Pacemakers

Question 1

Indications for a permanent pacemaker

Answer 1

1) 3rd degree heart block or advanced 2nd degree block resulting in symptomatic bradycardia, CHF, vent arrhythmias or exercise intolerance.
2) Vent escape rhythm <40
3) Asystolic periods >3s

Question 2

How to interpret pacemakers codes (e.g. VVI, etc)

Answer 2

1) 1st letter: indicates chamber paced. E.g. V (ventricle), A (atrium), D (dual), 0 (none)
2) 2nd letter: indicates chamber sensed. E.g. V,A,D,0
3) 3rd letter: Response to setting. T (triggered), I (inhibited), D (dual), 0

4) 4th letter: programmable functions. P (programmable rate, output or both), M (multiprogrammability of rate, output, sensitivity, etc), C (communication function, telemetry), R (rate modulation), 0
5) 5th letter: antitachycardia features. P (antitachycardia pacing), S (shock), D (dual), 0

Question 3

Causes of pacemaker malfunction

Answer 3

1) Failure to capture
2) Under-sensing (aka overpacing)
3) Over-sensing (aka underpacing)
4) Pacemaker mediated tachycardia
5) Runaway pacemaker

Question 4

Causes of failure to capture

Answer 4

1) Lead displacement (e.g. twiddler’s syndrome) –> MOST COMMON
2) Fractured lead (rare)
3) Disconnection of lead
4) Failure of pacemaker to generate signal
5) Battery depletion
6) Exit block: failure of myocardial depolarization due to fibrosis, metabolic derangement, ischemia, hypoxia, class III antiarrhythmics

Question 5

Most appropriate next management step in a symptomatic (bradycardic) patient with failure of pacemaker capture

Answer 5

Start external transcutaneous pacing

Question 6

Pathophys of pacemaker undersensing (aka overpacing)

Answer 6

Failure to sense native impulses (e.g. native QRS voltage low so get extra paced beats in addition to native beats)

Question 7

Biggest risk with pacemaker undersensing (overpacing)

Answer 7

R on T syndrome resulting arrhythmia.

If concerned that the pacemaker is undersensing, apply pads in preparation for cardioversion in the event of R on T

Question 8

Causes of pacemaker undersensing

Answer 8

Similar to failure to pace.

E.g. battery exhaustion, lead displacement, improper programming, poor lead contact with endocardium

Question 9

What is the pathophys of pacemaker over-sensing (aka under-pacing)

Answer 9

Inappropriate pacemaker sensing of ‘false’ extra-cardiac impulses with pacer inhibit (‘I’) mode. Causes inappropriate inhibition of pacemaker impulse –> no paced beat (bradycardia)

Causes may include pectoralis muscle contraction, electrocautery, digital cell phones (? lol really…??), MRI

text recommends magnet but this doesn’t make sense to me?? Because you WANT the pacemaker to generate MORE beats, not less??

Question 10

MOA of pacemaker-mediated tachycardia

Answer 10

Get a re-entry dysrhythmia:
- Native ventricular depolarization –> retrograde atrial depolarization –> pacemaker sensing –> ventricular output via pacer wire (‘endless loop tachycardia’)

E.g.: Get a PVC -> retrograde atrial depolarization -> sensed by atrial lead -> paced ventricular impulse -> retrograde atrial depolarization (etc)

Question 11

Treatment of pacemaker-mediated tachycardia

Answer 11

Interrupt 1 limb of re-entrant tachycardia with VALSALVA or adenosine.
Can place cardiac magnet which terminates pacemaker sensing and arrhythmia

Question 12

What is a runaway pacemaker?

Answer 12

Pulse generator discharges at rate above present upper limit, making pacemaker entirely responsible for malfunction independent of myocardium (unlike pacemaker-mediated tachycardia).

RARE: caused by electrical malfunction or unintended pacemaker reprogramming.

Occurs with dual chamber pacers in synchronous (demand) AV packing mode

Question 13

Treatment of runaway pacemaker

Answer 13

Magnet.
Converts pulse generator to asynchronous or ‘fixed rate’ mode (preset regardless of native electrical activity).
May be ineffective in cases of true pacemaker malfunction.

Question 14

Potential symptoms/exam w/ pacemaker dysfunction

Answer 14

With exception of runaway pacemaker, typically same symptoms that prompt pacemaker placement (pre/syncope, dyspnea, CP, palpitations)

Question 15

Work up for pts with suspected pacemaker malfunction

Answer 15

CXR –> look for fractured lead/displacement.
US: look for tamponade (due to ventricular rupture)
Electrolytes, cardiac enzymes, drug levels (e.g. dig, flecainide)
Pacemaker interrogation/battery assessment by cardio

Question 16

What does the magnet do when placed over a pacemaker?

Answer 16

Converts the pacemaker to fixed-rate pacing mode, disables sensing and turns off the external(?) pacemaker generator

Question 17

ECG findings to look for with pacemaker malfunction

Answer 17

1) Absence of pacer spikes when indicated –> failure to output signal
2) Pacer spikes but no depolarization –> failure to capture
3) Pacer spikes despite native beats –> undersensing native beats
4) Absence of pacer spikes with external motion/interference pattern –> oversensing

Question 18

What is pacemaker syndrome?

Answer 18

Occurs due to loss of AV synchrony, most common with VVI pacemakers.

Essentially pacemaker causes atria to contract while tricusp/mitral valves are closed. Get increased atrial pressures resulting in pulmonary/hepatic congestion as well as reduced ventricular filling due to loss of atrial kick resulting in reduced CO (20-50%).

Pts may present with fatigue, malaise, CHF, throat fullness, cough, sense of pulsations in neck/abdomen.

Typically a clinical diagnosis. Get ECG to evaluate for AV dissociation.