Herbs considered important for the cardiovascular system are classified according to traditional actions of cardioactive, cardioprotective, cardiotonic, and circulatory stimulants. Anticoagulants are a more modern application of herbs to cardiovascular disease and nervines and diuretic herbs are traditionally included in formulas. The diseases that are indicated for these herbs include cardiomyopathy (dilatative and hypertrophic), congestive heart failure / valvular disease, heartworm disease, and hypertension.
Cardioactive herbs are some of the most potentially toxic herbs. Many of these contain cardioactive glycosides such as Foxglove (Digitalis purpurea) and Lily of the Valley (Convallaria majalis), which are ionotropic and lead to a more efficient and coordinated cardiac contraction. Perhaps the most useful from a veterinary perspective is Bugleweed (Lycopus europaeus, L. virginicus). It does not contain cardiac glycosides but is still cardioactive. L. virginicus was recognized by the early Eclectics as an excellent sedative with properties similar to digitalis but without adverse side effects. L. europaeus may have applications in feline hyperthyroidism as well as cardiovascular disease. L. europaeus was compared to atenolol in hyper-thyroid rats (induced with thyroxine). Lycopus extract and atenolol reduced the increased heart rate and blood pressure. The cardiac hypertrophy was alleviated significantly by both treatment regimes. The Lycopus extract or the beta-blocking agent showed an almost equal efficacy in terms of significantly reduced beta-adrenoceptor density in heart tissue. Although the mode of action remains unclear, these organospecific antithyroid effects may help patients with latent hyperthyroidism.
Cardioprotective herbs are used by herbalists to reduce the risk of damage due to ischemia or toxins. Potential actions include increasing cardiac blood flow, raising intracellular levels of cAMP, reducing capillary fragility, reducing peripheral vascular resistance through vasorelaxant activity, reducing cholesterol, and reducing hypertension. These herbs are generally rich in flavonoids, providing antioxidant benefits for systems undergoing oxidative stress. Perhaps the best known and used cardioprotective herb is Hawthorn (Crataegus spp), although it is also mildly cardiotonic and possibly even mildly cardioactive. Its activity has been attributed to the flavonoid components, particularly the procyanidins. The beta-adrenoceptor blocking activity of flower, leaf, and fruit extracts (standardized for their procyanidin content) have been demonstrated in vivo in the dog and in vitro in the frog heart. Hawthorn has demonstrated hypotensive activity due to a vasodilation action rather than via adrenergic, muscarinic, or histaminergic receptors. Extracts increased coronary blood flow in vivo (in the dog, cat, and rabbit), reduced blood pressure in vivo (in the dog, cat, rabbit, and rat), increased (skeletal muscle, kidney, head) and reduced (gastrointestinal tract, skin) peripheral blood flow in vivo (in the dog), and reduced peripheral resistance in vivo (in the dog).
A crude extract of Crataegus has been reported to exert a protective action on experimental ischemic myocardium in anesthetized dogs. It was shown to decrease left ventricular work, decrease the consumption of oxygen index, and increase coronary sinus blood oxygen concentrations, resulting in a decrease in oxygen consumption and balance of oxygen metabolism. An increase in coronary blood flow was not observed, in contrast to other studies. The opposing results were attributed by the authors to variation in concentrations of active constituents in different plant parts.
Several clinical studies in humans support the use of Hawthorn. In mildly hypertensive humans, 500 mg daily of Hawthorn extract led to a reduction in diastolic blood pressure. In a randomized, double-blind, placebo-controlled trial involving 40 patients with chronic heart failure, a commercial Hawthorn / Passion flower extract (standardized on flavone and proanthocyanidin content) given at a dose of 6 mL daily for 42 days demonstrated significant improvements for the treatment group, compared with the placebo with regards to exercise capacity, heart rate at rest, diastolic blood pressure at rest, and concentrations of total plasma cholesterol and low-density lipids. In a randomized, double-blind, controlled trial in 60 patients with stable angina, 60 mg of Hawthorn 3 times daily was reported to increase coronary perfusion and reduce myocardial oxygen consumption. Thirty mg of Hawthorn extract (standardized to 1 mg procyanidin) was assessed in a double-blind, placebo-controlled study involving 80 patients. Compared to the placebo, treated patients showed greater overall improvement of cardiac function and symptoms such as dyspnea and palpitations, although there was no significant difference in ECG between the 2 groups. Most trials demonstrate the greatest effect after 6 to 8 weeks of use, and it may enhance the effects of cardiac glycosides.
