Cardiac Radiofrequency Ablation Research Articles

Intracardiac acoustic radiation force impulse imaging: a novel imaging method for intraprocedural evaluation of radiofrequency ablation lesions.

Arrhythmia recurrence after cardiac radiofrequency ablation (RFA) for atrial fibrillation has been linked to conduction through discontinuous lesion lines. Intraprocedural visualization and corrective ablation of lesion line discontinuities could decrease postprocedure atrial fibrillation recurrence. Intracardiac acoustic radiation force impulse (ARFI) imaging is a new imaging technique that visualizes RFA lesions by mapping the relative elasticity contrast between compliant-unablated and stiff RFA-treated myocardium. To determine whether intraprocedure ARFI images can identify RFA-treated myocardium in vivo. In 8 canines, an electroanatomical mapping-guided intracardiac echo catheter was used to acquire 2-dimensional ARFI images along right atrial ablation lines before and after RFA. ARFI images were acquired during diastole with the myocardium positioned at the ARFI focus (1.5 cm) and parallel to the intracardiac echo transducer for maximal and uniform energy delivery to the tissue. Three reviewers categorized each ARFI image as depicting no lesion, noncontiguous lesion, or contiguous lesion. For comparison, 3 separate reviewers confirmed RFA lesion presence and contiguity on the basis of functional conduction block at the imaging plane location on electroanatomical activation maps. Ten percent of ARFI images were discarded because of motion artifacts. Reviewers of the ARFI images detected RFA-treated sites with high sensitivity (95.7%) and specificity (91.5%). Reviewer identification of contiguous lesions had 75.3% specificity and 47.1% sensitivity. Intracardiac ARFI imaging was successful in identifying endocardial RFA treatment when specific imaging conditions were maintained. Further advances in ARFI imaging technology would facilitate a wider range of imaging opportunities for clinical lesion evaluation.

Mathematical Models Based on Transfer Functions to Estimate Tissue Temperature During RF Cardiac Ablation in Real Time

Radiofrequency cardiac ablation (RFCA) has been used to treat certain types of cardiac arrhythmias by producing a thermal lesion. Even though a tissue temperature higher than 50ºC is required to destroy the target, thermal mapping is not currently used during RFCA. Our aim was thus to develop mathematical models capable of estimating tissue temperature from tissue characteristics acquired or estimated at the beginning of the procedure (electrical conductivity, thermal conductivity, specific heat and density) and the applied voltage at any time. Biological tissue was considered as a system with an input (applied voltage) and output (tissue temperature), and so the mathematical models were based on transfer functions relating these variables. We used theoretical models based on finite element method to verify the mathematical models. Firstly, we solved finite element models to identify the transfer functions between the temperature at a depth of 4 mm and a constant applied voltage using a 7Fr and 4 mm electrode. The results showed that the relationships can be expressed as first-order transfer functions. Changes in electrical conductivity only affected the static gain of the system, while specific heat variations produced a change in the dynamic system response. In contrast, variations in thermal conductivity modified both the static gain and the dynamic system response. Finally, to assess the performance of the transfer functions obtained, we conducted a new set of computer simulations using a controlled temperature protocol and considering the temperature dependence of the thermal and electrical conductivities, i.e. conditions closer to those found in clinical use. The results showed that the difference between the values estimated from transfer functions and the temperatures obtained from finite element models was less than 4ºC, which suggests that the proposed method could be used to estimate tissue temperature in real time.

FBG Sensor for Contact Level Monitoring and Prediction of Perforation in Cardiac Ablation

Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, the catheter is accidently pushed through the heart wall due to the application of excessive force. Despite the various capabilities of currently available technology, there has yet to be any data establishing how cardiac perforation can be reliably predicted. Thus, two new FBG based sensor prototypes were developed to monitor contact levels and predict perforation. Two live sheep were utilized during the study. It was observed during operation that peaks appeared in rhythm with the heart rate whenever firm contact was made between the sensor and the endocardial wall. The magnitude of these peaks varied with pressure applied by the operator. Lastly, transmural perforation of the left atrial wall was characterized by a visible loading phase and a rapid signal drop-off correlating to perforation. A possible pre-perforation signal was observed for the epoxy-based sensor in the form of a slight signal reversal (12–26% of loading phase magnitude) prior to perforation (occurring over 8 s).

