Ventricular excitation maps using tissue Doppler acceleration imaging: potential clinical application

The left ventricular intracavitary vortex during the isovolumic contraction period as detected by vector flow mapping

AIMS

The purpose of this study was to characterize left ventricular (LV) intracavitary flow during the isovolumic contraction (IVC) period in humans using vector flow mapping.

METHODS

Color flow Doppler imaging was performed from the apical long-axis view in 61 patients with heart failure and 58 healthy volunteers. Doppler flow data obtained during IVC were analyzed offline with vector flow mapping.

RESULTS

A large vortex was formed from the LV inflow toward the outflow during IVC. In normal subjects, the area of the vortex was sustained, but the flow volume decreased significantly during IVC (P < 0.001). A significant apex-to-base flow velocity gradient was shown along the outflow axis on aortic valve opening. However, both the area and flow volume of the vortex decreased more severely during IVC in the patients (P < 0.001). The apex-to-base flow velocity gradient along the outflow axis disappeared and a reversed velocity gradient was observed at the basal-mid level on aortic valve opening. In multivariate models, a decreased LV ejection fraction was the only independent predictor of the percentage decrease in area of the vortex during the IVC (P < 0.001), and a larger QRS width (P = 0.028) and LV end-systolic long diameter (P = 0.002) were independent predictors of the percentage decrease in flow volume of the vortex.

CONCLUSIONS

The vortex across the LV inflow-outflow region during IVC facilitates the ejection of blood during early systole, and an unsustained vortex may be associated with impaired cardiac function.

Intracardiac echocardiography-guided his bundle pacing and atrioventricular nodal ablation

BACKGROUND

His bundle pacing (HBP) results in rapid synchronous ventricular activation, but has been associated with long procedure times and compromised pacing and sensing performance. This study sought to reduce procedure time and radiation exposure, and improve electrical performance through more accurate lead placement.

METHODS

Intracardiac echocardiography (ICE) was used to guide ablation and lead implantation at the His bundle, right atrial appendage (RAA), and right ventricular apex (RVA), and to assess cardiac function. Custom bipolar screw-in leads with steerable delivery sheaths and an ablation catheter were navigated using ICE (local detailed imaging) and fluoroscopy (global imaging) in anesthetized closed-chest canines (N = 6).

RESULTS

HBP (N = 1) or His + ventricular septal pacing (N = 5) was achieved in all canines. The QRS width was 59.7 +/- 5.3 ms for canines in sinus rhythm (SR) and 82.8 +/- 16.6 ms for canines with HBP (P = 0.0086). The QRS width for RVA pacing was 106.3 +/- 18.4 ms (P = 0.042 vs HBP; P = 0.00013 vs SR). HBP thresholds were 3.0 +/- 1.0 volts at 0.5 ms (N = 5 due to a late exit block in one canine). The average procedure duration for His lead placement was 40 +/- 28 minutes (range of 3-81 minutes) and the total procedural X-ray exposure was 12 +/- 12 minutes (range of 2-30 minutes). Hemodynamic performance was similar for HBP and RAA pacing.

CONCLUSIONS

Feasibility of ICE guidance for His pacing and precision ablation of the atrioventricular (AV) node has been shown. This anatomic approach improved accuracy, limited X-ray exposure, and might allow His pacing in patients with preexisting AV nodal block.

Quantitative echocardiographic assessment of myocardial acceleration in normal left ventricle by using velocity vector imaging

To investigate the characteristics of myocardial acceleration in normal left ventricular walls, velocity vector imaging was performed in 30 normal volunteers. Peak accelerations during early systole and early diastole and time to peak acceleration during early systole were calculated for each segment of the standard 16-segment model. A gradient of accelerations from base to apex and a homogeneity of accelerations among different walls at the same level were observed. There were homogeneities of time to peak acceleration during early systole in both longitudinal and latitudinal directions on left ventricular walls. In 82.29% of all segments, the onset of contraction acceleration during early systole could not be identified. Further research with larger populations is needed to clarify the role of myocardial acceleration in the assessment of the site of initial electrical stimulation and the sequence of ventricular depolarization.

