JACC: CARDIOVASCULAR IMAGING
VOL. 8, NO. 7, 2015
ª 2015 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
ISSN 1936-878X/$36.00
PUBLISHED BY ELSEVIER INC.
http://dx.doi.org/10.1016/j.jcmg.2014.12.031
EDITORIAL COMMENT
Athletic Left Atrial Dilation Size Matters?* Aaron L. Baggish, MD
T
he cardiovascular system’s ability to generate
mild wall thickening in the absence of chamber dila-
high cardiac output is essential for athletic
tion. Sport-specific right ventricular adaptations have
performance, and its failure underlies many
similarly been documented (5). To date, the literature
forms of disease. During exercise, the heart and ves-
on the athlete’s heart has been dominated by studies
sels circulate energy-rich substrate to exercising
that focused on ventricular characteristics, with atrial
muscle and simultaneously remove the metabolic
structure and function receiving comparatively little
byproducts of muscular metabolism. This process
attention. Atrial metrics among athletes, with a few
occurs in an elegant and coordinated fashion whereby
notable exceptions (6,7), have largely been reported
cardiac output is tightly linked to external work such
as supporting data in papers focused on the ventri-
that the energy demand-supply balance is maintained
cles. As such, comparatively little is known about
across the entire intensity spectrum of physical activ-
atrial adaptations to exercise training.
ity. During exercise, the cardiovascular system expe-
SEE PAGE 753
riences changes in intravascular and intraventricular pressure and volume. In simplistic terms, endurance
In this issue of iJACC, Iskandar et al. (8) present the
activities including running, cycling, and swimming
results of a meta-analysis examining left atrial (LA)
are characterized by the generation and maintenance
size in athletes. Using a systematic literature search
of high cardiac output and thereby represent a car-
and a priori retention criteria chosen to ensure cap-
diovascular volume challenge. Strength activities, in
ture of the intended study population (i.e., youthful
contrast, are associated with repetitive surges in sys-
elite athletes) and the desired dependent variables
temic blood pressure that translate into a cardiovascu-
(i.e., LA diameter or volume), the authors amassed a
lar pressure challenge. Repetitive exposure to these
robust study population consisting of 7,018 athletes
cardinal forms of hemodynamic stress stimulates
and 1,044 control subjects. Regression analyses using
the process of exercise-induced cardiac remodeling,
both fixed and random effect variables were used to
which results in the myriad of structural and func-
compare LA size between athletes and control sub-
tional adaptations that often are broadly referred to
jects and to examine the relationships between LA
as the “athlete’s heart” (1).
dimensions, sex, and exercise training type. Results
Forty years ago, a sentinel paper by Morganroth
from this important effort are summarized as follows.
et al. (2) provided preliminary data suggesting that
First, athletes were found to have a pooled mean LA
the heart, specifically the left ventricle (LV), remodels
diameter that was 4.1 mm (95% confidence interval:
in a sport-dependent fashion. Despite some debate in
2.8 to 5.4 mm; p < 0.0001) greater and a pooled mean
the literature, the majority of subsequent cross-
LA volume index that was 7.0 ml/m 2 (95% confidence
sectional studies (3) and more recent longitudinal
interval: 2.3 to 11.6 ml/m 2; p < 0.01) greater than
work (4) confirm this notion. Specifically, endurance
sedentary control subjects. Second, LA dilation,
training promotes dilated LV geometry with or
relative to control subjects, tracked closely with
without mild hypertrophy, whereas strength training
physiological sporting discipline, with endurance
is associated with LV remodeling characterized by
athletes demonstrating the largest difference (4.6 mm; p < 0.0001), strength athletes the smallest difference (2.9 mm; p < 0.03), and mixed trained athletes
*Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology. From the Cardiovascular Performance Program, Massachusetts General
falling in between (4.2 mm; p < 0.02). Finally, a comparison of male and female athletes found that LA diameter was 2.3 mm greater in men but that sex-based
Hospital, Boston, Massachusetts. Dr. Baggish has reported that he has
differences were eliminated when body surface
no relationships relevant to the contents of this paper to disclose.
area–indexed LA volumes were compared.
