EFFECT OF HEART RATE, EXERCISE, AND NITROGLYCERIN ON THE CARDIAC DYNAMICS IN COMPLETE HEART BLOCK

Genetic influence on electrocardiogram time intervals and heart rate in aging mice

Understanding the genetic influence on ECG time intervals and heart rate (HR) is important for identifying the genes underlying susceptibility to cardiac arrhythmias. The objective of this study was to determine the genetic influence on ECG parameters and their age-related changes in mice. ECGs were recorded in lead I on 8 males and 8 females from each of 28 inbred strains at the ages of 6, 12, and 18 mo. Significant interstrain differences in the P-R interval, QRS complex duration, and HR were found. Age-related changes in the P-R interval, QRS complex duration, and HR differed among strains. The P-R interval increased with age in 129S1/SvlmJ females. The QRS complex duration decreased with age in C57BR/J males and DBA2/J females but increased in NON/ShiLtJ females. HR decreased in C57L/J females and SM/J and P/J males but increased in BALB/cByJ males. Differences between males and females were found for HR in SJL/J mice and in the P-R interval in 129S1/SvlmJ mice. Broad-sense heritability estimates of ECG time intervals and HR ranged from 0.31 for the QRS complex duration to 0.52 for the P-R interval. Heritability estimates decreased with age for the P-R interval. Our study revealed that genetic factors play a significant role on cardiac conduction activity and age-related changes in ECG time intervals and HR.

Artificial pacing by electrode catheter for heart block or asystole complicating acute myocardial infarction

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Effect of nitroglycerin on cardiovascular function at fixed and at variable heart rate

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CORONARY FLOW, BLOOD PRESSURE, AND HEART RATE DOSE–RESPONSE CHANGES AFTER NITROGLYCERIN ADMINISTRATION

Changes in left circumflex coronary flow, femoral blood pressure, and heart rate (ECG-Lead II) were recorded simultaneously in pentobarbitalized artificially respired open-chest dogs. A gated sine wave electromagnetic flowmeter was used for coronary flow measurements. After intravenous nitroglycerin (glyceryl trinitrate) administration in six satisfactory experiments, changes in dose–response patterns were studied. (1) Doses of 0.1 μg/kg were ineffective; doses of 1.0, 10, and 100 μg/kg induced in 10 to 15 seconds maximal increases in mean coronary flow averaging 22, 65, and 100%, respectively; blood pressure concurrently decreased showing a maximum fall (in 20 to 25 seconds) associated with reflex tachycardia; a transient initial increase in pulse pressure also occurred. (2) Coronary flow subsequently decreased, reaching below-control values; the magnitude of this decrease appeared to be related to the degree of fall in blood pressure and to the reflex tachycardia; and pulse pressure markedly decreased below the control values. (3) After intravenous injections of pentobarbitone sodium (1 and 10 mg/kg) brief initial (within 10 seconds) dose-related increases in coronary flow were also observed but associated with less-marked blood pressure decreases and no significant changes in either heart rate or pulse pressure.