Visualization of the site of the onset of ventricular depolarization by acceleration mode Tissue Doppler imaging technique

Tissue Doppler imaging (TDI) is a relatively new echocardiographic technique that shows regional myocardial wall velocities. The aim of this study was to evaluate the potential value of acceleration mode TDI technique for the visualization of the origin of ventricular activation site using the model of right ventricular pacing. Twenty-seven patients with implanted permanent pacemakers were studied by acceleration mode TDI, 4 of these patients were pacemaker dependent. Parasternal and apical chamber views were recorded on video tape by using acceleration mode TDI technique during sinus rhythm with preserved atrioventricular conduction in 23 subjects who were not pacemaker-dependent, and also during right ventricular apical pacing in VVI mode in 27 subjects in whom pacing lower rate was increased if necessary. Fifty images recorded during sinus and pacing rhythm in cineloop were examined by two independent observers who were unaware of the rhythm patterns and by the same observer on two different occasions for localizing the site of onset of ventricular acceleration. The origin of ventricular activation during sinus rhythm started at basal septal part of the ventricle and during pacing started at apical part of the ventricle was considered as correct localizations. The origin of ventricular depolarization was correctly localized for 46 of 50 images (92%) and 44 of 50 images (88%) by the first and the second observers, respectively. Concordant results between observers appeared in 48 of 50 (96%) of images. The diagnostic accuracy of the concordant results was 44 of 48 (91.6%) images. The kappa for interobserver variability was 0.77 (p<0.001), and for intraobserver variability was 0.64 (p<0.001) and 0.63 (p<0.001) for the first and the second observers, respectively. These results suggest that acceleration mode TDI can be used to detect the initial ventricular excited position and seems to have a potential value for localizing of the origin of normal or abnormal myocardial depolarization.

Quantitative assessment of regional peak myocardial acceleration during isovolumic contraction and relaxation times by tissue Doppler imaging

OBJECTIVE

To examine regional wall acceleration and its relation to relaxation.

STUDY DESIGN

8 sheep were examined by tissue Doppler ultrasound imaging (VingMed Vivid FiVe) in apical four chamber views to evaluate the left ventricular wall divided into six segments and the mitral annulus in two segments. Peak myocardial acceleration during isovolumic periods (pIVA) derived from tissue Doppler echocardiography was analysed during isovolumic contraction (ICT) and relaxation times (IRT) in each segment.

INTERVENTIONS

After scanning at baseline, haemodynamic status was changed by administration of blood, dobutamine, and metoprolol. Changes of pIVA during IRT and ICT were compared over the four haemodynamic conditions in parallel with their peak positive and negative dP/dt measured with a high frequency manometer tipped catheter.

RESULTS

pIVA of the basal lateral segment during ICT correlated most strongly with peak positive dP/dt (r = 0.96, p < 0.0001) and there was good correlation between pIVA of the mitral valve annulus in the septum during IRT and peak negative dP/dt (r = 0.80, p < 0.0001). pIVA differed significantly between the four haemodynamic conditions during ICT in all segments (p < 0.05); pIVA during IRT did not differ significantly between the four conditions.

CONCLUSIONS

pIVA of the basal lateral wall during ICT correlated most strongly with peak positive dP/dt, and pIVA of the septal mitral valve annulus during IRT correlated well with peak negative dP/dt.

Tissue tracking imaging as a new modality for identifying the origin of idiopathic ventricular arrhythmias

Tissue tracking imaging was performed in 33 patients with idiopathic ventricular arrhythmias before radiofrequency catheter ablation. The site of the arrhythmia origin, defined as the site where the earliest color-coded signal appeared on the myocardium at the onset of the arrhythmia, corresponded to the site of origin as determined on fluoroscopy during activation mapping in all patients. Catheter ablation at that site abolished the arrhythmia in 29 patients (88%).

