Abnormal electrocardiographic findings in athletes: recognising changes suggestive of cardiomyopathy.(onderdeel reeks ECG bundel, deel 2 (3b) van dit artikel)

Introductie

Na publicatie (met toestemming) van de eerste twee delen van de “ECG bundel”, overgenomen uit BJSM 2013 in Sport & Geneeskunde, volgt hier het tweede deel van deel 3. In dit deel wordt het ECG bij sporters met een cardiomyopathie onder de loep genomen.
Hierin kunt u lezen dat differentiatie tussen fysiologie en pathologie op het ECG bij een sporter soms zeer moeilijk kan zijn, vooral omdat het ECG van een sporter bedrieglijk veel kan lijken op dat van iemand met CMP.
Voor de complete introductie zie Sport & Geneeskunde 3-2013, pag. 26-27.

Deel II: Arrhythmogenic right ventricular cardiomyopathy

ARVC is an inherited heart muscle disease characterised by fibro-fatty replacement of right ventricular myocardium and corollary life-threatening ventricular arrhythmias or SCD, mostly in young people and athletes. Progressive dilation/dysfunction predominantly involves the right ventricle with involvement of the left ventricle in late-stage disease. Variants with predominantly LV involvement are described in about 10% of patients (hence the alternative term of arrhythmogenic cardiomyopathy). Mutations in the desmosomal genes account for approximately 50% of ARVC cases.^{44 45} In addition, there is emerging evidence that intense endurance sports may lead to a similar phenotype (with similar prognosis) in the absence of desmosomal mutations, so-called exercise-induced ARVC, which may be the result of increased RV wall stress during exercise.^46–48 The prevalence of familial ARVC is estimated at 1 : 2000–1 : 5000 persons.^{44 45}

Contribution as a cause of SCD

According to data from the Veneto region of Italy where postmortem investigation of young sudden death victims is performed systematically, ARVC is a leading cause of sport-related sudden death accounting for approximately one-fourth of fatalities in young competitive athletes.3 Data from the USA, notably without a mandatory registry for SCD in athletes, suggest that ARVC is a less common cause of SCD.¹

Diagnostic criteria

The original (1994) and the revised (2010) Task Force Criteria for diagnosis of ARVC are based on major and minor criteria encompassing familial/genetic, ECG, arrhythmic, morphofunctional ventricular and histopathological features.⁴⁹ The diagnosis is fulfilled in the presence of two major criteria, one major plus two minor criteria, or four minor criteria from different groups.⁴⁹

Abnormal ECG findings in ARVC

Over 80% of patients with ARVC will have an abnormal ECG.^{45 50 51} ECG abnormalities include TWI in the anterior precordial leads, epsilon waves, delayed S wave upstroke, lowvoltage in limb leads and premature ventricular beats with an LBBB morphology and superior axis. If there is primarily LV involvement, the TWI involves the lateral precordial leads and the premature ventricular beats can have an RBBB morphology.

T wave inversion
TWI in the anterior precordial leads (V1–V3/V4) is present in approximately 85% of patients with ARVC in the absence of RBBB (figures 10 and 11).⁵⁰ TWI occasionally extends to the left precordial leads V5–V6 or inferior limb leads II, III and aVF. TWI in V1–V3 or beyond in individuals >14 years of age (in the absence of complete RBBB) represent a major diagnostic criterion for ARVC, while TWI confined to just leads V1 and V2 in individuals >14 years of age (in the absence of complete RBBB) represents a minor diagnostic criterion.⁴⁹ In Italian children ≥14 years with TWI in the anterior precordial leads beyond V2 (ie, V3 or V4), 3 of 26 (11%) fulfilled diagnostic criteria for ARVC (1 definitive, 2 borderline).²⁸ In the presence of complete RBBB, right precordial (V1–V3) TWI is more likely secondary to RBBB rather than a sign of underlying ARVC. TWI extending beyond V3 is uncommon in patients with RBBB and represents a minor diagnostic criterion for ARVC.⁴⁹ Thus, TWI involving at least two consecutive precordial leads, excluding V1, should prompt further investigation in the athlete.

