Increased blood pressure and neural tone in the silent ischemia of hypertension: disparate effects of immediate release nifedipine
DD Lee,
K Rigonan,
and
V Dequattro
Clinical Hypertension Service, University of Southern California School of Medicine, Los Angeles 90033.
OBJECTIVES. The aims of this study were 1) to evaluate the role of blood pressure and associated neural tonicity in ambient ischemia of a group of hypertensive patients with stable angina, and 2) to determine the efficacy of immediate release nifedipine therapy in controlling the total ischemic burden in both office-measured and ambulatory blood pressure. BACKGROUND. Low heart rate ischemia, as detected by Holter ambulatory electrocardiographic monitoring, suggests that reduced coronary flow is the major factor leading to ischemia. We previously found that 91% of the ischemic episodes in our hypertensive patients with stable angina were silent. METHODS. We measured plasma norepinephrine content during ischemic events from blood obtained from automatic pump withdrawal with the assistance of a real-time ST segment depression monitor. We then related the norepinephrine content to ischemic episodes assessed by 48-h Holter recording, blood pressure reading by ambulatory blood pressure monitoring and patients' diaries. Measurements were taken during the placebo period and immediate-release nifedipine therapy in 30 hypertensive patients (20 with and 10 without stable angina). RESULTS. More than half of the patients had ischemic episodes; 95% of these were silent. Ischemic episodes peaked in the early morning, and 55% occurred during routine sedentary activities. There was a 10% to 15% increase in heart rate at the onset of ischemia associated with a 30% higher plasma norepinephrine level. Seventy-five percent of patients had increased norepinephrine after nifedipine therapy. Nifedipine therapy controlled measured blood pressure but not 24-h ambulatory blood pressure. Ischemic episodes were reduced only in patients whose ambulatory blood pressure was controlled. CONCLUSIONS. The results suggest that increased neural tone at the time of the ischemic event may play a role in reducing coronary perfusion leading to silent ischemia. Nifedipine therapy (immediate release) was effective in control of ischemia only when both ambulatory and office-measured blood pressure were controlled.
