Hypertension Blog

A 12-lead ECG, which records the electrical activity of the heart, may help in diagnosing cardiac complications of hypertension such as left ventricular hypertrophy, myocardial ischemia, an MI, and arrhythmias.

Nursing Considerations

Before obtaining a 12-lead ECG, document any antihypertensive drugs your patient is taking. Some of these drugs produce effects that show up on the ECG such as sinus bradycardia or tachycardia, heart block, or a prolonged QT interval. Diuretics in particular may cause electrolyte abnormalities that alter the ECG.

If a hypertensive patient complains of chest pain, evaluate his 12-lead ECG for ischemic changes. Perform the ECG before administering pain-relieving drugs so that you’ll have a base­line ECG. If the patient is using antianginal drugs, repeat the ECG as appropriate to assess his response to therapy.

Test Implications

If the patient has left ventricular hypertrophy, the ECG shows some characteristic changes:

• The QRS complex shows left-axis deviation.
• The Rand S waves of the QRS complex increase in amplitude or depth.
• The ST segment is depressed.
• The T wave is inverted in certain leads .

If the patient has myocardial ischemia, you’ll note ST-segment and T-wave changes. The ST segment, which represents repolarization (the period of recovery after ventricular activation), normally appears flat on the ECG tracing. When coronary blood flow to the myocardium diminishes, however, the ST segment becomes depressed, and the normally upright T wave becomes inverted. Less commonly, ischemia causes an ST-segment elevation.

If a hypertensive patient is taking a diuretic, he may be at risk for developing electrolyte imbalances, which can precipitate arrhythmias. Thiazide diuretics can produce hypercalcemia, which may cause shortening of the ST segment and QT interval. Diuretics also cause hypokalemia, which can lead to ventricular ectopy. ECG abnormalities caused by hypokalemia include ST-segment depression, which can make assessment of ischemic changes difficult; decreased T-wave amplitude; and, occasionally, T-wave inversion.