ECG Basic Principles Flashcard 2

A. Rationale: If the net voltage flowing to the positive or negative end of the electrodes of the ECG machine is 0 millivolts, then the ECG tracing will reflect a flat line or asystole.

D. Rationale: The escape beat is an impulse generated by the Purkinje fibers to force the conduction system within the ventricles to produce an action potential. This only occurs if the sinoatrial node impulses are delayed.

Answer choice A – Torsade’s de pointes is a cardiac dysrhythmia related to decreased magnesium levels.
Answer choices B & C – Premature atrial beats and premature ventricular beats are action potentials produced by an irritable conduction cell that disturbs the normal sinus rhythm.

B. Rationale: An electrocardiogram (ECG) machine measures the galvanic energy produced by the heart and transmitted to the skin. It uses electrodes to detect this energy and translate them into a graph. The output is an ECG tracing that records the amplitude of the electrical vector over time.

A. Rationale: The P wave represents atrial depolarization. The impulses from the P wave come from the sinoatrial node.

Answer choice B – The QRS complex represents ventricular depolarization.
Answer choice C – The T wave represents ventricular repolarization.
Answer choice D – The U wave represents repolarization of the Purkinje fibers.

A. Rationale: A sinus rhythm pattern has an upward deflection of the P wave and a PR interval of 0.12–0.2 seconds. The remaining choices are not characteristic of sinus rhythm. A saw-tooth appearance represents atrial flutter, while a PR interval of 0.25 seconds is prolonged, representing an AV block.

D. Rationale: To systematically analyze an ECG tracing ensures that nothing is missed. The correct order in analyzing the ECG strip involves (1) Determine rhythm, (2) Determine the presence of a P-wave, (3) Determine the rate, (4) Measure the PR interval, and (5) Measure the QRS duration. Determining the rhythm gives the reader an idea if there is an arrhythmia, which represents an irregular rhythm pattern. The presence of a P wave determines if the impulse is generated from the atrium. The rate identifies if the patient has bradycardia or tachycardia. The PR interval indicates normal AV conduction or an AV block. A prolonged QRS complex may point to an impulse generated from the ventricles or a bundle branch block.

C. Rationale: There are 4 types of cardiac arrest rhythms: (1) ventricular fibrillation, (2) pulseless ventricular tachycardia, (3) pulseless electrical activity, and (4) asystole. Pulseless electrical activity and asystole are cardiac arrest rhythms that are non shockable. Supraventricular tachycardia is not a cardiac arrest rhythm.

A normal or typical sinus ECG wave is labeled alphabetically, starting with the P wave, followed by the QRS complex, and then a T wave.

C. Rationale: A 12-lead ECG report must have all of the above information for a complete study. A normal rhythm has a regular R-R interval, a rate between 60 and 100 bpm, a normal P wave morphology, a normal PR interval, and a normal QRS complex. Therefore, each study must indicate regularity, rate, the presence of a P wave, the PR interval, and the QRS complex. Additional patterns such as ST depression or ST elevation must also be included if the patient is suspected of having myocardial ischemia or infarction.

A. Rationale: ST elevation represents a myocardial infarction.

Answer choice B – Myocardial ischemia manifests as ST depression.
Answer choice C – Stable angina does not typically produce ECG changes.
Answer choice D – Atrial fibrillation manifests as fibrillatory waves on ECG as the atria are “quivering” as opposed to contracting normally.