Biventricular Devices

Coronary Sinus Anatomy

The optimal placement of a left ventricular lead in a tributary of the coronary sinus is one of the most challenging technical aspects of CRT device implantation. The coronary sinus is the main vein of the greater venous system that runs in the posterior aspect of the atrioventricular groove.[9] The coronary sinus is formed when the great cardiac vein joins the main posterior lateral vein. Other major tributaries entering the coronary sinus (CS) include the inferior left ventricular vein and the middle cardiac vein that drain the posterior aspect of the left ventricle. The middle cardiac vein is the largest tributary of the coronary sinus, which receives communications from the anterior veins as well as from the septal wall and inferior walls of both ventricles.[10]

Pathophysiology of Dyssynchrony

Reduction in left ventricular systolic function is associated with neurohumoral activation, which leads to ventricular remodeling and dilatation.[11] The majority of patients with cardiomyopathy have conduction delays such as a left bundle branch block (LBBB), which results in electromechanical dyssynchrony. The resulting contractile dyssynchrony generates regional heterogeneity of myocardial work with the early stimulated region having reduced load and territories of late activation higher load.[12] This displacement of blood from early to late and back to early activation sites results in a net decline in ejected stroke volume. This volume shift is much more significant when the differences in muscle activation are greatest between early and late contracting zones.[13] Thus in heart failure, where the underlying function is already compromised, electromechanical dyssynchrony further increases morbidity and mortality.[14] A simultaneous bi-ventricular pre-excitation, which is characteristic for CRT, restores coordinated contraction and therefore improves net systolic performance by augmenting chamber ejection and work.[15]

Biventricular pacing device (CRT) is indicated in the following patients.[16][17]

1. It is a class I recommendation for patients with;

• Left ventricular ejection fraction of less than 36%
• Sinus rhythm with LBBB morphology
• QRS duration of >149ms
• New York Heart Association (NYHA) II, III, or ambulatory IV symptoms on optimal medical therapy.
• Acceptable non-cardiac health.

2. It is a class IIa recommendation in patients with;

• Left ventricular ejection fraction of less than 36%
• Sinus rhythm with LBBB morphology
• QRS duration of 120 to 149ms
• New York Heart Association (NYHA) II, III, or ambulatory IV symptoms on optimal medical therapy.
• Acceptable non-cardiac health

3. It is a class IIa recommendation in patients with;

• Left ventricular ejection fraction of less than 36%
• Sinus rhythm with non-LBBB pattern
• QRS duration of >149ms
• New York Heart Association (NYHA) III, or ambulatory IV symptoms on optimal medical therapy.
• Acceptable non-cardiac health.

4. It is a class IIa recommendation in patients with;

• Left ventricular ejection fraction of less than or equal to 35%, on optimal medical therapy
• Atrial fibrillation and requires ventricular pacing.
• Rate control will end up on 100% ventricular pacing
• Acceptable non-cardiac health.

5. It is a class IIb recommendation in patients with;

• Left ventricular ejection fraction of less than 36%
• Sinus rhythm with non-LBBB pattern
• QRS duration of 120 to 149ms
• New York Heart Association (NYHA) III, or ambulatory IV symptoms on optimal medical therapy.
• Acceptable non-cardiac health.

6. It is a class IIb recommendation in patients with;

• Left ventricular ejection fraction of less than 36%, on optimal medical therapy.
• Undergoing a pacing device implantation for other indications
• Anticipated to have >40% ventricular pacing.
• Acceptable non-cardiac health.

There are no established absolute contraindications for CRT in appropriately selected patients.

Relative contraindications may include:[18]

• Dementia
• Advanced malignancy requiring palliative care
• Chronic disease with a life expectancy of less than one year
• Acute decompensated heart failure
• Active infection or sepsis
• Coagulopathy

Following equipment is required for implanting a biventricular pacing device.

• Cardiac catheterization laboratory with fluoroscopy and hemodynamic monitors
• Ultrasound machine (for access)
• Needles and sheaths
• Pacing leads and generator
• Device programmer
• Sutures etc.

Following personnel are required for biventricular pacing device implantation.

• Cardiac electrophysiologist
• Cardiac catheterization laboratory technician
• Electrophysiology technologist for programming
• Nursing staff for administering medications
• Anesthesiologist

Sometimes a cardiac surgeon may be required to implant epicardial left ventricular lead implantation if it is not possible to put it percutaneously.

Preparation

Preparation is similar to other cardiac catheterization procedures.

