Helen Høgh Petersen

Lesion dimensions during temperature-controlled radiofrequency catheter ablation of left ventricular porcine myocardium: impact of ablation site, electrode size, and convective cooling.

BACKGROUND It is important to increase lesion size to improve the success rate for radiofrequency ablation of ischemic ventricular tachycardia. This study of radiofrequency ablation, with adjustment of power to approach a preset target temperature, ie, temperature-controlled ablation, explores the effect of catheter-tip length, ablation site, and convective cooling on lesion dimensions. METHODS AND RESULTS In vitro strips of porcine left ventricular myocardium during different levels of convective cooling and in vivo pig hearts at 2 or 3 left ventricular sites were ablated with 2- to 12-mm-tip catheters. We found increased lesion volume for increased catheter-tip length </=8 mm in vitro (P<0.05) and 6 mm in vivo (P<0. 0001), but no further increase was found for longer tips. For the 4- to 10-mm catheter tips, we found smaller lesion volume in low-flow areas (apex) than in high-flow areas (free wall and septum) (P<0.05). Increasing convective cooling of the catheter tip in vitro increased lesion volume (P<0.0005) for the 4- and 8-mm tips but not for the 12-mm tip as the generator reached maximum output. In contrast to power-controlled ablation, we found a negative correlation between tip temperature reached and lesion volume for applications in which maximum generator output was not achieved (P<0. 0001), whereas delivered power and lesion volume correlated positively (P<0.0001). CONCLUSIONS Lesion size differs in different left ventricular target sites, which is probably related to convective cooling, as illustrated in vitro. Longer electrode tips increase lesion size for tip lengths </=6 to 8 mm. For temperature-controlled ablation, the tip temperature achieved is a poor predictor of lesion size.

Tissue Temperatures and Lesion Size During Irrigated Tip Catheter Radiofrequency Ablation: An In Vitro Comparison of Temperature-Controlled Irrigated Tip Ablation, Power-Controlled Irrigated Tip Ablation, and Standard Temperature-Controlled Ablation

The limited success rate of radiofrequency catheter ablation in patients with ventricular tachycardias related to structural heart disease may be increased by enlarging the lesion size. Irrigated tip catheter ablation is a new method for enlarging the size of the lesion. It was introduced in the power‐controlled mode with high power and high infusion rate, and is associated with an increased risk of crater formation, which is related to high tissue temperatures. The present study explored the tissue temperatures during temperature‐controlled irrigated tip ablation, comparing it with standard temperature‐controlled ablation and power‐controlled irrigated tip ablation. In vitro strips of porcine left ventricular myocardium were ablated. Temperature‐controlled irrigated tip ablation at target temperatures 60°C, 70°C, and 80°C with infusion of 1 mL saline/min were compared with standard temperature‐controlled ablation at 70°C and power‐controlled irrigated tip ablation at 40 W, and infusion of 20 mL/min. Lesion size and tissue temperatures were significantly higher during all modes of irrigated tip ablation compared with standard temperature‐controlled ablation (P < 0.05). Lesion volume correlated positively with tissue temperature (r = 0.87). The maximum recorded tissue temperature was always 1 mm from the ablation electrode and was 67 ± 4°C for standard ablation and 93 ± 6°C, 99 ± 6°C, and 115 ± 13°C for temperature‐controlled irrigated tip ablation at 60°C, 70°C, and 80°C, respectively, and 112 ± 12°C for power‐controlled irrigated tip ablation, which for irrigated tip ablation was significantly higher than tip temperature (P < 0.0001). Crater formation only occurred at tissue temperatures > 100°C. We conclude that irrigated tip catheter ablation increases lesion size and tissue temperatures compared with standard ablation in the temperature‐controlled mode at the same or higher target temperatures and in the power‐controlled mode. Furthermore, tissue temperature and delivered power are the best indicators of lesion volume during temperature‐controlled ablation.