Epsilon waves
Epsilon waves are defined as distinct low-amplitude potentials localised at the end of the QRS complex. Epsilon waves are challenging to detect and appear as a small negative deflection just beyond the QRS in V1–V3 (figure 10). The presence of epsilon waves in the right precordial leads V1–V3 represents a major diagnostic criterion for ARVC.⁴⁹

Delayed S wave upstroke
Delayed S wave upstroke of >55 ms in leads V1–V3 in the absence of complete RBBB represents a minor diagnostic criterion for ARVC (figure 11).⁴⁹ This feature is most commonly observed among ARVC patients with mild QRS prolongation (100–120 ms). The S wave upstroke is measured from the nadir of the S wave to the end of the QRS (including epsilon wave if present). Prolonged S wave upstroke may be present in up to 95% of patients with ARVC in the absence of RBBB.⁵⁰

Low voltage in limb leads
Low voltage in limb leads, defined as a QRS amplitude ≤5 mm in each of the limb leads (I, II and III), also can be suggestive of ARVC (figure 11).

Premature ventricular contractions
Premature ventricular contractions (PVCs) originating from the right ventricle typically show an LBBB pattern with a predominantly negative QRS complex in V1. On the basis of the QRS axis in the limb leads the origin of the PVC can be further suggested. PVCs with LBBB morphology and an inferior axis ( positive in the inferior leads) originate from the right ventricular outflow tract consistent with idiopathic right ventricular outflow tract arrhythmia which is a benign condition, non-familial and not associated with structural ventricular abnormalities. PVCs with an LBBB morphology and superior axis (negative in the inferior leads) originate from the right ventricular free wall or apex and are more suggestive of ARVC (figure 12).

Evaluation of suspected ARVC
Disease expression in ARVC is variable, and clinical manifestations vary with age and stage of disease.⁴⁹ Similarly, the extent of ECG abnormalities are associated with the severity of disease.⁵¹ In patients with diagnosed ARVC (‘overt stage’) or known desmosome mutation positive subjects, 95% have an abnormal ECG marked by abnormal TWI, a prolonged S wave upstroke in the anterior precordial leads (V1–V3), and/or an epsilon wave.^50–52 However, in cardiac screening, physicians may encounter asymptomatic athletes in the early ‘concealed stage’ of the disease, showing less pronounced ECG changes.
The extent of evaluation is dependent on the specific ECG findings suggestive of ARVC and will be more extensive in the presence of warning symptoms or significant family history. A combination of tests is needed to effectively make the diagnosis or to rule out ARVC. Echocardiography, ambulatory ECG (Holter) monitoring, signal-averaged ECG (SAECG), and ventricular angiography provided optimal evaluation, while cardiac MRI (false-positives) and biopsy (low-sensitivity) were considered less useful for diagnosis in suspected ARVC.^{53 54}
The evaluation of major diagnostic ECG findings according to the 2010 Task Force criteria of TWI in the right precordial leads (V1–V3) or beyond in ages >14 years (in the absence of complete RBBB) should be extensive. In addition to a comprehensive symptom history, family history and physical examination, evaluation of TWI in V1–V3 or beyond should include echocardiography, Holter monitoring, SAECG, maximal exercise-ECG test and possibly a cardiac MRI.⁴⁹ Isolated epsilon waves in the right precordial leads, a less specific major ECG criteria, still require an echocardiography and ECG monitoring for an arrhythmia (Holter or exercise-ECG test).⁴⁹
Evaluation of minor diagnostic ECG-findings according to the Task Force criteria (without accompanying positive family history or alarming symptoms), may be less extensive.⁴⁹ TWI in V1–V2 may require simply a careful personal and family history and physical examination.
Repolarisation variants in the anterior precordial leads in black/African athletes must be distinguished from pathological repolarisation changes found in ARVC. In ARVC, the ST segment is usually isoelectric prior to TWI, in contrast to the ‘domed’ ST segment elevation which is the hallmark feature of the normal repolarisation variant in black/African athletes (figure 13). TWI involving at least two consecutive precordial leads from V2 to V6 with an isoelectric ST segment, regardless of ethnicity, requires additional investigation.

