New generation of transvenous left ventricular leads – first experience with implantation of multipolar left ventricular leads

Abstract

BACKGROUND:

Aside from unfavourable anatomy, inacceptable pacing thresholds and phrenic nerve stimulation represent major obstacles for successful left ventricular (LV) lead placement for cardiac resynchronization therapy (CRT).

OBJECTIVE:

To implant, for the first time, a new generation of transvenous multipolar LV leads (a quad-electrode lead) in combination with a CRT-cardioverter defibrillator, and to demonstrate that this combination allows for 10 different pacing vectors to combat the problems cited above.

METHODS:

Thirty patients were selected for CRT-cardioverter defibrillator implantation. At implantation, standard lead parameters were recorded. The reason for choosing a vector other than the standard bipolar vector for LV pacing, the LV lead implantation time, x-ray exposure time required for lead placement, and the reason for and number of repositions were documented. Before hospital discharge, a system inspection was performed.

RESULTS:

The implantation lead parameters were satisfactory. In 17 patients, a vector other than the standard bipolar vector was chosen to avoid phrenic nerve stimulation or to establish a better pacing threshold. In seven cases, the LV lead was repositioned (three phrenic nerve stimulations, two inacceptable pacing captures and two nonstable lead positions). Phrenic nerve stimulation was noted in eight cases; however, in five, this was eliminated by changing the stimulation vector. At hospital discharge, two-thirds of patients retained the implantation stimulation vector and in one-third, the vector was modified to further optimize the system.

CONCLUSIONS:

The quad-electrode lead provides good handling and may reduce the risk of inacceptable pacing thresholds and phrenic nerve stimulation. Consequently, implantation time, x-ray exposure and contrast agent load may be decreased, leading to lower kidney stress. Furthermore, the option for vector change after implantation may reduce the number of necessary reinterventions resulting from the pacing threshold and impedance increase.

Implanted devices for cardiac resynchronization therapy (CRT), such as pacemakers and/or cardioverter defibrillators (CRT-Ds), along with medical treatment have been shown to be an effective adjunctive therapy for patients with advanced heart failure (1,2). The rationale for CRT is the resynchronization of ventricular dys-synchrony and subsequent improvement of the impaired pump function of a failing ventricle. For this purpose, the right atrium, right ventricle and left ventricle are stimulated via transvenous or epicardial leads. Because of less invasive access and, therefore, lower operative risk, transvenous leads represent the ‘gold standard’ for cardiac pacing (3). A crucial step, and the most common reason for an unsuccessful transvenous CRT implantation, is the placement of the left ventricular (LV) lead via the coronary sinus. First, the coronary sinus needs to be cannulated with a coronary sinus catheter. Afterward, the coronary venous system needs to be visualized under fluoroscopy to identify an appropriate venous branch over the left ventricle. Then, a coronary guidewire must be introduced into the selected venous branch. Finally, the over-the-wire (OTW) technique is performed to correctly position the LV lead (4). During placement, several obstacles must be overcome. The first is unfavourable anatomy of the coronary venous system, eg, no appropriate venous branch over the left ventricle is present. In this case, epicardial LV leads are indicated. Furthermore, as a consequence of calibre mismatch between the target vein and LV lead, positioning of the lead might be unfeasible or a stable lead position might not be achieved. Even if a stable position of the LV lead over the left ventricle is achieved, the pacing threshold and impedance might be unsuitable for accurate function of the lead. Furthermore, with reasonable parameters, a simultaneous phrenic nerve stimulation may occur. Consequently, if the pacing threshold difference between the left ventricle and phrenic nerve is not large enough, the LV lead cannot operate permanently. In this case, the lead will be deactivated but left in the position. After six weeks, the lead will be re-evaluated and, if phrenic nerve stimulation still occurs, it might be circumvented with simultaneous implantation of an epicardial LV lead via lateral thoracotomy.

