Effect of ECG-gating Retinal Photographs on Retinal Vessel Caliber Measurements in Subjects with and without Type 2 Diabetes.

Purpose/Aim of this study: Retinal vessel caliber is an independent risk marker of cardiovascular disease risk. However, variable mechanical delays in capturing retinal photographs and cardiac cycle-induced retinal vascular changes have been shown to reduce the accuracy of retinal vessel caliber measurements, but this has only ever been investigated in healthy subjects. This cross-sectional study is the first study to investigate this issue in type 2 diabetes. The aim of this study was to determine whether ECG-gating retinal photographs reduce the variability in retinal arteriolar and venular caliber measurements in controls and type 2 diabetes.Materials and Methods: Fifteen controls and 15 patients with type 2 diabetes were arbitrarily recruited from Westmead Hospital, Sydney, Australia. A mydriatic fundoscope connected to our novel ECG synchronization unit captured 10 ECG-gated (at the QRS) and 10 ungated digital retinal photographs of the left eye in a randomized fashion, blinded to study participants. Two independent reviewers used an in-house semi-automated software to grade single cross-sectional vessel diameters across photographs, between 900 and 1800 microns from the optic disc edge. The coefficient of variation compared caliber variability between retinal arterioles and venules.Results: Our ECG synchronization unit reported the smallest time delay (33.1 ± 48.4 ms) in image capture known in the literature. All 30 participants demonstrated a higher reduction in retinal arteriolar (ungated: 1.02, 95%CI 0.88-1.17% vs ECG-gated: 0.39, 95%CI 0.29-0.49%, p < .0001) than venular (ungated 0.62, 95%CI 0.53-0.73% vs ECG-gated: 0.26, 95%CI 0.19-0.35%, p < .0001) coefficient of variation by ECG-gating photographs. Intra-observer repeatability and inter-observer reproducibility analysis reported high interclass correlation coefficients ranging from 0.80 to 0.86 and 0.80 to 0.93 respectively.Conclusion: ECG-gating photographs at the QRS are recommended for retinal vessel caliber analysis in controls and patients with type 2 diabetes as they refine measurements.

Acoustic signal emission monitoring as a novel method to predict steam pops during radiofrequency ablation: preliminary observations.

UNLABELLED: Steam pop is an explosive rupture of cardiac tissue caused by tissue overheating above 100 °C, resulting in steam formation, predisposing to serious complications associated with radiofrequency (RF) ablations. However, there are currently no reliable techniques to predict the occurrence of steam pops. We propose the utility of acoustic signals emitted during RF ablation as a novel method to predict steam pop formation and potentially prevent serious complications. METHODS: Radiofrequency generator parameters (power, impedance, and temperature) were temporally recorded during ablations performed in an in vitro bovine myocardial model. The acoustic system consisted of HTI-96-min hydrophone, microphone preamplifier, and sound card connected to a laptop computer. The hydrophone has the frequency range of 2 Hz to 30 kHz and nominal sensitivity in the range -240 to -165 dB. The sound was sampled at 96 kHz with 24-bit resolution. Output signal from the hydrophone was fed into the camera audio input to synchronize the video stream. An automated system was developed for the detection and analysis of acoustic events. RESULTS: Nine steam pops were observed. Three distinct sounds were identified as warning signals, each indicating rapid steam formation and its release from tissue. These sounds had a broad frequency range up to 6 kHz with several spectral peaks around 2-3 kHz. Subjectively, these warning signals were perceived as separate loud clicks, a quick succession of clicks, or continuous squeaking noise. Characteristic acoustic signals were identified preceding 80% of pops occurrence. Six cardiologists were able to identify 65% of acoustic signals accurately preceding the pop. An automated system identified the characteristic warning signals in 85% of cases. The mean time from the first acoustic signal to pop occurrence was 46 ± 20 seconds. The automated system had 72.7% sensitivity and 88.9% specificity for predicting pops. CONCLUSIONS: Easily identifiable characteristic acoustic emissions predictably occur before imminent steam popping during RF ablations. Such acoustic emissions can be carefully monitored during an ablation and may be useful to prevent serious complications during RF delivery.

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.

A thermochromic dispersive electrode can measure the underlying skin temperature and prevent burns during radiofrequency ablation.

UNLABELLED: Evaluation of a thermochromic dispersive electrode. INTRODUCTION: Burns at the dispersive electrode are serious complications of diathermy and radiofrequency (RF) ablation procedures. We aimed to create a new methodology to reduce the incidence of dispersive electrode related skin burns. We hypothesized that a dispersive electrode incorporating a thermochromic liquid crystal (TLC) layer could accurately measure underlying skin temperatures and help prevent burns. METHODS AND RESULTS: The TLC electrode was compared with a standard dispersive electrode in 12 male sheep. RF current was delivered with the dispersive electrode fully applied or partially detached to simulate different clinical scenarios. The temperature of the TLC layer, calculated from the hue (color) every 15 seconds, was compared with fluoroptic skin temperature probes. TLC electrodes with a temperature range of 45-58 degrees C were used in six sheep to assess the correlation of TLC temperature distribution with skin temperature and burns. TLC electrodes with a temperature range of 40-50 degrees C were used in another 6 sheep to simulate clinical conditions in which the ablation was stopped if the TLC temperature was >42 degrees C. The TLC measured temperatures correlated well with fluoroptic probes at the skin surface (r=0.94+/-0.05, mean of the absolute difference in temperature difference 0.9+/-0.58 degrees C). Ablations with partial application of standard dispersive electrodes consistently caused skin burns. There were no burns under the TLC electrode when ablations were ceased for temperatures>42 degrees C. CONCLUSIONS: TLC-equipped dispersive electrodes were able to accurately measure skin temperature under the electrode. This technology is likely to prevent dispersive electrode related burns.