Dilated cardiomyopathy

DCM is a heart muscle disorder characterised by weakened myocardial contraction, which over time leads to cavity enlargement and eccentric heart muscle hypertrophy. It is a common cause of heart failure, the inability of the heart to meet the demands of the body. DCM can be caused by a variety of aetiologies ranging from coronary artery disease, infections/myocarditis, toxins (alcohol and other drugs), metabolic or endocrine abnormalities, autoimmune disorders, infiltrative processes and a variety of genetic/inheritable disorders. In many cases, a distinct cause of the compromised heart muscle is never found. DCM can be asymptomatic, or it can result in symptoms of exercise intolerance, shortness of breath, swelling, congestive heart failure or SCD from ventricular arrhythmia.

Prevalence
The exact prevalence of DCM in the general population is not known and estimates depend on the population demographics and the cut-off used to define LV dysfunction.⁵⁵ The majority of cases with early stages of LV dysfunction may be asymptomatic.⁵⁶ DCM prevalence is increased with older age, male gender and the presence of cardiovascular risk factors. Among a relatively young, healthy population without coronary risk factors, asymptomatic LV dysfunction was present in about 0.2% of individuals.⁵⁷

Contribution as a cause of SCD
DCM is associated with an increased risk of ventricular arrhythmias and sudden cardiac arrest, with highest risk seen among individuals with severe LV dysfunction. Notably, SCD can occur even in the absence of heart failure symptoms. In the Framingham Heart Study, the death rate from asymptomatic LV dysfunction was 6.5% per 100 person-years, with 53% of deaths occurring prior to the onset of symptoms, emphasising the importance of screening for this disorder.⁵⁸ DCM accounts for about 2% of cases in a series of young athletes with sudden cardiac arrest.²

Diagnostic criteria
DCM is diagnosed on non-invasive imaging (echocardiography or cardiac MRI) by detecting LV chamber enlargement and decreased LV systolic (contractile) function. Systolic function is usually quantified using either fractional shortening (FS) or ejection fraction (EF), but there is no consensus cut-off definition of DCM based on these parameters. Normal ranges vary by lab and imaging modality.

Abnormal ECG findings in DCM
Several studies have examined ECG abnormalities in patients with symptomatic DCM, but few have reported findings among non-ischaemic DCM or among individuals with asymptomatic LV dysfunction.^59–61 Overall, approximately 90% of individuals with DCM have abnormal ECG findings (figures 14 and 15). Patients with prior myocardial infarction may manifest pathological Q waves. Among individuals with non-ischaemic cardiomyopathy, the most common abnormalities seen include voltage criteria for LVH (33–40%), TWIs (25–45%), LAE (15–33%), LAD (15–25%), pathological Q waves (10–25%), LBBB (9–25%), premature ventricular contractions (5–10%) and RBBB (4%).⁶² These findings are non-specific for DCM. Goldberger has proposed a triad of findings that may offer more specificity: (1) LVH in the anterior precordial leads; (2) low limb lead voltage and (3) poor precordial R wave progression.⁶³ Given the overlap of some of these findings with physiological ECG changes found in athlete’s heart, distinctly abnormal ECG criteria unrelated to regular training and requiring additional evaluation to rule out an underlying cardiomyopathy are listed in table 1.