Over the past decade, numerous technical innovations of CRT systems were introduced. Besides improved CRT devices, manufacturers offered improved catheters and LV leads. Bipolar leads complemented the originally unipolar LV leads. Moreover, the industry made an effort to find a solution for stable positioning of the LV leads. Some newer leads (eg, EASYTRACK 2 [Boston Scientific Corp, USA], ACUITY [Boston Scientific Corp], QuickFlex [St Jude Medical Inc, USA], QuickSite [5.6 Fr; St Jude Medical Inc], Attain 4194 [5.1 Fr; Medtronic Inc, USA], etc) were preformed to provide better stability, even in bigger and/or curved target vessels (5,6). Another improvement was noted in the flexibility and miniaturization of the leads. Current LV leads are highly flexible, with diameters of less than 5 Fr (eg, Quickflexμ [4.3 Fr; St Jude Medical Inc] or Attain Ability [5.1 Fr; Medtronic Inc]). This facilitates insertion of these leads, even in curved and small venous branches. However, the problems concerning inacceptable pacing thresholds and phrenic nerve stimulation remain. The latest technical innovation (Quartet 1458Q [St Jude Medical Inc]) has been developed to address these issues.

The Quartet 1458Q is a highly flexible LV lead with an innovative quad-electrode lead designed for LV sensing and pacing. The Quartet lead has four contact spots at the lead tip (Figure 1A) instead of the common one (unipolar leads) or two (bipolar leads) (Figure 1B). Combining the Quartet lead with the Promote Q (St Jude Medical Inc) device (CRT-D) allows for programming of 10 different vectors for LV pacing (Table 1). These properties may provide more flexibility to reduce the risk of common complications during LV placement by being able to program different electrode configurations rather than needing to reposition the entire lead. Therefore, it should be easier to find a stable position with reasonable pacing thresholds and without phrenic nerve stimulation. Additionally, avoiding lead repositioning may reduce exposure to x-rays. Furthermore, the extensive programming possibilities may reduce the number of necessary reinterventions due to an inadequate pacing threshold and/or impedance increase by being able to change the stimulation vector weeks after implantation.

Figure 1).

Differences between a common bipolar left ventricular lead (QuickFlex*) and the new Quartet* left ventricular lead. A Multipolar Quartet lead; B Bipolar QuickFlex lead. Arrows in A and B indicate the available contact spots. *St Jude Medical Inc, USA

TABLE 1.

Programmable vectors for left ventricular stimulation

Vector	Polarization
1	Tip 1 to tip 2
2	Tip 1 to tip 4
3	Tip 1 to right ventricular coil
4	Tip 2 to tip 4
5	Tip 2 to right ventricular coil
6	Tip 3 to tip 2
7	Tip 3 to tip 4
8	Tip 3 to right ventricular coil
9	Tip 4 to tip 2
10	Tip 4 to right ventricular coil

In October 2009, we performed the first successful Quartet LV lead implantation. More than 30 Quartet implantations followed, and the current report illustrates our first impressions and experiences with this new lead.

METHODS

Between October 2009 and January 2010, 30 patients were scheduled for a Promote Q CRT-D system implantation (consisting of the Quartet left heart lead [model 1458Q] and the Promote Q CRT-D device [model CD3221–36]). All patients fulfilled the classical CRT indications according to accepted guidelines (for patient characteristics, refer to Table 2). The implantation procedure was performed using standard techniques: cannulation of the coronary sinus, visualization of the target vessel using a contrast agent and fluoroscopy, and then, lead placement via the OTW technique. At the time of implantation, the capture threshold (at 0.5 ms), sensing amplitude and impedance were recorded for various pacing vectors. The reason for choosing a vector other than the standard bipolar vector for LV pacing was documented. Additionally, LV lead implantation time, x-ray exposure time required for LV lead placement and, if necessary, the reason for and number of repositions (phrenic nerve stimulation, inacceptable pacing capture, nonstable lead position) were monitored (Table 3). Before discharging patients from the hospital, a routine system inspection was performed.

