CRT Optimization

NICOM Guided CRT Optimization

NICOM offers a method for optimization of Cardiac Resynchronization Therapy devices (CRT). 

CRT aims to restore synchrony of contraction, improve chamber contractility and thus improve quality of life, exercise tolerance and prolong life. This is accomplished by implantation of a pacemaker that connects to the heart with three electrodes: one in the right atrium (RA), one in the right ventricle (RV) and one placed via the coronary sinus and epicardial coronary veins on the left ventricular (LV) free wall. Once an atrial activation is detected, pacing signals are delivered to the RV and LV electrodes with the goal of activating all of the LV muscle as simultaneously as possible.

As shown In the example to the right, the patient is connected to a NICOM device with the CRT device turned off.

After a steady Cardiac Output reading is attained, the CRT device is turned on and, at intervals of ~2 minutes, the value of the AV or VV delay is changed.

Within the course of 30 minutes, one can scan approximately 15 different AV-VV delay combinations.

In this example, it is evident that NICOM reveals consistent peaks in Cardiac Output when the AV delay is set between 120 and 160 ms.

Clinical Data Kahn and colleagues have performed several systematic studies to explore the clinical utility of the Cheetah NICOM devices for CRT optimization (5-9).

These studies have demonstrated the following points:

1. Optimization of AV and VV delays based on NICOM Measurement of cardiac output yielded values for these parameters that are nearly identical to those obtained with the standard echo-Doppler is used to optimize these parameters.
2. When cardiac output was measured using NICOM following CRT Implantation, there was a good correlation between the extent of acute improvements in cardiac output and the degree of reverse remodeling (indexed by a reduction of LV end systolic volume) after 3 months of therapy.

In a recent article Khan and team demonstrated the impact of NICOM based CRT optimization on a group of over 200 heart failure patients. About 75% of the patients received NICOM optimization while 25% of the population chosen consecutively received the generic “out of the box settings” whereby AV delay is set to 120 ms and VV delay to zero.

With 6 months of follow up, the group optimized by NICOM had a better clinical response with lower NYHA class (2.1±0.8 vs 2.4 ± 0.8, P = 0.048) and quality of life scores (35 ± 18 vs 42 ± 20, P = 0.045). Echocardiographic response was also better in the NICOM optimization group with lower LV end systolic volume (108 ± 51 vs 126 ± 60 mL, P = 0.048) and higher ejection fraction (30 ± 7 vs 27 ± 8, P = 0.01) compared to empiric settings. The authors concluded that “Device optimization using noninvasive measures of CO is associated with better clinical and echocardiographic response compared to empiric settings"⁹.

The implication is that NICOM can be used to help optimize LV lead position during the implant procedure. If the lead is placed at the site which increases cardiac output the most, there is a greater likelihood of inducing LV reverse remodeling, which may also correlate with the best clinical outcomes.

Potential impact on compliance and practice efficiency

Most CRT patients are either not-optimized at all or are optimized only once, early following the original CRT implantation procedure. In light of the growing body of evidence regarding the long-term clinical value of CRT optimization this is a growing concern.

Studies point to the time-consuming Doppler echocardiography technique, the need for a trained echocardiographist and inter-user variation as limitations to greater adoption of CRT optimization.

NICOM-based CRT optimization may address these inefficiencies by:

• Offering a procedure that is quick to set up and simple to perform
• Delivering user-independent optimization that can be performed by a nurse or technician, thus relieving valuable physician time and echocardiography equipment
• Providing a cost-effective solution

About CRT Cardiac Resynchronization Therapy (CRT)

CRT is a pacemaker based treatment for patients with advanced heart failure (e.g. NYHA Class III symptoms) and ejection fraction less than 35%, who also have dyssynchronous activation of the muscle in different parts of the heart.

CRT devices have two important parameters that can be adjusted to optimize the clinical effectiveness of this therapy: the AV delay and the VV delay.

The AV delay is the delay between the time when the atrial activation is detected and the time the RV pacing impulse is delivered.

The VV delay is the time delay between RV and LV pacing impulse delivery.

Clinical Problem Suboptimal programming of the AV and/or VV interval may partially contribute to the presence of AV or LV dyssynchrony and, consequently, may limit the beneficial effects of CRT. Indeed, at present, up to 40% of patients do not show improvement in left ventricular (LV) performance or clinical symptoms after cardiac resynchronization therapy (CRT).

Various reasons have been postulated to account for this high figure. Guided AV and VV delay settings selection may reduce the rate of non-responders and optimize response in those patients that do respond to CRT. Furthermore, in addition to optimization immediately after implantation, there is evidence that the optimal settings obtained immediately after CRT implantation may change during follow-up (1-3). One study by Valzania and colleagues found a difference of 40 ms in the optimal VV interval in 57% of CRT patients at 12 months follow-up(2). More recently, Zhang and team found that in a cohort of CRT patients the optimal AV delay had changed in 56% of the patients at long-term follow-up (as compared with acutely after CRT implantation)(3). Currently, the most commonly used method for optimizing these delays is traditional Doppler echocardiography during which peak aortic flow is measured over a range of AV and VV delay combinations. This method, used by ~60% of CRT implanters, is cumbersome, time consuming, expensive and requires highly trained technicians to perform the tests. The remaining 40% of implanters either do not perform any type of optimization or they use less traditional methods of evaluating cardiac function.

The conclusion of one recent study was that: “A less time-consuming and easier optimization method might enable a more systematic optimization of the AV and VV delays at routine follow-up visits in all recipients of CRT systems.”(4)