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ECG
Question | Answer |
---|---|
P WAVE | represents depolarization of the atria |
QRS COMPLEX | correspond to the depolarization of the ventricles |
T WAVE | represents ventricular repolarization |
LARGER SIZEOF THE QRS COMPLEX OVER SMALLER P WAVE | caused by the greater muscle mass of the ventricles and hence greater number of cellular depolarizations |
SMALL Q WAVE | occurs during the activation of the septal fascicle and the depolarization of the interventricular sseptum |
R WAVE SPIKE | occurs when both ventricles are depolarizing at the same rate |
ECG | useful for the clinician in diagnosing heart attacks (MI), conduction abnormalities, arrhythmias, toxicity and electrolyte imbalances |
Cardiac muscle contains 3 types of cells that are involved in synchronized contraction of the 4 chambers of the heart | NODAL CELLS, SPECIALIZED CONDUCTING FIBERS, CONTRACTILE OR MYOCARDIAL CELLS |
1. NODAL CELLS | involved in generating the internal action potentials of the heart. They are localized in 2 areas of the heart, the SA and AV node. |
2. SPECIALIZED CONDUCTING FIBERS | allows for the quick transmission of the action potentials from one part of the chambers to another. AV bundle and the PURKINJE fibers |
Nodal cells and specialized conducting fibers | INTRINSIC CONDUCTION SYSTEM OF THE HEART |
3. CONTRACTILE OR MYOCARDIAL CELLS | makes up over 90 percet of the heart and is responsible for muscle contraction and the pumping of blood |
ELECTRICAL AXIS OF THE HEART | important for clinical diagnosis because it indicates the position of the heart in the thoracic cavity and hypertrophy of the chambers |
ELECTRICAL AXIS RANGE | nomally between -30 degrees and +90 degrees. |
LEFT AXIS DEVIATION | when the electrical axis is less than -30 degrees and can be caused by left ventricular hypertrophy, COPD, obesity, or an inferior myocardial infarction. |
RIGHT AXIS DEVIATION | when electrical axis is greater than +90 degrees and can be caused by right ventricular hypertrophy, an anterior-lateral myocardial infarction, pulmonary emboli, or normally occurs in tall thin adults |
PR INTERVAL | represents the time it takes electrical impulse to spread from the beginning of atria depolarization to the beginning of ventricular depolarization and is normally 0.12 to 0.20 seconds |
PR INTERVAL | calculated from the beginning of the P wave to the first Q wave deflection in the QRS complex. |
PROLONGED PR INTERVAL | may be caused by longer delay at the AV node, hypothyroidism, or various drugs. |
SHORTEND PR INTERVAL | suggests that the impulse has originated in areas other than the SA node. |
PR SEGMENT | is a component of the interval and is measured from the end of the P wave to ventricular depolarization. |
PR INTERVAL | if longer, AV node block |
QRS DURATION | the time it takes to complete depolarization within the ventricles. |
QRS DURATION | measured from the beginning of the Q wave to the end of the S wave and is normally between 0.08 to 0.11 seconds |
QRS - prolonged | prolonged time might suggest a bundle block or ventricular hypertrophy |
QT INTERVAL | is a measurement of the duration of the action potential and thus the refractory period in the ventricles and is calculated from the beginning fo the Q wave to the end of the T wave |
QT INTERVAL | changes with physical activity, calcium or potassium imbalances and various drugs. |
ST SEGMENT | part of the QRS interval and is measured from the end of the S wave to the beginning of the T wave. Represents the PLATEAU phase of the action potential |