• Patients should be adequately assessed for the procedure and counseled in detail about the risks, benefits, and complications of the procedure.
• Blood tests are done before proceeding to check the coagulation profile, especially if the patient is taking anticoagulants.
• The patient is kept on fasting for at least six hours before the procedure. Intravenous cannulas are maintained, and antibiotics with an anti-staphylococcal coverage are administered as a prophylaxis for implant infection.
• After arriving in the catheterization laboratory, the patient is draped after cleaning the access site with an antiseptic solution.
• Intravenous sedation is given before the procedure, and local anesthetic agents are given at the site of venous puncture and pocket formation.

Technique or Treatment

Venous Access

Since its introduction in the early 1990s, the CRT device implantation technique has evolved rapidly. Originally a limited thoracotomy approach was used for epicardial lead placement, but advances in left ventricular (LV) transvenous lead delivery systems have led to the entirely transvenous implanted system.[19] Despite the advances, technical challenges of implanting three leads (right atrial, right ventricular, and LV epicardial) arise when considering the site of approach. Commonly used venous approaches include subclavian, axillary, and cephalic veins.[20] The cephalic vein is the preferred venous access for lead implantation, followed by the subclavian vein. Subclavian can be accessed either by using axillary vein access or intrathoracic access.[21]

Some operators prefer combined cephalic and subclavian vein access to facilitate easy catheter manipulation and coronary sinus cannulation. This technique minimizes lead interaction and the risk of lead dislodgement during sequential lead placement. However, subclavian vein puncture carries a significant risk of pneumothorax, and it may lead to densely fibrotic tracts as the leads pass through the ligamentous tissues between the medial end of the clavicle and the first rib. And this fibrosis can potentially make percutaneous lead extraction impossible.[22][23]

CRT Leads Implantation

In the case of CRT-D (CRT devices combined with defibrillator), three long hydrophilic guidewires are placed in the accessed vein (cephalic or subclavian). An 11Fr sheath is advanced over one of the wires to introduce a 9Fr right ventricular (RV) defibrillator lead followed by slitting of the sheath. The RV lead is then positioned at an appropriate site. After RV led positioning, two separate sheaths are advanced over each of the two retained guidewires. To avoid lead interaction, these sheaths (for the left ventricle and right atrium) are not slit until all three leads are positioned at their appropriate places.[24]

A guide catheter is then placed via the sheath into the coronary sinus over a hydrophilic wire or deflectable catheter for the left ventricular lead placement. Coronary sinus (CS) venography can be performed via a balloon-tip catheter inserted into the guide catheter. Left ventricular lead is placed in an appropriate tributary of the CS guided by fluoroscopy. In the end, the right atrial (RA) lead is placed. Once the three leads are positioned. The sheath is slit, and the RA and RV leads are sutured onto the pectoral muscle. Finally, the guide sheath is slit, followed by slitting the short 9F sheath and suturing the CS lead onto the pectoral muscle.[25]

In the case of CRT-P (CRT device without defibrillator), two long hydrophilic guidewires are placed in the accessed vein. A 9F sheath was advanced over one of the guidewires to position an RV pacing lead, followed by slitting of the sheath. After positioning the RV lead, two separate sheaths are advanced over each of the two guidewires. Then a guide catheter is placed for the placement of the LV lead guided by fluoroscopy. The RA lead is then placed via the remaining sheath.  Sheaths are slit, and leads are secured by suturing into the pectoral muscle.[26] Leads are then connected to the generator, which is placed in a pocket created in the pectoral region.

Successful resynchronization is achieved by placement of the LV lead in an appropriate tributary of CS, preferably at the site in the proximal third to the middle third of the LV, and LV lead positioned in the apical region is associated with an unfavorable outcome.[27]

Difficulties in LV Lead Placement

The inability to cannulate the coronary sinus or a preselected tributary is usually due to the tortuosity of the branch. This can be overcome by using multiple angulations to explore the anatomy and advancing the lead coaxial to the wire and the CS tributary. Different lead sizes and shapes can also be utilized to overcome this technical difficulty.  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. 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 to advance the pacing lead and the other used for placement of a stent, which is deployed at low pressure to secure the pacing lead.[28]

CRT Programming

An individually adapted AV interval is essential to achieve maximum benefit from resynchronization. Optimized AV interval programming synchronizes atrial and ventricular contraction, maximizes the atrial contribution to left ventricular diastolic filling, and prevents presystolic mitral regurgitation. Interventricular synchrony and LV contraction can be further optimized by VV interval adjustment, although the impact of VV optimization on CRT outcome is still under debate. Non-invasive AV and VV interval optimization methods by electro- and echocardiography can be considered, although clinical outcome data does not support these methods.[29]

Complications

Major complications associated with CRT device implantation include:

