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.
Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
M
M
Takagaki
P M
PM
McCarthy
M
M
Chung
J
J
Connor
R
R
Dessoffy
Y
Y
Ochiai
M
M
Howard
K
K
Doi
M
M
Kopcak
T N
TN
Mazgalev
K
K
Fukamachi
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