A nurse is caring for a client who has myasthenia gravis. The nurse should recognize that this disease is caused by which of the following types of hypersensitivities?

The P wave is the first wave on the ECG strip and represents the electrical activity of the atria. It reflects the depolarization of the atrial myocardium, which is the process of changing the electrical charge of the cardiac cells from negative to positive, triggering a contraction. The P wave precedes the QRS complex, which represents ventricular depolarization, and the T wave, which represents ventricular repolarization.

The other options are not correct because:

a. Slow repolarization of ventricular Purkinje fibers. This statement is incorrect because it describes the U wave, which is a small and sometimes invisible wave that follows the T wave on the ECG strip. It reflects the repolarization of the ventricular Purkinje fibers, which are specialized cardiac cells that conduct electrical impulses to the ventricles. The U wave is more prominent in conditions that cause hypokalemia, such as diuretic use or vomiting.

c. Early ventricular repolarization. This statement is incorrect because it describes the ST segment, which is the flat line between the QRS complex and the T wave on the ECG strip. It reflects the early phase of ventricular repolarization, which is the process of restoring the electrical charge of the cardiac cells to negative after a contraction. The ST segment can be elevated or depressed in conditions that cause myocardial ischemia or injury, such as angina or myocardial infarction.

d. Ventricular depolarization. This statement is incorrect because it describes the QRS complex, which is the largest and most visible wave on the ECG strip. It reflects the depolarization of the ventricular myocardium, which triggers a ventricular contraction. The QRS complex follows the P wave and precedes the T wave on the ECG strip.

Phenytoin is an anticonvulsant medication that is used to prevent and treat seizures. It works by stabilizing the electrical activity of the brain and reducing the spread of abnormal impulses. Phenytoin is usually taken for life or until the seizures are controlled by other means, such as surgery or diet. The client should not stop taking phenytoin without consulting their doctor, as this can cause withdrawal symptoms or increase the risk of seizures.

The other options are correct and indicate that the client understands the discharge teaching because:

1. "I have made an appointment to see my dentist next week." This statement is correct because phenytoin can cause gingival hyperplasia, which is an overgrowth of gum tissue that can lead to bleeding, infection, or difficulty chewing. The client should practice good oral hygiene and see their dentist regularly to prevent or treat this condition.

1. "I will notify my doctor before taking any other medications." This statement is correct because phenytoin can interact with many other medications, such as antibiotics, anticoagulants, oral contraceptives, or antacids. These interactions can affect the blood levels and effectiveness of phenytoin or the other medications, causing adverse effects or reduced seizure control. The client should inform their doctor of any other medications they are taking or planning to take, including over-the-counter, herbal, or dietary supplements.
2. "I know that I cannot switch brands of this medication." This statement is correct because different brands of phenytoin may have different formulations or bioavailability, which can affect the absorption and metabolism of the drug. Switching brands can cause changes in the blood levels and effectiveness of phenytoin, leading to toxicity or reduced seizure control. The client should always use the same brand of phenytoin and check with their pharmacist if they notice any changes in the appearance or labeling of their medication.