Key result
CRT normalizes the ~3 mmHg rise in mean LAP and reduced diastolic distensibility during LBBB tachycardia.
Why the study?
The study investigated whether tachycardia in LBBB decreases LV diastolic distensibility and increases diastolic pressures due to incomplete relaxation, and if CRT modifies this response.
Does cardiac resynchronization therapy improve left ventricular diastolic distensibility and reduce diastolic pressures during tachycardia in a canine model of left bundle branch block?
Does cardiac resynchronization therapy improve left ventricular diastolic distensibility and reduce diastolic pressures during tachycardia in a canine model of left bundle branch block?
p-value: p=<0.006
In a canine model, tachycardia during LBBB impairs LV relaxation and increases diastolic pressures, effects which are normalized by cardiac resynchronization therapy.
CRT may normalize tachycardia-induced LA pressure rise and diastolic impairment in LBBB; leaves open clinical translation pending human studies.
We investigated whether tachycardia in left bundle branch block (LBBB) decreases left ventricular (LV) diastolic distensibility and increases diastolic pressures due to incomplete relaxation, and if cardiac resynchronization therapy (CRT) modifies this response. Thirteen canines were studied at baseline heart rate (120 beats/min) and atrial paced tachycardia (180 beats/min) before and after induction of LBBB and during CRT. LV and left atrial pressures (LAP) were measured by micromanometers and dimensions by sonomicrometry. The time constant τ of exponential pressure decay and degree of incomplete relaxation at mitral valve opening (MVO) and end diastole (ED) based on extrapolation of the exponential decay were assessed. Changes in LV diastolic distensibility were investigated using the LV transmural pressure-volume (PV) relation. LBBB caused prolongation of τ ( P < 0.03) and increased the degree of incomplete relaxation during tachycardia at MVO ( P < 0.001) and ED ( P = 0.08) compared with normal electrical activation. This was associated with decreased diastolic distensibility seen as upward shift of the PV relation at MVO by 18.4 ± 7.0 versus 12.0 ± 5.0 mmHg, at ED by 9.8 ± 2.3 versus 4.7 ± 2.3 mmHg, and increased mean LAP to 11.4 ± 2.7 versus 8.5 ± 2.6 mmHg, all P < 0.006. CRT shifted the LV diastolic PV relation downwards during tachycardia, reducing LAP and LV diastolic pressures ( P < 0.03). Tachycardia in LBBB reduced LV diastolic distensibility and increased LV diastolic pressures due to incomplete relaxation, whereas CRT normalized these effects. Clinical studies are needed to determine whether a similar mechanism contributes to dyspnea and exercise intolerance in LBBB and if effects of CRT are heart rate dependent. NEW & NOTEWORTHY Compared with normal electrical conduction, tachycardia in left bundle branch block resulted in incomplete relaxation during filling, particularly of the late activated left ventricular lateral wall. This further resulted in reduced left ventricular diastolic distensibility and elevated diastolic pressures and thus amplified the benefits of cardiac resynchronization therapy in this setting.
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Andersen et al. (2020) studied Left bundle branch block (n=13). Cardiac resynchronization therapy (CRT) vs. Normal electrical activation / Baseline was evaluated on Left ventricular diastolic distensibility and diastolic pressures (p=<0.006). Tachycardia in left bundle branch block increased mean left atrial pressure (11.4 vs 8.5 mmHg, P<0.006) and reduced diastolic distensibility, whereas CRT normalized these effects (P<0.03).
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