Cardiac Resynchronization Therapy Technique

Updated: Oct 28, 2021
  • Author: Akanksha Agrawal, MD; Chief Editor: Richard A Lange, MD, MBA  more...
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Approach Considerations

For the overwhelming majority of patients undergoing cardiac resynchronization therapy (CRT), conscious sedation combined with local anesthesia provides satisfactory analgesia. In rare cases, general anesthesia is required (eg, for children or for patients who are difficult to sedate).

Access to the coronary sinus (CS) for implantation of the left ventricular (LV) lead may be achieved via the axillary, subclavian, or cephalic vein. It is preferable to use an access site separate from the one used for the other leads; this allows easier sheath manipulation. Unfortunately, a separate access site may not be an option in certain patients (eg, those with existing hardware who require an upgrade to a CRT device).

The site where the device will be implanted (ie, the right or left side of the chest wall) is determined mainly by the patient’s preference or by the location of a preexisting device. In additional to chest wall placement, CS and LV lead placement from the femoral vein has been described, with or without pull-through to the subclavian vein [26, 27] ; however, such approaches are reserved for extraordinary circumstances. Further information on device implantation is available elsewhere (see Permanent Pacemaker Insertion).

If diaphragmatic or intercostal muscle capture occurs, several techniques can be used to overcome it. Changing the pacing vector (electronic repositioning) of the lead, the position of the lead, or the voltage output may be successful.


Placement of Pacing Leads

To facilitate stable left ventricular (LV) lead placement, it is practical first to place the right ventricular (RV) pacing lead and then to advance the LV lead into the coronary sinus (CS) branch, leaving the sheath in place. After the right atrial (RA) lead is positioned, the LV lead guiding sheath is removed, and the LV lead is sutured in place.

RV lead

In most cases, the delivery system sheath is passed over a guidewire into the RA and then advanced slowly into the RV, where 90-180° of counterclockwise rotation is subsequently applied while the sheath is gently withdrawn and then advanced. This maneuver generally brings the sheath to the CS or the vicinity of the CS os, allowing easy cannulation of the CS with a guidewire.

If cannulation of the CS proves difficult, it may be necessary to use a combination of the outer and inner sheaths to engage the CS. A number of different inner catheters, with different angulations of the terminal portion, are available. Injection of a small volume of contrast material may be used to facilitate identification and cannulation of the CS os.

A common difficulty is the inability to reach the CS os. If this problem is encountered, sheaths with a longer reach or an inner catheter may be used to extend the sheath and thereby enable cannulation.

LV lead

Although it may be possible to place the LV lead without knowing the anatomy of the CS and its branches, it is prudent to obtain a CS phlebogram to direct the selection and placement of this lead. Injection of a small volume of contrast material provides relevant information, and it is unlikely to cause significant deterioration of renal function, even in patients with renal dysfunction.

In most patients, a balloon angiography catheter should be used for contrast injection to achieve optimal opacification of the CS and its branches. To accomplish this, the outer sheath should be advanced relatively deeply into the CS, through which the angiography catheter is advanced. As the catheter approaches the end of the sheath, the sheath is slowly retracted to expose the balloon tip; this step minimizes the risk of CS dissection, which may occur if the angiographic catheter is advanced instead.

The entire system may be carefully retracted to adjust its placement and to make sure that all branches are visualized with contrast injection. Usually, injection of 10-15 mL of undiluted contrast material is necessary to achieve good opacification. The balloon should remain inflated during initial contrast injection and then deflated at the last phase of the phlebogram to allow visualization of any venous branches proximal to the balloon.

Phlebography should be obtained in the following two projections:

  • 35° left anterior oblique (LAO): This projection allows visualization of branches and their location along the LV wall (ie, posterior, lateral, or anterior)

  • Anteroposterior (AP) caudal: This projection allows visualization of the bifurcation of the branches from the main body of the CS

Successful resynchronization can be achieved with placement of the LV lead in almost any CS branch, provided that the site is in the proximal third to the middle third of the LV. [1] In small trials, placement of the lead in areas with maximal dyssynchrony has been associated with better CRT outcomes. Unfortunately, it is not always possible to place the leads in these areas, whether because of the lack of appropriate branches overlying the area of dyssynchrony, because of poor capture, or because of diaphragmatic capture.

Other markers associated with success of resynchronization include the physical distance between the RV and LV leads in the LAO projection (the larger the better) and late sensing on the LV lead (the terminal portion of the QRS). The final decision for branch selection should be based on consideration of the following factors:

  • Ease of cannulation

  • Expected stability of the lead (ie, likelihood of dislocation)

  • Possibility of diaphragmatic capture

Several techniques have been described for branch cannulation; the choice of technique should be dictated predominantly by the patient’s anatomy. For example, branches with acute-angle origins can often be cannulated with an angioplasty wire without any difficulty.

Frequently, however, branches originating at right or obtuse angles are difficult to cannulate. There are two techniques that can be used in such situations. An inner catheter may be inserted near the preselected branch so that the guidewire can be advanced into the branch. Once this is accomplished, the catheter may be exchanged for a packing lead while the wire position is maintained.

Alternatively, a larger-lumen inner catheter may be used to allow delivery of the pacing lead. This technique has been simplified by using a lead with an exaggerated curve, through which a stylet or angioplasty guidewire is advanced to direct the lead tip into the appropriate venous branch.

