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294  Section G: Congestive Heart Failure


              •	 Treatment	of	moderate	(nonregenerative)	anemia	with	  used  in  cats  with  refractory  heart  failure,  but  it  may
                erythropoietin	may	lessen	degree	of	volume	overload	  lessen  hypokalemia  and  reduce  potential  deleterious
                to	the	heart	and	improve	oxygen	handling	capacity.  effects  of  aldosterone  on  the  cardiovascular  system.
              •	 Pimobendan	is	a	positive	inotrope	and	balanced	arte-  Spironolactone  is  an  extremely  weak  diuretic,  so  it
                riolar	 and	 venous	 vasodilator	 and	 is	 used	 to	 treat	  should not be expected to significantly reduce the sever-
                refractory	heart	failure	in	all	etiologies	except	hyper-  ity of edema or pleural effusion accumulation (Jeunesse
                trophic	cardiomyopathy.	Treatment	of	refractory	heart	  et al. 2007). In a study of Maine coon cats and Maine
                failure	secondary	to	HCM	with	pimobendan	is	con-  coon  crossbred  cats  with  familial  HCM,  one-third  of
                troversial,	with	some	positive	anecdotal	experience.  cats treated with spironolactone developed severe ulcer-
                                                                 ative dermatitis attributed to a cutaneous drug reaction,
              Refractory heart failure patients are defined as suffering   and other cardiologists have similar anecdotal reports in
              from  recurrent  pulmonary  edema  or  pleural  effusion   some Maine coon cats (MacDonald et al. 2008). Another
              despite multidrug therapy including high dose furose-  option for refractory heart failure is substituting 1 to 2
              mide (3–4 mg/kg PO q 8 h) and an ACE inhibitor (see   subcutaneous doses of furosemide a week for the oral
              Table 19.1). These patients most commonly have been   doses,  since  oral  bioavailability  of  furosemide  is  only
              undergoing chronic treatment for months to years and   ∼50% and may be lower if GI edema, inappetence, or
                                                                 other  factors  interfere  with  absorption.  If  palatable,  a
              have suffered relapses in heart failure that have responded
      Congestive Heart Failure  tinue to have a good quality of life in the owner’s opinion.   limit sodium and water retention and should be tried.
                                                                 low-salt  diet  (0.15–0.2 g  sodium/1000 kcal)  will  help
              to increases in diuretic doses. Typically these cats con-
              Treatment  of  refractory  heart  failure  is  differentiated
                                                                 However, any commercial diet is preferable to anorexia,
              from terminal heart failure by subjective assessment: the
                                                                 and the furosemide dose is then raised accordingly to
              owner and the attending veterinarian agree that treat-
                                                                 offset increased sodium intake. Pimobendan (0.25 mg/
              ment and monitoring for improvement are humane and
                                                                 failure  from  all  etiologies  except  pressure  overload  or
              justified based on the cat’s demeanor and medical status.
              Eventually,  refractory  heart  failure  deteriorates  into  a   kg PO q 12 h) may be added in cats with refractory heart
                                                                 hypertrophic  cardiomyopathy.  Treatment  of  cats  with
              terminal state, when there is failure to respond to rescue/  HCM and heart failure with pimobendan is controver-
              refractory treatments, and end-of-life decisions must be   sial and may be contraindicated if there is significant left
              discussed.                                         ventricular outflow tract obstruction.
                 In cats with refractory heart failure, the first task is to
              increase the furosemide dose to the maximal tolerable   Other Loop Diuretics: Torsemide
              dose, and the maximal oral effective dose above which   Torsemide is a loop diuretic that has 10 times the potency
              no further diuretic effect is achieved is generally consid-  of furosemide. Although it is not typically used in clinical
              ered to be 4 mg/kg orally every 8 hours. If heart failure   medicine,  there  are  several  potential  advantages  over
              continues to recur, addition of a second diuretic (hydro-  furosemide. Torsemide has a longer acting diuretic effect,
              chlorothiazide  0.5–1 mg/kg  PO  q  12 hr  or  torsemide   with a peak effect in cats seen 4 hours after oral adminis-
              0.1–0.3 mg/kg  PO  q  12 hr)provides  additional  diuresis   tration (0.3 mg/kg) that persists for 12 hours, compared
              by inhibiting sodium absorption distal to furosemide’s   to only 6 hours of diuretic effect after oral administration
              site of action. Cats receiving high dose furosemide and   of furosemide (Uechi et al. 2003). Torsemide is nearly
              hydrochlorothiazide (1–2 mg/kg PO q 12 h) are prone to   completely absorbed from the gastrointestinal tract, and
              developing  significant  dehydration  and  azotemia.  The   has a high bioavailability of 80–100% in dogs, compared
              goal in these patients with advanced cardiac disease is to   to approximately 50% bioavailability of furosemide in
              balance some degree of dehydration and azotemia with   dogs (Ghys et al. 1985). Another advantage of torsemide
              reduced dyspnea and improved quality of life. Thiazide   over  furosemide  is  that  it  inhibits  the  secretion  and
              diuretics  are  1/3  as  potent  as  furosemide  for  urinary   receptor-ligand  binding  of  aldosterone  (Uchida  et  al.
              sodium  excretion.  They  inhibit  the  sodium  chloride   1992; Goodfriend et al. 1998). Torsemide, but not furose-
              cotransporter  in  the  distal  convoluted  tubule,  down-  mide, decreases myocardial fibrosis and collagen synthe-
              stream  from  the  site  of  action  of  loop  diuretics,  thus   sis in people with heart failure, which may be due to its
              exerting “sequential  nephron  blockade”  (Brater  1998).   inhibition of aldosterone (Lopez et al. 2004). Similarly,
              In an experimental feline isolated kidney model, chloro-  torsemide improves left ventricular diastolic function in
              thiazide doubled the urinary excretion of sodium and   heart failure patients to a greater extent than furosemide
              increased urinary loss of water and potassium (De Lima   and is associated with a lower mortality than furosemide
              and  Lockett  1961).  Spironolactone  (1–2 mg/kg  PO  q   in people with heart failure (Yamato et al. 2003; Cosin et
              12–24 h),  an  aldosterone  antagonist,  is  uncommonly   al. 2002). Currently, the authors consider adding torse-
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