Cardiovascular Medical Devices Flashcards
1
Q
Heart valve types
A
- mechanical vs. bioprosthetic tissue valves
- repair is preferred over replacement generally, as to avoid prosthesis-related complications and chronic anti-coagulation needed for mechanical valves
2
Q
Mechanical Heart Valves
A
- Dr. Albert Starr/Lowell Edwards fabricated and implanted first mechanical valve (stainless steel cage, silastic ball, and base with sewing cuff)
- today, valves use rigid metal occluders in a metallic cage (CoCr or Ti alloy), or two carbon hemi-disks in a carbon housing
- all occluders made from pyrolytic carbon
3
Q
Bioprosthetic Heart Valves
A
- Dr. Carpentier created the first, consisted of a chemically-treated biological tissue and mechanical structure
- chemical fixation minimizes immunogenicity (so immunosuppression is not mandatory)
- human allograft is an alternative (has several restraints like availability and size)
- pseudo-anatomic central flow, relative nonthrombogenicity, especially compared to mech. valves
- increasing in usage
4
Q
Complications
A
- at 10-15 years, 50-70% survival rate with 30-50% being serious complication-free (see graph)
- thromboembolic complications are major cause of issues after replacement (with mechanical valves)
- exposure of blood to an artificial surface causes systemic coagulation, complement, and platelets (thrombus can immobilize occluder parts)
- anticoagulation treatment increases hemorrhage risk
- endocarditis (3-6% incur prosthetic valve infections, requires surgical reintervention)
- structural dysfunction (mechanical failure, bioprosthetic degeneration – more common, 30-50% requiring replacement)
- non-structural dysfunction due to poor healing
5
Q
Using Mechanical vs. Bioprosthetic
A
- overall complication rates are similar
- patient age: older recipients have increased risk of hemorrhage (so wouldn’t want to take anticoagulants with mech. valves), younger patients have longer life-span (need to replace anyways, so mech. is fine)
- methods being investigated to prevent calcification, or that contain interstitial cells to repair integrity and enable valve growth
6
Q
Transcatheter Valve Replacement
A
- patients with valvular disease (can’t withstand open heart surgery) undergo percutaneous/through the skin catheter-based valve replacement
- place expandable stents with valves through periphery arteries, which can utilize balloons or be self-expanding
- valve component is bovine/equine/porcine tissue
- stents made from expandable or shape-memory materials (stainless-steel, platinum or nitinol, respectively)
- Edward-SAPIEN
6
Q
Cardiac Pacemakers
A
- provide 2-4 mA impulses to the conduction system to initiate contraction
- typically in the elderly, use lithium-iodide batteries with finite life-span of 5-8 years
- consist of: 1) pulse generator with power source and circuitry, 2) elec. insulated conductors from the pulse generator to the heart, 3) tissue or blood/tissue interface between electrode and myocardium
- most common indication for cardiac pacing is for conduction blocks (failure of impulse propagation due to disease)
6
Q
Materials of Pacemakers
A
- implanted pulse generator usually made of titanium alloy
- conducting parts of leads composed of MP35-N (nickel, cobalt, chromium, and molybdenum alloy with strength and corrosion resistance; and silver or stainless steel to provide electrical conductance)
- insulated with silicone and/or urethane
7
Q
Pacemaker Complications
A
- formation of layer of non-excitable fibrous tissue, increases impedance for the delivered impulse (leads can be designed to release steroids, or pacemaker to provide adjustable impulse to prevent)
- stable fixation is needed for leads, using specific designs or tissue ingrowth (then myocardial perforation)
- host response to implantation includes: thrombosis, pressure necrosis of skin over the generator, migration/rotation of generator
- infection can migrate along the leads (endocarditis)
7
Q
Angioplasty and Stents
A
- bare metal stents of stainless steel or nitinol, ranging from 2.5-4mm in diameter
- short-term thrombosis can occur within 7-10 days, but is treated with anticoagulation
- major long-term consequence is stent restenosis, 1/2 patients in 6 months (endothelial lining and vessel wall damage, wires can become embedded in fibrosis tissue)
- drug eluting stents (DES) and resorbable stents (RBS) in clinical trials as possible alternatives
7
Q
Percutaneous Transluminal Angioplasty (PTA)
A
- procedure using inflation of balloon-tipped catheter, unblocks plaque or thrombi deposits and restores blood flow
- nylon or polyethylene terephthalate balloons
- in 30-50% of patients that receive just angioplasty, restenosis occurs due to SMC proliferation (placing additional stent can help)
8
Q
Vascular Grafts
A
- bypass obstructed vessel or replace segment that’s formed an aneurysm or dissection
- criteria for success: resistant to thrombosis, SMC caused intimal thickening, fatigue, and aneurysm development, compliant material similar to normal vessel, sufficient mechanical properties
- grafts of <6-8 mm diameter are challenging, with patency rate less than 50%
- large-diameter have high flow and low-resistance, with 5-10 year patency rate of 90%
9
Q
Synthetic Vascular Grafts
A
- can be porous to enhance healing, made with connective tissue proteins to aid clotting or antibiotics to reduce infection risk, or pre-clotted with the patient’s own blood
- healing: 1) luminal surface coated with plasma proteins that develop into ‘pseudointima’ (platelet-fibrin coating), 2) SMC then endothelial cells cover this layer, NONTHROMBOGENIC, entire tissue thickness is neointima (covers 10-15mm)
10
Q
Synthetic vascular graft healing
A
- graft inner wall comes from overgrowth of anastomosed tissue, tissue ingrowth, and deposition of endothelial cell progenitors from blood
- grafts become encapsulated in surrounding connective tissue (typical foreign body response)
- exterior surface has layer of inflammatory cells, then collagen, fibroblasts, blood vessels, etc (capsule)
11
Q
Synthetic complications
A
- small diameter (<6 mm) frequently fail due to thrombus formation or fibrous tissue growth (surface thrombogenesis, delayed/incomplete endothelialization, disturbed flow across anastomosis zone, or compliance mismatch)
- intimal hyperplasia
- infection at suture line causing a disrupted connection and hemorrhage at graft site (pseudoaneurysm)
- endothelializaiton of entire graft would improve thrombo-resistance and help prevent bacterial attachment and infection