Evaluation of suspected DCM
When DCM is suspected, further evaluation of LV size and function is required. Echocardiography provides assessment of cardiac structure and function, including FS and/or EF, and is the first test of choice under most circumstances. Contrast echocardiography or cardiac MRI should be considered when image resolution is reduced.
Athletes may have LV chamber enlargement as a part of physiological adaptation to exercise.⁶⁴ This is most often seen in athletes participating in endurance sports such as cycling, crosscountry skiing or rowing. Mild reduction in LV contractility (EF 40–50%) is seen in a minority of athletes with LV cavity dilation, but is not an invariable component of physiological adaptation to exercise.^{64 65} Stress echocardiography can assess myocardial performance at submaximal or peak exercise which may help differentiate those with low normal or borderline systolic function, as systolic function is more likely to normalised in athlete’s heart than in DCM. Thus, LV dilatation and measures of systolic function should be interpreted carefully and in the context of the athlete’s level and amount of endurance training. All patients with DCM should be referred to a cardiologist for further aetiological evaluation, including assessment for myocardial ischaemia and infiltrative disorders.

LV non-compaction

LVNC is a heart muscle disorder in which loosely organised myocardial fibres fail to condense into a compact layer resulting in increased myocardial trabeculations and thinning of the compact myocardium (figure 16).^{66 67} LVNC can occur along with other congenital or embryological abnormalities, or can be found in isolation, and can be due to underlying gene mutations. However, the majority of LVNC remains genetically elusive. This disturbance of myocardial structure leads to progressive weakening of heart muscle contraction (lower EF) with ventricular dilation. Therefore, LVNC should be distinguished from DCM. Blood clots may also form within the trabecular recesses, increasing the risk for embolic strokes.

Prevalence
The exact prevalence of isolated LVNC is unknown, but is thought to be <0.1–0.2%. Reasons for the uncertainty in prevalence include challenges in imaging the non-compaction and disagreement regarding diagnostic criteria.

Contribution as a cause of SCD
LVNC is associated with an increased risk of abnormal heart rhythms and sudden cardiac arrest.68 LVNC is a rare (<1%) cause of SCD in a series of young athletes.²

Diagnostic criteria
Several sets of diagnostic criteria for isolated LVNC exist, but remain controversial.^69–73 These criteria are based generally on echocardiography or cardiac MRI findings of an increased ratio of trabeculations to compact myocardium. These criteria have been called into question recently for being non-specific, particularly among black individuals who have relatively greater degrees of myocardial trabeculations and among athletes.⁷⁴

Abnormal ECG findings in isolated LVNC
ECG abnormalities in isolated LVNC are common but nonspecific (figures 17 and 18). In a series of 78 patients with a clinical diagnosis of LVNC, only 13% had a normal ECG.⁷⁵ The most common abnormalities in this series included repolarisation changes (72%), QT prolongation (52%), ST segment depression (51%), TWI (41%), LVH voltage criteria (38%), IVCD (31%) including LBBB (19%) and RBBB (3%), and LAE (26%).⁷⁵ Given the overlap of some of these findings with physiological ECG changes found in athlete’s heart, abnormal ECG criteria requiring additional evaluation to rule out an underlying cardiomyopathy are listed in table 1.

Evaluation of suspected isolated LVNC
Echocardiography is usually the first investigation in the evaluation of ECG abnormalities suggestive of cardiomyopathy. The diagnosis and evaluation of suspected LVNC is quite challenging, and therefore patients should be referred to a cardiovascular specialist familiar with LVNC. Cardiac MRI provides a more detailed and accurate assessment of myocardial trabeculations and is recommended in cases with concerning or borderline findings on echocardiography. A smaller absolute thickness of compacted myocardium and the presence of LV dysfunction favour the diagnosis of LVNC. In select cases, LV angiography may be used to help delineate hypertrabeculation from compacted myocardium. Holter monitoring or more extended ambulatory monitoring for arrhythmias also should be diagnostic evaluation.

Other ECG findings possibly suggestive of a cardiomyopathy

Several additional ECG abnormalities including RBBB, nonspecific IVCD with QRS duration <140 ms, and isolated (one per tracing) ectopic/premature ventricular contractions (PVCs) have been associated with an underlying cardiomyopathy in non-athletic populations.^76–83 However, these findings are also more common in trained athletes without an underlying heart disease than among the general population.^{26 84–87} Each of these findings, particularly when observed in an asymptomatic athlete with no family history suggestive of heritable heart disease, has a low-positive predictive value for the cardiomyopathic conditions associated with an increased risk of SCD during exercise. As such, none of these ECG patterns, when found in isolation in asymptomatic athletes, clearly necessitate further evaluation. However, in athletes with cardiovascularrelated symptoms or a family history of sudden death or suspected cardiomyopathy, each of these findings should prompt additional evaluation to evaluate for cardiomyopathy.

