7.4 ECG Patterns and Dysrhythmias
Abnormal ECG waveforms indicate dysrhythmias (also referred to as arrhythmias). Some dysrhythmias can significantly affect the client’s clinical status and require rapid nurse response. Early and accurate identification of ECG patterns, assessment of the client’s clinical presentation, and knowledge of the agency’s policies and procedures regarding treatment will ensure clients receive optimal care.
Recall that the electrical conduction system stimulates the mechanical pumping action of the heart. If the ventricles become unable to effectively pump blood to the rest of the body due to altered electrical signals, signs and symptoms of decreased cardiac output occur, such as decreased blood pressure and pulses, prolonged capillary refill, chest pain, shortness of breath, dizziness, confusion, or loss of consciousness. When an ECG demonstrates new abnormal findings, the nurse must immediately assess the client for signs of decreased cardiac output and respond appropriately.
Some dysrhythmias can quickly lead to cardiac arrest, such as ventricular tachycardia, ventricular fibrillation, and third-degree heart block. The nurse must be aware of which rhythms require emergency assistance.
Medical treatments for symptomatic dysrhythmias can include antidysrhythmic medications, cardioversion, defibrillation, and/or implantation of medical devices such as pacemakers and implantable cardioverter defibrillators (ICDs). Cardioversion and defibrillation are further discussed in the “Cardioversion and Defibrillation” section of this chapter.
ECG patterns are generally classified into three categories depending on whether the signal originates from the SA node (i.e, sinus rhythms), the atria (i.e., atrial rhythms), or the ventricles (i.e., ventricular rhythms). Additionally, heart blocks refer to blocks in the normal pathway of electrical conduction through the heart and can be categorized as sinus node, atrioventricular (AV) node, or bundle branch blocks. The characteristics of each of these types of rhythms and blocks are further discussed in the following sections. A table summarizing the ECG images discussed in this chapter can be found in the “Appendix of Rhythm Strips.”
Sinus Rhythms
Sinus rhythm is a regular rhythm, but the rate varies depending on autonomic nervous system regulation of the sinus node. When the rhythm is regular but there is an abnormal rate, it is called “sinus arrhythmia.” Sinus arrhythmias include sinus tachycardia and sinus bradycardia. Characteristics and treatment of sinus rhythms are summarized in Table 7.4a at the end of this subsection.
Normal sinus rhythm (NSR) originates from the sinus node and describes the characteristic rhythm of a healthy human heart. All components of the ECG waveform are within normal limits. See Figure 7.16[1] for an image of normal sinus rhythm.
A sinus rhythm faster than a normal rate (i.e., greater than 100 in adults) is called a sinus tachycardia. Sinus tachycardia is