EHR519 Lecture Notes - Lecture 4: Cardiac Resynchronization Therapy, Cardiovascular Disease, Catheter Ablation
1. Week 4 – Clinical course of myocardial-related
cardiovascular disease (Part B)
Conduction Pathway Abnormalities: Risk Factors
Pharmacological effects (see provided reading source on Interact 2) titled “Toxic and drug-induced
changes of the electrocardiogram)
Congenital anatomical and physiological abnormalities
Changes induced by prior ischemia/infarct
Effects from toxins, chemicals, etc.
Effects from nutritional stimulants i.e. caffeine
Acute or chronic effects of insomnia
Effects of stress, anxiety and depressive disorders
Acute or chronic effects of tobacco smoking (nicotine and chemical constituents)
Pericarditis – inflammation of the pericardium
Thyroid dysfunction (both hypo- and hyper-thyroidism)
Vitamin D (25-hydroxy) deficiency
Essentially if an ECG trace is showing abnormalities a Q&A process should ensue to identify any modifiable
risk factors which could be inducing such abnormalities.
Obviously the purpose of screening is to identify factors from the outset (i.e. prior to exercise); however,
the screening process is not bullet-proof and things can slip through.
Conduction Pathway Abnormalities: Clinical Symptomology
P wave <0.3mV in height (3 small boxes) RA
enlargement
P wave <0.12 sec duration (3 small boxes) LA
enlargement
PR interval >0.12 but <0.20 (3-5 small boxes) AV
node issues
QRS duration >0.06 but <0.10 (1.5-2.5 small boxes)
RV-LV delay
QRS = upright in leads I and II
QRS and T waves = same direction in limb leads
All waves = negative in aVR
R wave increases in positive polarity from V1-V4
ST-segment should be isoelectric (may be raised in
V1-V2)
P and T waves = upright in I, II and V2-V6
Q wave = absent or <1 small box in size in I, II and V2-V6
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Clinical symptomology may relate to a client’s diagnosis as well as their post-diagnosis presentation in EP
practice.
Symptomology related to ECG abnormalities raise the need to question whether the client is/was feeling
well? A client should display the following:
No obvious pain or discomfort related to heart function i.e. angina
No obvious sensation of arrhythmia or palpitations or any other bodily sensation of altered
cardiac function
Mental coherence – are they getting adequate blood pressure (MAP) to permit adequate brain
perfusion and thus cognitive function – remember the heart is a pump and lack of output
(volume and pressure) will exhibit consequent symptomology such as: pallor, cyanosis, lack of
articulation, lack of concentration, confusion, light-headedness, etc.
Normal breathing – ECG abnormalities can be associated with reduced delivery of blood to lungs
and falling O2 sats which shifts acid-base balance towards acidic and stimulates a
hyperventilatory response from the respiratory center in the medulla oblongata. This will
present as dyspnea or “shortness of breath”.
Absence of fatigue at rest – If cardiac function (i.e. output) is adequate at rest we may assume
that the client would not evidence excessive fatigue at rest. Questions need to be asked related
to insomnia/lifestyle if fatigue is present.
Absence of nausea – altered cardiac function (potentially due to abnormal conduction pathway
activity) can elicit feelings of nausea, with sensation to vomit, unsettled gastrointestinal tract,
general feeling of lack of wellness.
Conduction Pathways Abnormalities: Surgical Intervention
Implantable artificial cardiac pacemaker:
Chronically required for SA and/or AV node dysfunction (may be congenital or acquired); AV
blocks; bundle branch blocks; atrial
fibrillation/flutter; bradycardia and tachycardia
often accompany most conditions.
May be acutely required after myocardial
infarction or other acute CV conditions (removed
upon recovery)
Surgery requires 2-3 hours normally; most
patients go home within 24 hours.
5cm incision in upper chest; thin insulated wires
inserted via vein leading to heart; device then
“implanted” and incision sewn up; surgical site
can be swollen, painful and tender to palpate;
over-counter pain killers.
Device is programmed by the
physician/cardiologist to tailor its function to the specific CV condition.
Pacemakers have one to three wires that are each placed in different chambers of the heart.
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1. Wires in single-chamber pacemaker usually carry pulses from the generator to the right
ventricle.
2. Wires in a dual-chamber pacemaker carry pulses from the generator to the right atrium
and the right ventricle. The pulses help coordinate the timing of these two chambers'
contractions.
3. Wires in a biventricular pacemaker carry pulses from the generator to an atrium and
both ventricles. The pulses help coordinate electrical signaling between the two
ventricles. This type of pacemaker also is called a cardiac resynchronization therapy
(CRT) device.
Catheter ablation:
Can treat arrhythmias and other sources of abnormal activity (e.g. atrial fib/flutter; PVC’s)
Uses radiofrequency energy (microwave heat technology) to target and destroy (“burn”)
irregular myocardial or vasculature tissue causing conduction pathway abnormalities.
Usually undertaken when pharmacological intervention is unable to control abnormalities.
Normally takes 2-4 hours in an electrophysiology or cardiac catheterization lab.
Surgery involves general sedation with local anesthetic applied to inguinal femoral artery area
which is where several electrode catheters are inserted to gain access to the heart.
A small electrical impulse from one catheter is generated proximal to the heart and the abnormal
tissue normally becomes active and can be identified for its anatomical location.
The microwave heat is then used to destroy the site (usually ~5mm clump of cells).
There may be several sites that need to be destroyed.
Recovery varies depending upon the ablation required, as well as age, physical condition, etc.
Conduction Pathway Abnormalities: Pharmalogical Intervention
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Document Summary
Week 4 clinical course of myocardial-related cardiovascular disease (part b) Pharmacological effects (see provided reading source on interact 2) titled toxic and drug-induced changes of the electrocardiogram) Effects of stress, anxiety and depressive disorders. Acute or chronic effects of tobacco smoking (nicotine and chemical constituents) Essentially if an ecg trace is showing abnormalities a q&a process should ensue to identify any modifiable risk factors which could be inducing such abnormalities. Obviously the purpose of screening is to identify factors from the outset (i. e. prior to exercise); however, the screening process is not bullet-proof and things can slip through. P wave <0. 3mv in height (3 small boxes) ra enlargement. P wave <0. 12 sec duration (3 small boxes) la enlargement. Pr interval >0. 12 but <0. 20 (3-5 small boxes) av node issues. Qrs duration >0. 06 but <0. 10 (1. 5-2. 5 small boxes) Qrs = upright in leads i and ii. Qrs and t waves = same direction in limb leads.
