Daniel R. Ludwig

Myocardial extravascular extracellular volume fraction measurement by gadolinium cardiovascular magnetic resonance in humans: slow infusion versus bolus

BackgroundMyocardial extravascular extracellular volume fraction (Ve) measures quantify diffuse fibrosis not readily detectable by conventional late gadolinium (Gd) enhancement (LGE). Ve measurement requires steady state equilibrium between plasma and interstitial Gd contrast. While a constant infusion produces steady state, it is unclear whether a simple bolus can do the same. Given the relatively slow clearance of Gd, we hypothesized that a bolus technique accurately measures Ve, thus facilitating integration of myocardial fibrosis quantification into cardiovascular magnetic resonance (CMR) workflow routines. Assuming equivalence between techniques, we further hypothesized that Ve measures would be reproducible across scans.MethodsIn 10 volunteers (ages 20-81, median 33 yr, 3 females), we compared serial Ve measures from a single short axis slice from two scans: first, during a constant infusion, and second, 12-50 min after a bolus (0.2 mmol/kg gadoteridol) on another day. Steady state during infusion was defined when serial blood and myocardial T1 data varied <5%. We measured T1 on a 1.5 T Siemens scanner using a single-shot modified Look Locker inversion recovery sequence (MOLLI) with balanced SSFP. To shorten breath hold times, T1 values were measured with a shorter sampling scheme that was validated with spin echo relaxometry (TR = 15 sec) in CuSO4-Agar phantoms. Serial infusion vs. bolus Ve measures (n = 205) from the 10 subjects were compared with generalized estimating equations (GEE) with exchangeable correlation matrices. LGE images were also acquired 12-30 minutes after the bolus.ResultsNo subject exhibited LGE near the short axis slices where Ve was measured. The Ve range was 19.3-29.2% and 18.4-29.1% by constant infusion and bolus, respectively. In GEE models, serial Ve measures by constant infusion and bolus did not differ significantly (difference = 0.1%, p = 0.38). For both techniques, Ve was strongly related to age (p < 0.01 for both) in GEE models, even after adjusting for heart rate. Both techniques identically sorted older individuals with higher mean Ve values.ConclusionMyocardial Ve can be measured reliably and accurately 12-50 minutes after a simple bolus. Ve measures are also reproducible across CMR scans. Ve estimation can be integrated into CMR workflow easily, which may simplify research applications involving the quantification of myocardial fibrosis.

Right ventricular apical pacing-induced left ventricular dyssynchrony is associated with a subsequent decline in ejection fraction.

BACKGROUND In patients with normal left ventricular (LV) ejection fraction (EF), the interposition of chronic, high-dose right ventricular apical (RVA) pacing may produce late EF decline. OBJECTIVE To test the hypothesis that LV dyssynchrony, defined echocardiographically and apparent early after interposition of pacing, would be greater in patients who subsequently demonstrated EF decline. METHODS Ninety-one patients with normal prepacing EF who underwent atrioventricular node ablation and subsequent high-dose RVA pacing were studied. Transthoracic echocardiograms were performed early (median 4 months) and late (median 28 months) after interposition of pacing, with a significant decline in EF between these studies defined as ≥5%. Speckle-tracking longitudinal strain analysis of the early echocardiogram was performed to quantify dyssynchrony. In addition to standard dyssynchrony indices, a novel index of apex-to-base mechanical propagation delay (MPD) was used. RESULTS Multivariable analysis determined that MPD of the septum correlated with a significant decline in EF, independent of all other dyssynchrony, clinical, or pacing variables. A septal MPD value exceeding 50 ms was associated with EF decline at 81% sensitivity and 88% specificity. CONCLUSIONS Dyssynchrony, in particular septal MPD, measured early after interposition of high-dose RVA pacing predicted a significant late decline in EF in patients who had normal prepacing EF.

