Benjamin Knowles

Acute pulmonary vein isolation is achieved by a combination of reversible and irreversible atrial injury after catheter ablation: evidence from magnetic resonance imaging.

Background— Pulmonary vein reconnection after pulmonary vein isolation is common and is usually associated with recurrences of atrial fibrillation. We used cardiac magnetic resonance imaging after radiofrequency ablation to investigate the hypothesis that acute pulmonary vein isolation results from a combination of irreversible and reversible atrial injury. Methods and Results— Delayed enhancement (DE; representing areas of acute tissue injury/necrosis) and T2-weighted (representing tissue water content, including edema) cardiac magnetic resonance scans were performed before, immediately after (acute), and later than 3 months (late) after pulmonary vein isolation in 25 patients with paroxysmal atrial fibrillation undergoing wide-area circumferential ablation. Images were analyzed as pairs of pulmonary veins to quantify the percentage of circumferential antral encirclement composed of DE, T2, and combined DE+T2 signal. Fourteen of 25 patients were atrial fibrillation free at 11-month follow-up (interquartile range, 8–16 months). These patients had higher DE (71±6.0%) and lower T2 signal (72±7.8%) encirclement on the acute scans compared with recurrences (DE, 55±9.1%; T2, 85±6.3%; P<0.05). Patients maintaining sinus rhythm had a lesser decline in DE between acute and chronic scans compared with recurrences (71±6.0% and 60±5.8% versus 55±9.1% and 34±7.3%, respectively). The percentage of encirclement by a combination of DE+T2 was almost similar in both groups on the acute scans (atrial fibrillation free, 89±5.4%; recurrences, 92±4.8%) but different on the chronic scans (60±5.7% versus 34±7.3%). Conclusions— The higher T2 signal on acute scans and greater decline in DE on chronic imaging in patients with recurrences suggest that they have more reversible tissue injury, providing a potential mechanism for pulmonary vein reconnection, resulting in arrhythmia recurrence.

3-D Visualization of Acute RF Ablation Lesions Using MRI for the Simultaneous Determination of the Patterns of Necrosis and Edema

Catheter ablation using RF energy is a common treatment for atrial arrhythmias. Although this treatment provides a potential cure, currently, there remains a high proportion of patients returning for repeat ablations. Electrophysiologists have little information to verify that a lesion has been created in the myocardium. Temporary electrical block can be created from edema, which will subside. MRI can visualize acute and chronic ablation lesions using delayed-enhancement techniques. However, the ablation patterns cannot be determined from 2-D images alone. Using the combination of T2-weighted and delayed-enhancement MRI, ablation lesions can be characterized in terms of necrosis and edema. A novel 3-D visualization technique is presented that projects the image intensity due the lesions onto a 3-D cardiac surface, allowing the complete, simultaneous visualization of the delayed-enhancement and T2 -weighted ablation patterns. Results show successful visualization of ablation patterns in 18 patients, and an application of this technique is presented in which electroanatomical mapping systems can be validated by overlaying the acquired ablation points onto the cardiac surfaces and assessing the correlation with the lesion maps.

Cardiac MRI to investigate myocardial scar and coronary venous anatomy using a slow infusion of dimeglumine gadobenate in patients undergoing assessment for cardiac resynchronization therapy.

To evaluate a cardiac MR (CMR) examination with slow infusion of a high‐relaxivity contrast agent to visualize coronary venous anatomy (CVA) and myocardial scar in heart failure patients awaiting cardiac resynchronization therapy (CRT).

Advanced image fusion to overlay coronary sinus anatomy with real-time fluoroscopy to facilitate left ventricular lead implantation in CRT.

Background: Failure rate for left ventricular (LV) lead implantation in cardiac resynchronization therapy (CRT) is up to 12%. The use of segmentation tools, advanced image registration software, and high‐fidelity images from computerized tomography (CT) and cardiac magnetic resonance (CMR) of the coronary sinus (CS) can guide LV lead implantation. We evaluated the feasibility of advanced image registration onto live fluoroscopic images to allow successful LV lead placement.

Pharmacokinetic modeling of delayed gadolinium enhancement in the myocardium

Delayed contrast‐enhanced magnetic resonance imaging (DCE‐MRI) provides prognostic information by delineating regions of myocardial scar. The mechanism of this delayed enhancement in myocardial infarctions (MIs) is hypothesized to result from altered kinetics and changes in the volumes of distribution in the myocardium. Pharmacokinetic models with two and three compartments were fitted to the concentration‐time curves of dynamic contrast‐enhanced MRI data obtained from five patients with known MI. Furthermore, the parameter stability was investigated in simulations for the two different models. The transfer constants and volumes of distribution showed a good correlation with imaging findings on early and delayed contrast‐enhanced MRI. The two compartment model showed higher parameter stability. The three compartment model allows a more in‐depth quantification of myocardial scarring. These models have the potential to improve the diagnosis of myocardial pathologies involving scar, with differing kinetics and volumes of distribution such as infarction or cardiomyopathy. Magn Reson Med 60:1524–1530, 2008.

