Athlete's heart electrocardiogram mimicking hypertrophic cardiomyopathy

Evaluation of left atrial function in physiological and pathological left ventricular myocardial hypertrophy by real-time tri-plane strain rate imaging

BACKGROUND

We investigated the difference between left ventricular (LV) hypertrophy caused by primary hypertension and physiological LV hypertrophy in athletes as seen in left atrial (LA) function by real-time tri-plane strain rate imaging.

HYPOTHESIS

A real-time tri-plane imaging technique using the same phase of the same cardiac circle was used to synchronously demonstrate the section of apical 4-chamber, 2-chamber, and apical left ventricle long axis.

METHODS

We measured standard Doppler echocardiographic quantitative analysis and the strain rate peak values of each LA wall in the systolic phase, in the early stage of diastole, and in the advanced stage of diastole and made a comparison of these values.

RESULTS

The alteration of configuration and function of the left atrium in hypertensive patients is an early sign of the myocardial damage caused by hypertension. Strain rate imaging could sensitively reflect LA function changes in the early stages of hypertension. While physiological, myocardial hypertrophy is a benign reaction, LA function is significantly different from that of hypertension.

CONCLUSIONS

Real-time tri-plane strain rate imaging techniques could simultaneously analyze 3 sections, which shortens scanning time and depletes the influence of variations of different cardiac cycles on quantitative analysis of local myocardial segments of the left atrium. This would improve the comparability of myocardial movement of different segments so that we could more comprehensively and accurately evaluate the systolic and diastolic function of the left atrium in primary hypertension and physiological LV hypertrophy in athletes.

The role of transient outward K+ current in electrical remodelling induced by voluntary exercise in female rat hearts

Regular exercise can lead to electrical remodelling of the heart. The cellular mechanisms associated with these changes are not well understood, and are difficult to study in human tissue but are important given that exercise is recommended to the general population. We have investigated the role played by the transient outward K+ current (I(to)) in the changes in electrical activity seen in response to voluntary exercise training in rats. Female rats undertook 6 weeks of voluntary wheel running exercise (TRN) or were sedentary controls (SED). Monophasic action potentials (MAPs) were recorded from the surface of whole hearts. Whole cell patch clamp recordings of I(to); mRNA and protein levels of selected targets in sub-epicardial (EPI) and sub-endocardial myocardium of SED and TRN hearts were compared. In TRN rats, heart weight:body weight was significantly increased and epicardial MAPs significantly prolonged. I(to) density was reduced in TRN EPI myocytes, such that the transmural gradient of I(to) was significantly reduced (P < 0.05). Computer modelling of these changes in I(to) predicted the observed changes in action potential profile. However, transmural gradients in mRNA and protein expression for Kv4.2 or mRNA levels of the Kv4.2 regulators; KChIP2 and Irx-5 were not significantly altered by voluntary exercise. We conclude that voluntary exercise electrical remodelling is caused, at least in part, by a decrease in EPI I(to), possibly because of fewer functional channels in the membrane, which results in a fall in the transmural action potential duration gradient.

Electrocardiographic reference values in whippets

The aim of this study was to determine the electrocardiographic characteristics of whippets and to compare the results with published reference values for a general dog population. Electrocardiographic parameters from 105 healthy whippets were used to establish reference values for the breed. The most important differences compared to published reference values were the higher median R-wave amplitudes in leads II, CV(6)LL and CV(6)LU. For some parameters (P-wave amplitude, ST-segment deflection and T-wave amplitude in lead II; R-wave amplitude in CV(5)RL), a marked percentage of the whippet values were above the published maximum reference data. The results confirmed that whippets have electrocardiographic characteristics similar to those reported in athletic heart syndrome in humans. Some of these characteristics could be erroneously taken as evidence of cardiac disease and clinicians should be aware of these factors to prevent unnecessary investigations in healthy dogs.

Cardiac risk factors and participation guidelines for youth sports

Accurate assessment of the cardiac system in pediatric and adolescent youth is important. The hemodynamic demands associated with exercise, training, and sport participation are usually positive and beneficial; however, when an underlying cardiac problem exists, it is imperative that such cardiac problems be identified. Safe sport-related cardiac participation guidelines should be provided for young athletes and their families and coaches. This chapter provides a physician perspective on the recognition and current cardiac management considerations for young athletes participating in both static and dynamic types of sports. The most recent guidelines for hypertension in youth are also provided.

Different regional effects of voluntary exercise on the mechanical and electrical properties of rat ventricular myocytes

Short-term (6 weeks) voluntary wheel running exercise in young female rats that were in an active growth phase resulted in whole-heart hypertrophy and myocyte concentric hypertrophy, when compared to sedentary controls. The cross-sectional area of ventricular myocytes from trained rats was significantly greater than for those isolated from sedentary rats, with the greatest change in morphology seen in sub-endocardial cells. There was no statistically significant effect of training on cell shortening in the absence of external mechanical loading, in [Ca2+](i) transients, or in myofilament Ca2+ sensitivity (assessed during re-lengthening following tetanic stimulation). Under the external mechanical load of carbon fibres, absolute force developed in myocytes from trained rats was significantly greater than in those from sedentary rats. This suggests that increased myocyte cross-sectional area is a major contractile adaptation to exercise in this model. Training did not alter the passive mechanical properties of myocytes or the relative distribution of titin isomers, which was exclusively of the short, N2B form. However, training did increase the steepness of the active tension-sarcomere length relationship, suggesting an exercise-induced modulation of the Frank-Starling mechanism. This effect would be expected to enhance cardiac contractility. Training lengthened the action potential duration of sub-epicardial myocytes, reducing the transmural gradient in action potential duration. This observation may be important in understanding the cellular causes of T-wave abnormalities found in the electrocardiograms of some athletes. Our study shows that voluntary exercise modulates the morphological, mechanical and electrical properties of cardiac myocytes, and that this modulation is dependent upon the regional origin of the myocytes.