Abstract 17144: Assessment of Tissue Heating During Cardiac Radiofrequency Ablation Using Referenceless MRI Thermography

Introduction: Imaging tissue heating during RF ablation may permit more accurate placement and titration of ablation lesions. Standard proton resonance frequency shift MRI thermography, however, is limited by sensitivity to physiologic motion and scanner phase drift between acquisition of ablation and reference pre-heating images. The aim of this study is to assess the feasibility of referenceless MRI thermography which addresses this limitation by eliminating need for a separate pre-heating image but has not yet been applied to cardiac ablation. Methods: An MRI compatible copper electrode catheter was inserted into the left ventricle in 6 dogs. Gradient recalled echo images were acquired while applying RF power in 3W increments until high impedance was reached. Gross pathology was obtained. The pre-heating image was estimated from the ablation image phase component (A) by unwrapping phase (B), masking the catheter tip region where heating was expected (C), and extrapolating phase from unmasked regions of the heart using a fourth order polynomial fit (D). Thermography images were then computed using standard methods (E). Thermography lesion extent was defined by tissue temperature above 50°C. Electrode artifact was defined by darkened myocardium adjacent to the catheter tip on the magnitude component of the ablation image. Results: Transmural lesion extent by referenceless MR thermography was within 20% of that obtained by pathology (inset F) in the four cases where the electrode artifact transmurality was less than 25%. However, thermography and pathology lesion extent differed by over 60% in the two cases where electrode artifact transmurality was greater than 40%. Conclusion: Referenceless MR thermography of cardiac RF ablation is possible and may permit more practical MR thermography monitoring of cardiac ablation. Reducing electrode artifact by using lower magnetic susceptibility materials appears required for more reliable temperature assessment.

The radiation issue in cardiology: the time for action is now.

The "radiation issue" is the need to consider possible deterministic effects (e.g., skin injuries) and long-term cancer risks due to ionizing radiation in the risk-benefit assessment of diagnostic or therapeutic testing. Although there are currently no data showing that high-dose medical studies have actually increased the incidence of cancer, the "linear-no threshold" model in radioprotection assumes that no safe dose exists; all doses add up in determining cancer risks; and the risk increases linearly with increasing radiation dose. The possibility of deterministic effects should also be considered when skin or lens doses may be over the threshold. Cardiologists have a special mission to avoid unjustified or non-optimized use of radiation, since they are responsible for 45% of the entire cumulative effective dose of 3.0 mSv (similar to the radiological risk of 150 chest x-rays) per head per year to the US population from all medical sources except radiotherapy. In addition, interventional cardiologists have an exposure per head per year two to three times higher than that of radiologists. The most active and experienced interventional cardiologists in high volume cath labs have an annual exposure equivalent to around 5 mSv per head and a professional lifetime attributable to excess cancer risk on the order of magnitude of 1 in 100. Cardiologists are the contemporary radiologists but sometimes imperfectly aware of the radiological dose of the examination they prescribe or practice, which can range from the equivalent of 1-60 mSv around a reference dose average of 10-15 mSv for a percutaneous coronary intervention, a cardiac radiofrequency ablation, a multi-detector coronary angiography, or a myocardial perfusion imaging scintigraphy. A good cardiologist cannot be afraid of life-saving radiation, but must be afraid of radiation unawareness and negligence.

Localized superficial femoral vein thrombosis coupled with iatrogenic arteriovenous fistulas presenting as pulmonary emboli

'Localized' femoral vein thrombosis (FVT) is a relatively rare condition usually associated with traumas, external compression or iatrogenic etiologies and the consequence can be pulmonary embolism. This is the case of a 46-year-old woman who presented with pulmonary emboli secondary to 'localized' superficial FVT, coupled with post-puncture arteriovenous fistulas (AVFs), two days after trans-femoral vein radio-frequency cardiac ablation. After placing a temporary IVC-filter, the AVFs were sutured directly while the residual FVT was treated conservatively. Close local monitoring and adequate medical and surgical management are mandatory to avoid possible dangerous complications, also in apparently 'low-risk' iatrogenic AVFs.