764
Baggish
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 7, 2015 JULY 2015:763–5
Editorial Comment
Meta-analyses are most useful when single studies
the exception, among trained athletes. Does this
lack adequate statistical power to confirm or refute an
mean that parameters of LA size hold no value for
observation or when aggregation of data permits
differentiating the athlete’s heart from cardiomyop-
meaningful subgroup analyses. The present report
athy? Returning to lessons learned from the athletic
accomplishes both of these objectives. With a few
LV, it becomes clear that the data presently available,
notable exceptions, the majority of studies examining
including those presented by Iskandar et al. (8), are
LA morphology in athletes are limited by factors
insufficient to address this question. The key to re-
including small sample size, lack of adequate control
solving this issue will be to determine whether
population, and focus on a single sex. Results from the
physiological LA dilation demonstrates a measurable
present study confirm, in convincing fashion, that
and consistent upper limit of normal. If so, absolute
average LA size is larger in elite athletes than in
or indexed LA dimensions may be as clinically useful
sedentary people. This finding has direct clinical
as LV wall thickness, which has been shown to adhere
relevance, because LA dilation is a common feature of
to sex- and ethnicity-specific physiological limita-
several cardiomyopathic conditions that may affect
tions (9), for differentiating health from disease.
young athletes, including hypertrophic and hyper-
If not, LA dimensions, much like LV chamber vol-
tensive cardiomyopathy. Clinicians charged with the
umes, which often dilate markedly and without a
daunting task of differentiating adaptive remodeling
clear normality limit because of exercise training (10),
from occult myopathy will benefit from an under-
may hold no discriminatory value. Again, further
standing that the presence of mild LA dilation is of
work is needed to assign LA dimension to the correct
minimal value in this diagnostic dilemma. In addition,
physiological camp.
the present paper demonstrates that LA size should be
Finally, and perhaps most intriguingly, is the issue
added to the list of exercise-induced cardiac adapta-
of clinical relevance with respect to atrial arrhythmia.
tions, a list that currently includes LV chamber size,
As succinctly outlined in the present paper, a growing
LV wall thickness, and right ventricular chamber size,
body of literature convincingly demonstrates an
that adhere to sport-specific remodeling patterns. This
association
important insight represents a key step in our quest to
pation, specifically endurance sport training (11), and
understand how different forms of physical activity
increased risk of atrial fibrillation (12). Although
lead to changes in cardiac structure and function.
routine physical exercise may favorably impact many
between
long-term
athletic
partici-
Having acknowledged the clinical and scientific
key determinants of cardiovascular disease (e.g., lipid
advances afforded by the present study, we turn to
profiles, blood pressure, and body mass), atrial
several key questions it raises and leaves unanswered.
fibrillation is the exception and is increasingly
Ventricular components of the athlete’s heart are
recognized as the Achilles heel of the aging master’s
typically regarded as adaptions that by definition
athlete (a group defined as competitors >40 years of
confer a physiological advantage. For example, the LV
age). Numerous underlying mechanisms, including
dilation or eccentric LV hypertrophy that develops in
those shared with the general, more sedentary pop-
experienced endurance athletes maximizes stroke
ulation (e.g., undiagnosed hypertension, excessive
volume reserve and thus cardiac output augmentation
alcohol consumption, sleep apnea), and some factors
during exercise. Similarly, the concentric LV hy-
more specific to the aging competitive athlete,
pertrophy that is common among strength-trained
including resting vagotonia, chronic inflammation,
athletes may, according to Laplace’s law, minimize
and
transmural wall stress during brief but intense periods
Although it is tempting to assume that LA dilation, a
indeed
LA
dilation,
have
been
proposed.
of LV pressure overload. Does LA dilation play a key
risk factor for atrial fibrillation in the general popu-
role in exercise physiology as a determinant of exercise
lation (13), carries similar prognostic implications
capacity or as a mechanism designed to offset the he-
among athletes, we should avoid this temptation
modynamic challenges of sport? Or is athletic LA
until confirmatory studies are completed. In the
dilation a physiologically inert byproduct of repetitive
interim, although it is safe to say that athletes have
pressure and/or volume challenge that serves simply
larger LAs than their sedentary counterparts, it re-
as a marker of prior exercise exposure? Further study
mains uncertain whether or not size really matters.
coupling cardiac imaging with exercise physiology will be required to address this intriguing question.
REPRINT REQUESTS AND CORRESPONDENCE: Dr.
The present study confirms in definitive fashion
Aaron L. Baggish, Cardiovascular Performance Pro-
that mild to moderate LA dilation, measured echo-
gram, Massachusetts General Hospital, Yawkey Suite
cardiographically as either major dimension or in-
5B, 55 Fruit Street, Boston, Massachusetts 02114.
dexed volume, should be considered the norm, not
E-mail: [email protected].
Baggish
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 7, 2015 JULY 2015:763–5
Editorial Comment
REFERENCES 1. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation 2011;123: 2723–35. 2. Morganroth J, Maron BJ, Henry WL, Epstein SE. Comparative left ventricular dimensions in trained athletes. Ann Intern Med 1975;82:521–4.
top-level athletes: a three-dimensional echocardiographic study. J Am Soc Echocardiogr 2012;25:1268–76. 6. Pelliccia A, Maron BJ, Di Paolo FM, et al. Prevalence and clinical significance of left atrial remodeling in competitive athletes. J Am Coll Cardiol 2005;46:690–6.
