ICL 4.2: Implantable Cardiac Devices

Question 1

what are the 3 types of implantable cardiac devices?

Answer 1

1. pacemakers
2. internal cardiac defibrillators (ICD)
3. cardiac assist devices

Question 2

which veins are used to place pacemakers?

Answer 2

catheter electrode is inserted via these veins to perform trasvenous pacing:

1. basilic (originally)
2. subclavian (current)
3. axillary (special training)

it’s outside the chest wall so you minimize having an air pocket in the linings around the lungs while you’re trying to get to the subclavian

4. cephalic (special training)

Question 3

how does a pacemaker work?

Answer 3

it’s a battery with a pulse generator; electricity is generated in the battery and it can self-pulse the patient

it does this by being plugged into insulated wires from the battery to the heart implant site = LEAD –> LEAD has an extendable/retractable corkscrew tip or a tyne tip

the corkscrew actively penetrates into the myocardium while the tyne tip causes a reaction at the endocardial level and is close enough to the muscle to depolarize it

the pacing pulses are then delivered to the myocardium via the LEAD

Question 4

what type of battery is in a pacemaker?

Answer 4

lithium iodide battery

and inside the battery is a small computer that generates pulses to pace the patient and depolarize the myocardium

it has alerts that can detect arrhythmia, low battery, etc.

Question 5

how long to pacemakers last?

Answer 5

15 years

Question 6

what are the 3 types of leads?

Answer 6

1. corkscrew
2. tyne tip
3. HIS bundle

Question 7

what are the different types of pacemakers?

Answer 7

1. single chamber
2. atrial only (if you have zero AV nodal disease)
3. ventricular only (if you have chronic Afib, you can’t put a pacemaker in the atrium so you’d do a ventricular only)
4. atrial and right ventricular
5. atrial and right ventricular and left ventricular
6. atrial and His bundle

Question 8

what is His bundle pacing?

Answer 8

a lead that is hooked right into the His bundle and will depolarize the RV and LV via the bundle which keeps your natural bundle depolarization

Question 9

what is the function of a pacemaker?

Answer 9

1. pace and sense the myocardium!

leads can be put into the atrium, His bundle, RV, or LV via the coronary sinus

2. inhibit pacemaker when pacing is not needed
3. software algorithm to increase HR with activity so that they have a proper rate response

Question 10

how is a pacemaker programed?

Answer 10

it’s programmed to pace, sense, inhibit and increase HR with activity

you can pace and sense the atrium, ventricle, dual or neither

you also need to program it so that it’s inhibited when you don’t need pacing; if you’re walking and you’re at 90 bmp, you don’t need your pacemaker and that saves battery

Question 11

how does a pacemaker increase HR with activity?

Answer 11

the pacemaker uses sensors to deliver pacing at elevated rates, proportional to exertion level –> this programming software in the PPM is called rate response

1. most commonly, it’s accomplished by the use of an accelerometer that identifies the postural changes and the body movements related to physical activity

all pacemakers have this functionality, but is only enabled as needed

2. some pacemakers use a Minute Ventilation sensor (MV), to drive the pacing rate

PPM measures the resistance between an electrode on the cardiac pacing lead and the metal housing of the device

the resistance measurement changes with respiration, and the PPM can use this to calculate the respiratory rate and chest excursion, allowing for a very natural heart rate (HR) response to exercise

Question 12

what are the positions/modes in pacemaker set up?

Answer 12

position i = pacing

position II = sensing

position III = response to sensing/inhibiting

position IV = rate response

Question 13

what are the various standardized programming settings available for a pacemaker?

Answer 13

1. DDD
2. DDDR
3. VVI
4. VVIR
5. VOO

Question 14

what is the DDD setting in a pacemaker?

Answer 14

dual pacing, dual sensing and dual inhibit but rate response is off

D = pacing in the atrium and ventricle

D = sensing in the atrium and ventricle

D = inhibit pacing if it’s not needed

you need to have the pacemaker set to activate only if you’re longer than your intrinsic P wave (atrial) and PR (ventricular) lengths

so like set the pacemaker to notice if your HR is lower than 60 bmp or if the PR is longer than 200 ms – if your HR gets slower, the atrium will start pacing and if the PR is elongated then the ventricle will start pacing

Question 15

what is the VVI setting in a pacemaker?

Answer 15

V = pacing in the ventricle

V = sensing in the ventricle

I = inhibit

you aren’t doing anything with the atrium because there’s no A lead! you’re only doing stuff with the ventricle!

do this for someone with chronic Afib whose atrium is ruined or in an elderly person with a thinned out atrium

Question 16

what is the VOO setting in a pacemaker?

Answer 16

V = pacing in the ventricle

O = sending is off

O = response to sensing is off

you use this to save battery; it’s a non-demand pacemaker it’s just always pacing, it doesn’t wait for you to demand it

you use this for a patient who’s going into surgery and you’re going to coterize tissue close to the heart like the left shoulder – this produces electricity and the heart will sense it and think it’s going really fast and if the pacemaker senses this then it’ll think the heart is going too fast and it will just stop – if the patient has 3rd degree heart block then they’re not going to have a rhythm in their ventricle and they won’t have their own heart beat

Question 17

how do defibrillators work?

Answer 17

in the setting of pulseless VT or VF, it can be converted to Sinus Rhythm by delivering sudden electrical massive depolarization = SHOCK to the heart

this causes all the myocardium to depolarize at once, and then hopefully after phase 3, the pacemaker signal gets through the AV node depolarizing the ventricles and sinus rhythm ensues

the energy of a delivered shock is measured in joules –> the joules needed for endocardial defibrillation is only a fraction of external defibrillation (15-40 j vs. 200-360 j)

ICDs with dual chamber insertion can both defibrillate and pace the heart!

Question 18

how did the first implantable cardiovertor defibrillator work?

Answer 18

the can was placed in the abdomen and the leads were tunneled to the heart surface

so it was placed epicardially, there was nothing actually inside the heart

Question 19

how are ICDs placed in the body?

Answer 19

it’s implanted in the chest and the lead goes through the axillary vein outside the chest wall which eliminates the risk for an air pocket to form in the lining around the lungs

then you go into the subclavian vein into the SVC into the RA and finally to the RV which generates electricity when you want to defibrillate

Question 20

what is a subcutaneous ICD?

Answer 20

it does not have pacing programing! it just defibrillates

you use them in infected patients who are diabetic and have high risks of infections like cancer patients also so you use this to avoid trans venous access to minimize the risk for infection