Contrast echocardiography for cardiac radio-frequency ablation.

The authors presented a first application of 2-D contrast-enhanced ICE in localizing RF ablation lesions and, more importantly, accurately and reproducibly quantifying their extent and depth within the myocardium in the intact beating heart. Furthermore, the study extended this application and presented, for the first time, a novel method based on contrast-enhanced 3-D ICE to describe details of contiguous linear lesions.

Feasibility of fast MR‐thermometry during cardiac radiofrequency ablation

Online MR temperature monitoring during radiofrequency (RF) ablation of cardiac arrhythmias may improve the efficacy and safety of the treatment. MR thermometry at 1.5 T using the proton resonance frequency (PRF) method was assessed in 10 healthy volunteers under normal breathing conditions, using a multi-slice, ECG-gated, echo planar imaging (EPI) sequence in combination with slice tracking. Temperature images were post-processed to remove residual motion-related artifacts. Using an MR-compatible steerable catheter and electromagnetic noise filter, RF ablation was performed in the ventricles of two sheep in vivo. The standard deviation of the temperature evolution in time (TSD) was computed. Temperature mapping of the left ventricle was achieved at an update rate of approximately 1 Hz with a mean TSD of 3.6 ± 0.9 °C. TSD measurements at the septum showed a higher precision (2.8 ± 0.9 °C) than at the myocardial regions at the heart-lung and heart-liver interfaces (4.1 ± 0.9 °C). Temperature rose maximally by 9 °C and 16 °C during 5 W and 10 W RF applications, respectively, for 60 s each. Tissue temperature can be monitored at an update rate of approximately 1 Hz in five slices. Typical temperature changes observed during clinical RF application can be monitored with an acceptable level of precision.

Could it be advantageous to tune the temperature controller during radiofrequency ablation? A feasibility study using theoretical models

Purpose: To assess whether tailoring the Kp and Ki values of a proportional-integral (PI) controller during radiofrequency (RF) cardiac ablation could be advantageous from the point of view of the dynamic behaviour of the controller, in particular, whether control action could be speeded up and larger lesions obtained.Methods: Theoretical models were built and solved by the finite element method. RF cardiac ablations were simulated with temperature controlled at 55°C. Specific PI controllers were implemented with Kp and Ki parameters adapted to cases with different tissue values (specific heat, thermal conductivity and electrical conductivity) electrode–tissue contact characteristics (insertion depth, cooling effect of circulating blood) and electrode characteristics (size, location and arrangement of the temperature sensor in the electrode).Results: The lesion dimensions and Tmax remained almost unchanged when the specific PI controller was used instead of one tuned for the standard case: Tmax varied less than 1.9°C, lesion width less than 0.2 mm, and lesion depth less than 0.3 mm. As expected, we did observe a direct logical relationship between the response time of each controller and the transient value of electrode temperature.Conclusion: The results suggest that a PI controller designed for a standard case (such as that described in this study), could offer benefits under different tissue conditions, electrode–tissue contact, and electrode characteristics.

Fluoroscopy-induced chronic radiation dermatitis: a report of two additional cases and a brief review of the literature

Fluoroscopy-induced chronic radiation dermatitis (FICRD) can be a challenging diagnosis for the dermatopathologist, as often a history of radiation exposure is not provided. With the expanded use of minimally invasive procedures, there is increased fluoroscopic exposure and a high index of suspicion for FICRD is prudent. Recognition of characteristic clinical and histopathological features can be helpful in distinguishing chronic radiation dermatitis from entities in the histological differential diagnosis such as morphea and lichen sclerosus. We present a brief review of the literature as well as two additional cases of FICRD. Case 1 is a 44-year-old man with an atrophic lateral back patch for several years. Chart review revealed a history of cardiac radiofrequency ablation and congenital heart disease with correction. Case 2 is a 64-year-old woman with an ulcerated, atrophic left flank plaque, with a history of mesenteric artery angiography and stent placement. In our two cases, as well as the cases in the literature, a diagnosis of FICRD is associated with key features. In the evaluation of a sclerosing process, chronic radiation dermatitis should be suspected histologically by the findings of ulceration, prominent telangiectasias, atypical stellate fibroblasts, absence of a lymphocytic infiltrate/inflammation and/or presence of hyperkeratosis.

