Defibrillation + Pacing

Question 1

What factors determine defibrillation success?

Answer 1

• transthoracic impedance (affected by pt hair, fat etc) only 4% reaches the heart
• electrode position

Question 2

What shock energies are used in ALS?

Answer 2

200J for first shock, up to 360J for subseqet

Question 3

How should you defib if there is a PPM/ICD?

Answer 3

• life-saving measures take priority over concerns re PPM/ICD/loop recorder/neurostimulator
• try to place pads at least 10cm, ideally 15cm, away from PPM/ICD - usually using AP positioning
• can place a magnet

Question 4

What effect does placing a magnet on a PPM have? ICD?

Answer 4

PPM: resets PPM into an asynchronous mode
ICD: disables defib, can still work as pacemaker

Question 5

Are QRS complexes in CHB usually narrow or wide?

Answer 5

Narrow, usually the block happens at the AV node and an intact bundle of His still transmits the signal rapidly to both ventricles

Question 6

What is a Stokes-Adams attack?

Answer 6

Syncope from AV block

Question 7

Which types of heart block require pacing?

Answer 7

CHB with broad QRS
symptomatic CHB
CHB with long ventricular pauses (>3s) - risk of asystole

Question 8

What are the invasive and non invasive methods of pacing

Answer 8

Non invasive

• percussion pacing
• transcutaneous pacing

Invasive

• temporary transvenous pacing
• permanent pacing

Question 9

How is transcutaneous pacing performed?

Answer 9

• attach pads to clean, dry skin - AP position if pt cooperative, otherwise normal position for ALS
• attach ecg leads (white-right, smoke over fire)
• explain to conscious pt whats up
• select pacing rate
• ANALGESIA
• increase the current until capture is acheived - each spike followed by QRS (usually 50-100mA)
• confirm output with manual pulse
• increase current 10mA or 10% above this point to ensure capture with change in respiration/movement/changes to impedance

Question 10

How can temporary transvenous pacing fail?

Answer 10

1. High threshold (seen as spike with no capture)
   - voltage needed to stimulate the ventricle is higher than what stimulus is set to
   - normally on insertion aim is for threshold of <1V - higher may mean poor contact with ventricle
   - usual to pace the heart at 3-4V well above the initial pacing threshold - over the first days to weeks after insertion a transient rise in threshold is expected
   - threshold should be checked daily
2. connection failure - no spike
   - wires may be disconnected (no spike), fractured (intermittent spike or no spike), turned off
3. Lead displacement
   - should be in apex of RV with enough slack to allow for changes in posture and deep inspiration
   - can perforate and cause tamponade
   - can be displaced and cause extrasystoles, VT/VF

Question 11

What is pseudo-wenkebach?

Answer 11

at faster heart rates there may appear to be an irregular paced rhythm with wenkebach. occurs when the atrial rate exceeds the max tracking rate to pace the ventricles preventing sensed rapid atrial activity from becoming a tachycardia in a dual-chamber pacemaker

Question 12

What is cardiac resynchronization therapy?

Answer 12

OVERVIEW

Cardiac Resynchronisation Therapy = the restoration of ventricular co-ordination by means of an implanted cardiac resynchronization device.

EQUIPMENT
-biventricular pace maker
-can pace both septal and lateral walls of the left ventricle -> can allow coordination of ventricular ejection.
-one lead – RV
-one lead – fed through coronary sinus to LV
-often have a lead in RA
-coordinated atrial and ventricular function possible
c-an also be combined with a pacemaker and AICD

BENEFITS

• improved LVEF, Q and haemodynamics
• improved exercise tolerance
• decreased NYHA class
• decreased hospitalisation
• improved quality of life