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Alternate Site Right Ventricular Pacing:

Defining Template Scoring

Harry G Mond OAM, MD, FRACP, FACC, FCSANZ, FHRS,

Alexander Feldman MD, Raphael Rosso MD and Thuy To Hung MD.

Department of Cardiology, Royal Melbourne Hospital, Melbourne, Australia

Address for correspondence:

Assoc. Prof. Harry G Mond,

Suite 22, Private Medical Centre, The Royal Melbourne Hospital,

Victoria, 3050, Australia. Tel: 613 9347 4296 Fax: 613 9347 6760

E-mail: [email protected]

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Running title: Right Ventricular Pacing

Key words: Right Ventricular Pacing

Template Scoring

Disclosures:

Dr Mond designed the right ventricular septal stylet used in the study,

but has no financial interest in the commercially available product.

Abstract:

Background: Prolonged right ventricle (RV) apical pacing is associated with

left ventricular (LV) dysfunction due to dysynchronous ventricular activation

and contraction. Alternate RV pacing sites with a narrower QRS compared to

RV pacing might reflect a more physiological and synchronous LV activation.

The purpose of this study was to introduce a new and novel way of evaluating

alternate site RV pacing sites using a template scoring system. This involved

measuring the angle of lead attachment to the endocardium in the 40o left

anterior oblique (LAO) fluoroscopic view. The effect of altering the loop of lead

in the RV was also investigated.

Methods: 23 consecutive patients with an indication for RV pacing were

enrolled in the study. Standard 58cm active fixation leads were positioned in

either the RVOT septum or mid RV septum. Using LAO cine fluoroscopy, a

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generous loop of lead was inserted into the RV chamber and the change in

angle of attachment to the endocardium determined.

Results: Successful positioning of the pacing leads at the RVOT septum (18)

and mid RV septum (5) was achieved without complications. The angle of

attachment of the lead tip altered in all patients over a range of 6o to 32o with a

mean of 14.6o ± 6.6o. In 91% of patients, the range was predominantly within

the same template score.

Conclusions: This prospective study shows that a template scoring system

can be applied to lead attachment in alternate RV sites, but more work is

required to determine the accuracy and efficacy of the templates. .

. 257 Words

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Introduction:

Prolonged pacing from the right ventricular (RV) apex is associated with

progressive left ventricular (LV) dysfunction1,2,3,4,5 which appears related to a

remodeling process consequent to abnormal ventricular activation and

contraction.6,7,8,9,10,11,12,13,14,15 This deleterious effect has lead to a growing

interest in alternate ventricular pacing sites with a more favorable

hemodynamic profile. Such a site is the RV septum, which is theoretically

associated with a more physiological ventricular activation resembling that of

normal atrio-ventricular conduction.16 The techniques and tools for reliable

placement of pacing leads onto the right ventricular septum have only recently

been described17,18 and consequently pacing from these areas have not been

studied in detail.

From recent studies, the 40o left anterior oblique (LAO) fluoroscopic view

appears to be the most desirable investigation to determine RV positioning

outside the apex. It can be easily performed during lead implantation and 40o

has been chosen as it is the near maximum orientation in the oblique position

that can be achieved without compromising the sterile field. The view,

however, has not been proven to be the gold standard and like many potential

clinical investigations is subject to patient anatomical variability. Other

methods to determine RV lead position may include echocardiography,

computerized tomography scanning and in patients with compatible pacing

systems even magnetic resonance imaging. However, such investigations are

currently limited to post operative evaluation.

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An LAO fluoroscopic template has been designed which defines the position

of the RV lead in the heart as septal, anterior or free wall. However, in order to

apply this template, we have investigated the effect of altering the amount of

lead in the heart to determine if this variable, adversely affects the

interpretation of lead positioning.

Methods:

Study population:

The study group consisted of 23 consecutive patients with indications for a

single or dual chamber pacemaker implant, undergoing the initial procedure at

the Royal Melbourne Hospital. In all patients, RV septal pacing was desirable.