Right bundle branch block
RBBB is defined as a QRS complex ≥120 ms in association with a terminal (final component of the QRS complex) R⁰ wave in lead V1 and terminal S waves in leads I, aVL and V6 (figure 19). The R⁰ may extend into lead V2 but is typically absent in other precordial leads. T waves in typical RBBB are in the same direction as the terminal QRS forces and are thus inverted in leads with an R⁰ (V1±V2). A QRS complex duration of 100–119 ms with these morphological features is termed an incomplete RBBB.
Although RBBB may be present in various forms of heart disease, complete and incomplete RBBB are found commonly among trained athletes without underlying heart disease. This ECG pattern has been shown to reflect the exercise-induced right ventricular remodelling common in endurance sport athletes. ⁸⁸ In asymptomatic athletes with an isolated complete or incomplete RBBB, no further diagnostic evaluation is required. In contrast, athletes presenting with symptoms suggestive of cardiomyopathy, a family history of sudden death or suspected cardiomyopathy, an RBBB with atypical features (extensive TWIs, ST-segment elevation or a markedly prolonged R⁰), or a RBBB in conjunction with other abnormal ECG findings should be further evaluated.

Non-Specific intra-ventricular conduction delay
IVCD is defined as a QRS complex >110 ms that does not have morphological features consistent with either LBBB or RBBB.
IVCD has been documented among patients with cardiomyopathy, but is also frequently seen in healthy athletes. The physiology underlying IVCD in athletes remains incompletely understood but likely includes some combination of neurally mediated conduction fibre slowing and increased myocardial mass.
Digital analysis of QRS duration can outperform standard visual measurement because the first onset and last offset in all of the leads can be considered.6 In asymptomatic athletes with an isolated IVCD with a QRS duration of 100–139 ms, no further diagnostic evaluation is required. In contrast, athletes presenting with symptoms suggestive of cardiomyopathy, a family history of sudden death or suspected cardiomyopathy, an IVCD with marked QRS prolongation (≥140 ms) or an IVCD in tandem with other abnormal ECG findings should be further evaluated.

Isolated premature ventricular contractions
PVCs are electrical impulses that originate from myocardial tissue below the AV node. They are defined as QRS complexes >100 ms that are not preceded by a triggering p-wave. PVCs may reflect pathological myocardial ‘irritability’ due to a cardiomyopathy, an underlying systemic disease process, or may be a completely benign normal variant. PVCs are common in athletes with high vagal tone and resting bradycardia and may increase in frequency in parallel with physical fitness. A single PVC captured during a routine 12-lead ECG in an asymptomatic athlete does not require further evaluation, unless the athlete performs a high-intensity endurance sport (mainly cycling, triathlon, rowing or swimming). In this select group of high-intensity endurance athletes, a single PVC, especially if it has an LBBB morphology, may be a hallmark of ‘exercise-induced’ ARVC, and further evaluation should be considered.46–48 The presence of PVCs in an athlete with cardiovascular symptoms or a family history of sudden death or suspected cardiomyopathy should prompt further evaluation. In addition, multiple PVCs (2 or more) during a single ECG tracing (10 s), multifocal PVCs or PVCs found in tandem with other abnormal ECG findings should be further evaluated.

Pulmonary hypertension

Pulmonary hypertension (PHT) is caused by a variety of aetiologies that result in elevation in the pulmonary artery pressure (mean pulmonary artery pressure greater than or equal to 25 mm Hg) and elevation in the pulmonary vascular resistance.⁸⁹ As a result of the increased afterload on the right heart, patients are predisposed to develop right heart failure and are at risk for sudden death. PHT is a rare cause of sudden death in athletes but may be suggested by ECG abnormalities and thus a clinically relevant finding in the cardiovascular care of athletes.

