A 60 y/o woman is evaluated in Preoperative Anesthesia Assessment Clinic. TSH and Free T4 levels are ordered after review of systems reveals cold intolerance, swollen ankles, and poor energy level. Which of the following best describes the circulatory changes seen in hypothyroidism?
Heart Rate | Peripheral Vascular Resistance | Cardiac diastolic function
A Bradycardia | Unchanged | Unchanged
B Tachycardia | Decreased |Unchanged
C Tachycardia | Increased | Impaired
D Bradycardia | Increased | Impaired
Correct answer:
D
Key concepts:
Hypothyroidism is associated with decreased cardiac contractility, cardiac output, diastolic function, and heart rate. Hypertension (primarily diastolic) is common, with increased peripheral vascular resistance.
The reduced LV function has several causes including increased afterload (high periph vasc resistance) and altered expression of genes encoding calcium regulatory proteins. Beta-adrenergic receptor expression is also reduced, leading to blunted inotropy in response to catecholamines.
Since thyroid hormone mediates vascular smooth muscle relaxation, it makes sense that thyroid deficiency results in increased peripheral vascular resistance.
Characteristic EKG changes include low voltage with nonspecific ST segment and Q wave changes. Pericardial effusion is common and may be large but is not often associated with tamponade physiology.
Nonpitting dependent edema is due to accumulation of glycosaminoglycans (i.e. hyaluronic acid and chondroitin sulfate), along with some extravascular water. Intravascular volume is often reduced.
Resources:
1. Klein I, Cardiovascular effects of hypothyroidism in UpToDate, last updated 2020
2. Wall RT III. Endocrine Disease, chapter 23 in Stoelting’s Anesthesia and Co-existing Disease, seventh edition; Hines RL & Marschall KE eds, 2018.