Pacemakers Flashcards
What is a stress test?
Provocative measure to disclose disease
What is it that’s being stressed?
Cardiovascular system, usually cardiac perfusion
Name five methods for stressing.
Harvard step test, treadmill, bicycle ergometer, arm ergometer, toe raises,
walk in hall
Name several indications for stress testing
Suspected CAD, detect arrhythmias, evaluate cardiac function, evaluate therapy, LE arterial disease, sports medicine
Which is most common?
TM
What is MVO2?
Myocardial oxygen demand
Define ischemia.
Lack of O2 delivery;lack of blood flow to tissue
In the cardiac cycle, when is demand created, and when is it
satisfied?
Demanded: Systole
Satisfied: Diastole
What does CAD stand for?
Coronary artery disease
What causes it? (CAD)
Obstruction of coronary arteries, usually by plaque/clot
What is the usual mechanism of M.I.?
Rupture of plaque, thrombosis, and occlusion of artery
How severe must plaque be to cause M.I.?
Not necessary hemodynamically significant
What implication does that have for the utility of stress testing?
It will miss some lesions that can still cause M.I.
How is cardiac ischemia detected during stress testing?
Changes in ECG
What are the ST criteria for stress-induced ischemia?
ST depression 2 mm, ST elevation 1 mm, ST slope (maybe), T wave
inversion
What is the J point?
End point of QRS complex; marks beginning of ST segment
What are three forms of ST sloping?
Downslope, upslope, horizontal
Which is a poor indicator of ischemia?
Upslope
Is chest pain the only symptom of CAD?
No; other symptoms (pressure, SOB, fatigue, etc.) possible, especially in female pts.
What test might be combined with treadmill to disclose ischemia?
Thallium (nuclear med) perfusion test
Define sensitivity and specificity.
Sensitivity: ability to call positive when it’s truly positive
Specificity: ability to call negative when it’s truly negative
What is the overall accuracy (positive and negative) of treadmill testing?
Roughly 75%
Is it treadmill testing therefore not that useful?
No, still useful, especially when positive
Name a couple of causes of false positive or false negative with TM.
BBB, MV prolapse, diuretics, previous M.I.
What is the “maximum heart rate”? How calculated?
Predicted max rate heart can achieve; 220 – age
What is the target heart rate? How calculated?
Rate to shoot for in test; usually 85% of max rate
What test data are/might be collected during a stress test?
Duration, heart rate, BP, ST changes, any arrhythmias, possibly oxygen
consumption, any anginal pain or claudication, any dyspnea
Why is electrode prep important (more than for resting ECG)?
All that moving creates ECG noise
What should you monitor carefully during the test?
Patient condition
What visual cues might be important to note?
Breathing, sweating, skin color, ability to talk and interact, facial expression
What two aspects of the exercise are changed during the Bruce protocol?
Speed and grade
How long are the stages?
3 minutes
How much increase in speed and grade with each stage?
About 0.8 mph per stage, 2% grade per stage
What are good reasons to stop the test?
Positive ECG changes Reach target HR Pain, angina or otherwise (like claudication) SOB Finish all stages! Arrhythmia Drop in BP Drop in O2 sat Patient desires to quit
What arrhythmias call for stopping?
V tach
PVCs (frequent)
Paired PVCs
Heart block develops (2nd or 3rd degree)
What is significant about the recovery period?
Must watch patient carefully; can be dangerous period if there’s disease
What condition usually calls for stress testing in the vascular lab?
Claudication; LE PAD
What forms can the stress take? (for stress testing)
TM, toe-raises, walk hallway
What causes a drop in ankle pressure compared to resting?
Exercise causes vasodilatation, increased flow through stenosis (and
through collaterals), increased loss of energy (i.e., pressure)
How much drop is mild? Severe?
20% is mild, 50% severe
What ABI suggests the stress test is unlikely to be useful?
Less than around 0.40; arterioles are likely already maximally dilated…
What is a pacemaker? Don’t we already have them?
Device to stimulate cardiac activity. Yes, but sometimes they don’t work so
well.
What two basic functions do pacemakers perform?
Sense cardiac activity; pace.
What are the basic components of pacemakers?
Generator and lead wires; those can be epicardial or endocardial.
What are the two basic categories of generators?
External and implantable.
What other function might the generator provide besides routine pacing?
Defibrillate
What is a Reed switch?
Switch in pacer controlled by magnetic field through skin.
What are the two usual fixation devices on pacer leads?
Tines and screw
Where is a pacemaker generator unit usually installed
Under skin below left clavicle
Name some indications for pacing.
Brady arrhythmias
3Rd degree AV block Cardiac surgery
Asystole: heart dependent on pacer for any activity at all
What is capture?
The pacer is able to bring about cardiac activity
What is capture dependent upon?
Voltage
Condition of myocardium Lead resistance
How do we know when we have capture?
Pacing spike is followed by a depolarization: QRS or P, depending
Define “undersensing” and “oversensing.”
Undersensing: pacer doesn’t recognize intrinsic cardiac activity
Oversensing: pacer responds to non-cardiac signals (hair-trigger)
How do we recognize when proper capture isn’t happening?
Spike not followed by appropriate ECG activity
What do the letters of the first, second, and third letters in the function codes mean?
PSR: chamber paced (A or V or Dual), chamber sensed (A or V or Dual), and response (Inhibit or Trigger)
How would a VVI pacemaker work?
Paces the ventricles, senses the ventricles, doesn’t pace if ventricles depolarize on their own
A VAT?
Paces ventricles, senses atria, paces when atrial depolarization is sensed
DDD?
Paces both, senses both, both responses possible
AAI?
Paces atrial, senses atria, doesn’t pace if atrial activity is sensed
How are pacemakers programmed once implanted under the skin?
Magnetic pulses
What is a fusion beat?
Paced beat created along with intrinsic beat
What does it look like on the ECG?
Pace and intrinsic beats both appear on ECG
What goes wrong with pacers most often?
Lead wire damage
What is “twiddler’s syndrome”?
Patient absent-mindedly twiddles wires under skin, possibly damaging them
