BME 501 Advanced Topics in Biomedical Systems Spring 2014 Dr. Kay 1BME 501 Lecture Notes – Apr 23 BME Applications for Cardiovascular Pathologies • Electrical Conduction Abnormalities • Leaky or Stenotic Valves • Open-Heart Surgery 2Electrical Conduction Abnormalities: Pacemakers Indications • Sinus Node Dysfunction – Malfunctioning SA node provides improper or zero pacing • Degrees of Heart Block – Signal propagation problems between chambers • De-Synchronization – Poor coordination between contraction of atria and ventricles 3Electrical Conduction Abnormalities: Pacemakers Old Pacemakers: 1950’s and 1960’s The “Bakken” Bulky, internal Streamlined 4Electrical Conduction Abnormalities: Pacemakers Problems with old pacemakers • Batteries – Power source (external, bulky) – Poor longevity – Hermetic sealing and corrosion • Leads – Inefficiency (coating, tip design) – Fixation designs • Physiology – Invasive placement (epicardial vs. transvenous) – Ventricular synchronization – No rate responsivity • Environmental Issues – Electrical interference – Waste (nuclear, incineration/cremation) 5Electrical Conduction Abnormalities: Pacemakers New Pacemaker Design • Implantability – Size – Packaging • Longevity – Power supply – Lead design – Power-saving algorithms • Monitoring – Sensing – Computational power 6Electrical Conduction Abnormalities: Pacemakers Power Supply • Batteries – Lithium iodide – 10-15 years (0.8 to 3.0 amp-hours) • Reliability – Linear discharge, drops off quickly at ~ 14 years – Elective Replacement Indicator (3-4 Months) volts 7Electrical Conduction Abnormalities: Pacemakers EKG Sensing • Intracardiac electrogram – Uses principles of EKG to sense heart’s electrical activity – Sensed from “perspective” of pacemaker • Pacemaker intervenes when irregularities detected • Most common pathology – Sinus block – 3rd degree AV block – Bundle branch block 8Electrical Conduction Abnormalities: Pacemakers Computational Improvements • Collection and storage of pacing information between follow-up visits • Sensing algorithms that only step in when necessary • Regular adjustment of pacing to minimize amount of power required (optimization) • Automatic capture verification Capture Curve Duration (ms) Amplitude (V) 9Electrical Conduction Abnormalities: Pacemakers Capture Curve 10Electrical Conduction Abnormalities: Pacemakers Lead Implantation • Electrical Issues – Contact surface area – Transmission line efficiency • Biological Issues – Products of inflammation increase lead resistance – Bacterial infections (high mortality of endocarditis) • Mechanical Issues – Microfractures introduced during insertion (poor technique) – Fixation of leads (passive and active) Steroid-Eluting Leads Passive-Fixation: Hook into trabeculae Active-Fixation: Screw into myocardium 11Electrical Conduction Abnormalities: Pacemakers Placement • Electrical leads guided through subclavian vein or cephalic vein Multiple possible lead configurations – Single-chamber pacing – Dual-chamber pacing – Bi-ventricular pacing • Pacing generator typically placed subcutaneously, below clavicle Posterior of Heart Coronary sinus 12Electrical Conduction Abnormalities: AICD AICD: Automatic Implantable Cardioverter-Defibrillator • Used to convert abnormal heart rhythms to normal ones • Indicated for people who have experienced – Ventricular tachycardia (VT) or fibrillation (VF) – Cardiac arrest or arrhythmia that caused loss of consciousness – Pathology of the heart muscle (e.g., cardiomyopathy) 13Electrical Conduction Abnormalities: AICD 14 Re-Entry can produce VT and/or VFElectrical Conduction Abnormalities: AICD Compared to Pacemaker: • Similar components: battery, processor, housing, leads • Increased battery requirements: – Must provide greater amplitude pulses to achieve cardioversion vs. just pacing – Effective battery live ~5-7 years • Larger battery, higher capacity leads (sometimes) 15Electrical Conduction Abnormalities: AICD Modes of Operation • VT/VF Detection – Monitor atria and ventricles for arrhythmias – Differentiate between types of arrhythmias – Store heart signals for physician evaluation • Anti-Tachycardia Pacing – Sequence of closely spaced pulses • Cardioversion – Single, medium-voltage pulse applied for arrhythmias that show temporal irregularities • Defibrillation – Single, high-voltage pulse of up to 800 volts 16Leaky and Stenotic Valves: Valve Repair or Replacement • Improperly functioning valves make heart work harder (e.g., turbulence, backflow) • If more than only a minor irregularity, must be repaired or replaced • Valve repair desirable if possible (e.g., valve only slightly abnormal) • Valve replacement usually requires open-heart surgery 17Leaky and Stenotic Valves: Valve Replacement • Mechanical valves – Long-lasting, made of durable materials – More likely to damage blood cells and produce clots • Tissue valves – Animal or human donor tissue – Break down more rapidly 18Leaky and Stenotic Valves: Valve Replacement Replacement Valve Considerations • Minimal thrombogenesis – Foreign material – Cellular maceration • Failure safety • Minimal leakage • Dynamic responsiveness • Wear • Trans-valvular pressure gradient • Blockage 19 Tissue Valve Mechanical ValveOpen-Heart Surgery: Heart-Lung Machine • Open-heart surgery requires heart to be stopped • Must provide oxygenated blood to body and brain during operation • Cardiopulmonary bypass (CPB) allows for systemic delivery of oxygenated blood 20Open-Heart Surgery: Heart-Lung Machine • Multiple cannulae sewn into patient’s body to carry blood to and from machine • Blood taken from venous circulation • Blood oxygenated and then returned to arterial circulation • Blood often cooled to lower body temperature Pump Reservoir Oxygenator 21Open-Heart Surgery: Heart-Lung Machine • Two main components – Oxygenator  Provides O2  Removes CO2 – Pump  Moves blood through tubing and machine  Goal: avoid damaging blood cells Roller pump Membrane oxygenator 22Open-Heart Surgery: Heart-Lung Machine • Oxygenators – Bubble oxygenators – Membrane oxygenators – Heparin-coated blood oxygenator • Pump – Roller/peristaltic pump – Centrifugal pump Centrifugal pump Bubble oxygenator 23Open-Heart