Near real time evaluation of cardiac radiofrequency ablation lesions with intracardiac echocardiography based acoustic radiation force impulse imaging.

[Cardiac radiofrequency (rf) ablation is used to treat cardiac arrhythmias. Multiple rf lesions are created to form lines of electrical block to disrupt arrhythmic wavefronts. However, image based lesion evaluation is not performed and clinicians rely on changes in electrical propagation to evaluate lesion quality. A near real time lesion evaluation system was developed and tested in vitro and in canines using acoustic radiation force impulse imaging (ARFIi) combined with a catheter tracking system (CARTO, Biosense Webster). rf ablation was performed and delivery sites were indicated on a CARTO electroanatomic map. A CARTO spatially tracked SoundStar® catheter was then used to steer the imaging plan to transect lesions, and intracardiac echocardiography (ICE) based ARFIi (Siemens, S2000 Acuson) was used to evaluate lesion contiguity and transmurality. Imaging was gated to diastole when unablated tissue is soft; motion filtering was employed to reduce the effects of catheter and cardiac movement. ARFIi based evaluation of rf lesions demonstrated a resolution of less than 2mm in vitro and lesion assessment correlated with electrical block in animal studies (λ=0.8). Combining catheter tracking with ICE based ARFIi allows near real time evaluation of cardiac ablation lesions. [Work supported by Siemens Medical, Biosense Webster, and NIH Grant No. R01‐EB‐012484 and R37‐HL096023.]

Contrast-Enhanced C-Arm CT Evaluation of Radiofrequency Ablation Lesions in the Left Ventricle

The purpose of this study was to evaluate use of cardiac C-arm computed tomography (CT) in the assessment of the dimensions and temporal characteristics of radiofrequency ablation (RFA) lesions. This imaging modality uses a standard C-arm fluoroscopy system rotating around the patient, providing CT-like images during the RFA procedure. Both cardiac magnetic resonance (CMR) and CT can be used to assess myocardial necrotic tissue. Several studies have reported visualizing cardiac RFA lesions with CMR; however, obtaining CMR images during interventional procedures is not common practice. Direct visualization of RFA lesions using C-arm CT during the procedure may improve outcomes and circumvent complications associated with cardiac ablation procedures. RFA lesions were created on the endocardial surface of the left ventricle of 9 swine using a 7-F RFA catheter. An electrocardiographically gated C-arm CT imaging protocol was used to acquire projection images during iodine contrast injection and after the injection every 5 min for up to 30 min, with no additional contrast. Reconstructed images were analyzed offline. The mean and SD of the signal intensity of the lesion and normal myocardium were measured in all images in each time series. Lesion dimensions and area were measured and compared in pathologic specimens and C-arm CT images. All ablation lesions (n = 29) were visualized and lesion dimensions, as measured on C-arm CT, correlated well with postmortem tissue measurements (linear dimensions: concordance correlation = 0.87; area: concordance correlation = 0.90. Lesions were visualized as a perfusion defect on first-pass C-arm CT images with a signal intensity of 95 HU lower than that of normal myocardium (95% confidence interval: -111 HU to -79 HU). Images acquired at 1 and 5 min exhibited an enhancing ring surrounding the perfusion defect in 24 lesions (83%). RFA lesion size, including transmurality, can be assessed using electrocardiographically gated cardiac C-arm CT in the interventional suite. Visualization of RFA lesions using cardiac C-arm CT may facilitate the assessment of adequate lesion delivery and provide valuable feedback during cardiac ablation procedures.

Response to “Resolution of Dyssynchronous Left Ventricular Failure via Cardiac Resynchronization and Subsequent Radiofrequency Ablation in an Infant with Preexcitation”

Ventricular pre-excitation causing reversible left ventricular (LV) systolic dysfunction has been reported in adults and children. We describe severe heart failure secondary to ventricular pre-excitation in a 3-month-old girl who presented with echocardiographic evidence of marked intraventricular dyssynchrony. The patient was initially considered for transplantation, but dual chamber left atrioventricular epicardial pacing initiated at 4.5 months of age resulted in a marked clinical and echocardiographic improvement. Five years later, successful radiofrequency ablation resulted in loss of pre-excitation and reversal of LV dyssynchrony, thus allowing pacemaker explantation. To our knowledge, this is one of very few reported cases of pre-excitation-induced cardiomyopathy affecting a young infant and the only case palliated with resynchronization pacing.

