Patients

Fifty-five patients were screened for this study, 50 of whom had 3D transthoracic echocardiographic images of sufficient quality to allow enrollment (feasibility of 3D TTE, 91%); 3D transthoracic echocardiographic images were accepted if all anatomic landmarks used to establish lead position were seen. Patients were recruited from consecutive newly implanted patients ( n = 38) or from consecutive previously implanted patients who came for regular follow-up visits ( n = 12). Pacemakers were implanted for usual indications, and pacing modes were as follows: VVI(R) in 35, DDD(R) in 13, and biventricular pacemakers for cardiac resynchronization therapy in two. Passive fixation leads (Medtronic CapSure SP Novus 5092; Medtronic, Inc., Minneapolis, MN) were used only for RV apical positions. Active fixation leads were used for all sites (Medtronic CapSureFix Novus 5076, Medtronic, Inc.; Biotronik Setrox S60, Biotronik GmbH, Berlin, Germany; and St. Jude Tendril 1788/1888, St. Jude Medical, St. Paul, MN).

Anatomy of the Right Ventricle and Implantation Technique

Anatomically, the right ventricle has three main regions: the outflow tract, the inflow tract, and the apex. The RVOT is defined inferiorly by the ventriculo-infundibular fold and septomarginal trabeculation and superiorly by the pulmonary valve. For the purposes of this study, the RVOT was divided into two main regions, in accordance with previous definitions : the septal wall and the free wall. The RVOT septal wall, considered as defined in electrophysiologic procedures, is oriented posteriorly and to the left, in close relationship with the left ventricular outflow tract and aortic valve. The caudal part of this region (often referred to as the “low RVOT”) contains the septoparietal trabeculations and is the only region of the RVOT that is strictly septal from an anatomic point of view (i.e., where the septum is defined as “a structure that can be removed without exiting the heart” ). The septoparietal trabeculations of the RVOT constitute the theoretical stable target site for RVOT pacing lead positioning, while pacing in the infundibular part of the RVOT septal wall (above the supraventricular crest, often referred to as the “high RVOT”) is not. The RVOT free wall was defined as the rest of the RVOT that remains after excluding the septal wall. The RV inflow tract (which corresponds to the mid RV level) is bordered posteriorly and to the left by the mid interventricular septum and anteriorly and to the right by the mid RV free wall. The RV apex is the region where all the walls converge and is adjacent to the left ventricular apex.

Single-chamber and double-chamber pacemaker systems were implanted from the right side, using either a cephalic or a subclavian approach. A left-sided approach was used for biventricular pacemaker implantation. For RVOT placements, we used the technique and the double-curved shaped stylet described by Mond and colleagues. For locations different from the RVOT, we used other, well-established techniques. No acute complications were recorded at implantation, and pacing thresholds, lead impedance, and R-wave sensing were adequate in all patients.

Fluoroscopic Criteria for Lead Position

Fluoroscopic criteria for permanent pacing lead implantation have been previously described. Documentation of lead position was acquired in each patient using three standard projections: anterior-posterior, 40° left anterior oblique, and 40° right anterior oblique.

The 40° right anterior oblique view was used to attribute the lead position to one of the following anatomic locations: RVOT, mid ventricular, and RV apex ( Figure 1 ). In this view, the level of the tricuspid valve and its inferior border was documented by the vertical radiolucent area and/or by appreciating the slight indentation of the lead at the base of its descendant curve from the superior vena cava. Because of the lack of any fluoroscopic definition of the RV apex, we decided to arbitrarily define the RV apex as the most rightward and caudal 2.5 cm of the cardiac shadow, because in clinical practice, leads attributed to the RV apex are in fact located in a region rather than at a single point. The 2.5-cm distance was found to correspond roughly to the echocardiographic definition of the RV apex (see below). For calculating distances, we used as reference the tip-to-ring distance of the pacing lead (seen from a fluoroscopic image parallel to the direction of the lead). The tip-to-ring distance of all the active fixation ventricular pacing leads used in this study was 1 cm, while the tip-to-ring distance of the passive fixation Medtronic CapSure SP Novus 5092 ventricular leads was 1.7 cm. The RVOT was defined as the superior part of the cardiac shadow at the right and superiorly to the tricuspid annular plane; the upper border of the tricuspid annulus was approximated to be 4 cm above its inferior aspect (defined previously). The mid septal region was defined as the region remaining after the exclusion of the RV apex and RVOT.

Fluoroscopic criteria for pacemaker lead position. LAO 40° , left anterior oblique projection at 40°; RAO 40° , right anterior oblique projection at 40°; RV , right ventricle; RVOT , right ventricular outflow tract.

The 40° left anterior oblique view was used to differentiate between septal (if the tip of the lead was pointing toward the patient’s left) and RV free wall (if the tip of the lead was pointing toward the patient’s right or in an indeterminate mid position) positions.

Two observers, blinded to the results of 3D TTE and electrocardiography, assessed all radiograms and decided about lead position; disagreements were solved by consensus.

ECG Criteria for Lead Position

According to the ECG criteria (assessed during fully paced QRS complexes) the location of the lead was classified into three main categories: RV apex (paced QRS complex with left bundle branch block [LBBB] pattern and superior axis), RVOT (paced QRS complex with LBBB pattern and inferior axis), and nonapical, non-RVOT locations (all other paced QRS patterns). Among all RVOT locations (defined above), the lead was classified as being RVOT septal if the paced QRS complexes showed no notching in inferior leads and transition in precordial leads earlier than or at lead V ₄ and as being RVOT free wall if the paced QRS complexes were >140 msec, with notching in inferior leads and transition beyond lead V ₄ . The presence of negative initial deflection of the paced QRS complexes in lead I for RVOT pacing sites was also noted.