Template Scoring:

Prior to the commencement of the study, a template was created using LAO

fluoroscopic examples of RV lead positioning from an ongoing data base of

over 500 lead implantations (figure 1). The lead position was determined

using measured angles from 0o to 140o in the LAO view.

The RV anterior position of the lead is a narrow zone where the lead tip lies

on or immediately adjacent to the septum on the front of the heart and is

ltraversed by the left anterior descending coronary artery. The angulation

onthe template is from 80o to 100o and for ongoing studies, this zone is

awarded “0” points. To the left is a zone 60o to 80o, where the lead points

slightly towards the spine and is a transition zone between septal and anterior

and is awarded one point. True septal pacing is awarded either “2” (40o to 60o)

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How to define the angle: drawing a horizontal line and making up with the end of the lead an angle.

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or “3” (0o to 40o) points. To the right of true anterior is another transition zone

(100o to 120o) between anterior and free wall and is awarded “-1”. True free

wall is designated 120o to 140o and awarded “-2” points. Both septal and free

wall lead positions can have angulation beyond these limits, but this has not

been seen in the data base. Such positions would still be awarded “3” and “-2”

points.

Implant procedure:

The pacemaker implantation was performed or supervised by a single

operator (HM) with experience in RV septal lead placement. Pacemaker

implantation was done under local anesthesia, conscious sedation and pre-

operative prophylactic intravenous antibiotics. The RV lead was inserted via

the left or right cephalic or subclavian venous approach. Commercially

available 58 cm bipolar active fixation leads with steroid-eluting electrodes

were used for RV implants. A specifically shaped stylet designed to facilitate

positioning of active fixation ventricular leads onto the RV septum (Mond®

RVOT Stylet, model 4140, St.Jude Medical, St. Paul, MN, USA) was used for

all RV lead implants. The positioning of the ventricular leads into the RV was

guided by the posterior-anterior fluoroscopic view. In all cases, the lead was

passed to the pulmonary artery and withdrawn across the pulmonary valve

into the RV outflow tract (RVOT) or mid RV. The first lead position was

accepted and no septal mapping attempted. The implant technique has been

described in detail.18

Septal deployment of the lead was confirmed by the LAO position and cine

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RV septal

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recordings were made at a frame rate of 10 per second. Immediately prior to

the recording, the RV lead was partially withdrawn, so as to leave a minor

loop in the RV (figure 2). During the 3 second recording, the amount of loop in

the RV was rapidly increased until a bend was noted across the tricuspid

annulus or the distal end of the lead became distorted at its deployment site

(figure 2). Following this recording, the lead was once again slowly withdrawn

about 1cm under fluoroscopic control until the desired final position was

determined and the extra-vascular portion secured by the collar using non-

absorbable sutures.

Following recruitment of patients, the cine fluoroscopies of all cases were

analyzed and hard copy prints made for every alternate frame, so as to have

approximately 20 prints per case. In all instances, the first and last images

were excluded, because of the extreme positions. In a number of cases,

significant lead tip distortion was still noted after first and last recordings were

excluded. As such distortion would never be accepted as the final position,

these recordings were also excluded.

The images were all analyzed by hand using a protractor to determine the

angles of the lead tip in the LAO position (figure 2). The limits of the angles

during lead insertion were determined to see if the scores for any individual

patient moved from one template group to another. The study was accepted

as a quality assurance/quality improvement project by the hospital Research

Directorate and Ethics Committee, thus not requiring ethical review or formal

patient consent.

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Statistical analysis

All continuous data was tested for normal distribution using One-sample

Kolmogorov-Smirnov test and Q-Q plots. All variables were found to follow

normal distribution and hence were expressed as mean (SD). The

comparison of continuous variables between the two groups was done using

independent student t-test. For categorical variables, the Fisher’s exact test

was used. A P value of <0.05 was accepted as indicating significance.

