Electrical Activity of the Heart Flashcards
What are the 5 phases of cardiac muscle action potential?
Phase 0 - Depolarization due to Na+ influx
Phase 1 - Initial repolarization due to K+ outflux
Phase 2 - Plateau due to increase of Ca2+
Phase 3 - Repolarization due to outflux of K+ and decreased influx of Ca2+
Phase 4 - Resting potential
What period of a cardiac action potential ensures that cardiac muscle cells cannot be tetanized?
Absolute refractory period. No activation potential can be generated at this point
What period of a cardiac action potential is abnormal?
Period of Supernormality. Reduced level of stimulation produces same action potential
What do Catecholamines do?
Enhance calcium movement and increase size of action potential
What are calcium channel blockers used for?
To treat cardiac arrhythmia and high blood pressure. They depress calcium movement resulting in smaller action potentials
What is the pacemaker of the heart?
SA node
What are two important things to keep in mind about SA node action potentials?
- Phase 4 imparts arrhythmia; baseline is not flat but slopes toward theshold
- Calcium depolarizes
What does an ECG NOT do?
ECG can NOT give direct info about contractile performance
Know the different wave points of an ECG.
Got it?!?! P, Q, R, S, T.
Figure out what is happening at P and you should be able to figure it out from there
What is Eintoven’s Triangle?
3 leads that are the electrical discharge values across the chest are measured across the distance between the 3 leads, respectively. If the values are summed, they add up to 0.
What is a respiratory sinus arrythmia?
Found in healthy hearts. Due to cyclic changes in autonomic activity to SA nodes
What is sinus tachycardia?
interval between cycles is shorter; opposite for sinus bradycardia
What is premature ventricular/atrial contraction?
Spontaneous generation of action potentials. Increased by smoking, stress, caffeine, fatigue
What is atrial fibrillation?
Small, random waves of depolarization in ECG. Bad sign.
What happens if ventricular fibrillation is left uncorrected?
patient dies
What is the first sign of a myocardial infarction on an ECG?
Inversion of T wave
In a myocardial infarction, progressive ischemia results in elevation of - segment.
ST segment
Infarction leads to development of __ waves in front of an elevated ___
development of Q waves in front of ST segment
Modification of contractile force at the cellular level, independent of loading, is called ____ _____
ionotropic modification
What is the Bowditch phenomenon?
Gradual increase in muscular contraction following rapidly repeated stimulation
What does digitalis do?
Inhibits Na-K ATPase, resulting in an increased intracellular concentration of Na which in turn increases intracellular Ca. This strengthens muscle contraction.
What is the first heart sound in a cardiac cycle?
The closure of mitral and tricuspid valves
What is the second heart sound in a cardiac cycle?
Closure of aortic and pulmonary semilunar valves. Transition to diastole.
What is the difference between ventricular end-diastolic volume and end-systolic volume?
Stroke Volume
What is the stroke volume/end diastolic volume?
Ejection fraction
What are the factors affecting contractile strength of the heart?
- Preload - initial muscle length
- Afterload - Forces against which muscle must contract to shorten
- Contractility - inotropic state
- Inotropic effect of increased heart rate
What is cardiac output?
Volume of blood ejected from the heart per unit of time?
What is Starling’s Law of the heart?
Within physiological limits, the more the heart fills, the more it pumps
What factors increase contractility and cardiac output?
- Increased intracellular Ca
- Decreased extracellular Na
- Digitalis
- Sympathetic stimulation
What factors decrease contractility and cardiac output?
- heart failure
2. loss of myocardial cells due to infarction, acidosis, or hypoxia
What are the four pressures within Arterial Pressure Waveform?
- Arterial - ratio of systolic over diastolic
- Systolic
- Diastolic
- Pulse - systolic minus diastolic pressure
Why might older adults with atherosclerosis give a false high blood pressure reading?
a greater external pressure is required to compress the blood vessels and stop the flow