No ECG criteria were used to define the mid RV level (mid septal and mid free wall), because of the lack of reliable characteristic ECG patterns for this region.

Two observers, blinded to the results of 3D TTE, assessed all electrocardiograms and established lead position. Disagreements between observers were solved by consensus.

Echocardiographic Criteria for Lead Position

We used multiple-beat 3D TTE for exact documentation of the anatomic location of pacing leads. Full-volume echocardiographic data sets were acquired during end-expiratory held respiration, using a Vivid 7 Dimension machine equipped with a 3V probe (GE Vingmed Ultrasound AS, Horten, Norway), from the left parasternal, apical, and (if good resolution was obtained) subcostal windows. These full-volume echocardiographic data sets were reconstructed by the machine using electrocardiographically triggered acquisitions of narrow volumes of data over four cardiac cycles that were subsequently stitched together to create a single volumetric data set. Narrow volumes of data were also recorded in some patients if the insertion site of the lead was clearly visible in these images. The echocardiographic data set was then analyzed offline using dedicated software (EchoPAC BT 11.0; GE Vingmed Ultrasound AS).

The exact lead position, defined as the myocardial attachment site of the tip of the lead, was documented using true long-axis and transverse cropping planes (in relation to the long axis of the left ventricle) from the full-volume echocardiographic data set. Five main cropping planes were used to classify lead position ( Figure 2 ): four true transverse planes representing the parasternal short-axis (PSAX) view (apical level, papillary muscle level, mitral valve level, and aortic valve level) and one orthogonal plane representing a modified apical four-chamber view that included the RVOT. The full-volume data sets acquired from the parasternal window were used primarily to identify the leads implanted at the RVOT and mid ventricular levels. Full-volume data sets acquired from the apical window were used primarily to identify leads implanted at the apical and mid ventricular levels. The full-volume data sets acquired from the subcostal window were also used to create the cropping planes described above. The position of the lead was verified using all available acoustic windows.

Echocardiographic criteria for pacemaker lead position. The dotted vertical orange line in the mid lower figure represents the plane of the interventricular septum. For further details see the “Methods” section of the text. A4c , Apical four-chamber view; LV , left ventricle; PV , pulmonary valve; RV , right ventricle; RVOT , right ventricular outflow tract.

Using these cropping planes, we classified the position of the leads as being (1) apical (using a true transverse cropping plane equivalent with the PSAX view at the apical level) if the tip of the lead was attached apically from the base of the left ventricular papillary muscles; (2) mid septal (using a true transverse cropping plane equivalent with the PSAX view at the papillary muscles level) if the tip of the lead was attached to the interventricular septum or in the groove made by the RV free wall and the septum, proximally from the base of the left ventricular papillary muscles and caudally from the upper border of the tricuspid valve; (3) mid RV free wall (using a true transverse cropping planes equivalent with the PSAX view at the papillary muscles level) if the tip of the lead was attached to the RV free wall at the same level as for the mid septal region; or (4) RVOT (using the true transverse cropping plane equivalent with the PSAX view at the mitral valve level, the aortic valve level, and an orthogonal plane equivalent to a modified apical four-chamber view showing the RVOT) if the tip of the lead was attached to the RVOT at a level cranially to the upper border of the tricuspid annulus (this level was identified using a coronal cropping plane perpendicular to the tricuspid annular plane).

For RVOT locations, we classified the position of the leads as RVOT septal wall or RVOT free wall on the basis of the following consensus: (1) RVOT septal wall position was attributed if both the direction of the tip of the lead and its insertion site were seen to the left of the plane of the interventricular septum (defined using a true sagittal cropping plane), and (2) RVOT free wall position was attributed if the previous criteria were not met.

This consensus favored fluoroscopy because it classified together the leads implanted into the low RVOT septal wall (at the level of the septoparietal trabeculations, as seen from the PSAX view at the mitral valve level) and leads implanted in the high RVOT septal wall (in the infundibulum, as seen from the PSAX view at the aortic valve level).

Two observers, blinded to the results of fluoroscopy and electrocardiography, assessed all 3D transthoracic echocardiographic images and established lead position. Disagreements between observers were solved by consensus.

Thus, using the above-described criteria, lead positions were attributed by each technique (fluoroscopy, electrocardiography, and 3D TTE) to the following locations: RV apex, mid septum, mid RV free wall, RVOT septal wall, and RVOT free wall.

Reproducibility

Intraobserver and interobserver agreement for each of the three technique was calculated using Cohen’s κ coefficient by reanalyzing all fluoroscopic, ECG, and 3D TTE readings by two observers on different days.

Statistical Analysis

Agreement between fluoroscopic and ECG criteria and exact pacemaker lead location defined by 3D TTE was assessed using κ coefficients. We defined high agreement as κ > 0.81, good agreement as κ = 0.61 to 0.80, moderate agreement as κ = 0.41 to 0.60, poor agreement as κ = 0.21 to 0.40, and very poor agreement as κ = 0.01 to 0.20. Additionally, sensitivity, specificity, and positive likelihood ratio and negative likelihood ratio were computed.