Cardio

9/13/99

 

Looking at:

1. Rate
2. Rhythm
3. Axis
4. Blocks
5. MI

 

• Rate is determined by the pacemaker (SA node)
• Normal is 60-100 bpm
• <60 is Bradycardia
• >100 is Tachycardia
• Pacemaker
• Group of muscle cells
• Depolarization signal is sent our in a circular fashion
• Cavernous sinus in the atria
• Has the ability on its own to depolarize 60-100 /min
• Right Coronary Artery supplies the SA node
• Rate becomes uncontrollable during atherosclerosis when the R coronary artery is blocked
• Rate change leads to pacemaker difficulty
• Can scar over the SA node
• Result of ischemia
• Poor circulation
• Leads to infarction and the cells die
• Can't get signal from these cells
• Block is when the SA node fails—almost always from scar
• Only way to find out that the SA node is not firing would be an ECG
• Look at the P wave
• Depolarization of the R and L atria
• If lose SA node, move down to AV node which can work as the pacemaker
• AV node is not capable to fire at 60-100bpm—will slow down
• Next down is the common bundle—signal enters the ventricles
• Bundle branches in the ventricles—doesn't matter where the signal came from
• Purkenje fibers—leads to normal contraction of ventricles
• The rhythm remains the steady
• (A-V) Nodal Rhythm—A-V node is in control
• Sinus Rhythm is when the SA node is in control
• A-V can send the signal retrograde (back into the atria)—retrograde conduction
• When this occurs, the atria will contract later than they would normally
• Would see an inverted P wave possibly somewhere else in the cycle
• Could show up b/w the S and T wave
• Common Bundle (40-50 bpm) is the next area to take over
• Purkenje Fibers (30bpm)—variations in people and in the literature

Septal Scarring

§         Can create a barrier b/w the atria and the ventricles

§         Signal cannot get through

§         Atria contraction normally

§         Ventricles have to find a different source depolarization

§         3° block

§         Purkenje fibers become the pacemaker of the ventricles

§         Complete Heart Block

§         A-V dissociation

§         Result of serious damage to a heart

§         Pacemaker is a solution for this problem

o       This brings the heart rate of the ventricles up

 

Ectopic Beat

§         Away from the normal site

§         When something other than the SA node is the pacemaker

§         Any muscle cell in the heart can become the pacemaker

 

PVC

• Premature ventricular contraction
• The heart is jumping
• There is no blood in the chambers and the contraction is felt stronger
• Somewhere in the ventricular muscle there is an ectopic site that is irritated and fires
• When it fires, it sends out a wave of depolarization
• Stress is the most common cause—increased catacholamines
• Unifocal PVC—only one site
• No caffine or nicotine
• This will sometimes help control
• b blockers can help
• Multifocal PVC
• Ventricular defibrillation
• More than one site causing a signal
• This is very serious condition

 

Normal ECG Graph

• 5 big boxes/sec
• 300 big boxes/min
• .04 little box/min
• Inverted T wave is a sign of ischemia, problem to repolarize the atria
• Problem to R coronary artery supply, has a feedback loop to vagus node, leading to increased firing of vagus—nausea and vomitting