Dirar S. Khoury

Preserved left ventricular twist and circumferential deformation, but depressed longitudinal and radial deformation in patients with diastolic heart failure

AIMSnTo examine myocardial deformation and rotation in patients with heart failure, and elucidate the underlying mechanisms that account for normal ejection fraction (EF) in patients with diastolic heart failure (DHF).nnnMETHODS AND RESULTSnFifty consecutive patients presenting with congestive heart failure (age: 58 +/- 16 years) underwent simultaneous right heart catheterization and transthoracic echocardiography. Left ventricular (LV) volumes, mass, EF, meridional, and circumferential wall stress were measured in addition to haemodynamic measurements. 2-D speckle tracking was applied to measure longitudinal, radial, and circumferential strain and twist. Twist was reduced only in patients with systolic heart failure (SHF: 5 +/- 2 degrees, DHF: 13 +/- 6 degrees, control: 14 +/- 5 degrees, P < 0.001). Circumferential strain was not different between DHF (-15 +/- 5%) and control groups (-20 +/- 3%, P > 0.05), though it was significantly lower in patients with SHF (-7 +/- 3%, P < 0.05). Importantly, longitudinal (DHF:-12%, SHF: -4%, control: -19%, P < 0.001) and radial (DHF: 28 +/- 9%, SHF: 14 +/- 8%, control: 47 +/- 7%, P < 0.001) strains were significantly lower in both heart failure groups than in controls, and were depressed to a larger extent in SHF patients than in those with DHF (both P < 0.05).nnnCONCLUSIONnLV longitudinal and radial strains are reduced, but circumferential deformation and twist are normal in DHF patients. On the other hand, in patients with SHF, longitudinal, radial, and circumferential deformation, and twist are all reduced. Multivariable regression analysis suggests that preserved LV twist and circumferential strain may contribute to normal EF in patients with DHF.

Global Diastolic Strain Rate for the Assessment of Left Ventricular Relaxation and Filling Pressures

Background— Diastolic strain rate (SR) measurements that comprise all left ventricular (LV) segments are advantageous over myocardial velocity for assessment of diastolic function. Mitral early diastolic velocity (E)/SR ratio during the isovolumetric relaxation (IVR) period can be used to estimate LV filling pressures. Methods and Results— Simultaneous echocardiographic imaging and LV pressure measurements (7F catheters) were performed in 7 adult dogs. Loading conditions were altered by saline infusion and caval occlusion, and lusitropic state was changed by dobutamine and esmolol infusion. A curve depicting global SR was derived from each of the 3 apical views, and SR was measured during IVR (SRIVR) and early LV filling (SRE). SRIVR had a strong correlation with time constant of LV pressure decay during the IVR period (&tgr;) (r=−0.83, P<0.001), whereas SRE was significantly related to LV end-diastolic pressure (r=0.52, P=0.005) in the experimental stages where &tgr; was <40 ms. In 50 patients with simultaneous right heart catheterization and echocardiographic imaging, mitral E/SRIVR ratio had the best correlation with mean wedge pressure (r=0.79, P<0.001), as well as in 24 prospective patients (r=0.84, P=0.001). E/SRIVR was most useful in patients with ratio of E to mitral annulus early diastolic velocity (E/Ea ratio) 8 to 15 and was more accurate than E/Ea in patients with normal ejection fraction and regional dysfunction (both P<0.01). Conclusions— Global SRIVR by 2-dimensional speckle tracking is strongly dependent on LV relaxation. E/SRIVR can predict LV filling pressures with reasonable accuracy, particularly in patients with normal ejection fraction and in those with regional dysfunction.