TABLE 2.

Patient characteristics

Sex, n
Male	24
Female	6
Age, years, median (range)	64.1 (39–86)
Height, cm	174.5±9.7
Weight, kg	82.0±16
Body mass index, kg/m2	26.8±3.9
Ischemic cardiomyopathy, n	14
Dilated cardiomyopathy, n	16
Diabetes mellitus, n	8
Hypertension, n	20
Creatinine, μmol/L	106.1±21.3
Glomerular filtration rate, mL/min	71.9±28.6
Ejection fraction, %	23.2±5.2
New York Heart Association classification	2.9±0.24
Sinus rhythm, n	21
Atrial fibrillation, n	7
Asystole, n	2
Left bundle-branch block, n	29
Right bundle-branch block, n	1
QRS complex time, ms	153.5±25.2

Data presented as mean ± SD unless otherwise indicated

TABLE 3.

Implantation data

First implantation, n	18
System upgrade, n	12
Cardioverter defibrillator device, n
Promote Q*	27
Promote Accel*	3
Lead device, n
Quartet 1458Q*	27
Epicardial lead EnPath 1084T*	2
Quickflexμ*	1
Operation time, min	106.5±30.2
Left ventricular lead placement time, min	13.7±10.0
Left ventricular x-ray exposure time, min	9.2±6.9

Data presented as mean ± SD unless otherwise indicated.

^*St Jude Medical Inc, USA

RESULTS

Patients

Thirty consecutive patients were scheduled for a Promote Q CRT-D system implantation. All patients fulfilled the common CRT criteria. Of these 30 patients, 24 were men and six were women; 14 had ischemic cardiomyopathy and 16 had dilated cardiomyopathy; 29 had left and one had right bundle-branch block; and seven had atrial fibrillation. The mean New York Heart Association classification was 2.9, with a mean ejection fraction of 23.2%, a mean QRS complex time of 153.5 ms, an LV end-systolic diameter of 53.5 mm and an LV end-diastolic diameter of 63.8 mm. The detailed characteristics of the patients are shown in Table 2. All patients who underwent the operation signed an informed consent form.

Implantation parameters

At the time of implantation, the mean capture threshold was 1.2 V (at 0.5 ms), the mean sensing amplitude was 12.2 mV and the mean impedance was 786 ohm (for details, refer to Table 4). In 17 patients, a vector other than the standard bipolar vector for LV pacing was chosen. The reasons for choosing a vector other than a standard bipolar vector included a better pacing threshold in most cases and, in some cases, to avoid phrenic nerve stimulation. The mean LV lead implantation time was 13.7 min; the mean x-ray exposure time required for LV lead placement was 9.2 min (Table 3).

TABLE 4.

Implantation and hospital discharge data according to lead position

Lead position	Intraoperative measurement	Measurement at hospital discharge
Right atrium
Capture threshold, V	0.9±0.3	0.8±0.3
Impedance, ohm	399±69	377±52
Sensing amplitude, mV	2.8±1.1	3.2±1.1
Right ventricle
Capture threshold, V	0.7±0.3	0.7±0.3
Impedance, ohm	548±120	529±108
Sensing amplitude, mV	12.6±4.0	11.4±1.2
Left ventricle
Capture threshold, V	1.2±0.6	1.1±0.5
Impedance, ohm	786±241	767±221
Sensing amplitude, mV	12.2±5.6	10.7±2.0

Data presented as mean ± SD

In seven cases, an intraoperative repositioning of the LV lead was necessary. Three repositions were due to phrenic nerve stimulation, two were due to inacceptable pacing capture and two were due to a nonstable lead position. Overall, phrenic nerve stimulation was noted in eight cases; however, it was possible to eliminate this in five cases by changing the stimulation vector. In these cases, excellent pacing thresholds and impedances were maintained.