• Access site bleeding and pocket hematoma: The incidence in clinical trials is reported up to 2.5%.[30] However, in routine clinical practice, the actual incidence of pocket hematomas may be higher than this, as the trials only reported those hematomas, which required intervention. Pocket hematoma and early re-intervention for pocket hematoma are associated with an increase in device infection incidence.
• Lead dislodgement: CRT trials demonstrated a rate of lead dislodgement from 2.9% to 10%.The incidence of left ventricular lead dislodgement is higher than that of the right atrial and right ventricular lead.[31]
• Infection: It is one of the challenging complications related to CRT and other cardiac implantable devices. The incidence of device-related infection for CRT implantation is reported up to 3.3%. Male gender, prior device-related infection, and re-implantation are reported to have a higher incidence of device-related infections.[32]
• Pneumothorax: It is a rare complication, reported up to 0.66% in cardiac pacing device implantation. Subclavian access, chronic obstructive pulmonary disease advanced age (>80 years) at implantation are reported with a higher pneumothorax incidence. The cephalic vein cut-down technique should be used whenever possible to avoid this complication.[33]
• Coronary sinus perforation/dissection: Coronary venous dissection is a rare but known complication of left ventricular lead placement during implantation of a cardiac resynchronization therapy device. It is reported up to 0.28% and reported to prolong post-procedural hospital stay.[33]

Other complications may include cardiac tamponade, myocardial injury, lead fracture, pocket erosion, and phrenic nerve stimulation. Inappropriate phrenic nerve stimulation occurs in up to 13% of the patients undergoing left ventricular lead placement and is more common at mid-lateral, mid-posterior and apical sites.[34]

Clinical Significance

With the advancing age of the population and improved survival from ischemic heart disease, the incidence, and prevalence of heart failure have increased significantly.[35] Medical therapy in the form of angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, beta-adrenergic blockers, aldosterone antagonists, and angiotensin receptor neprilysin inhibitor (ARNI) have improved the outcome for most patients.[36][37] 

Despite the aforementioned medical therapy, a significant number of patients continue to suffer poor outcomes and require device-based therapy. Cardiac resynchronization therapy (CRT) device provides a survival benefit to such patients. Other than the survival benefit, in appropriately selected patients with severe heart failure, CRT leads to improved functional class, quality of life scores, physiological measures such as peak VO, and reduced hospitalizations.[38][31]

Enhancing Healthcare Team Outcomes

Heart failure is the major cause of death and a rapidly growing cardiovascular diagnosis in the era of advanced management of coronary artery disease.[39] To improve survival in heart failure patients, therapies need to reduce the sudden cardiac death (the most common cause of death in patients with New York Heart Association [NYHA] Class I or II symptoms) and progressive heart failure (a common cause of death in patients with NYHA Class III or IV symptoms).[40]

The majority of patients with cardiomyopathy have conduction delays such as a left bundle branch block (LBBB), which results in electromechanical dyssynchrony. The resulting contractile dyssynchrony generates marked regional heterogeneity of myocardial work with the early stimulated region having reduced load and territories of late activation higher lead.[12] Cardiac resynchronization therapy (CRT) device provides a survival benefit to such patients. Other than the survival benefit, in patients with severe heart failure, CRT leads to improved functional class, quality of life scores, physiological measures such as peak VO, and reduced hospitalizations.[38]

The CRT implantation is a complex procedure that requires operative skills and expertise, proper selection, and preparation of the patients. Therefore it is necessary to have a system to ensure the completion of all aspects of patient care. In pre-procedure care, in addition to discussing the risks and benefits of the procedure with the patient and family, the assessment must be done to ensure that patient meets the recommended criteria for the procedure. Proper sterile technique is fundamental to better outcomes in terms of device-related infection.

The placement of LV epicardial lead is the mainstay of CRT implantation. Successful resynchronization is achieved by placement of the LV lead in an appropriate tributary of CS, preferably at the site in the proximal third to the middle third of the LV.  Left ventricular lead positioned in the apical region is associated with unfavorable outcomes.[27] Optimized AV interval programming is fundamental to resynchronization. It synchronizes atrial and ventricular contraction, maximizes the atrial contribution to left ventricular diastolic filling, and prevents presystolic mitral regurgitation. Interventricular synchrony and LV contraction can be further optimized by VV interval adjustment.

Patients need regular monitoring by trained nursing staff for complications. It is now recommended to have a multidisciplinary team approach that may include a primary care provider,  cardiac electrophysiologist, heart failure, cardiac transplant specialist, cardiac surgeon, and a cardiac nurse to enhance patient care, optimize procedural success and minimize peri-procedural complications.