Apex-to-base dispersion in regional timing of left ventricular shortening and lengthening.
OBJECTIVE
We investigated whether the onset and progression of regional left ventricular (LV) shortening and lengthening parallel the apex-to-base differences in depolarization and repolarization.


BACKGROUND
Limited information exists regarding apex-to-base differences in longitudinal and circumferential deformation sequence of the LV.


METHODS
The apex-to-base differences in electric activation and the progression of longitudinal and circumferential shortening and lengthening sequences were determined in 8 porcine beating hearts in situ by implanting bipolar electrodes and an array of 14 sonomicrometry crystals in the LV free wall.


RESULTS
Electric activation started at the apical subendocardium and showed significant delay in reaching the LV base. The onsets of mechanical activation and subsequent 20%, 40%, and 80% peak longitudinal shortenings required longer time to occur at base compared to the apex. The repolarization sequence propagated in reverse, with the base repolarizing before the apex. Subendocardial longitudinal shortening at base and subepicardial circumferential shortening at apex continued beyond the period of LV ejection, resulting in an apex-to-base gradient in the onset of lengthening. This gradient correlated with the duration of isovolumic relaxation (r = 0.85, p = 0.004) and the time required for reaching the lowest LV diastolic pressure (r = 0.70, p = 0.04).


CONCLUSIONS
Apex-to-base delay in mechanical shortening of LV parallels the apex-to-base direction of the electric activation sequence. Basal subendocardial and apical subepicardial regions deform through a characteristic phase of postsystolic shortening. Short-lived apex-to-base and subendocardial-to-subepicardial relaxation gradients at the onset of diastole may have a physiologic significance in facilitating active restoration of the LV cavity in diastole.
Sengupta
Partho P
PP
Division of Cardiovascular Diseases, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Khandheria
Bijoy K
BK
Korinek
Josef
J
Wang
Jianwen
J
Jahangir
Arshad
A
Seward
James B
JB
Belohlavek
Marek
M
D000818:Animals; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D009200:Myocardial Contraction / Q000502:physiology*; D013552:Swine; D016277:Ventricular Function, Left / Q000502:physiology*