Fiber Optic Sensorized Tools for Cardiology Applications

Public information for the IFOS/BDML NIH SBIR

Background

Cardiac Arrhythmias

Cardiac arrhythmias are abnormal heart rhythms that can be develop throughout life. The heart rhythm can be abnormal either because it may be beating too slowly, too rapidly or becomes irregular. Arrhythmias are in the top 10 causes for hospital attendances. There are 700,000 people in the UK that suffer from these symptoms. Some arrhythmias such as ectopic beats are benign but others such as ventricular arrhythmias arising from the lower ventricular pumping chamber can be life threatening. Atrial fibrillation (AF) shown in Figure 1 is the commonest arrhythmia in man, with an estimated prevalence of 1% under 60 years and increases rapidly with age to more than 10% in those over 80 years (Figure 10). AF is the commonest arrhythmic cause for hospitalisations, and is associated with increased morbidity (adverse events) and mortality (risk of death). (source: http://www.thewellingtoncardiacservices.com/our-treatments-rhythm-management.asp#n15)

Figure 1. In atrial fibrillation, the electrical signals from the upper chambers of the heart (the atria) are fast and irregular, causing the atria to quiver instead of beating effectively. To fix it, surgeons seek to isolate the electrical signals causing the problem. This is typically done by creating a lesion or burn around the atrium through microwave energy. (http://www.rwjuh.edu/news/new_atrial_fibrillation.html)

Catheter Ablation Therapy

Radiofrequency catheter ablation is a technique used to treat arrhythmia, an abnormal heart rhythm created by a disturbance in the heart's electrical system. Most catheter ablations utilize radiofrequency energy to heat the tip of a special catheter. Catheter ablation destroys or disrupts parts of the electrical pathways causing the arrhythmias. RF energy produces small, homogeneous, necrotic lesions approximately 5-7 mm in diameter and 3-5 mm in depth. Although catheter ablation has revolutionized treatment for arrhythmias and has become first-line therapy for some electro physiologists, the optimum protocol for energy delivery has not yet been determined recently [Greenberg, Haines]. Atrial fibrillation is a disorder found in about 2.2 million Americans. it was estimated that 30,000 to 35,000 catheter ablations for atrial fibrillation were performed in the U. S. in 2006. This number has jumped up in recent years [Haimovitch]. Figure 2(a) [Biosense] and Figure 2(b) [CryoCath] show two types of catheter ablation to destroy the abnormal tissues. Figure 3 shows an example of cryablation catheter from CryoCath.

Figure 2. Catheter Ablation: (a) Radiofrequency Ablation: The catheter tip delivers the bursts of high-energy waves that destroys the abnormal areas – Source: [Biosense], (b) Cryoablation using catheter based approach – Source: [CryoCath]; It is required the tip to apply consistent contact pressure to the tissue to make the width and depth of the lesion predictable in both cases.

Figure 3. Cryo-ablation Catheter (CryoConsole) [CryoCath]

Need for Contact Force/Tactile Sensing

It is well known that contact pressure (or force) of the ablation tip is one of the crucial factors which determine the lesion size [Haines, Muller]. This contact pressure is also critical to the formation of the lesion in cryoablation (cooled ablation) [Weiss#1]. If the contact pressure is too low, the ablation will take too long to burn the target tissues while there will be a perforation risk if the pressure is too high [Erick]. A large survey of 8745 patients who had undergone catheter ablation reported a complication rate of 6%, and 20% of the complications were cardiac tamponade which is caused by a perforation of the heart [NICE]. This rate takes the largest portion of the most significant complications. In case the ablation catheter perforates the heart, the blood may escape out of the heart. If enough blood becomes trapped in a rigid fibrous coat called pericardium which encloses the heart, the blood can compress the heart and prevent it from pumping normally. This is called “cardiac tamponade” [HRC]. Any intracardiac catheter has a risk of vascular perforation [Boston].

References

[Boston] "Cooled Ablation Catheters," Boston Scientific, 2007, Available: http://www.bostonscientific.com/sl/medical-devices-procedures/17303-chilli-ii-cooled-ablation-catheters.html

[CryoCath] "Cryoablation using a catheter-based approach in cardiology. Temperature profile," CryoCath Technologies Inc., 2003.

[Erick] OJ Erick, "Factors Influencing Lesion Formation During Radiofrequency Catheter Ablation," Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 3(3): 117-128, 2003.

[Greenberg] ML Greenberg, A Chandrakantan, "Radiofrequency Catheter Ablation," E-medicine from webMD, 2005, Available: http://www.emedicine.com/med/topic2957.htm

[Haines] D Haines, "Determinants of Lesion Size During Radiofrequency Catheter Ablation: The Role of Electrode-Tissue Contact Pressure and Duration of Energy Delivery," Journal of Cardiovascular Electrophysiology, 2 (6):509-515,1991

[Haimovitch] L Haimovitch, "Innovative methods for treating atrial fibrillation and other rhythm problems keep growing – but so do the many questions," Cardiovascular Device Update, 2007

[HRC] The Heart Ryhythm Charity, "Catheter Ablation for Atrial Fibrillation – Promoting better understanding, diagnosis, treatment and quality of life for individuals with cardiac arrhythmias," 2007. Available: http://www.heartrhythmcharity.org.uk/Documents/Booklets/Catheter%20Ablation%20for%20Atrial%20Fibrillation.pdf

[NICE] National Institute for Health and Clinical Excellence, "Interventional Procedures Programme – Interventional procedure overview of radiofrequency catheter ablation for atrial fibrillation," Interventional Procedures Programme, 2006. Available: http://guidance.nice.org.uk/page.aspx?o=266overview

[Weiss#1] C Weiss, M Anez, O Eick, K Eshagzaiy, T Meinertz, and S Willems, "Radiofrequency Catheter Ablation Using Cooled Electrodes: Impact of Irrigation Flow Rate and Catheter Contact Pressure on Lesion Dimensions," Journal of pacing and clinical electrophysiology, 25(4):463-469, 2002