In some patients in whom cannulation of the branches is achieved with the inner catheter and branch size is satisfactory, the CS sheath may be gently advanced over the inner catheter to allow selective branch cannulation. At that time, the inner catheter may be removed without the need for an exchange wire, and the pacing lead may be advanced through the main sheath whose tip is located in the preselected branch.

Difficulties in lead placement

Inability to cannulate the preselected venous branch is usually due to tortuosity of the branch. The best way of overcoming this difficulty is to use multiple angulations to explore the anatomy and to make sure the lead is advanced coaxially to the wire and the branch. Different lead sizes and shapes can also be used. If these maneuvers are not helpful, it may be worthwhile to try double-wiring the branch with a stiff wire to help straighten it.

Lead instability is uncommon but may occur more often as the leads are more frequently placed in the proximal third to the medial third of the LV vein. To prevent this, a lead with a more aggressive curve or active fixation may be used. Stenting may also be used to improve lead stability. With this technique, two guidewires are placed in the venous branch, with one used for advancement of the pacing lead and the other used for placement of a stent, which is deployed at low pressure to secure the pacing lead.

Unusual lead placement techniques

Some patients may have extensive connections between distal aspects of the CS branches, and these connections can be explored for lead placement. Such exploration may be particularly helpful when the number of branches is limited or when the most desirable branches are difficult to cannulate. In these circumstances, it is often possible to access the middle cardiac vein and advance the lead to the lateral LV via distal branch connections.

When cannulation of the CS is very difficult, different sheath shapes may be tried. Alternatively, different electrophysiologic catheters (either fixed curve or adjustable) may be used for CS access, or advancement of the guide sheath may be attempted. In rare cases, advancement of the guide sheath may be blocked by stenosis or a muscle band at the proximal portion of the CS. If a muscle band is present, one has to wait for diastole to advance the sheath.

Splitting of LV sheath

Splitting of the LV sheath is a critical part of the procedure. If it is not done properly, it may result in dislodgement of the lead. Before the sheath is split, the guidewire should be advanced past the end of the lead to provide maximal support. Subsequently, the pacing lead must be securely placed within the splitter.

Splitting should be done expeditiously and efficiently. When the sheath is split in a very slow fashion, it can point inferiorly upon exiting the CS os and consequently can place undue tension on the lead that may lead to dislodgement. When the sheath is split rapidly, the transit over the CS os is very quick, and undue traction on the lead is avoided. Exercise caution in splitting the short sheath that is used for vascular access.

Once splitting is completed, the angioplasty wire should be withdrawn to allow deployment of the lead with its curve. At this time, the slack in the lead should be adjusted. Finally, the lead is secured to the pectoralis fascia in the usual manner.


Diaphragmatic capture or a change in the capture threshold may be seen soon after implantation as the patient is moved from the procedural table. This occurs because of a change in the anatomic relationship of the heart to the surrounding structures (the diaphragm or the phrenic nerve) or because of a change in lead position. In this situation, electronic repositioning is usually helpful in avoiding diaphragmatic capture and improving the capture threshold.

After lead placement, chest radiography should always be performed (in the posteroanterior [PA] and lateral views) to document lead position. This facilitates assessment for possible lead dislodgement if a change in lead parameters should be observed in the future.


Programming of Device

Appropriate device programming should yield reliable biventricular pacing. Only patients with at least 95% of biventricular pacing will benefit from cardiac-resynchronization therapy (CRT); therefore, the atrioventricular (AV) delay should be programmed to be short.

The various device manufacturers have developed several algorithms that allow automatic programming of AV delay as well as right ventricular (RV)-to-left ventricular (LV) delay. However, these algorithms have not been associated with improved outcomes as compared with programming of the AV delay to 130 and 100 msec (paced and sensed, respectively). Another option is to use echocardiography-based parameters for AV optimization, although this is not supported by clinical outcome data.

Typically, the lower pacing rate should be programmed to be about 50 beats/min unless sinoatrial (SA) node dysfunction is present. The maximum tracking rate should be extended as far as is feasible in the device to allow biventricular pacing throughout a wide span of sinus rates. In patients who have SA node dysfunction, rate response should also be programmed.



Complications of Cardiac-resynchronization therapy (CRT) include the following:

  • Dissection of the coronary sinus: In most cases, this is of no clinical consequence; if it occurs to a significant extent, the sheath should be removed and the coronary sinus (CS) recannulated, with care taken to ensure that the true lumen is accessed; echocardiography should be performed to assess for the presence of pericardial effusion

  • CS perforation or branch rupture: These are very rare events and may be associated with pericardial effusion; usually, they are of little consequence because the venous circulation is a low‑pressure system; however, if pericardial effusion is present, serial echocardiograms may be obtained to evaluate for continuing accumulation or development of tamponade physiology

  • Inability to cannulate the CS: In about 5% of patients, either the CS cannot be cannulated or no branches are available for left ventricular (LV) lead placement; in these circumstances, epicardial placement of the LV lead should be seriously considered

  • Lead dislodgement: This occurs in approximately 5%-7% of cases but is becoming less common with the development of leads that possess improved fixation mechanisms; if it cannot be overcome by changing pacing vectors, the lead may have to be repositioned