ECG findings in pulmonary hypertension
The ECG findings in PHTare due to physiological and anatomic adaptions of the right heart as a result of elevated pulmonary artery pressures and/or pulmonary vascular resistance. Findings suggestive of PHT include right ventricular hypertrophy (RVH), right axis deviation, right ventricular strain and right atrial enlargement (figure 20).^89–91 In adults with idiopathic PHT, 87% demonstrated RVH and 79% demonstrated right axis deviation.⁸⁹ However, in patients with PHT, the ECG remains an inadequate screening tool to completely rule out the presence of this disease.⁹²

Right ventricular hypertrophy pattern
RVH pattern is defined as an R wave in lead V1 plus S wave in V5 greater than 1.05 mV (10.5 mm at standard amplification) AND right axis deviation >120° (figure 20). Additional criteria for RVH associated with PHT include a tall R wave and small S wave with R/S ratio greater than 1 in lead V1 and a qR complex in lead V1. The presence of RHV pattern on ECG should prompt further investigation in the athlete.

Right axis deviation
Right-axis deviation is defined as a frontal plane QRS axis of >120° (figure 20).

Right atrial enlargement
Right atrial enlargement is defined as a P wave greater than or equal to 2.5 mm in leads II, III and aVF (figure 20).

RV strain
Right ventricular ‘strain’ is defined as ST depression and TWI in the right precordial leads (V1–V3) (figure 20). As with LVH, these ST-T changes are referred to as ‘secondary ST-T abnormalities.’

Evaluation of suspected pulmonary hypertension
Evaluation should include clinical assessment with appropriate diagnostic testing. Pulmonary artery pressures often can be assessed by Doppler echocardiography, and both echocardiography and cardiac MRI can evaluate RVH and function, and assess for secondary causes of PHT such as intracardiac shunts. Definitive diagnosis of PHT is made by cardiac catheterisation.

Conclusions

The cardiomyopathies are a heterogeneous group of heart muscle diseases associated with important clinical implications. In aggregate, HCM, ARVC, DCM and LVNC underlie the majority of autopsy-positive sudden death cases in young athletes. Each of these cardiomyopathies can manifest in athletes with a broad spectrum of clinical severity ranging from completely asymptomatic to markedly symptomatic disease with associated exercise limitations. The ECG plays an important role in the cardiovascular assessment of athletes given its capacity to detect cardiomyopathies. As delineated in this paper, there is a concise list of ECG findings that may indicate the presence of an underlying cardiomyopathic condition. Importantly, these ECG findings are not characteristic of the benign exercise-induced cardiac remodelling common in athletes, and, thus, the ECG can be useful for differentiating physiological cardiac enlargement in athletes from pathological myocardial disease.
Clinicians charged with the cardiovascular care of athletes should be familiar with the ECG findings associated with cardiomyopathy. During pre-participation screening that includes the use of ECG, asymptomatic athletes with any of these abnormal findings should undergo further testing. Athletes presenting with symptoms that may be indicative of an underlying cardiomyopathy (ie, exercise intolerance, inappropriate exertional dyspnoea, chest pain, palpitations or syncope) should undergo a prompt evaluation including an ECG. The symptomatic athlete with an ECG suggestive of a cardiomyopathy requires a comprehensive and definitive assessment that will include some combination of non-invasive cardiac imaging, exercise testing and ambulatory rhythm monitoring. This evaluation should be conducted by a sports medicine team that includes a cardiovascular specialist familiar with cardiomyopathic diseases and with experience in caring for athletes.

Additional resources
For a free online training module on ECG interpretation in athletes, please visit:http://learning.bmj.com/ECGathlete. For the November 2012 BJSM supplement on ‘Advances in Sports Cardiology’, please visit:http://bjsm.bmj.com/content/46/Suppl_1.toc.