Left Ventricular Untwisting Rate by Speckle Tracking Echocardiography

Background— Recent studies validated the measurement of left ventricular (LV) untwisting rate (UR) by speckle tracking echocardiography. A few reports suggest that it may provide additional noninvasive insight into LV diastolic function. Methods and Results— Simultaneous echocardiographic imaging and LV pressure measurements (7F Millar catheters) were performed in 8 adult dogs. Loading conditions were altered by caval occlusion, whereas lusitropic state was changed by dobutamine and esmolol infusion. Inferior vena cava occlusion at all experimental stages (baseline, dobutamine, esmolol) led to a significant decrease (P⩽0.01) in LV end-systolic volume (ESV) and a significant increase in UR (P=0.03). The best relation was observed between LV UR and ESV (r=−0.8, P<0.001). The clinical study was conducted in 67 patients (age 57±17 years, 19 women) undergoing simultaneous right heart catheterization and echocardiographic imaging, with 20 healthy subjects as a control group. There were 34 patients with ejection fraction (EF) <50% (25±9%), and 33 patients with normal EF and diastolic dysfunction (64±7%). Patients with LV systolic dysfunction had a significantly lower UR (−55 &ogr;/s) in comparison with the control group (−89 &ogr;/s) and patients with normal EF (−104 &ogr;/s, P<0.05), and the determinants of LV UR were twist, ESV, and &tgr; (r2=0.83, P<0.001). In patients with diastolic dysfunction and normal EF, twist and ESV were the independent predictors (r2=0.71, P<0.001). Conclusions— LV UR is reduced in patients with depressed EF, but not in those with diastolic dysfunction and normal EF, and is primarily determined by twist and ESV.

Ambulatory monitoring of congestive heart failure by multiple bioelectric impedance vectors.

OBJECTIVESnThis study was designed to investigate the properties of multiple bioelectric impedance signals recorded during congestive heart failure (CHF) by utilizing various electrode configurations of an implanted cardiac resynchronization therapy system.nnnBACKGROUNDnThe monitoring of CHF has relied mainly on right-side heart sensors.nnnMETHODSnFifteen normal dogs underwent implantation of cardiac resynchronization therapy systems using standard leads. An additional left atrial (LA) pressure lead sensor was implanted in 5 dogs. Continuous rapid right ventricular (RV) pacing was applied over several weeks. Left ventricular (LV) catheterization and echocardiography were performed biweekly. Six steady-state impedance signals, utilizing intrathoracic and intracardiac vectors, were measured through ring (r), coil (c), and device Can electrodes.nnnRESULTSnCongestive heart failure developed in all animals after 2 to 4 weeks of pacing. Impedance diminished gradually during CHF induction, but at varying rates for different vectors. Impedance during CHF decreased significantly in all measured vectors: LV(r)-Can, -17%; LV(r)-RV(r), -15%; LV(r)-RA(r), -11%; RV(r)-Can, -12%; RV(c)-Can, -7%; and RA(r)-Can, -5%. The LV(r)-Can vector reflected both the fastest and largest change in impedance in comparison with vectors employing only right-side heart electrodes, and was highly reflective of changes in LV end-diastolic volume and LA pressure.nnnCONCLUSIONSnImpedance, acquired by different lead electrodes, has variable responses to CHF. Impedance vectors employing an LV lead are highly responsive to physiologic changes during CHF. Measuring multiple impedance signals could be useful for optimizing ambulatory monitoring in heart failure patients.

Retrograde ethanol infusion in the vein of Marshall: regional left atrial ablation, vagal denervation and feasibility in humans.

Background— The vein of Marshall (VOM) is an attractive target during ablation of atrial fibrillation because of its autonomic innervation, its location anterior to the left pulmonary veins, and its drainage in the coronary sinus.nnMethods and Results— We studied 17 dogs. A coronary sinus venogram showed a VOM in 13, which was successfully cannulated with an angioplasty wire and balloon. In 5 dogs, electroanatomical maps of the left atrium were performed at baseline and after ethanol infusion in the VOM, which demonstrated a new crescent-shaped scar, extending from the annular left atrium toward the posterior wall and left pulmonary veins. In 4 other dogs, effective refractory periods (ERP) were measured at 3 sites in the left atrium, before and after high-frequency bilateral vagal stimulation. The ERP decreased from 113.6±35.0 to 82.2±25.4 ms ( P <0.05) after vagal stimulation. After VOM ethanol infusion, vagally-mediated ERP decrease was eliminated (from 108.6±24.1 to 96.4±16.9 ms, P =NS). The abolition of vagal effects was limited to sites near the VOM (ERP, 104±14 versus 98.6±12.2 ms postvagal stimulation; P =NS), as opposed to sites remote to VOM (ERP, 107.2±14.9 versus 78.6±14.7 ms postvagal stimulation; P <0.05). To test feasibility in humans, 6 patients undergoing pulmonary vein antral isolation had successful VOM cannulation and ethanol infusion; left atrial voltage maps demonstrated new scar involving the inferoposterior left atrial wall extending toward the left pulmonary veins.nnConclusions— Ethanol infusion in the VOM achieves significant left atrial tissue ablation, abolishes local vagal responses, and is feasible in humans.nnReceived August 29, 2008; accepted November 24, 2008.Background—The vein of Marshall (VOM) is an attractive target during ablation of atrial fibrillation because of its autonomic innervation, its location anterior to the left pulmonary veins, and its drainage in the coronary sinus. Methods and Results—We studied 17 dogs. A coronary sinus venogram showed a VOM in 13, which was successfully cannulated with an angioplasty wire and balloon. In 5 dogs, electroanatomical maps of the left atrium were performed at baseline and after ethanol infusion in the VOM, which demonstrated a new crescent-shaped scar, extending from the annular left atrium toward the posterior wall and left pulmonary veins. In 4 other dogs, effective refractory periods (ERP) were measured at 3 sites in the left atrium, before and after high-frequency bilateral vagal stimulation. The ERP decreased from 113.6±35.0 to 82.2±25.4 ms (P<0.05) after vagal stimulation. After VOM ethanol infusion, vagally-mediated ERP decrease was eliminated (from 108.6±24.1 to 96.4±16.9 ms, P=NS). The abolition of vagal effects was limited to sites near the VOM (ERP, 104±14 versus 98.6±12.2 ms postvagal stimulation; P=NS), as opposed to sites remote to VOM (ERP, 107.2±14.9 versus 78.6±14.7 ms postvagal stimulation; P<0.05). To test feasibility in humans, 6 patients undergoing pulmonary vein antral isolation had successful VOM cannulation and ethanol infusion; left atrial voltage maps demonstrated new scar involving the inferoposterior left atrial wall extending toward the left pulmonary veins. Conclusions—Ethanol infusion in the VOM achieves significant left atrial tissue ablation, abolishes local vagal responses, and is feasible in humans.

