Cardiac arrhythmias and heart blocks can interrupt the normal rhythm and pumping ability of the heart. The ECG waveforms will provide a picture of the heart’s electrical system. It is important that respiratory therapists be able to recognize and interpret ECG waveforms. The increased medical cost and healthcare reform forced many hospitals to consolidate departments in efforts to reduce operating costs. This process resulted in the respiratory therapy departments being called â€œCardiopulmonary Departments.â€ The name of the department implies that the respiratory therapist is responsible for cardiology and pulmonary duties supervised by a physician or cardiologist. Therefore, it is important that RT’s have an understanding of lung diseases as well as heart disease.
As mention earlier, the electrocardiogram (ECG) measures the electrical activity of the heart to show whether or not it is performing normally. In a previous course, you learned the proper placement of electrodes to perform ECG’s tracings. The placement of special electrodes on the patient’s chest, arms, and legs, and when prompted by the operator, the ECG machine records the heart’s rhythm and electrical activity on a moving strip of paper, or it may appear on a monitor screen.
A physician who specializes in reading the recording obtained from the ECG is called a cardiologist. The cardiologist evaluates the spikes and dips in the tracings referred to as waves. Each wave deflection on the ECG is preferred to as positive and negative waves described below.
- P wave
- Q wave
- R wave
- S wave
- T wave
The P Wave
The P wave is a small upward curve on an ECG tracing. This curve is the first deflection of a heartbeat indicating atrial depolarization. The beginning portion of the P wave is the right atrial depolarization, and the terminal portion is a reflection of left atrial depolarization. Almost immediately after the P wave begins the atria contract.
The P waves should all look alike and be no larger than 0.3mV (3 mm). Taller waves may indicate right atrial enlargement. Wider P waves may be caused by left atrial enlargement. Multiple P waves are seen with a second and third-degree heart block.
The Q Wave
When visible, the Q wave is an initial downward deflection after the P wave. A normal Q wave represents septal depolarization. A Q wave that is seen following a heart attack may be wide and deep. Because a heart attack may result in dead heart muscle, there is no conduction or current where the damage occurred, so the ECG picks up the current flowing away from this muscle, producing a strong negative deflection.
The R Wave
The R wave is the first upward deflection after the P wave, even when Q waves are absent. The R wave is normally the easiest waveform to identify on the ECG tracing, and it represents early ventricular depolarization. The R wave may be enlarged with a condition called ventricular hypertrophy. Factors such as a thin chest wall, obesity, or an athletic physique may reduce the size of the R wave.
The S Wave
The S wave is the first negative deflection after the R wave. It represents the late ventricular depolarization
The T Wave
The T wave is the represents repolarization of the ventricles. It is normally upright, somewhat rounded, and slightly asymmetric. Its shape will alter with breath-holding and digitalis toxicity. The T wave may be inverted or flat with myocardial ischemia, bundle branch block, ventricular hypertrophy, and ventricular ectopic beats.
The T wave may be tall and peaked with hyperkalemia. The elevated levels of potassium will decrease the duration of the refractory period and enhance repolarization. The T wave is flat and notched with conditions such as pericarditis, hypothyroid, and cardiomyopathies and flat without a notched with hypokalemia.
ECG Intervals and Segments
The cardiologist will evaluate the recording of other findings such as intervals and segment abnormalities, which relate directly to phases of cardiac conduction. Each one will be briefly discussed below:
The PR Interval
The PR interval represents the time the impulse takes to reach the ventricles from the sinus node. This interval begins at the beginning of the P wave and ends at the start of the QRS complex. Normal values are 0.12 to 0.20 seconds.
The PR Segment
The PR segment begins at the endpoint of the P wave and ends at the onset of the QRS complex. It represents the duration of the conduction beginning at the atrioventricular node as it travels to the bundle of His and the bundle branches down to the heart muscles stimulating a contraction.
The QRS Complex
The QRS complex starts at the Q wave and ends at the endpoint of the S wave. It is the duration of ventricular depolarization. Normally, all QRS complexes look alike. They are still termed QRS complexes even if all three waves are not visible.
The QT Interval
The QT interval is the duration of the depolarization to the repolarization of the ventricles. It begins at the onset of the QRS complex and ends at the endpoint of the T wave. The duration of the QT interval varies with the patient’s heart rate, gender, and age. Short QT intervals are seen with conditions such as hypercalcemia, hyperthyroidism, hyperkalemia, and digitalis toxicity.
A long QT interval can be noted in patients with slow heart rates, myocarditis, hypokalemia, hypocalcemia, myocardial disease, anorexia, congenital heart disease, and coronary heart failure, and can increase the risk of ventricular ectopic beats.
The ST Segment
The ST segment begins at the endpoint of the S wave and ends at the onset of the T wave. During the ST segment, the atrial cells are relaxed, and the ventricles are contracted, so electrical activity is not visible. The ST segment is normally isoelectric. When an ST-segment depression occurs, the ventricles are being starved of oxygen (normally due to blocked arteries), this is termed myocardial ischemia. An ST-segment elevation may also occur with a recent cardiac injury, ventricular aneurysms, prinzmetal’s angina (Links to an external site.), or pericarditis.
The RR Interval
The RR interval describes the time measurement between the R wave of one heartbeat and the R wave of the preceding heartbeat. RR intervals are normally regular but maybe irregular with sinus node disease and supraventricular arrhythmias.
Interpreting ECGs is a skill that is taught through an educational course or acquired from years of working in a critical care unit observing cardiac monitors. As vital members of a code team, respiratory therapists must be familiar with basic rhythms to adequately assess patients and recognize abnormalities when they are present. We will discuss advanced cardiac life support (ACLS) later in this course, and you will better understand the importance of ECG interpretation. This course will teach you how to Initiate ACLS protocols based on heart rhythms. These protocols will direct the administration of lifesaving cardiac drugs to patients in cardiac arrest. Before you continue in the lesson watch this short video on ECG/EKG Interpretation.
EKG/ECG Interpretation(Basic)- (Total time 12:23 minutes)
For this assignment answer each question in 150 words or more relating to the heart conduction system and ECG interpretation.
1. Discuss in detail the changes that occur in the cells of the heart conduction system.
2. Compare and contrast the depolarization and repolarization of the cardiac cycle.
3. List and discuss the three types of heart blocks. Describe in your answer clinical causes of heart blocks and how the conduction system and pumping of the heart affected by heart blocks.
4. Trace the blood flow through the heart; include all veins, valves, and arteries.
Submit this assignment in IWG formatted paper on a word document. You must cite at least three references in IWG format, with appropriate in-text citations.