Tissue Doppler-derived myocardial acceleration for evaluation of left ventricular diastolic function

OBJECTIVES

Our purpose was to evaluate a tissue Doppler-based index-peak myocardial acceleration (pACC)-during isovolumic relaxation and in evaluating left ventricular (LV) diastolic function.

BACKGROUND

Simple, practical indexes for diastolic function evaluation are lacking, but are much desired for clinical evaluation.

METHODS

We examined eight sheep by using tissue Doppler ultrasound images obtained in the apical four-chamber views to evaluate mitral valve annular velocity at the septum and LV wall. The pACC thus derived was analyzed during isovolumic relaxation (IVRT) and during the LV filling period (LVFP). We then changed the hemodynamic status of each animal by blood administration, dobutamine, and metoprolol infusion. We compared the pACC values during IVRT and LVFP over the four different hemodynamic conditions with a peak rate of drop in LV pressure (-dP/dt(min)) and the time constant of LV isovolumic pressure decay (tau), as measured with a high-frequency manometer-tipped catheter.

RESULTS

The pACC of the septal side of the mitral valve annulus during IVRT showed a good correlation with -dP/dt(min) (r = -0.80, p < 0.0001) and tau (r = -0.87, p < 0.0001). The mean left atrial pressure (LAP) correlated well with the septal side pACC during LVFP (r = 0.81, p < 0.0001). There was a weak correlation between the mitral valve annulus pACC at the LV lateral wall and mean LAP.

CONCLUSIONS

The pACC during IVRT is a sensitive, preload-independent marker for evaluation of LV diastolic function. In addition, pACC during LVFP correlated well with mean LAP.

A simple and accurate method to identify early ventricular contraction sites in Wolff-Parkinson-White syndrome using high frame-rate tissue-velocity imaging

The high frame-rate tissue-velocity imaging method may be superior to the conventional M-mode method in accurately localizing accessory pathways without consuming large amounts of time.

Localization of the ventricular preexcitation site in Wolff-Parkinson-White syndrome with Doppler tissue imaging

PURPOSE

The objective of this study was to evaluate the ability of Doppler tissue imaging (DTI) to localize the ventricular emergence site of accessory atrioventricular pathways (Wolff-Parkinson-White syndrome).

METHODS

Thirty-three patients were studied prospectively by Doppler tissue imaging (128XP and Sequoia 256 echocardiographic systems; Acuson, Mountain View, Calif) before investigation of Wolff-Parkinson-White syndrome and after radiofrequency ablation of the accessory pathways. The normal appearance of the ventricular contractions was defined in a group of 10 control subjects. The preexcitation zone was determined as a zone of maximum acceleration in "DTI acceleration mode" or as a coded contraction zone in "DTI velocity mode," at the time of the delta wave or before the onset of the QRS complex.

RESULTS

The earliest ventricular activation site was correctly localized for 12 of the 15 left-sided pathways (8 anterior or anterolateral, 2 lateral or posterolateral, 2 inferior). When wall motion abnormalities were detected in the left ventricle by DTI, the left-sided localization was confirmed by electrophysiologic exploration. For the right-sided pathways, the localization was correct in only 4 of 11 cases (3 posteroseptal and 1 anterolateral). After effective ablation in all patients, the abnormalities corresponding to the electrophysiologic data disappeared totally in only 11 of 16 patients.

CONCLUSION

In the presence of Wolff-Parkinson-White syndrome, DTI localizes contraction abnormalities associated with early activation of a part of the ventricle. However, the interpretation of the images remains difficult because the normal coding of the contraction of the ventricular walls depends on the incidence for which they are investigated. This noninvasive examination seems to be an effective tool for localizing the left-sided accessory pathways of the left ventricle, in particular in the anterior, anterolateral, or inferior walls.