Exercise and Diabetes. Sheri R. Colberg

with diabetes, however, identification of cardiovascular risk factors and risk stratification may assist health-care providers in justifying the use of graded exercise testing, but is not currently recommended (Bax 2007). In any case, all decisions regarding the necessity of such testing should attempt to more effectively target the select individuals at higher risk for underlying cardiovascular disease (Sigal 2004). For example, individuals with silent myocardial ischemia have a poorer prognosis than those with normal stress tests,

      and their risk is further accentuated if cardiac autonomic neuropathy coexists

      (ADA 2013).

       Use of Stress Testing to Detect Ischemia

      A systematic review for the U.S. Preventive Services Task Force (2004) concluded that stress testing should not be routinely recommended to detect ischemia in asymptomatic individuals with a low coronary risk (<10% risk of a cardiac event over 10 years) because the risks resulting from the invasive testing done after a false-positive test outweigh the benefits of detection (Fowler-Brown 2004). Individuals who exhibit nonspecific electrocardiograph changes in response to exercise or who have nonspecific ST- and T-wave changes at rest may need follow-up testing. The Detection of Ischemia in Asymptomatic Diabetics (DIAD) trial involving 1,123 individuals with T2D and no symptoms of coronary artery disease, however, found that screening with adenosine-stress radionuclide myocardial perfusion imaging for myocardial ischemia over 4.8 years did not alter rates of cardiac events (Young 2009). Therefore, the cost-effectiveness and diagnostic value of more-intensive testing remain in question (Sigal 2004, 2006; Colberg 2010).

      Case in Point: Event Discussion

      At the end of 12 weeks of intense aerobic training and just before starting his resistance workouts, AB is being instructed on the use of the resistance equipment by his personal trainer when he falls to the floor following a short cardio warm-up and goes into full cardiac arrest within 5 min. The community center houses an automated external defibrillator (AED), which his personal trainer brings to his side while a concerned onlooker calls 911 to summon emergency medical assistance. The AED indicates that AB needs cardioversion, and his trainer initiates the shock that restarts AB’s heart before the paramedics arrive on the scene from a nearby fire station another 5 min later.

      Following this event AB is hospitalized, but no myocardial damage is found. His cardiac arrest is determined to have been caused by a potentially fatal arrhythmia (ventricular fibrillation), which was found after later review of the rhythm recorded by the AED during the event. Upon further examination by a cardiologist, AB is found to have 100% blockage of one of his primary coronary vessels (left anterior descending) but appears to have developed collateral circulation there, likely as the result of the vigorous exercise training program that he undertook before having this event, which prevented any infarction of the myocardium in the area fed by that vessel. Thus, it is decided that his cardiac arrest was simply caused by the arrhythmia initiated by the agitated state of his heart as a result of the blockage. Following bypass surgery, he is released from the hospital and cleared to participate in cardiac rehabilitation after a few weeks.

      Additional Questions to Consider

      1. Should the pretraining medical and exercise stress testing have been able to detect AB’s coronary artery disease before it became potentially fatal?

      2. Is there another form of testing that AB should have undergone before starting his training?

      3. Did the intense exercise training actually help or hurt AB, given his undiagnosed cardiovascular disease?

      (Continued)

       Testing of Low-Risk Individuals for Fitness Assessment

      Although graded exercise testing currently is advised primarily for previously sedentary people with diabetes who want to undertake activity more intense than brisk walking to assess cardiovascular risk (Sigal 2006, Colberg 2010), in some cases, testing (with or without ECG monitoring of heart function) may be undertaken for other purposes. In addition to diagnosing or defining the prognosis of known cardiac disease, exercise stress testing is presently used to assess physical fitness, determine functional capacity, prescribe an exercise plan, and guide cardiac rehabilitation training. With these alternate assessments in mind, the aforementioned risk-based criteria do not exclude the possibility of conducting graded exercise stress testing on individuals with a low risk of cardiovascular disease or those who are planning to engage in less-intense exercise (Stevens 2001). In the absence of contraindications to maximal stress testing, it still can be considered for anyone with T1D or T2D who simply wants to assess his or her fitness level or use the maximal or peak results to determine appropriate exercise training intensities and other fitness goals. Although clinical evidence does not definitively determine who should never consider undergoing such testing, potential benefits should be weighed against the risk associated with unnecessary procedures for each individual, especially in individuals with a higher risk profile (Kothari 2002, Sigal 2004).

       Pre–resistance Training Exercise Testing

      As for resistance training, no studies have yet addressed whether pre-exercise stress testing is necessary or beneficial before participation in such activity. At present, most testing centers are equipped for maximal stress testing, but not for an alternate form of testing involving resistance exercise. Because coronary ischemia is less likely to occur during resistance compared with aerobic exercise eliciting the same heart rate, resistance exercise may not even induce ischemia in most individuals (Ghilarducci 1989, Featherstone 1993). A review of 12 studies of resistance exercise in men with known coronary artery disease reported no angina, ST-segment depression (indicative of coronary ischemia), abnormal hemodynamics, ventricular dysrhythmias, or other complications during such exercise (Wenger 1995).

      Case in Point: Wrap-Up

      AB was completely asymptomatic of coronary artery disease before this event, and it was not detected by a graded exercise test, which shows that this testing is not infallible and far from conclusive. Given his lack of any cardiac symptoms, it would not have been advisable—either from a medical standpoint or a financial one—to recommend or require additional, possibly more invasive, testing of his cardiovascular status before this event.

      Finally, the intense exercise training that AB had completed before this event was completely appropriate under the circumstances and, in fact, it likely helped save his life by stimulating the growth of new, collateral vessels that prevented myocardial damage despite full blockage of a crucial coronary artery feeding the left ventricle. Effectually, his exercise participation saved his life twice: once by stimulating the growth of new collateral circulation to his heart and again by placing him in a facility that had an AED available to treat him during his event. AB later said to his personal trainer that had his event occurred on the golf course, where he had spent the whole day before, he likely would not have survived it.

      For most people with diabetes, low-level physical activities can be undertaken without the need for a medical exam or graded exercise test that potentially could create barriers to participation. In some cases, however, higher-risk individuals desiring to undertake moderate- or vigorous-intensity exercise training may benefit from undergoing a medical evaluation and possible stress testing with ECG before participation to diagnose pre-existing cardiovascular problems that may make such training more risky.

      Professional Practice Pearls

      • Most individuals diagnosed with diabetes should consult a health-care provider before beginning an intense physical activity program, but an absolute requirement to do so in all cases would create unnecessary barriers to participation in low-level activities.

      • Before undertaking new higher-intensity physical activity, providers may use their judgment in recommending whether individuals with any type of diabetes should undergo a detailed medical evaluation and screening.

      • For individuals wishing to participate in low-intensity activities only, pre-exercise testing is likely not beneficial, and providers should use their clinical judgment in deciding whether to recommend it.

      • Graded exercise testing should not be routinely recommended to detect ischemia in asymptomatic individuals