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Influence of hypertension with minimal hypertrophy on diastolic function during demand ischemia
B H Lorell1, W N Grice, C S Apstein
1Cardiac Muscle Research Laboratory, Cardiovascular Institute of Boston University School of Medicine, Massachusetts.
Insights
Mild hypertension and early cardiac hypertrophy increase susceptibility to diastolic dysfunction during ischemia. This suggests early hypertensive changes, not just advanced disease, impair heart function under stress.
Area of Science:
- Cardiovascular Physiology
- Cardiac Pathophysiology
Background:
- Advanced pressure-overload hypertrophy from hypertension increases susceptibility to diastolic dysfunction during hypoxia/ischemia.
- It remains unclear if this propensity depends on significant left ventricular mass increase or mild, early hypertrophy.
Purpose of the Study:
- To test if systemic hypertension with mild left ventricular hypertrophy increases susceptibility to diastolic dysfunction during demand ischemia.
Main Methods:
- Isolated, isovolumic rabbit hearts (hypertensive vs. control) were subjected to 6 minutes of global ischemia and pacing tachycardia.
- Left ventricular pressures and coronary flow were monitored.
- Left ventricular end-diastolic pressure was measured during long diastoles.
Main Results:
- Hypertensive hearts had higher baseline systolic and developed pressures.
- During ischemia with tachycardia, left ventricular end-diastolic pressure significantly increased in hypertensive hearts compared to controls (29 +/- 3 vs. 18 +/- 2 mm Hg).
Conclusions:
- Systemic hypertension associated with mild left ventricular hypertrophy enhances susceptibility to diastolic dysfunction during demand ischemia.
- Early hypertensive cardiac changes, even without substantial mass increase, can impair diastolic function under ischemic stress.
Abstract:
Hearts with advanced pressure-overload hypertrophy from systemic hypertension have been shown to have an increased susceptibility to the development of diastolic dysfunction in response to tissue hypoxia and ischemia. It is not known if this propensity to develop diastolic dysfunction in response to ischemia is dependent on the presence of a substantial increase in left ventricular mass, or alternatively, is characteristic of hearts subjected to mild chronic hypertension early in the development of cardiac hypertrophy. We tested the hypothesis that systemic hypertension associated with mild left ventricular hypertrophy increases the susceptibility to the development of diastolic dysfunction in response to demand ischemia. The effects of demand ischemia (6 minutes) were studied in hearts from New Zealand white rabbits with chronic systemic hypertension produced by the one-kidney, one-wrap method (n = 15) and compared with age-matched, sham-operated control rabbits (n = 11) with similar left ventricular mass (5.4 +/- 0.2 vs. 5.4 +/- 0.3 g, respectively). The hearts were studied using an isolated, isovolumic (balloon in left ventricle) preparation with absent pericardium that was perfused with fresh whole blood. At baseline, coronary perfusion pressure was 100 mm Hg with comparable coronary flow per gram left ventricular weight; the hearts were paced at a physiological rate of 3 Hz, and the left ventricular balloon volume was adjusted to achieve a left ventricular end-diastolic pressure of 15 mm Hg in both groups. Left ventricular balloon volume was similar in both groups and volume was thereafter held constant. At baseline, left ventricular systolic pressure (114 +/- 4 vs. 95 +/- 3 mm Hg, p less than 0.001) and developed pressure (18.9 +/- 1.2 vs. 15.1 +/- 0.9 mm Hg/g, p less than 0.05) were higher in the hearts from the hypertensive group in comparison with the control group. During the first minute of global ischemia produced by reducing coronary perfusion pressure from 100 to 20 mm Hg, there was an immediate fall in left ventricular systolic pressure in both groups without an increase in diastolic pressure. In response to the superimposition of pacing tachycardia (heart rate, 6 Hz) during the remaining 5 minutes of the period of ischemia, left ventricular developed pressure was comparable. However, isovolumic left ventricular end-diastolic pressure (measured during long diastoles obtained with transient cessation of pacing) rose to a significantly higher level in the hearts from hypertensive rabbits than in those from the control rabbits (29 +/- 3 vs. 18 +/- 2 mm Hg, p less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)