3. D’Andrea A, Caso P, Scarafile R, et al. Biventricular myocardial adaptation to different training
7. Grunig E, Henn P, D’Andrea A, et al. Reference values for and determinants of right atrial area in healthy adults by 2-dimensional echo-
protocols in competitive master athletes. Int J Cardiol 2007;115:342–9.
cardiography. Circ Cardiovasc Imaging 2013;6: 117–24.
4. Baggish AL, Wang F, Weiner RB, et al. Trainingspecific changes in cardiac structure and function: a prospective and longitudinal assessment of competitive athletes. J Appl Physiol 2008;104: 1121–8.
8. Iskandar A, Mujtaba MT, Thompson PD. Left atrium size in elite athletes. J Am Coll Cardiol Img 2015;8:753–62.
5. D’Andrea A, Riegler L, Morra S, et al. Right ventricular morphology and function in
9. Sharma S, Maron BJ, Whyte G, Firoozi S, Elliott PM, McKenna WJ. Physiologic limits of left ventricular hypertrophy in elite junior athletes: relevance to differential diagnosis of athlete’s
heart and hypertrophic cardiomyopathy. J Am Coll Cardiol 2002;40:1431–6. 10. Pelliccia A, Culasso F, Di Paolo FM, Maron BJ. Physiologic left ventricular cavity dilatation in elite athletes. Ann Inter Med 1999;130:23–31. 11. Mont L, Elosua R, Brugada J. Endurance sport practice as a risk factor for atrial fibrillation and atrial flutter. Europace 2009;11:11–7. 12. Sorokin AV, Araujo CG, Zweibel S, Thompson PD. Atrial fibrillation in endurance-trained athletes. Br J Sports Med 2011;45:185–8. 13. Vaziri SM, Larson MG, Benjamin EJ, Levy D. Echocardiographic predictors of nonrheumatic atrial fibrillation: the Framingham Heart Study. Circulation 1994;89:724–30.
KEY WORDS athlete, echocardiography, left atrium
765
VOL. 8, NO. 7, 2015
ª 2015 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
ISSN 1936-878X/$36.00
PUBLISHED BY ELSEVIER INC.
http://dx.doi.org/10.1016/j.jcmg.2014.12.031
EDITORIAL COMMENT
Athletic Left Atrial Dilation Size Matters?* Aaron L. Baggish, MD
T
he cardiovascular system’s ability to generate
mild wall thickening in the absence of chamber dila-
high cardiac output is essential for athletic
tion. Sport-specific right ventricular adaptations have
performance, and its failure underlies many
similarly been documented (5). To date, the literature
forms of disease. During exercise, the heart and ves-
on the athlete’s heart has been dominated by studies
sels circulate energy-rich substrate to exercising
that focused on ventricular characteristics, with atrial
muscle and simultaneously remove the metabolic
structure and function receiving comparatively little
byproducts of muscular metabolism. This process
attention. Atrial metrics among athletes, with a few
occurs in an elegant and coordinated fashion whereby
notable exceptions (6,7), have largely been reported
cardiac output is tightly linked to external work such
as supporting data in papers focused on the ventri-
that the energy demand-supply balance is maintained
cles. As such, comparatively little is known about
across the entire intensity spectrum of physical activ-
atrial adaptations to exercise training.
ity. During exercise, the cardiovascular system expe-
SEE PAGE 753
riences changes in intravascular and intraventricular pressure and volume. In simplistic terms, endurance
In this issue of iJACC, Iskandar et al. (8) present the
activities including running, cycling, and swimming
results of a meta-analysis examining left atrial (LA)
are characterized by the generation and maintenance
size in athletes. Using a systematic literature search
of high cardiac output and thereby represent a car-
and a priori retention criteria chosen to ensure cap-
diovascular volume challenge. Strength activities, in
ture of the intended study population (i.e., youthful
contrast, are associated with repetitive surges in sys-
elite athletes) and the desired dependent variables
temic blood pressure that translate into a cardiovascu-
(i.e., LA diameter or volume), the authors amassed a
lar pressure challenge. Repetitive exposure to these
robust study population consisting of 7,018 athletes
cardinal forms of hemodynamic stress stimulates
and 1,044 control subjects. Regression analyses using
the process of exercise-induced cardiac remodeling,
both fixed and random effect variables were used to
which results in the myriad of structural and func-
compare LA size between athletes and control sub-
tional adaptations that often are broadly referred to
jects and to examine the relationships between LA
as the “athlete’s heart” (1).
