Patients and study protocol
18 patients were included into this study. The clinical characteristics of the patients are shown in Table . All patients underwent EP study and subsequent ablation procedures for supraventricular tachycardia. The Ethics Committee of Erasmus MC, Rotterdam, The Netherlands approved this study. Written, informed consent was obtained. Regardless of the final diagnosis, Koch's triangle was visualized with ICE in all patients at baseline without echocontrast and immediately thereafter, during continuous echocontrast infusion (SonoVue, Bracco). After the ablation procedure, which was either inside or outside Koch's triangle, the ICE procedure was repeated in six patients without echocontrast and in all patients using echocontrast. All ICE procedures were performed using a respiration and ECG gated and triggered pullback technique allowing three dimensional (3D) reconstruction of Koch's triangle. All 2D recordings were analyzed off-line by two independent echocardiographers and they provided confidence scores using a 1–10 grade scale. They were not aware that 6 patients were not ablated in Koch's triangle. This protocol implies that this was a prospective single blind study. 3D reconstruction of the ablation lesions was performed in patients where ablation lesions were seen.
Clinical characteristics and procedural outcome of the study patients
Electrophysiology testing and ablation
Standard electrophysiology (EP) and ablation procedures were undertaken using quadripolar electrode catheters in the high right atrium, to record the His bundle electrogram, in the right ventricle and a decapolar diagnostic catheter was inserted into the coronary sinus (CS). The initial portion of the EP procedure was directed at determining the presence of dual AV nodal physiology or accessory pathways, measuring the conduction properties and refractory periods of the fast and slow AV nodal pathways (if present), and determining the mechanism of the paroxysmal SVT. Mapping was performed and after the target site was identified, ablation was applied. Cryothermy and radiofrequency energy were used alternately during the study period.
Myocardial contrast echocardiography
MCE was performed using SonoVue (Bracco), which is a second generation contrast agent made of microbubbles stabilized by phospholipids and containing sulphur hexafluoride. The mean bubble diameter is 2.5 μm and more than 90% of the bubbles are smaller than 8 μm. The blood level curve shows a distribution half-life of about 1 minute and an elimination half-life of about 6 minutes[9
]. In this study we administered SonoVue by continuous intravenous infusion through the cubital vein at a rate of 100 ml/hour. Gain settings were not changed throughout the study.
Intracardiac echocardiography (ICE)
The ClearView™ system (CardioVascular Imaging Systems Inc, Fremont, CA) was used with an 8F sheath-based ICE imaging catheter that incorporates a 9 MHz beveled single-element transducer rotating at 1800 rpm (model 9900, EP Technologies, Boston Scientific Corp., San Jose, CA, USA).
ECG- and respiration-gated image acquisition and 3-D image processing
A custom-designed ECG- and respiratory-gated pullback device and a 3D-ultrasound workstation (EchoScan, TomTec GmbH, Munich, Germany) were used to acquire and process the ICE images using a technique described elsewhere[10
]. The pullback device is controlled by the 3D workstation and uses a stepping motor to move the catheter stepwise and linearly through the right atrium. The workstation receives video input from the ICE system and an ECG- and respiration-signal (impedance measurement) from the patient. Prior to the acquisition run, the range of RR- and breathing-intervals are measured to define the upper- and lower-limits. The workstation starts acquisition of 2D images after detecting the peak of the R-wave and in the same phase of respiration, at a speed of 25 images/ sec (image interval 40 ms). After acquiring one cardiac cycle, the workstation stores the images, and the catheter is then pulled back by a 0.5-mm axial increment. This process is repeated until the inferior vena cava (IVC) is reached. The acquisition time is much shortened when all cardiac cycles are of the same length, therefore, the right ventricular apex is paced at 100 bpm. In accordance with their timing in the cardiac cycle, all images are formatted in volumetric data sets (256*256*256 pixels/each 8 bits). During post-processing, several algorithms are applied to reduce noise, enhance edges, and reduce spatial artifacts (ROSA filter).
Continuous variables are expressed as mean ± standard deviation. Correlation analysis between the confidence scores and number of ablation lesions were performed using Pearson's test. The level of significance was set at a p value of 0.05.