Peripheral Stimulation Device to Improve Coronary Flow Reserve in Coronary Artery Disease

Angina pectoris or anginal equivalent dyspnoea are frequent symptoms related to impaired myocardial blood supply. The supply-demand imbalance that arises in the setting of coronary artery disease can be addressed by improving myocardial blood supply through mechanical revascularization with percutaneous coronary intervention or bypass surgery or by reducing myocardial energy demand through pharmacotherapy including the use of negative chronotropic agents such as beta blockers. When further revascularization is not an option, or standard therapies are insufficient to control symptoms, other novel therapies are attempted to improve myocardial blood supply and decrease angina. Enhanced external counterpulsation (EECP) devices have been demonstrated to augment cardiac performance and coronary flow and have a beneficial effect in reducing anginal symptoms in patients with CAD.(1-4) Transcutaneous (non-invasive) electrical nervous stimulation of skeletal muscle to improve venous return to the heart and provide a potential mechanism to augment and improve blood flow, including coronary flow, is a potential alternative method to achieve a similar effect,(5,6) but is less cumbersome and more easily integrated into clinical practice. The gekoTM device is a small transcutaneous nerve stimulator (weight 18g, dimensions 149mm x 42mm x 11mm) that is applied non-invasively to the skin over the common peroneal nerve in the lower limb that has been demonstrated to safely stimulate blood flow from the gastrocnemius and soleus venous system via activation of the venous 'pump' system, intrinsic to the calf muscles. As a result, the gekoTM device is approved for use in Canada to improve blood flow and is already being used in clinical practice at University Hospital. By improving venous return, this device has the potential to have a therapeutic effect in the management of CAD by augmenting coronary blood flow. The purpose of the PERCCAD Study is to investigate the effect of the gekoTM device on coronary blood flow in order to assess its potential role as a therapeutic modality for the treatment of symptomatic CAD. Further, since previous studies with EECP also demonstrated improvement in endothelial function, the investigators plan to study the effect of the gekoTM device on endothelial function and peripheral blood flow in the same patients via non invasive techniques(4, 7, 8) given the established relationship between endothelial dysfunction and cardiovascular risk. (9-12)

The primary objective of the PERCCAD study is to assess the effect of the gekoTM device on coronary blood flow in patients with symptomatic CAD who are undergoing invasive angiographic assessment and management with PCI. This evaluation of the gekoTM device is to be performed at the time of the patient's already planned invasive assessment and management so that invasive data can be collected without exposing the patient to risks other than those already associated with their planned procedure and usual clinical care. The secondary objective of the study is to assess the effect of muscle stimulation with the gekoTM device on endothelial function and peripheral blood flow measured via non-invasive techniques.

Study Design:

Single arm clinical study where patients act as their own controls (coronary flow reserve and endothelial function measured in patients already undergoing angiography and PCI) with measurements recorded pre and post application of the gekoTM device.

Coronary flow assessment: The PCI procedure will be performed according to standard practice. As part of routine practice, a guidewire is inserted into the coronary artery and used as a "rail" for delivering balloons and stents. Often, we use a special Doppler guidewire with a sensor at the tip that is used for measurements of blood flow. We will use such a guidewire for the current study (13-16). Velocity signals are obtained by the guidewire and average peak velocity (APV) is determined. Intracoronary adenosine will be given to induce hyperemia and increase coronary flow (17-21). Intracoronary adenosine is used routinely during PCI. Coronary flow reserve (CFR) will be calculated as the ratio of APV during hyperemia compared to APV at baseline. After measurement of baseline APV and CFR, we will perform two minutes of muscle stimulation using the gekoTM device at a low pulse width setting and record APV. After this, a further two minutes of muscle stimulation using the gekoTM device at a higher pulse width setting will occur with repeated APV and CFR measurements recorded. This process will be performed in at least two coronary arteries at the time of patient's usual invasive assessment and management. Calf muscle stimulation with the gekoTM device: The gekoTM device will be fitted bilaterally behind the patient's knees in the popliteal fossa. At the appropriate time the device will be set to stimulate the common peroneal nerve transcutaneously (the low setting will be set at the level at which the patient has a sensation of stimulation but where there is no visible movement of the lower leg; the high setting will be at the patient's highest tolerable level, but not lower than the level which elicited slight visible movement of the lower leg).

Endothelial Function Assessment: Endothelial function study will be performed on a separate visit following the PCI, by measurement of peripheral vasodilator response using fingertip pulse amplitude tonometry (peripheral arterial tonometry-PAT). PAT signals will be obtained with the EndoPAT2000 (EndoPAT) device (Itamar Medical Inc., Caesarea, Israel). The EndoPAT is an FDA approved device for noninvasive assessment of endothelial dysfunction, it is widely used for clinical and research purposes and validated as a method of endothelial function assessment.(22-24) Specially designed finger probes are placed on the index finger of each patient's hand. The probes are comprised of a system of inflatable latex air cuffs connected by pneumatic tubes to an inflating device controlled through a computer algorithm. There is no occlusion of arterial blood flow. Pulsatile volume changes of the distal digit induce pressure alterations in the finger cuff, which are sensed by pressure transducers and transmitted to and recorded by the EndoPAT. Endothelial function is measured via a reactive hyperemia-peripheral arterial tonometry index (RH-PAT index). A reactive hyperemia protocol consists of a 5-minute baseline measurement, after which a blood pressure cuff placed on the test arm is inflated to 60 mmHg above baseline systolic blood pressure, or at least 200 mmHg for 5 minutes. After 5 minutes, the cuff is deflated, and the PAT tracing recorded for a further 5 minutes. The ratio of the PAT signal after cuff release, compared to baseline, is calculated through a computer algorithm automatically normalizing for baseline signal, and indexed to the contra lateral arm. The calculated ratio reflects the RH-PAT index, a reflection of degree of endothelial function. This process is non-invasive and does not require percutaneous vascular access. Endothelial function will also be assessed at baseline and following 1 hour treatment with the gekoTM using the EndoPAT to calculate the RH-PAT index as described. In addition, the effect on popliteal artery vessel diameter and Doppler flow velocity will also be recorded using a surface ultrasound probe at baseline and following 1 hour of treatment with the gekoTM.