dimensions, sex, and exercise training type. Results
Forty years ago, a sentinel paper by Morganroth
from this important effort are summarized as follows.
et al. (2) provided preliminary data suggesting that
First, athletes were found to have a pooled mean LA
the heart, specifically the left ventricle (LV), remodels
diameter that was 4.1 mm (95% confidence interval:
in a sport-dependent fashion. Despite some debate in
2.8 to 5.4 mm; p < 0.0001) greater and a pooled mean
the literature, the majority of subsequent cross-
LA volume index that was 7.0 ml/m 2 (95% confidence
sectional studies (3) and more recent longitudinal
interval: 2.3 to 11.6 ml/m 2; p < 0.01) greater than
work (4) confirm this notion. Specifically, endurance
sedentary control subjects. Second, LA dilation,
training promotes dilated LV geometry with or
relative to control subjects, tracked closely with
without mild hypertrophy, whereas strength training
physiological sporting discipline, with endurance
is associated with LV remodeling characterized by
athletes demonstrating the largest difference (4.6 mm; p < 0.0001), strength athletes the smallest difference (2.9 mm; p < 0.03), and mixed trained athletes
*Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology. From the Cardiovascular Performance Program, Massachusetts General
falling in between (4.2 mm; p < 0.02). Finally, a comparison of male and female athletes found that LA diameter was 2.3 mm greater in men but that sex-based
Hospital, Boston, Massachusetts. Dr. Baggish has reported that he has
differences were eliminated when body surface
no relationships relevant to the contents of this paper to disclose.
area–indexed LA volumes were compared.
764
Baggish
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 7, 2015 JULY 2015:763–5
Editorial Comment
Meta-analyses are most useful when single studies
the exception, among trained athletes. Does this
lack adequate statistical power to confirm or refute an
mean that parameters of LA size hold no value for
observation or when aggregation of data permits
differentiating the athlete’s heart from cardiomyop-
meaningful subgroup analyses. The present report
athy? Returning to lessons learned from the athletic
accomplishes both of these objectives. With a few
LV, it becomes clear that the data presently available,
notable exceptions, the majority of studies examining
including those presented by Iskandar et al. (8), are
LA morphology in athletes are limited by factors
insufficient to address this question. The key to re-
including small sample size, lack of adequate control
solving this issue will be to determine whether
population, and focus on a single sex. Results from the
physiological LA dilation demonstrates a measurable
present study confirm, in convincing fashion, that
and consistent upper limit of normal. If so, absolute
average LA size is larger in elite athletes than in
or indexed LA dimensions may be as clinically useful
sedentary people. This finding has direct clinical
as LV wall thickness, which has been shown to adhere
relevance, because LA dilation is a common feature of
to sex- and ethnicity-specific physiological limita-
several cardiomyopathic conditions that may affect
tions (9), for differentiating health from disease.
young athletes, including hypertrophic and hyper-
If not, LA dimensions, much like LV chamber vol-
tensive cardiomyopathy. Clinicians charged with the
umes, which often dilate markedly and without a
daunting task of differentiating adaptive remodeling
clear normality limit because of exercise training (10),
from occult myopathy will benefit from an under-
may hold no discriminatory value. Again, further
standing that the presence of mild LA dilation is of
work is needed to assign LA dimension to the correct
minimal value in this diagnostic dilemma. In addition,
physiological camp.
the present paper demonstrates that LA size should be
Finally, and perhaps most intriguingly, is the issue
added to the list of exercise-induced cardiac adapta-
of clinical relevance with respect to atrial arrhythmia.
tions, a list that currently includes LV chamber size,
As succinctly outlined in the present paper, a growing
LV wall thickness, and right ventricular chamber size,
body of literature convincingly demonstrates an
that adhere to sport-specific remodeling patterns. This
association
important insight represents a key step in our quest to
pation, specifically endurance sport training (11), and
understand how different forms of physical activity
increased risk of atrial fibrillation (12). Although
lead to changes in cardiac structure and function.
routine physical exercise may favorably impact many
between
long-term
athletic
partici-
Having acknowledged the clinical and scientific
key determinants of cardiovascular disease (e.g., lipid
advances afforded by the present study, we turn to
profiles, blood pressure, and body mass), atrial
several key questions it raises and leaves unanswered.