Ethanol infusion in the vein of Marshall: Adjunctive effects during ablation of atrial fibrillation.

BACKGROUNDnThe vein of Marshall (VOM) is a left atrial (LA) vein that contains autonomic innervation and triggers of AF. Its location coincides with areas usually ablated during pulmonary vein (PV) antral isolation (PVAI).nnnOBJECTIVEnThis study sought to delineate the safety and ablative effects of ethanol infusion in the VOM during catheter ablation of atrial fibrillation (AF).nnnMETHODSnPatients undergoing PVAI (n = 14) gave consent for adjunctive VOM ethanol infusion. In 10 of 14 patients, the VOM was cannulated with an angioplasty wire and balloon. Echocardiographic contrast was injected in the VOM under echocardiographic monitoring. Two infusions of 100% ethanol (1 ml each) were delivered via the angioplasty balloon in the VOM. LA bipolar voltage maps were created before and after ethanol infusion. Radiofrequency ablation times required to isolate each PV and other procedural data were compared with those of 10 age-, sex-, AF type- and LA size-matched control subjects undergoing conventional PVAI.nnnRESULTSnThe VOM communicated with underlying myocardium, as shown by echocardiographic contrast passage into the LA. There were no acute complications related to VOM ethanol infusion, which led to the creation of a low-voltage area in the LA measuring 10.6 +/- 7.6 cm(2) and isolation of the left inferior PV in 4 of 10 patients. Radiofrequency ablation time required to achieve isolation of the left inferior PV was reduced (2.2 +/- 4 min vs. 11.4 +/- 10.3 min in control subjects, P <.05).nnnCONCLUSIONnVOM ethanol infusion is safe in humans, decreases radiofrequency ablation time in the left inferior PV, and may have a role as an adjunct to PVAI.

Left Ventricular Twist Mechanics in a Canine Model of Reversible Congestive Heart Failure: A Pilot Study

BACKGROUNDnLeft ventricular (LV) twist dynamics play an important role in LV systolic and diastolic function. The aim of this preliminary study was to investigate LV twist dynamics in a canine model of reversible congestive heart failure (CHF).nnnMETHODSnPacing systems were implanted in adult dogs, and continuous chronic right ventricular pacing (230-250 beats/min) was applied until CHF induction. Pacing was then stopped to allow the heart to recover. Echocardiography and LV catheterization were performed at baseline, during CHF while pacing was temporarily switched off, and during recovery. LV twist was computed as the difference between apical and basal rotation measured using 2-dimensional speckle tracking. Torsion was further calculated as LV twist divided by the LV long axis. The untwisting rate was computed as the peak diastolic time derivative of twist.nnnRESULTSnIn 6 dogs that completed the study, we found that CHF developed after 2 to 4 weeks of pacing, with LV end-diastolic volume, end-systolic volume, end-diastolic pressure, and the time constant of relaxation during isovolumic relaxation period (tau) all increasing significantly compared with baseline and recovering to normal levels 2 to 4 weeks after pacing was stopped. LV twist, torsion, and untwisting rate decreased significantly with CHF compared with baseline and improved during recovery from CHF.nnnCONCLUSIONnLV twist dynamics reflect pacing-induced CHF and its reversal as assessed by echocardiographic speckle tracking.