Temperature-controlled irrigated tip radiofrequency catheter ablation: comparison of in vivo and in vitro lesion dimensions for standard catheter and irrigated tip catheter with minimal infusion rate

Temperature‐Controlled Irrigated Tip Ablation. Introduction: In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, hut has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature‐ controlled mode, target temperature 60°C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80°C.

Temperature-controlled Radiofrequency Ablation of Cardiac Tissue: An In Vitro Study of the Impact of Electrode Orientation, Electrode Tissue Contact Pressure and External Convective Cooling

Background: A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size.Methods and Results: In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 °C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size.Conclusions: During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.

LESION SIZE IN RELATION TO ABLATION SITE DURING RADIOFREQUENCY ABLATION

This study was designed to investigate the effect of the convective cooling of the tip of the ablation electrode during temperature controlled radiofrequency ablation. In vivo two different application sites in the left ventricle of anaesthetised pigs were ablated and in vitro ablation was performed during two different flow‐velocities in a tissue bath, while electrode contact pressure and position were unchanged. Target temperature was 80 °C. Obtained tip temperature, power consumption and lesion dimensions were measured. In vivo lesion volume, depth and width were found significantly larger for septal applications than apical applications (p<0.01) and more power was used (p<0.001). Obtained tip temperature was significantly lower in the septal applications (p<0.001). In vitro increased convective cooling by induction of flow yielded larger lesion volume, depth and width (p<0.01), and had higher power consumptions (p<0.01). Obtained tip temperature did not differ significantly. For the given chosen target temperature power consumption was positively related to lesion volume (r= 0.66 in vivo and 0.65 in vitro), whereas obtained tip temperature was not (r = ‐ 0.49 in vivo and ‐ 0.61 in vitro). We conclude that during temperature controlled radiofrequency ablation lesion size differs for septal and apical left ventricular applications. Differences in convective cooling might play an important role in this respect. This is supported by our in vitro experiments, where increased convective cooling by induction of a flow around the electrode tip increases lesion dimensions and power consumptions. Furthermore we conclude that for the given target temperature the power consumption is positively correlated with lesion volume (p<0.001), whereas the obtained tip temperature is not.

The impact of co-morbidity burden on appropriate implantable cardioverter defibrillator therapy and all-cause mortality: insight from Danish nationwide clinical registers

In a nationwide cohort of primary (PP‐ICD) and secondary prevention (SP‐ICD) implantable cardioverter defibrillator (ICD) patients, we aimed to investigate the association between co‐morbidity burden and risk of appropriate ICD therapy and mortality.

Safety of magnetic resonance scanning without monitoring of patients with pacemakers.

Aims The objective of this study was to investigate whether it is safe to perform 1.5-Tesla magnetic resonance imaging (MRI) scans in pacemaker (PM) patients without pulse oximetry or electrocardiogram monitoring and with no special specific absorption rate (SAR) or time limits, provided that the PMs are interrogated and programmed to asynchronous mode prior to the scan. Methods and results This study reports the outcome of 207 MRI scans on PM patients at Rigshospitalet, Copenhagen University Hospital from June 2010 to September 2013. All MRIs were performed with the PMs in asynchronous mode and without additional monitoring. There were no adverse events registered among the PM patients during the study period. The only statistically significant change after MRI scans was a small, but clinically insignificant increase in atrial sense. No occurrences of reprogramming to power-on-reset were registered. Conclusion It is possible to perform MRI scans relatively safely in PM patients without additional monitoring or change in the normal MRI protocol, given that the PM has been assessed and reprogrammed prior to MRI. This is especially important to remember in the acute setting where MRI scans may be delayed when monitoring facilities are unavailable.