Impedance measurement to assess epicardial fat prior to RF intraoperative cardiac ablation: a feasibility study using a computer model

Radiofrequency (RF) cardiac ablation is used to treat certain types of arrhythmias. In the epicardial approach, efficacy of RF ablation is uncertain due to the presence of epicardial adipose tissue interposed between the ablation electrode and the atrial wall. We planned a feasibility study based on a theoretical model in order to assess a new technique to estimate the quantity of fat by conducting bioimpedance measurements using a multi-electrode probe. The finite element method was used to solve the electrical problem. The results showed that the measured impedance profile coincided approximately with the epicardial fat profile measured under the probe electrodes and also that the thicker the epicardial fat, the higher the impedance values. When the lateral fat width was less than 4.5 mm, the impedance values altered, suggesting that measurements should always be conducted over a sizeable fat layer. We concluded that impedance measurement could be a practical method of assessing epicardial fat prior to RF intraoperative cardiac ablation, i.e. ‘to map’ the amount of adipose tissue under the probe.

A Theoretical and Experimental Analysis of Radiofrequency Ablation with a Multielectrode, Phased, Duty-Cycled System

The development of a unique radiofrequency (RF) cardiac ablation system, for the treatment of cardiac arrhythmias, is driven by the clinical need to safely create large uniform lesions while controlling lesion depth. Computational analysis of a finite element model of a three-dimensional, multielectrode, cardiac ablation catheter, powered by a temperature-controlled, multiphase, duty-cycled RF generator, is presented. The computational model for each of the five operating modes offered by the generator is compared to independent tissue temperature measurements taken during in vitro ablation experiments performed on bovine myocardium. The results of the model agree with experimental temperature measurements very closely-the average values for mean error, root mean square difference, and correlation coefficient were 1.9°C, 13.3%, and 0.97, respectively. Lesions are shown to be contiguous and no significant edge effects are observed. Both the in vitro and computational model results demonstrate that lesion depth decreases consistently as the bipolar-to-unipolar ratio increases-suggesting a clinical application to potentially control lesion depth with higher fidelity than is currently available. The effect of variable design parameters and clinical conditions on RF ablation can now be expeditiously studied with this validated model.

Noninvasive Assessment of Tissue Heating During Cardiac Radiofrequency Ablation Using MRI Thermography

Failure to achieve properly localized, permanent tissue destruction is a common cause of arrhythmia recurrence after cardiac ablation. Current methods of assessing lesion size and location during cardiac radiofrequency ablation are unreliable or not suited for repeated assessment during the procedure. MRI thermography could be used to delineate permanent ablation lesions because tissue heating above 50°C is the cause of permanent tissue destruction during radiofrequency ablation. However, image artifacts caused by cardiac motion, the ablation electrode, and radiofrequency ablation currently pose a challenge to MRI thermography in the heart. In the current study, we sought to demonstrate the feasibility of MRI thermography during cardiac ablation. An MRI-compatible electrophysiology catheter and filtered radiofrequency ablation system was used to perform ablation in the left ventricle of 6 mongrel dogs in a 1.5-T MRI system. Fast gradient-echo imaging was performed before and during radiofrequency ablation, and thermography images were derived from the preheating and postheating images. Lesion extent by thermography was within 20% of the gross pathology lesion. MR thermography appears to be a promising technique for monitoring lesion formation and may allow for more accurate placement and titration of ablation, possibly reducing arrhythmia recurrences.

Real-time monitoring of cardiac radio-frequency ablation lesion formation using an optical coherence tomography forward-imaging catheter

Radio-frequency ablation (rfa) is the standard of care for the treatment of cardiac arrhythmias; however, there are no direct measures of the successful delivery of ablation lesions. Optical coherence tomography (OCT) imaging has the potential to provide real-time monitoring of cardiac rfa therapy, visualizing lesion formation and assessing tissue contact in the presence of blood. A rfa-compatible forward-imaging conical scanning probe is prototyped to meet this need. The forward-imaging probe provides circular scanning, with a 2-mm scan diameter and 30-mum spot size. During the application of rf energy, dynamics are recorded at 20 frames per second with a 40-kHz A-line rate. Real-time monitoring of cardiac rfa lesion formation and imaging in the presence of blood is demonstrated ex vivo in a swine left ventricle with a forward, flexible, circular scanning OCT catheter.

