Acute coronary syndromes (ACSs), in particularly, acute myocardial infarction (AMI),
kill
or debilitate a large number of patients in the world. Despite the fact that not all
patients develop ventricular dysfunction after the event, there is still a high
prevalence of post-AMI heart failure,
1,2
which is considered a public health
problem. Although the management of post-ACS is based on a wide range of drugs, usually
associated with the revascularization procedure, different non-pharmacological
strategies have been shown useful. In this regard, physical exercise is
indicated,
3
including cardiac
rehabilitation programs that usually combine aerobic and resistance training with
stretching exercises.
Nevertheless, there is no single recipe for prescribing exercise after an acute coronary
event. In my opinion, cardiologists should formally prescribe physical exercise in
addition to cardiovascular drugs, considering aspects such as dosage, intervals,
intensity and potential side effects. With respect to physical training, a vast of
different exercise modalities have emerged and applied in health. Pilates, Tai Chi
Chuan, functional training, crossfit, high-intensity interval training (HIIT) among
others have spread across gyms and physical centers over the country and have been
practiced primarily by apparently healthy individuals. As time passed, animal
experiments and clinical studies on cardiovascular disease patients have been
conducted.
4-7
HIIT was first proposed to Japanese Olympic skaters by
Izumi Tabata. Today, HIIT consists in sessions of one to four-minute of high-intensity
submaximal load alternating with low-to-moderate intensity exercises. Randomized
clinical trials involving small samples have suggested a superiority of the method
in
increasing peak oxygen uptake (VO2peak) as compared with conventional
continuous training. Due to its peculiarities and results, HIIT has boomed all over
the
world; however, international literature showing the impact of the method in ischemic
heart disease patients, particularly in post-AMI patients is still lacking.
4,8,9
In this journal issue, Winter et al.
10
report information on the effects of HIIT on functional capacity and ventricular
function in 29 Wistar rats after AMI. On day 21 after the event, the animals were
randomized to control group (n = 10), or to undergo continuous training (n = 9) or
HIIT
(n = 10). All animals had ejection fraction equal to or greater than 50%, i.e., without
ventricular dysfunction. An important finding was that the authors did not find within-
or between group differences in echocardiographic findings before and after training
in
the animals allocated to continuous training or to HIIT. The authors suggest that
both
methods can increase functional capacity without altering ventricular function
(remodeling). Based on this, one may ask the following question: can patients at early
stage after AMI, without ventricular dysfunction, undergo this type of physical
training?
In a classical study by Wisloff et al.,
5
the authors evaluated three groups of elderly patients with heart failure and reduced
ejection fraction (HFrEF), who were clinically stable and had had a myocardial
infarction more than one year before the study. Patients were randomized to control,
moderate continuous training (MCT) or HIIT group.
5
Individuals assigned to HIIT showed improved peak
VO2, left ventricular remodeling and reduced natriuretic peptide (BNP) levels
as compared with MCT. Also, a meta-analysis involving 160 patients showed that interval
training (regardless of its intensity) increased peak VO2 in HFrEF
patients.
11
Similarly, in a
meta-analysis including 230 patients, Elliott et al.
12
reported that interval training seems to increase peak
VO2 in patients with stable coronary artery disease.
12
In the last years, different strategies that can be included in early post-acute
rehabilitation programs have emerged, such as Tai Chi Chuan.
13
In any case, all interventions that may improve
patients’ recovery and functional capacity, and whenever possible, increase patients’
survival should be used. With respect to the applicability of HIIT in the management
of
early post-AMI patients, it may be speculated that the method is efficient in improving
peak VO2, an important prognostic marker. In fact, in the world of coronary
stents and since post-AMI myocardial function is preserved in many patients, HIIT
may be
an attractive training strategy for some patients. On the other hand, the body of
scientific knowledge is not sufficiently consistent to definitely recommend HIIT as
a
training modality for early post-AMI patients. Anyway Winter et al.,
10
in their investigation on laboratory
animals, take an important step towards an effective alternative for cardiac
rehabilitation programs in this group of patients.