Can lesion size during radiofrequency ablation be predicted by the temperature rise to a low power test pulse in vitro

During radiofrequency ablation sufficient power must be delivered to achieve a proper lesion, while tissue temperatures are kept below 100°C. Tissue temperature and hence lesion size are determined by electrode to tissue contact and convective cooling, which vary with any obtained electrode position in the beating heart. A tool for evaluation of the combined effect of these parameters prior to ablation to predict the resulting lesion size for any actually obtained electrode position would be valuable. A low power pulse prior to ablation will cause a small increase in tip temperature, which will reflect tissue contact and convective cooling of the tip for that particular electrode position and may thereby predict lesion dimensions after subsequent ablation at that site. Ablation was performed in vitro on strips of left ventricular porcine myocardium during different levels of convective cooling, variable contact pressure, and two electrode orientations in temperature‐controlled and power‐controlled modes. A 4‐mm tip catheter was used. Prior to ablation a 30‐second, 0.6‐W test pulse was delivered and the increase in tip temperature (ΔT) registered. The study found that ΔT and lesion size were mainly affected by the external cooling of the electrode tip and less by the electrode to tissue contact. Increased cooling caused a lower ΔT (P < 0.001), and the effect on lesion dimensions depended on the ablation mode. For temperature‐controlled ablation a larger lesion due to increased power output was obtained (P < 0.0001) for increased cooling, whereas for power‐controlled ablation a smaller lesion was obtained for increased cooling (P < 0.05). ΔT can predict lesion size, but the interpretation of ΔT depends on the ablation mode. For temperature‐controlled ablation a high ΔT indicates a small lesion and for power‐controlled ablation a high ΔT indicates a large lesion. (PACE 2003; 26:1653–1659)

Cooperative Epistemic Work in Medical Practice: An Analysis of Physicians' Clinical Notes

We examine an important part of the medical record that has not been studied extensively: physicians’ clinical notes. These notes constitute an explanatory medical narrative that documents the patient’s illness trajectory by combining each physician’s notes into a common text. Although several prior CSCW studies have addressed the role of the medical record in patient care, they have not dealt specifically with the role, structure, and content of these notes. In this article, we present a detailed analysis of a set of physicians’ clinical notes recording the acute hospitalization and subsequent treatment of a patient with chronic heart disease. We show that clinical notes are highly structured and conventionalized texts that promote conciseness while at the same time allowing physicians to express themselves in a precise and nuanced way. Based on this analysis, we argue that physicians’ clinical notes form the core of the medical record. They serve both as a ‘tool for thinking’ for the individual physician, enabling him or her to make sense of the patient’s past history and current condition, and as a coordinative artifact used by physicians, nurses, and other health care professionals. We conclude by discussing the implications of this research for the design of Electronic Medical Record (EMR) systems.

Validation of defibrillator lead performance registry data: insight from the Danish Pacemaker and ICD Register

Aims The validity of registry data on defibrillator lead performance is described only sparsely, despite its clinical importance. This study investigated the validity of defibrillator lead performance registry data in a nationwide and population-based registry. Methods and results We identified all reported surgical interventions due to defibrillator lead events in the Danish Pacemaker and ICD Register (DPIR) from 2000 to 2013. Medical records of all patients (n = 753) were examined blinded for 5 predefined intervention types and 18 reasons for lead intervention. The overall level of agreement for the types of lead intervention had a positive predictive value (PPV) of 89.4% [95% confidence interval (CI): 87.0-91.5%] and an adjusted agreement (κ value) of 0.81 (95% CI: 0.77-0.85) representing an almost perfect match. Regarding the reasons for lead intervention, the overall PPV was 63.0% (95% CI: 54.8-61.7%) with a κ value of 0.60 (95% CI: 0.55-0.64) representing a moderate match with only few subcategories having low PPV. By redistribution of the specific reasons for lead interventions into three categories commonly used to report lead performance, the overall PPV improved to 87.9% (95% CI: 85.2-90.2%) with a κ value of 0.82 (95% CI:0.78-0.86) representing an almost perfect match. Conclusion The validity of data on defibrillator lead performance recorded in the DPIR is excellent for the specific types of lead intervention and good for the specific reasons for defibrillator lead intervention. The validity of the less detailed overall reasons for lead interventions commonly used to report lead performance is also excellent. These findings indicate high registry data quality appropriate for scientific analysis and industry-independent post-marketing surveillance.