Results:

The study group was composed of 23 patients with 13 males and a mean age

of 77 6 years. The indications for the pacemaker were high grade atrio-

ventricular block in 9, sick sinus syndrome in 7, paroxysmal or established

atrial fibrillation in 5 and syncope of unknown cause in 2. The pacing leads

used were the St. Jude Tendril® 1888TC in 14 cases, the Medtronic

CapsureFix® Novus 5076 (Medtronic Inc., Minneapolis, MN, USA) in 5 and

the Boston Scientific Dextrus® 4137 (Boston Scientific Inc. Natick, MA, USA) in

4 cases.

Lead Measurements at RVOT and mid-septal locations

Electrical parameters for the RV leads at implant were satisfactory, regardless

of their positioning at the RVOT or mid RV septum (table 1).

Ventricular pacing lead positioning

In 18 patients (88.2%), the pacing leads were deployed in the RVOT and in 5

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the mid RV septum. In 5 cases, (4 RVOT and 1 Mid RV), the leads were

classified during study analysis as within the transition zone between anterior

and septal (figure 3). In no cases were difficulties encountered deploying the

RV lead. There were no complications associated with the study.

Angle of lead tip during loop formation:

By increasing the loop of lead in the RV, the angle of attachment of the lead

tip altered in all cases (figure 3). The range was from 6o to 32o with a mean of

14.6o ± 6.6o. In 9 cases, the angle classification was 3, in 6 cases it was 2, in 5

cases it was 1 and indeterminate in 3 cases (between 2 and 3). Although

there was some overlap, in 87% of cases, the angle change was

predominantly within one group.

Discussion:

The ideal ventricular pacing site should resemble normal ventricular

depolarization with the synchronicity of ventricular activation as observed with

an undamaged conduction system. RV septal pacing allows a narrower QRS

compared to RV apical pacing,7 which in turn might reflect a more

physiological and synchronous form of ventricular activation.7,19,20,21 In theory

RV septal pacing should be preferable to RV apical pacing, but the

physiological advantages as demonstrated with long-term studies, although

suggestive, have yet to be confirmed.7, 22, 23, 24

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One of the main reasons that such studies have not been confirmatory is that

true RV septal pacing has until recently been difficult to consistently achieve.

Some of these difficulties relate to the lack of suitable lead technology, the

non-standardized nomenclature and the inability to consistently and

accurately position pacing leads onto the septum because of its posterior

orientation within the RV chamber.25 We now have a much clearer

understanding of the relationship between the anatomy of the RV chamber

and the fluoroscopic appearances and electrocardiographic patterns, which in

turn has allowed successful development of tools to reliably direct active

fixation leads onto the true RV septum.26

To date, the most important tool for septal pacing confirmation is the LAO

fluoroscopic view, which can be performed during RV lead implantation.

However, more studies are required to confirm whether this truly identifies septal

positioning. In this study, a LAO fluoroscopic template method has been

developed to assist in assessing lead position. The endocardial attachment of

pacing leads in alternate RV pacing sites can be identified and graded as to

whether the lead attachment is septal, anterior or free wall. This template can

be used to determine the success or otherwise of different implant strategies

and tools. However, before this can be done a number of variables that could

alter the angulation of the RV lead attachment must be considered.

An important variable is chest wall shape. Factors such as pulmonary and

vertebral column disease can distort the positioning and orientation of the

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heart in the mediastinum, thus potentially altering the lead position in the LAO

fluoroscopic view. However, this should be obvious with the postero-anterior

and right anterior oblique fluoroscopic views and thus taken in to account

when observing the LAO fluoroscopic view. To also minimize this variable

from patient to patient, exact 40o LAO angulation is essential and has been

strictly adhered to in this study.

The effect of the amount of loop left in the RV at the end of implantation was

investigated by measuring the change of angle when more lead is introduced.

