Regional Mechanical Changes Assessed by 2D Speckle-Tracking Longitudinal Strain do not Parallel Electrical...

Cardiac memory (CM) refers to persistent T-wave changes that appear after cessation of a period of abnormal ventricular activation, such as ventricular pacing. Prior animal studies using tagged magnetic resonance imaging have suggested that CM is associated with prolonged action potential duration and increased strain of late-activated myocardial segments.

The aim of the present study is to determine whether CM induced by ventricular pacing in human subjects is accompanied by regional mechanical changes in late-activated myocardial segments, assessed by left ventricular (LV) longitudinal strain (peak LS) and time-to-peak longitudinal strain (TTP-LS), using 2D-speckle tracking echocardiography (2DSE).

We included 20 patients (16 women, age 71±11 years), with DDD pacemakers and with normal AV conduction and QRS/T morphology at baseline. CM was induced by DDD pacing with a short AV delay. ECGs and 2DSE were performed before pacing (baseline), at peak CM (immediately after two weeks of pacing), and at CM washout (4 weeks after cessation of pacing). We measured by echocardiography: left ventricular (LV) ejection fraction, LV diastolic function (E, A, E/E'), peak LS and TTP-LS for the earliest (i.e. adjacent to the pacing site) and latest (i.e. latest-activated during ventricular pacing) segments, using an 18-segment LV model.

All patients had electrical (ECG) CM changes, which disappeared by CM washout. LV global systolic and diastolic functions, as well as regional LS (peak LS for both the latest and earliest activated segments) were similar between evaluations. TTP for the latest and earliest activated segments, as well as mean TTP-LS, increased from baseline to peak CM, but did not decrease at CM washout. The dispersion of TTP-LS was not changed.

These results suggest that regional mechanical changes, as can be assessed by 2DSE longitudinal strain, do not overlap electrical CM.