Further Deterioration of LV Ejection Fraction and Mechanical Synchrony During RV Apical Pacing in Patients with Heart Failure and LBBB

Electrocardiographic left bundle branch block (LBBB) may be due to intrinsic disease of the left bundle branch or induced by right ventricular apical (RVA) pacing. Prior reports clearly delineate the derogatory impact of LBBB on left ventricular (LV) mechanical function but suggest equivalent impact between varieties. We hypothesized that their effects were disparate and performed a within-patient comparison to test this notion. Patients (n = 20) with heart failure, intrinsic LBBB, and an implanted pacing device with right atrial and RVA leads were studied. Each patient underwent transthoracic three-dimensional speckle-tracking echocardiography during atrial pacing (intrinsic LBBB) and short atrioventricular delay atrial-RVA pacing, and these studies were compared. Relative to intrinsic LBBB, RVA pacing-induced LBBB produced greater intra-LV and interventricular dyssynchrony, a deterioration in LV function, and a shift in the site of latest activation. In patients with heart failure and LBBB, acute RVA pacing induces greater mechanical dyssynchrony and further impairs LV function.

On the Importance of Image Gating for the Assay of Left Ventricular Mechanical Dyssynchrony Using SPECT

The potential of SPECT for quantifying left ventricular mechanical dyssynchrony is increasingly appreciated. We sought to examine the incidence and impact of image gating errors on this quantification and to test a possible solution for affected studies. Methods: First, to establish whether and how gating error alone could affect the measurement of dyssynchrony, we performed a prospective study in which patients with pacemakers were studied twice: during normal rhythm without gating error and with gating error caused by pacemaker-induced dysrhythmia. Second, to understand the pattern and magnitude of gating error during our typical imaging practice, we retrospectively examined studies from a separate cohort of 64 patients who were referred for dyssynchrony evaluation. Third, to understand whether studies with gating error could be repaired for the purpose of quantifying dyssynchrony, we tested a correction algorithm on the pacemaker-induced dysrhythmia image set to see whether it repaired this set so as to approximate the patients’ normal rhythm image data. We subsequently applied this algorithm to the 64-patient cohort. Results: Pacemaker-induced gating error caused a spurious decrease in dyssynchrony magnitude. Among the 64-patient cohort, similar gating errors were common, and an inverse exponential relationship between gating-error magnitude and dyssynchrony magnitude was observed. The correction algorithm accurately repaired the pacemaker-induced dysrhythmia image set; when it was applied to the 64-patient cohort, the magnitude of the postcorrection increase in dyssynchrony magnitude was proportional to the magnitude of the gating error. Conclusion: Gating errors cause a spurious reduction in SPECT assay of dyssynchrony magnitude. In our standard imaging practice, gating errors were common. Post hoc correction appears to be feasible.

Impact of scar on SPECT assay of left ventricular contraction dyssynchrony.

PurposeMany patients presently receiving cardiac resynchronization therapy (CRT) do not respond. A disproportionate number of nonresponders have ischemic cardiomyopathy, with significant left ventricular (LV) scar burden. Current selection criteria, such as electrocardiography or echocardiography, may not reliably portray the magnitude of CRT-remediable LV contraction dyssynchrony. Although phase analysis of gated single photon emission computed tomography (SPECT) image data is increasingly appreciated as a tool for quantifying dyssynchrony, its use in the setting of scar has not been adequately evaluated.MethodsConsecutive patients with ischemic (ICM, n = 50) or nonischemic (NICM, n = 39) cardiomyopathy underwent SPECT imaging prior to receiving CRT. In each patient, phase analysis of the raw images was performed to yield a phase standard deviation (PSD), an index which varies directly with the magnitude of dyssynchrony. ICM patient image data were also reanalyzed after scarred segments were stripped away.ResultsRaw image analysis demonstrated that PSD was significantly larger among ICM (57 ± 17°) than NICM (35 ± 13°, p < 0.001) patients. Among ICM patients, PSD after stripping of scarred segments was significantly decreased (40 ± 13°, p < 0.001). Signals emanating from scarred segments were of low amplitude and presented a random pattern, suggestive of noise rather than indicating contraction.ConclusionPSD values may be spuriously increased by scar. These findings may be important when using SPECT in selecting ischemic cardiomyopathy patients for CRT.

