33
involved in high endurance training [ 30 , 53 ]. Tipically, this arrhythmia is paroxys-
mal self limiting AF and occurs during the night or after meals, demonstrating that
the vagal overtone is an important trigger.
4 Left Ventricle
In the last 35 years, the development of echocardiographic technique has allowed to
study the adaptation of the LV to physical exercise in order to discriminate the
physiological adaptation from the pathologhycal changes. The two principal catego-
ries of exercise (strength and endurance) determine different adaptations of the LV,
as hypothized by Morganroth [ 54 ]. According to this hypothesis, endurance training
would lead a volume overload and, so to an increased diastolic wall stress. The
adaptation of the LV to this work is eccentric ventricular hypertrophy (increase of
both ventricular mass and ventricular cavity dimension). In contrast, strength train-
ing determines pressure overload and increased systolic wall stress. In this case the
answer of the LV is a concentric hypertrophy (increase of ventricular mass and of
wall thickness with normal cavity dimension). Both of them result in increased LV
mass. LV hypertrophy is definided by a LV mass index >115 g/m^2 in male and
95 g/m^2 in female. The relative wall thickness (2 × posterior wall thickness/LV
internal end-diastolic diameter) defines the type of hypertrophy: eccentric when the
relative wall thickness is ≤0.42, concentric when the relative wall thickness is >0.42
[ 55 ].
The “Morganroth Hypothesis” has some limitations because some types ofsports, such as cycling and rowing, imply both endurance and strength exercise, and
the hypertrophy results in an intermediate phenotype (Fig. 2.3). Furthermore, espe-
cially with strength exercise, the phenotype could be not completely explained
because of the confounding factor of the drug abuse (for example steroids).
Generally, athletes show a 10–20% increase of the wall thickness and 10–15%enlargement of the cavity [ 48 ] compared with individual of similar age and size.
The LV enlargement is always proportionate to the enlargement of the other cardiac
chambers. Adaptations of right chambers to the physical exercise are visible right
after a prolonged physical training, instead the LV adaptation to the exercise become
visible after a period of training of several months. In fact in adolescent athletes, the
magnitude of this modifications is lower because of the shorter period of training
[ 56 – 58 ]. The LV adaptation regresses after a period of de-training of about 3
months. After this “physical de-conditioning”, it has been demonstrated a reduction
of 15–33% of the septal wall thickness, whereas the reduction of both septal thick-
ness (of about 15%) and LV cavity dimension (of about 7%) may be observed after
a period of 1–13 years of de-training. This demonstrated that the LV cavity reduce
more slowly and slightly than the LV wall thickness. The regression of the “ath-
lete’s heart” allows to make differential diagnosis with the pathologic hypertrophy
(DCM and HCM). In these cardiomyopathies, the hypertrophy do not decrease
after a period of de-training. Other aspects of the cardiomyopathies help to make
2 Acute and Chronic Response to Exercise in Athletes: The “Supernormal Heart”