Usefulness of monitoring congestive heart failure by multiple impedance vectors

Introduction: We investigated trends in intrathoracic impedance measured between multiple implanted electrodes for monitoring pulmonary edema secondary to congestive heart failure (CHF) in an experimental model. Methods: Biventricular ICDs were implanted in 16 dogs and 5 sheep. Continuous RV pacing (230–250 bpm) was applied over several weeks. Meanwhile, impedance was measured every hour along 4 intrathoracic and 2 intracardiac vectors. Four cardiogenic impedance vectors were also monitored. Cardiac function was assessed biweekly by catheterization and echocardiography. Left atrial (LA) pressure was measured daily by an implanted LA pressure sensor. Results: All animals developed CHF after 2–4 weeks of pacing as evidenced by changes in function (EF, 52 vs. 34%; LV end-diastolic volume, 65 vs. 97 ml; LV end-diastolic pressure, 7 vs. 16 mmHg; LA volume, 17 vs. 33 ml; LA pressure, 7 vs. 26 mmHg), clinical symptoms, or autopsy. Steady state impedance decreased during CHF: LV-Can, 17±9%; LV-RV, 15±8%; LV-RA, 13±6%; RV-Can, 13±8%; RVcoil-Can, 8±6%; RA-Can, 6±6%. Change in LV-Can impedance was greater than that of RA-Can, RV-Can, and RVcoil-Can (P<0.05). LV-Can impedance correlated well with LA pressure (r2=0.73), while RV-Can and RVcoil-Can were weakly correlated (r2=0.43 and r2=0.52, respectively). Changes in LV-RV and LV-RA impedances were also larger than those of RVcoil-Can and RA-Can (P<0.05). Meanwhile, all impedances were associated with circadian variability at baseline (5±2%) which diminished during CHF (2±1%); P=0.02. Furthermore, significant variations were observed in cardiogenic impedances during progression into CHF as evidenced by reduced peak-to-peak amplitude and increased fractionation of the signals. Conclusions: All impedance vectors decreased during CHF. Impedance measurement employing left heart sensors correlated well with LA pressure, and may improve detection of CHF onset compared to sensing by RA or RV leads alone. This approach has important clinical implications for managing heart failure patients in the ambulatory setting.

Assessment of Left Ventricular Relaxation by Untwisting Rate Based on Different Algorithms

BACKGROUNDnThis study was performed in both animals and human subjects to test whether different approaches to calculate untwisting rate may lead to different results in the assessment of left ventricular (LV) relaxation.nnnMETHODSnIn animal experiments, congestive heart failure was successfully induced in 8 adult dogs. Transthoracic echocardiography was performed with simultaneous LV pressure recording at baseline and the stage of heart failure. In the clinical study, 72 patients undergoing right-sided heart catheterization were studied by transthoracic echocardiography. LV twist was calculated as the difference between apical and basal rotations measured using two-dimensional speckle tracking. Untwisting rate was calculated using 3 different algorithms as the peak negative time derivative of twist (UR(max)) during early diastole, the slope of the linear regression of untwisting over time (UR(slope)), or the average untwisting over the isovolumic relaxation period (UR(mean)).nnnRESULTSnUR(max) significantly correlated with tau and -dP/dt in dogs (r=-0.81 and 0.77, respectively, both P < .001) and was reduced at the stage of heart failure (P < .01). In 55 patients (76%) with adequate image quality, only UR(max) among untwisting rates calculated by 3 different algorithms was significantly related to tau (r=-0.51, P < .001). UR(max) was significantly lower in patients with tau>/=48 ms than in patients with tau<48 ms (P=.004), most of whom had a depressed LV ejection fraction.nnnCONCLUSIONnUR(max) best reflects LV relaxation in comparison with the 2 other algorithms.

Simulation study of EIT inverse problem based on Bayesian method

The prior of blocky resistivity profile is formulated based on the minimal of total variation using Bayesian method, and the resistivity distribution is reconstructed by Maximum a posteriori (MAP). The Markov chain Monte Carlo (MCMC) method with Gibbs sampler is used to sample from posterior density. The simulations on the 2D model show the feasibility of the method.