Cumulative deterioration of myocardial function after repeated episodes of exercise-induced ischemia

Abstract

To determine whether progressive regional myocardial dysfunction occurs after repetitive episodes of exercise-induced ischemia, 10 dogs were instrumented with ultrasonic microcrystals for determination of regional myocardial wall thickening, circumflex artery electromagnetic flow probes, and hydraulic coronary artery occluders. Dogs performed treadmill exercise in the presence of a coronary artery stenosis, which limited coronary blood flow to control levels. Dogs performed a single 10-min exercise period one day and three identical runs separated by 1-h rest periods on the alternate day. At rest before the first exercise period, circumflex wall thickening was 18.8 +/- 6.7% and increased to 25.5 +/- 10.6% during exercise before the application of coronary stenosis. On the day that three exercise trials were performed, circumflex systolic wall thickening at rest before the third exercise period (9.7 +/- 4.0%) and during exercise without coronary stenosis (17.3 +/- 7.3%) were both significantly lower than during the first exercise period (P less than 0.0125). During exercise with stenosis, circumflex systolic wall thickening fell to 4.6 +/- 4.7% during a single run, and 5.0 +/- 2.0% during the third of three consecutive runs. Wall thickening was significantly lower 2 h after the third consecutive run (9.1 +/- 2.4%) than 2 h after a single period of exercise-induced ischemia (14.8 +/- 7.6%; P 0.0125). Transmural myocardial blood flow to circumflex myocardium during the third period of exercise-induced ischemia (0.93 +/- 0.47 ml.min-1.g-1) was not different than during the single period of exercise (0.84 +/- 0.47 ml.min-1.g-1). It is concluded that repetitive episodes of exercise-induced ischemia result in cumulative postexercise regional myocardial dysfunction.

Hemodialysis-Induced Repetitive Myocardial Injury Results in Global and Segmental Reduction in Systolic Cardiac Function

“…Intradialytic hypotension (IDH) is known to be associated with increased mortality. Given the underlying vulnerability of hibernating myocardium to increases in demand (12) coupled with decreased coronary flow reserve in HD patients, it may be that this adaptive process actually leads to further segmental injury by exacerbating intradialytic instability. This may be one of the reasons that prevalence of heart failure is so high and survival so poor in HD patients.…”

“…In the nondialysis population, repeated episodes of demand ischemia and stunning can result in chronic reduction in left ventricular (LV) function (12). This observation led to the hypothesis that repeated episodes of myocardial ischemia leads to a spectrum of disease-encompassing myocardial stunning through to myocardial hibernation (13) and ending in myocardial remodeling and scarring (14).…”

Medical and Cellular Implications of Stunning, Hibernation, and Preconditioning

“…1 Animal studies have shown that repeated brief bouts of ischemia have a cumulative effect on contractility, such that the duration and severity of myocardial stunning greatly exceed those induced by a single ischemic episode. 7,9,25,33,72,73 If regional perfusion is not measured simultaneously with regional contractile function, the protracted but ultimately reversible dysfunction associated with repetitive stunning may mimic myocardial hibernation. 74 With repetitive stunning, regional perfusion should recover while function remains depressed.…”

Frequent Hemodialysis Schedules Are Associated with Reduced Levels of Dialysis-induced Cardiac Injury (Myocardial Stunning)

“…It is becoming clear that processes relating to the dialysis procedure itself are implicated. In the nonuraemic population, recurrent myocardial stunning (resulting from coronary artery disease) contributes to development and progression of myocardial injury resulting in heart failure (6,7). Studies have demonstrated that standard HD induces global and segmental cardiac ischemia (8,9).…”