As expected the angle of attachment did alter as more lead was delivered to

the RV. However, this was only important in 13% of patients, where the angle

changed from one zone to the next. To overcome this and thus minimize this

variable, the amount of loop left in the RV follows a strict protocol at

implantation in order to prevent lead dislodgement.18

Another variable not investigated was the effect of the cardiac cycle on lead

angulation. This would require an electrical gate to synchronize the

fluoroscopic images with the ECG, which in a practical sense is infrequently

used. An attempt was made to do this visually without ECG gating, but

became impractical as many patients had poor left ventricular function and

therefore little change in fluoroscopic appearances during the cardiac cycle.

However, during the loop study there were at least two cardiac cycles within

each study and thus the change in angulation with cardiac contraction was

within the range demonstrated in figure 3. A further variable to be considered

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is respiration. Because of sedation and shallow respiration, it was never

necessary to control breathing during the cine fluoroscopy acquisition and

thus this variable is of little significance.

The template defines two narrow zones close to zero angulation. Although

previously defined as septal or free wall, these zones appear so close to zero

that in reality they may well be actually anterior. This indeterminate or

transition zone needs further investigation, but in the interim they are

allocated only 1 or -1 points.

Study Limitations:

This manuscript describes a new and novel way of evaluating pacing or ICD

lead positioning in alternate RV sites. Potential limitations of the templates

such as body shape, the loop of lead in the RV chamber and effects of the

cardiac cycle and respiration have been addressed. More work needs to be

done to determine the accuracy of the templates and whether they have

relevance to physiologic studies or evaluating implantation tools and

techniques.

Conclusions:

The RV septum has been proposed as a safer and hopefully more physiologic

pacing site than the RV apex. True septal pacing can be recognized by the

LAO fluoroscopic view during implantation, but more work is required to

establish this as a gold standard. A new and novel way of evaluating alternate

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RV pacing sites using a template scoring system is proposed to assist in future

studies. This involves measuring the angle of lead attachment to the

endocardium in the LAO fluoroscopic view. A number of variables that may

alter the angle of attachment have been investigated and although the angle

does alter, nevertheless, leaving a standard loop of lead in the RV will

minimize this variable.

Legend to the Illustrations:

Figure 1: Template scores for LAO lead positioning.

The lead attachment angles range from 0o - 140o. True anterior positioning is

from 80o - 100o and allocated “0” points, whereas septal positioning is divided

into two areas 40o - 60o “2” points and 0o - 40o “3” points. Free wall positioning

is from 120o - 140o and allocated “-2” points. To each side of true anterior are

transition zones with 60o - 80o allocated “1”point and 100o - 120o allocated “-1”

point.

Figure 2: Four fluoroscopic prints from a single 3-second cine run to

demonstrate the change in angle of attachment with insertion of more lead (1

to 4) into the RV. The angles drawn and measured visually are shown. A

guide wire for right atrial lead insertion also lies in the heart.

Figure 3: The angle distribution for the 23 patients in the study. There are

nine instances allocated 3 points, six with 2 points and five with 1 point. In

three instances, the angle range lies in the zone between 2 and 3 points and

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labeled *. The allocation of points in these instances would depend on the

measured cine frame in each individual case. The RVOT leads are the solid

lines and the mid RV leads broken lines.

Figure 1

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Figure 2:

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Figure 3:

Table 1:

Parameter All Patients23

RVOT18

Mid RV5

P Value(RVOT/Mid RV)

Males(%) 13 (56.5) 9 (50) 4 (80) 0.24 (ns)

Age (years) 77±7.8 76.5±7.8 78.8±7.6 0.57 (ns)

R wave (mV) 12±5 12±5 14±5 0.41 (ns)

Threshold (V) 0.9±0.4 0.9±0.3 1±0.5 0.56 (ns)

Impedance (Ω) 829±181 821±186 854±180 0.73 (ns)

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References:

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