a solid foundational knowledge of normal electrocardiogram ( ecg ) variants is important in clinical practice , particularly in the general practice environment or internal medicine .
few studies have collected and reported pre and postrace ecg findings , particularly in a group including female and older , socalled , mastersclass ( 40 + years ) runners .
marathon finishes over the past 20 years , with female and masters finishers reaching alltime highs in 2013 1 . in 1995 , female runners accounted for only 26% of marathon finishers , while mastersclass runners accounted for 41% .
this is in stark contrast to 2013 when females and mastersclass runners each represented 47% of marathon finishers 1 .
these demographic changes along with growth overall in the popularity of marathon running 1 should motivate clinicians not only to better understand the potential deleterious effects of endurance sports 2 , 3 , but also better appreciate normal and common electrocardiographic findings in endurance athletes across the lifespan .
our results , while not breaking new ground in understanding the physiologic response of the heart to marathon running , can reinforce to the general practice healthcare provider the normal athlete variants common on ecg . early ventricular repolarization pattern ( erp ) .
the subjects consisted of 13 female ( 42.54  12.00 years old ) and nine male runners ( 46.55  13.90 years old ) who ran the 2015 hartford ( ct ) marathon .
the age distribution of the participants ranged from 22 to 63 years of age with the following number of subjects recruited from each age range 2029 ( n = 3 ) , 3039 ( n = 5 ) , 4049 ( n = 6 ) , 5059 ( n = 5 ) , and 6065 ( n = 3 ) . for each subject , a standard , resting 12lead ecg
in addition , serum cardiac biomarkers ( troponin i and b type natriuretic peptide ) were measured at the same time points , plus at an intermediate interval , at the conclusion of the marathon .
ten subjects demonstrated sinus arrhythmia ( sa ) ; of these , three had sa present pre and postmarathon , five subjects had sa prerace but a regular sinus rhythm postrace , and two had the reverse , a prerace normal sinus rhythm with postmarathon sinus arrhythmia . sinus bradycardia ( hr < 60 bpm ) was common , befitting a group of aerobically fit runners , but no subject had a resting heart rate below 30 bpm , a clinical marker indicative of pathology .
one subject had an ectopic atrial rhythm present at baseline that persisted to their followup ecg .
two subjects had slight p wave notching insufficient to be characterized as atrial enlargement by standard criteria and without a change in morphology postrace .
while a number of subjects had q waves , none were by definition pathologic ( > 3 mm or > 40 msec ) and are not considered a significant finding .
a single subject demonstrated an ischemic pattern of st changes , with st depression of 0.51 mm in leads v3v5 and flattened t waves across the precordium that manifested postmarathon .
this was a significant finding , although the subject was entirely asymptomatic and serum biomarkers were not disproportionately elevated .
the most common finding , and one present among the majority of participants ( 16 ) , was early ventricular repolarization pattern ( erp ) . typically manifesting with st elevation , jpoint elevation or terminal slurring of the qrs ; erp is generally thought to be a benign process unreflective of an underlying structural abnormality and commonly observed in healthy athletes ( fig . 1 ) 4 . ten participants with erp had the phenomenon present to the same degree pre and postrace .
the six remaining subjects with erp had more pronounced erp postrace . no leftaxis deviation was observed . in one
five of the subjects had isolated voltage criteria for left ventricular hypertrophy ( lvh ) , a normal finding in the athlete , and interestingly , in a study with greater female representation , the five were all males .
age was not strongly correlated with particular types of ecg variants , and isolated lvh was the only characteristic that tended to predominate in one gender compared to another , perhaps owing to differences in the left ventricular muscle mass of men versus women . finally , no correlations between ecg changes and serum cardiac biomarkers were found .
it is established science and commonly understood that exercise is a foundational element for achieving optimal health .
routine physical activity is known to be associated with the prevention and treatment of some of the most prevalent chronic diseases of our time , including heart disease , obesity , various cancers , depression , and diabetes . for those willing and able
, regular healthpromoting exercise lowers an individual 's susceptibility to disability and provides for a longer life expectancy 5 .
it is not surprising then , in the united states , participation in marathon running has nearly doubled in the past two decades , reaching an alltime high of approximately 541,000 finishers in 2013 2 . despite its popularity , it has been well established that marathon running places extensive strain on the human body , including the cardiovascular system 6 , 7 , 8 , 9 , 10 .
strain placed on the cardiovascular system can manifest in a number of ways , including serum biomarkers , negative remodeling , and electrocardiographic changes that may be a harbinger of increased morbidity and mortality .
concern regarding the effect on the heart from endurance exercise , of the sort encountered in marathon running , is not misguided . in an early study on the cardiac effects of endurance exercise , benito et al .
prodded a group of rats to run at high intensity for 60 min daily over 16 weeks . when compared to a control group ,
the runners had developed right and left ventricular hypertrophy , fibrosis , and were inducible for ventricular tachycardia at a 42% rate , compared to 6% in the control group 11 .
more recently in humans , lagerche et al . analyzed a cohort of 40 highly trained aerobic athletes .
they found the right ventricle more profoundly affected by highintensity exercise than the left , and although the insult was transient , led to speculation about a dosedependent arrhythmogenic effect of exercise on the rv 12 .
early repolarization pattern deserves specific mention because it has been associated with an increased risk of ventricular fibrillation and sudden cardiac death 4 , 13 , 14 .
however , in otherwise , healthy athletes without heart disease the strong association between athletic performance and erp appears benign 4 .
typically , erp will cooccur with other manifestations of the athlete 's heart , including isolated voltage criteria for lvh 13 .
there are ongoing efforts to more clearly and consistently define a prognostic role for erp , but it appears based on the most respected , current literature on the subject , to be a benign process in athletes 14 . while the current literature focuses on young , male , competitive ultraendurance athletes rather than the increasingly common gender and agediverse recreational marathon runner , it is the latter that healthcare providers are more likely to encounter in the clinical setting .
an unfamiliarity with common ecg manifestations of regular or prolonged aerobic exercise may lead to misdiagnosis , unnecessary treatment , unwarranted specialist referral , and the avoidable consumption of scarce healthcare resources .
while our study was not sufficiently powered to draw conclusions about subsets of individuals in the population of marathon runners and their propensity to manifest cardiac stress / injury on the ecg , our work does serve as a building block to better understand typical electrocardiographic responses to marathon running , and perhaps by extension , endurance activity more generally . in doing so , we identified several normal ecg variations in marathon runners spanning age and gender subgroups . while clinicians can and do provide education to their patients about the potential risks associated with marathon running , they should also be familiar with the normal ecg variants associated with significant aerobic activity .
with respect to our case report , each of the results considered above represent normal electrocardiographic findings in athletes , with the exception of the ischemic st changes observed in a single participant 15 . in particular , the presence of ecg findings such as incomplete right bundle branch block , qrs complexes meeting voltage criteria for left ventricular hypertrophy and alterations in the usual electrocardiographic pattern for ventricular repolarization have the potential , when taken out of context , to prompt misguided concern on the part of healthcare providers .
this case report serves as a reminder for clinicians to consider the individual and the contextual basis of ecg findings .
 key clinical messageelectrocardiographic changes can be present in marathon runners . 
 these findings may be misinterpreted as malignant by healthcare providers . 
 for example , incomplete right bundle branch block , early ventricular repolarization , and left ventricular hypertrophy by voltage criteria alone are quite common in athletes , yet considered benign . 
Introduction
Case Histories
Outcomes
Discussion
Conflict of Interest