Black-box modeling to estimate tissue temperature during radiofrequency catheter cardiac ablation: feasibility study on an agar phantom model

The aim of this work was to study linear deterministic models to predict tissue temperature during radiofrequency cardiac ablation (RFCA) by measuring magnitudes such as electrode temperature, power and impedance between active and dispersive electrodes. The concept involves autoregressive models with exogenous input (ARX), which is a particular case of the autoregressive moving average model with exogenous input (ARMAX). The values of the mode parameters were determined from a least-squares fit of experimental data. The data were obtained from radiofrequency ablations conducted on agar models with different contact pressure conditions between electrode and agar (0 and 20 g) and different flow rates around the electrode (1, 1.5 and 2 L min−1). Half of all the ablations were chosen randomly to be used for identification (i.e. determination of model parameters) and the other half were used for model validation. The results suggest that (1) a linear model can be developed to predict tissue temperature at a depth of 4.5 mm during RF cardiac ablation by using the variables applied power, impedance and electrode temperature; (2) the best model provides a reasonably accurate estimate of tissue temperature with a 60% probability of achieving average errors better than 5 °C; (3) substantial errors (larger than 15 °C) were found only in 6.6% of cases and were associated with abnormal experiments (e.g. those involving the displacement of the ablation electrode) and (4) the impact of measuring impedance on the overall estimate is negligible (around 1 °C).

An in vivo comparison of radiofrequency cardiac lesions formed by standard and magnetically steered 4 mm tip catheters.

Background. In vivo comparison of cardiac radiofrequency ablation lesions between standard and magnetically steered 4 mm tip catheters has never been reported.Methods. High and low right atrium (RA) free wall, isthmus, right ventricle (RV) free wall and outflow tract lesions were studied macroscopically and microscopically five days after lesion formation in seven pigs. Shape, size, thrombus formation, and ablation parameters were compared. The effect of minimal, medium and high wall contact was assessed by a contact measurement utility for magnetic catheters.Results. All 14 RA free wall lesions were transmural with a similar epicardial and endocardial surface area. In the RV, the epicardial area usually appeared to be smaller than the endocardial area with standard catheters. Isthmus lesions were difficult to assess transmurality. There was no difference in endocardial area: standard 39 mm(2) (range 16 to 82 mm(2)) vs. magnetic 36 mm(2) (range 23 to 111 mm(2)). If the catheter tip was perpendicular to the tissue, magnetic lesions were more often round or oval, while standard lesions were more often elongated (p<0.05). When the catheter tip was parallel to tissue, lesions always tended to be elongated. Microscopic characteristics were similar. The contact utility was not useful. Average impedance (p<0.0001) and energy delivered (p<0.05) were less with magnetic catheters.Conclusion. Lesions from magnetically steered catheters are transmural of similar size, but with less variability than standard catheter lesions when the tip is perpendicular to the tissue. Magnetic lesions are associated with lower impedance and energy delivery. This suggests a more stable tip-to-tissue contact. (Neth Heart J 2010;18:66-71.).

In vitro characterization of cardiac radiofrequency ablation lesions using optical coherence tomography

Currently, cardiac radiofrequency ablation (RFA) is guided by indirect signals. We demonstrate optical coherence tomography (OCT) characterization of RFA lesions within swine ventricular wedges. Untreated tissue exhibited a consistent birefringence artifact within OCT images due to the organized myocardium, which was not present in treated tissue. Birefringence artifacts were detected by filtering with a Laplacian of Gaussian (LoG) to quantify gradient strength. The gradient strength distinguished RFA lesions from untreated sites (p=5.93 x 10(-15)) with a sensitivity and specificity of 94.5% and 86.7% respectively. This study demonstrates the potential of OCT for monitoring cardiac RFA, confirming lesion formation and providing feedback to avoid complications.