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Changes in diastolic time with various pharmacologic agents: implication for myocardial perfusion
Insights
Cardioactive drugs significantly alter percent diastole (%D), a measure of diastolic time relative to heart rate. Some drugs increase %D by slowing heart rate or shortening systole, while others decrease it.
Area of Science:
- Cardiology
- Pharmacology
- Physiology
Background:
- Diastolic time (DT) is crucial for coronary blood flow, particularly in conditions like coronary artery disease and left ventricular hypertrophy.
- Percent diastole (%D), calculated as (RR-QS2)/RR * 100, is a key indicator of diastolic function and varies nonlinearly with heart rate (HR).
Purpose of the Study:
- To investigate the effects of common cardioactive agents on percent diastole (%D) in normal subjects.
- To determine whether these drugs influence %D by altering heart rate (HR) or electromechanical systole (QS2).
Main Methods:
- Five groups of normal subjects received different cardioactive agents: propranolol, dobutamine, Cedilanid-D, isoproterenol, and lidocaine.
- Measurements included RR interval (cycle length) and QS2 (electromechanical systole) to calculate %D.
- Statistical analysis was performed to assess significant changes in %D.
Main Results:
- Propranolol and Cedilanid-D significantly increased %D by slowing HR and/or shortening QS2.
- Dobutamine increased %D primarily by shortening QS2.
- Isoproterenol significantly decreased %D despite shortening QS2 due to increased HR.
- Lidocaine had no significant effect on %D.
Conclusions:
- Cardiovascular drugs can significantly impact the relative duration of diastole (%D) through effects on heart rate and/or systolic duration.
- These findings have potential clinical implications for managing patients with conditions where diastolic filling is critical for coronary perfusion.
Abstract:
Diastolic time (DT) is calculated as the cycle length (RR) minus electromechanical systole (QS2). The ratio of DT (RR-QS2) to RR interval times 100, or the percent diastole (%D), varies nonlinearly with heart rate (HR), increasing rapidly with decreasing HR. The effect of commonly used cardioactive agents on %D was studied in five groups of normal subjects. In group 1 (n = 12), propranolol (160 mg daily) increased %D from 55.9 +/- 1.7 to 64.7 +/- 1.3 (p less than 0.001) by slowing HR. In group 2 (n = 12), dobutamine (2.5 micrograms/kg/min) increased %D from 56.4 +/- 1.4 to 61.8 +/- 1.3 (p less than 0.005) by shortening the QS2. In group 3 (n = 10), Cedilanid-D (1.6 mg i.v.) increased %D from 55.5 +/- 1 to 63.2 +/- 0.7 (p less than 0.001), both by slowing the HR and shortening the QS2. In group 4 (n = 12), isoproterenol (2 micrograms/min) increased HR and shortened the QS2 significantly. The net result was a significant reduction of %D from 56.1 +/- 1.4 to 53.5 +/- 1.1, (p less than 0.05). In group 5 (n = 15), a 100-mg bolus of i.v. lidocaine did not have a significant effect on %D. This study indicates that cardiovascular drugs may have significant effects on the relative duration of diastole either by affecting HR or the duration of systole. This may have clinical implications for patients with coronary artery disease and patients with left ventricular hypertrophy, since in both cases coronary flow in mostly diastolic.