Preload-adjusted maximal power: a novel index of left ventricular contractility in atrial fibrillation.
BACKGROUND
Left ventricular contractility in atrial fibrillation is known to change in a beat to beat fashion, but there is no gold standard for contractility indices in atrial fibrillation, especially those measured non-invasively.


OBJECTIVE
To determine whether the non-invasive index of contractility "preload-adjusted PWR(max)" (maximal ventricular power divided by the square of end diastolic volume) can accurately measure left ventricular contractility in a beat to beat fashion in atrial fibrillation.


METHODS
Atrial fibrillation was induced experimentally using 60 Hz stimulation of the atrium and maintained in 12 sheep; four received diltiazem, four digoxin, and four no drugs (control). Aortic flow, left ventricular volume, and left ventricular pressure were monitored simultaneously. Preload-adjusted PWR(max), the slope of the end systolic pressure-volume relation (E(max)), and the maximum rate of change of left ventricular pressure (dP/dt(max)) were calculated in a beat to beat fashion.


RESULTS
Preload-adjusted PWR(max) correlated linearly with load independent E(max) (p < 0.0001) and curvilinearly with load dependent dP/dt(max) (p < 0.0001), which suggested the load independence of preload-adjusted PWR(max). After five minutes of diltiazem administration, preload-adjusted PWR(max), dP/dt(max), and E(max) fell significantly (p < 0.0001) to 62%, 64%, and 61% of baseline, respectively. Changes were not significant after five minutes of digoxin (103%, 98%, and 102%) or in controls (97%, 96%, and 95%).


CONCLUSIONS
Preload-adjusted PWR(max) correlates linearly with E(max) and is a useful measure of contractility even in atrial fibrillation. Non-invasive application of this method, in combination with echocardiography and tonometry, may yield important information for optimising the treatment of patients with atrial fibrillation.
Takagaki
M
M
Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
McCarthy
P M
PM
Chung
M
M
Connor
J
J
Dessoffy
R
R
Ochiai
Y
Y
Howard
M
M
Doi
K
K
Kopcak
M
M
Mazgalev
T N
TN
Fukamachi
K
K
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001281:Atrial Fibrillation / Q000503:physiopathology*; D002317:Cardiovascular Agents / Q000494:pharmacology; D004077:Digoxin / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D009200:Myocardial Contraction / Q000502:physiology*; D012756:Sheep; D016277:Ventricular Function, Left / Q000502:physiology*
D000889:Anti-Arrhythmia Agents; D002317:Cardiovascular Agents; D004077:Digoxin; D004110:Diltiazem