Realtime fusion of cardiac magnetic resonance imaging and computed tomography venography with X-ray fluoroscopy to aid cardiac resynchronisation therapy implantation in patients with persistent left superior vena cava.

Persistent left superior vena cava can lead to significant technical difficulties when implanting a left ventricular (LV) lead for cardiac resynchronisation therapy. We present two cases in which coronary sinus anatomy was reconstructed with computed tomography and magnetic resonance imaging and fused with live fluoroscopy to facilitate LV lead implantation.

A Novel Cardiac MRI Protocol To Guide Successful Cardiac Resynchronization Therapy Implantation

Cardiac MRI (CMR) is recognized as an important imaging modality for assessing patients with heart failure. With improved segmentation and image registration tools, data acquired using CMR can help with planning and intraprocedural guidance as well as with defining etiology of heart failure and ventricular function. Here, we describe a successful CRT implantation where segmented CMR images were registered with the fluoroscopic images during the procedure to guide device implantation. A 23-year-old man with a history of repair of hemianomalous pulmonary venous drainage and biventricular noncompaction (Figure 1A and B) presented with a 3-month history of reduced exercise tolerance and peripheral edema. Despite optimal medical therapy, he remained in New York Heart Association class 3. His ECG showed sinus rhythm with a PR interval of 154 milliseconds (ms), QRS duration of 134 ms, and left bundle branch block (LBBB) morphology. Transthoracic echocardiography showed a dilated left ventricle with severe global impairment, an ejection fraction of 23%, and an end-systolic volume of 141 mL. The patient had significant intraventricular dyssynchrony, with 3D echo assessment giving a systolic dyssynchrony index (SDI) of 16.7%. A CMR examination was performed to assess cardiac function and …

Three-dimensional late gadolinium-enhanced MR imaging of the left atrium: a comparison of spiral versus Cartesian k-space trajectories.

To investigate the feasibility of high‐resolution late gadolinium enhancement (LGE) imaging using a three‐dimensional (3D) stack of spirals k‐space trajectory for the detection of left atrial (LA) ablation lesions. LGE imaging inherently suffers from low SNR, so that improvements in spatial resolution and imaging time are challenging. The spiral trajectory offers greater acquisition efficiency, and this is used for increased spatial resolution.

Acute Pulmonary Vein Isolation Is Achieved by a Combination of Reversible and Irreversible Atrial Injury After Catheter AblationClinical Perspective: Evidence From Magnetic Resonance Imaging

Background— Pulmonary vein reconnection after pulmonary vein isolation is common and is usually associated with recurrences of atrial fibrillation. We used cardiac magnetic resonance imaging after radiofrequency ablation to investigate the hypothesis that acute pulmonary vein isolation results from a combination of irreversible and reversible atrial injury. Methods and Results— Delayed enhancement (DE; representing areas of acute tissue injury/necrosis) and T2-weighted (representing tissue water content, including edema) cardiac magnetic resonance scans were performed before, immediately after (acute), and later than 3 months (late) after pulmonary vein isolation in 25 patients with paroxysmal atrial fibrillation undergoing wide-area circumferential ablation. Images were analyzed as pairs of pulmonary veins to quantify the percentage of circumferential antral encirclement composed of DE, T2, and combined DE+T2 signal. Fourteen of 25 patients were atrial fibrillation free at 11-month follow-up (interquartile range, 8–16 months). These patients had higher DE (71±6.0%) and lower T2 signal (72±7.8%) encirclement on the acute scans compared with recurrences (DE, 55±9.1%; T2, 85±6.3%; P<0.05). Patients maintaining sinus rhythm had a lesser decline in DE between acute and chronic scans compared with recurrences (71±6.0% and 60±5.8% versus 55±9.1% and 34±7.3%, respectively). The percentage of encirclement by a combination of DE+T2 was almost similar in both groups on the acute scans (atrial fibrillation free, 89±5.4%; recurrences, 92±4.8%) but different on the chronic scans (60±5.7% versus 34±7.3%). Conclusions— The higher T2 signal on acute scans and greater decline in DE on chronic imaging in patients with recurrences suggest that they have more reversible tissue injury, providing a potential mechanism for pulmonary vein reconnection, resulting in arrhythmia recurrence.

Acute pulmonary vein isolation lesions consist of interstitial oedema and tissue necrosis: possible mechanism of pulmonary vein reconnection

Methods 15 patients with paroxysmal atrial fibrillation (PAF) underwent CMR scanning pre and immediately post WACA. 12 patients (4 male; mean age 56±11 years) had good quality images for delayed enhancement DE (necrosis) [Figure 1a,1b] and high T2-weighted signal (oedema) [Figure 1c,1d]. Images were analysed to quantify the circumferential extent of lesion formation with both imaging sequences. Clinical follow-up results at 6 months were then correlated with the MR findings.