MI+VT- group. In scar, myocytes adjacent to fibrofatty interfaces demonstrated increased connexin43 lateralization. A gradient increase in adipose was observed at sites that supported preferential presystolic VT activation and exhibited attenuation of excitation wavelength (P<0.001). CONCLUSIONS: Intramyocardial adiposity, in association with myocardial discontinuity within left ventricular scar borders, is a significant factor associated with altered electrophysiological properties, aberrant connexin43 expression, and increased propensity for VT after MI.

High spatial resolution thermal mapping of radiofrequency ablation lesions using a novel thermochromic liquid crystal myocardial phantom.

BACKGROUND: Radiofrequency (RF) ablation causes thermal mediated irreversible myocardial necrosis. This study aimed to (i) characterize the thermal characteristics of RF ablation lesions with high spatial resolution using a thermochromic liquid crystal (TLC) myocardial phantom; and (ii) compare the thermochromic lesions with in vivo and in vitro ablation lesions. METHODS AND RESULTS: The myocardial phantom was constructed from a vertical sheet of TLC film, with color change between 50 °C (red) to 78 °C (black), embedded within a gel matrix, with impedance titrated to equal that of myocardium. Saline, with impedance titrated to blood values at 37 °C, was used as supernatant. A total of 51 RF ablations were performed. This comprised 17 ablations in the thermochromic gel phantom, bovine myocardial in vitro targets and ovine in vivo ablations, respectively. There was no difference in lesion dimensions between the thermochromic gel and in vivo ablations (lesion width 10.2 ± 0.2 vs 10.2 ± 2.4, P = 0.93; and depth 6.3 ± 0.1 vs 6.5 ± 1.7, P = 0.74). The spatial resolution of the thermochromic film was tested using 2 thermal point-sources that were progressively opposed and was demonstrated to be <300 µm. CONCLUSIONS: High spatial resolution thermal mapping of in vitro RF lesions with spatial resolution of at least 300 µm is possible using a thermochromic liquid crystal myocardial phantom model, with a good correlation to in vivo RF ablations. This model may be useful for assessing the thermal characteristics of RF lesions created using different ablation parameters and catheter technologies.