Effect of Exercise on Systolic Left Ventricular Outflow Velocity in Healthy Adults

INTRODUCTION

Cases of exercise-induced left intraventricular pressure gradient detected thru exercise Doppler echocardiography have been reported recently.^1-3 The clinical significance of this condition has not been definitively established although it may be related to symptoms of dyspnea or effort angina of no apparent cause.^2,3

The presence of small pressure gradients in healthy ventricles, detected with high fidelity 6-10 mm Hg magnitude micromanometers was described some years ago.^4,5 More recently, Yotti et al⁶ confirmed their existence and the possibility of recording them with Doppler echocardiography. However, the information available about flow velocity behavior and intraventricular gradients during exercise in healthy adults⁷ is limited. Consequently, values that might be considered "normal" during exercise are poorly-defined.

The objective of this study is to analyze the behavior of systolic left ventricular outflow velocity (SLVO) during exercise in healthy adults.

PATIENTS AND METHOD

We studied 23 healthy, male volunteers, without pathologic antecedents whose physical examination, electrocardiogram and Doppler echocardiogram gave normal results.

Baseline and post-exercise echocardiography was performed by an experienced cardiologist with a VingMed echocardiograph equipped with Super-VHS recording system and Pinnacle DV500 Plus video-digitalizer, using a 2.5-3.25 MHz probe

We performed a complete standard baseline Doppler echocardiogram. Measurements were taken according to American Society of Echocardiography recommendations.⁸

Immediately after exercise (30-60 s), with the volunteer in lateral decubitus, we again analyzed SLVO, transmitral flow and systolic function.

Exercise was taken on a Marquette Case 8000 treadmill ergometer (Marquette Medical Systems Inc., Milwaukee, US) following the Bruce protocol after 4 hours fasting, and continued until subjects presented symptoms of exhaustion or achieved maximum theoretical heart rate.

RESULTS

The 23 subjects were men of age 32.5±5.9 years (range, 25-45), weight 78.7±7.1 kg, height 176.6±4.9 cm, mean body mass index 25.7±2.4, and body surface area 1.94±0.09 (range, 1.74±2.13). Baseline echocardiogram data appears in Table 1. Maximum SLVO velocity at rest was 0.77-1.44 m/s, mean 1.07±0.18 m/s.

Mean exercise time was 12 min 45 s±2 min 32 s after which subjects achieved a mean heart rate of 97.6±6.7% of the estimated theoretical maximum for their age. Data relative to performance is in Table 2.

Following exercise (Table 3), maximum SLVO velocity was 1.09-2.45 m/s (mean, 1.58±0.35 m/s). None of the subjects presented morphology indicating dynamic gradient or anterior movement of the mitral valve.

DISCUSSION

The appearance of left intraventricular gradients in patients without hypertrophic cardiomyopathy is well documented in relation to hypercontractile states,⁹ following valvular surgery,^10-13 acute coronary syndromes,^14,15 or dobutamine stress echocardiography.^16,17 Recently, it has also been reported in relation with exercise.^1-3,18 Elsewhere, we reported on a series³ that constitued a population with high incidence of hypertension and of women in which the only predictor factor of this phenomenon was left ventricular outflow tract diameter.

However, the presence of small intraventricular gradients in healthy ventricles is known. In 1980, Falsetti et al⁴ found 2.10±0.47 mm Hg gradients between the left ventricular apex and base using high precision micromanometers in dogs. Later, Pasipoularides et al⁵ also used catheters in 6 patients without valvular or ventricular abnormalities and found gradients at rest of 6.7±1.9 mm Hg, which increased to 13±2.3 mm Hg following bicycle exercise. More recently, Yotti et al⁶ have confirmed the existence of this phenomenon and the possibility of recording it using a new echocardiographic method, detecting values of 3.3±1.6 mm Hg in 20 healthy volunteers at rest.

However, little data is available on the behavior of these small "physiologic" gradients during physical exercise.⁷ In the series of 6 cases, Pasipoularides et al⁵ specifically studied this aspect and found that gradients doubled with submaximal physical exercise of decubitus pedaling.

Various studies^19,20 related with the effects of exercise show an increase in SLVO velocities during exercise and, although they studied different populations, none of them found a two-fold increase in flow velocity at rest.

In our series of 23 healthy volunteers, SLVO flow velocity exceeded 1.07±0.18 m/s (range, 0.77-1.44) at rest, reaching 1.58±0.35 m/s (range, 1.09-2.45) after exercise, which represents a 50% increase.

These data suggest that, in the post-exercise treadmill echocardiogram, SLVO velocities of 1.58±0.35 m/s, with a range of 1 up to 2.4 m/s can be considered normal.

We conclude that maximum exercise tolerated by healthy adults increases left ventricular outflow velocity by up to 50% but that in no case does it reach 2.5 m/s. Although this does not entirely exclude the possibility that elevated intraventricular gradients may be a habitual response to exercise in healthy adults, it does make this highly unlikely.

Limitations of the Study

In addition to the sample size, this study is limited by the fact that the SLVO velocities were recorded immediately after exercise and not during maximum exercise. This is inevitable with treadmill exercise but could lead to an underestimate, given the tendency to diminish in the minutes after ceasing exercise, despite the fact we recorded high levels of exercise (97.61±6.71%).

This series only included young men. Although this implies a bias in terms of gender and age, we considered on this study design to facilitate optimization of echocardiographic images (as pectoral anatomy is easier in men) and to attain high levels of exercise. Moreover, the appearance of dynamic obstruction during exercise has not been linked with gender.³

Use of the simplified Bernouilli equation to calculate intraventricular gradients in these cases is inexact due to the absence of anatomic obstruction and the relatively low velocities; consequently, it may be more adequate to express results in terms of velocity without transforming this into gradient, or rather, to apply the recently described method of measurement with color M-mode Doppler⁶.

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Correspondence: Dr. F. Cabrera Bueno.
Madame Bovary, 21, casa 14. 29620 Torremolinos. Málaga. España.
E-mail: [e-mail]

Received January 31, 2005.
Accepted for publication May 13, 2006.