A routine system inspection performed before hospital discharge showed that two-thirds of patients retained the implantation stimulation vector and in one-third, the vector was modified. The modifications were not due to phrenic nerve stimulation but were performed to further optimize the system (eg, to achieve a lower pacing threshold).

DISCUSSION

Of 30 scheduled patients, the implantation of the Promote Q CRT-D system was unsuccessful in only three cases. In one patient, the implantation did not succeed because of a missing target vessel, and had to be completed by epicardial LV lead implantation (EnPath 1084T [St Jude Medical Inc]) in a second intervention. Another two patients showed a significant calibre mismatch between the lead and target vessel, resulting in epicardial lead implantation in one case and switching to a smaller transvenous lead (Quickflexμ) in the other case. In the remaining 27 patients, we successfully implanted the Promote Q CRT-D system consisting of a Quartet left heart lead (Figure 2A) and a Promote Q CRT-D device (Figure 2B).

Figure 2).

A The quad-electrode Quartet 1458Q*. B Promote Q* (cardio-verter defibrillator) multipolar header. *St Jude Medical Inc, USA

The Quartet 1458Q is a novel, highly flexible LV lead with a 5.1 Fr body diameter and an innovative quad-electrode lead for LV sensing and pacing (Figure 2A). The Quartet LV lead could be introduced into the target vessel using the common OTW technique (Figures 3A to 3D). Handling of the Quartet LV lead is comparable with commonly used LV leads. Usually, the inner sheath catheter can be inserted into the coronary sinus catheter (outer sheath catheter) to locate the target vessel. However, compared with other inner sheath catheters, this catheter can be removed after completing the LV lead placement, resulting in more stability during advancement of the lead, especially in small and strongly curved vessels (Figures 3E and 3F). Unfortunately, the inner sheath catheter is only marginally longer than the outer sheath catheter, which makes a relatively deep insertion of the outer sheath catheter into the coronary sinus necessary. Furthermore, the Quartet LV lead should be longer to prevent its dislocation when removing the catheters. Finally, the Quartet lead requires a special lead connector (SJ4 [St Jude Medical Inc]) that is not pin compatible with other standard CRT systems (Figure 2B). Adapters are not currently available.

Figure 3).

A to D Intraoperative x-ray images of different cases with a stable lead position. E and F Left ventricular lead placement using the slit-table inner sheath catheter

The capture threshold, sensing amplitude and impedance at the time of implantation were satisfactory. Only seven leads required repositioning during the implantation procedure. Three repositions were due to phrenic nerve stimulation, two were due to inacceptable pacing capture and two were due to a nonstable lead position. The mean implantation time was 13.7 min and the mean x-ray time was 9.2 min. Phrenic nerve stimulation in the bipolar position was detectable in eight patients at the time of implantation. However, only three repositions resulting from phrenic nerve stimulation were required. This was particularly due to the unique Quartet feature that offers the possibility of using 10 different LV pacing vectors (Table 1), in contrast to other bipolar LV leads that are currently marketed and only offer up to six pacing vectors. Consequently, one of the main expected advantages of the Quartet LV lead is a reduction of phrenic nerve stimulation leading to diaphragmatic stimulation via a simple reprogramming rather than lead repositioning. This may reduce the number of repositions required during implant procedures, and reduce operation time and x-ray exposure.

CONCLUSIONS

The Quartet lead may provide more flexibility to reduce the risk of common complications, eg, phrenic nerve stimulation (causing diaphragmatic muscle stimulation) and elevated capture thresholds, during LV lead placement. Furthermore, reprogramming of the stimulation vector is noninvasive and requires no physical repositioning of the lead. The potential decrease in the number of repositions may decrease x-ray exposure time and the need for contrast agent infusion, leading to lower kidney stress.

Of course, a prospective, randomized study with long-term follow-up and comparison with currently available transvenous leads is necessary to verify our initial positive impressions, and the theoretical advantages of this new and promising generation of LV leads.