fibrillation is the exception and is increasingly
Ventricular components of the athlete’s heart are
recognized as the Achilles heel of the aging master’s
typically regarded as adaptions that by definition
athlete (a group defined as competitors >40 years of
confer a physiological advantage. For example, the LV
age). Numerous underlying mechanisms, including
dilation or eccentric LV hypertrophy that develops in
those shared with the general, more sedentary pop-
experienced endurance athletes maximizes stroke
ulation (e.g., undiagnosed hypertension, excessive
volume reserve and thus cardiac output augmentation
alcohol consumption, sleep apnea), and some factors
during exercise. Similarly, the concentric LV hy-
more specific to the aging competitive athlete,
pertrophy that is common among strength-trained
including resting vagotonia, chronic inflammation,
athletes may, according to Laplace’s law, minimize
and
transmural wall stress during brief but intense periods
Although it is tempting to assume that LA dilation, a
indeed
LA
dilation,
have
been
proposed.
of LV pressure overload. Does LA dilation play a key
risk factor for atrial fibrillation in the general popu-
role in exercise physiology as a determinant of exercise
lation (13), carries similar prognostic implications
capacity or as a mechanism designed to offset the he-
among athletes, we should avoid this temptation
modynamic challenges of sport? Or is athletic LA
until confirmatory studies are completed. In the
dilation a physiologically inert byproduct of repetitive
interim, although it is safe to say that athletes have
pressure and/or volume challenge that serves simply
larger LAs than their sedentary counterparts, it re-
as a marker of prior exercise exposure? Further study
mains uncertain whether or not size really matters.
coupling cardiac imaging with exercise physiology will be required to address this intriguing question.
REPRINT REQUESTS AND CORRESPONDENCE: Dr.
The present study confirms in definitive fashion
Aaron L. Baggish, Cardiovascular Performance Pro-
that mild to moderate LA dilation, measured echo-
gram, Massachusetts General Hospital, Yawkey Suite
cardiographically as either major dimension or in-
5B, 55 Fruit Street, Boston, Massachusetts 02114.
dexed volume, should be considered the norm, not
E-mail: [email protected].
Baggish
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 7, 2015 JULY 2015:763–5
Editorial Comment
REFERENCES 1. Baggish AL, Wood MJ. Athlete’s heart and cardiovascular care of the athlete: scientific and clinical update. Circulation 2011;123: 2723–35. 2. Morganroth J, Maron BJ, Henry WL, Epstein SE. Comparative left ventricular dimensions in trained athletes. Ann Intern Med 1975;82:521–4.
top-level athletes: a three-dimensional echocardiographic study. J Am Soc Echocardiogr 2012;25:1268–76. 6. Pelliccia A, Maron BJ, Di Paolo FM, et al. Prevalence and clinical significance of left atrial remodeling in competitive athletes. J Am Coll Cardiol 2005;46:690–6.
3. D’Andrea A, Caso P, Scarafile R, et al. Biventricular myocardial adaptation to different training
7. Grunig E, Henn P, D’Andrea A, et al. Reference values for and determinants of right atrial area in healthy adults by 2-dimensional echo-
protocols in competitive master athletes. Int J Cardiol 2007;115:342–9.
cardiography. Circ Cardiovasc Imaging 2013;6: 117–24.
4. Baggish AL, Wang F, Weiner RB, et al. Trainingspecific changes in cardiac structure and function: a prospective and longitudinal assessment of competitive athletes. J Appl Physiol 2008;104: 1121–8.
8. Iskandar A, Mujtaba MT, Thompson PD. Left atrium size in elite athletes. J Am Coll Cardiol Img 2015;8:753–62.
5. D’Andrea A, Riegler L, Morra S, et al. Right ventricular morphology and function in
9. Sharma S, Maron BJ, Whyte G, Firoozi S, Elliott PM, McKenna WJ. Physiologic limits of left ventricular hypertrophy in elite junior athletes: relevance to differential diagnosis of athlete’s
heart and hypertrophic cardiomyopathy. J Am Coll Cardiol 2002;40:1431–6. 10. Pelliccia A, Culasso F, Di Paolo FM, Maron BJ. Physiologic left ventricular cavity dilatation in elite athletes. Ann Inter Med 1999;130:23–31. 11. Mont L, Elosua R, Brugada J. Endurance sport practice as a risk factor for atrial fibrillation and atrial flutter. Europace 2009;11:11–7. 12. Sorokin AV, Araujo CG, Zweibel S, Thompson PD. Atrial fibrillation in endurance-trained athletes. Br J Sports Med 2011;45:185–8. 13. Vaziri SM, Larson MG, Benjamin EJ, Levy D. Echocardiographic predictors of nonrheumatic atrial fibrillation: the Framingham Heart Study. Circulation 1994;89:724–30.
KEY WORDS athlete, echocardiography, left atrium
765