CT-Electromagnetic Three-Dimensional Tracking for Renal Endovascular Sympathetic Ablation Catheter Positioning in an Animal Model

PURPOSE To examine the feasibility of a computed tomography (CT)-guided renal endoarterial ablation procedure. MATERIALS AND METHODS Five large (40-60 kg) pigs were studied. Abdominal CT images that were obtained preoperatively were registered to the operative field, and subsequent virtual navigation of a multielectrode ablation catheter within the CT environment was performed. The ablation electrodes were visualized using an impedance technique. Ablation lesions were applied within each artery. Histologic analysis was performed to judge accuracy of the catheter location as portrayed in the virtual image. RESULTS The error between virtual and actual lesion locations along the longitudinal plane of the artery was 3.0 mm ± 2.5 (range, 0-6 mm) in the left renal artery and 3.4 mm ± 2.7 (range, 0-7 mm; P = .7) in the right renal artery. The accuracy of circumferential localization of the electrode was 92% in the right artery and 88% in the left artery. CONCLUSIONS These data demonstrate that a CT-guided renal artery ablation procedure is feasible.

A Novel Toolkit to Improve Percutaneous Subxiphoid Needle Access to the Healthy Pericardial Sac

The current practice of percutaneous subxiphoid needle access to the “healthy” pericardial sac has significant limitations. We sought to examine the feasibility of a novel toolkit designed to improve this procedure.

Nuclear image-guided left ventricular pacing lead navigation feasibility of a new technique

PurposeCurrent techniques for left ventricular (LV) lead implantation in patients with ischemic cardiomyopathy (ICM) typically underutilize information which is important for optimal lead location, including LV mechanical activation pattern and scar location. We sought to develop a technique in which this information, contained in single-photon emission computed tomographic (SPECT) images, could be integrated as to guide the electrophysiologist during the implantation procedure.MethodsFive ICM patients underwent SPECT as well as multidetector cardiac computed tomographic (MDCT) imaging prior to the LV lead implantation procedure. Images were merged to create a “fusion” image, in which the SPECT data were projected onto the anatomically accurate MDCT epicardial surface. The fusion image was registered to the operative field using the coronary veins, apparent on the MDCT image, as a fiducial system. After registration, LV lead implantation was guided by the fusion image using a commercial catheter navigation system.ResultsSuccessful guidance was achieved in each patient, with minimal disturbance to standard workflow. Leads were implanted in late-activating, unscarred regions according to the fusion image, with locations corroborated by fluoroscopic and electrographic features. In regions where leads were contiguous to the phrenic nerve shown on the fusion image, pacing consistently demonstrated diaphragmatic stimulation.ConclusionsIn this technical report, the description and feasibility of a new technique for SPECT image-guided LV pacing lead navigation is demonstrated. Prospective study will be required to confirm image precision and registration/navigation accuracy, as well as to demonstrate value relative to standard implantation techniques.

A SIMPLIFIED FORMULA FOR ESTIMATION OF EJECTION FRACTION FROM SPECKLE TRACKING ECHOCARDIOGRAPHIC GLOBAL STRAIN: COMPARISON WITH CARDIAC MAGNETIC RESONANCE

Global strain by speckle tracking echocardiography (STE) is emerging as a reproducible quantitative means to assess left ventricular function. Our aim was to determine a simplified formula to estimate ejection fraction (EF), using cardiac magnetic resonance (CMR) for comparison. We studied 80

HE UTILITY OF A NOVEL OFF-LINE APPROACH TO QUANTIFY DYSSYNCHRONY FROM ROUTINE CARDIAC MAGNETIC RESONANCE IMAGES: COMPARISON WITH ECHOCARDIOGRAPHIC SPECKLE TRACKING

Methods: We studied 50 consecutive pts who had both CMR and echo with a wide range of QRS width and ejection fractions (EF). Mid-LV short axis CMR images were analyzed from routine DICOM data sets using a novel software program (Image-Arena VA, TomTec, Corp) and compared with similar short axis echo images for speckle tracking radial strain (TomTec, Corp). Radial dyssynchrony was deined as the time difference between the anteroseptal and posterior wall peak strain.