Arjun tree (Terminalia arjuna) also reduced blood pressure and demonstrated positive inotropic activity and beta-2-adrenergic activity in an uncontrolled study in dogs. Astragalus (Astragalus membranaceus) can control a rise in blood pressure and lower the blood pressure of cats, dogs, and rats under anesthesia, and can increase coronary blood flow and decrease coronary circulation resistance (Modern traditional Chinese medicine Pharmacology). Garlic (Allium sativum) has mild antihypertensive properties in humans, rats, and dogs. Garlic reduced diastolic blood pressure and heart rate in a study in dogs.
Valerian (Valeriana officinalis), which is better known for its mild sedating properties, dilated pulmonary vascular smooth muscle in cats, probably via nonselective gamma-aminobutyric acid (GABA)-mediated mechanism. Dan Shen (Salvia miltiorrhiza) has traditionally been used in China for cardiovascular and cerebrovascular disease; and is contemporarily used in Chinese hospitals to treat angina, acute heart attacks, and hypertension and to assist in recovery from stroke. It improves coronary blood flow in dogs with experimental acute myocardial infarction. This may be a result of it improving the opening and formation of coronary collateral circulation, thereby protecting myocardia from ischemia. Korean ginseng (Panax ginseng) saponins have different actions on cardiac hemodynamics, including increasing and decreasing cardiac performance. They also have calcium antagonist activity and a protective effect on experimental myocardial infarction in rabbits. Tienchi ginseng (Panax notoginseng) increased coronary blood flow and had a positive inotropic effect in vitro.
Cardiotonic herbs, like cardioprotective herbs, have a gentle action on the heart compared to the cardioactive herbs which have a much more profound action. Withania (Witbania somnifera) is a very useful cardiotonic and general tonic for geriatric animals. The effect of Withania was studied on the cardiovascular and respiratory systems in dogs. The alkaloids had a prolonged hypotensive, bradycardiac activity and stimulated the vasomotor and respiratory centers in the brainstem of dogs. The cardioinhibitory action in dogs appeared to be due to ganglion blocking and direct cardiodepressant actions. Withania extract induced a significant decrease in arterial and diastolic blood pressure in normotensive pentobarbital-anesthetized dogs; 5 mg / kg of Withania extract caused a blood pressure drop in dogs (blocked by atropine, not by mepyramine or propranolol). Motherwort (Leonurus cardiaca) is traditionally used for palpitations, arrhythmias, and anxiety. One of its constituents, lavandulifolioside, causes decreased blood pressure, significant negative chronotropism, and prolongation of the P-Q and Q-T intervals and the QRS complex.
Circulatory stimulants are traditionally used to “warm” the circulation when there is stagnation of circulation or where blood flow is compromised. Ginkgo leaf extract (Ginkgo biloba) has been studied in normal rats and those with ischemic brain damage, and Ginkgo extract given at a dose of 100 mg / kg orally was reported to increase cerebral blood flow in normal rats. The increase was less marked in rats with cerebral artery occlusion, however. Dong guai (Angelica sinensis) (2 g / kg body weight) given intravenously to anesthetized dogs increased coronary blood flow from 88 ml before administration to 128 ml (per 100 g cardiac muscle / minute post-injection). Both coronary vascular resistance and myocardial oxygen consumption were reduced, while the heart rate decreased or remained unchanged. Dong guai injection also has a therapeutic effect in treating acute cerebral infarction in people. In rabbits with peripheral circulatory disturbances, Dan Shen (Salvia miltiorrhiza) tanshinone derivatives improved blood flow, de-aggregated red blood cells, and inhibited platelet activity. Dan Shen also provided good results in disseminated intravascular coagulation.
Nervines may be useful in animals with restlessness, insomnia, and anxiety associated with cardiovascular disease. Valerian (Valeriana officinalis), when compared to a placebo, significantly attenuated heart rate and blood pressure changes in people. Others include Lemon balm (Melissa officinalis), Motherwort (Leonurus cardiaca), and Linden (Tilia platyphyllos).
Many herbs, including the cardioactive herbs, have traditionally been used to treat “dropsy;” there are too many to list here. Herbs such as Parsley (Petroselinum crispum) and Dandelion are frequently included in formulas for heart disease. Dandelion leaf (Taraxacum officinale) extracts given orally had a diuretic effect in rats and mice, and the effect was assessed as equal to that of furosemide and stronger than Juniper berry and Horsetail. However, diuretic activity was not observed in another study after oral or intraperitoneal administration.
Anticoagulant herbs are a more modern application and probably have more use in human medicine; however, their use may be important in conditions associated with thrombosis. Garlic (Allium sativum) inhibits platelet aggregation; however, its potential for red blood cell toxicity in cats and dogs may limit its use. In this author’s experience, the tincture does not appear to cause this problem. Ginkgo extract (Ginkgo biloba) containing ginkgolides inhibits platelet aggregating factors (PAF); this may have additive effects for human patients or cats taking anticoagulants to prevent thrombosis. Dan Shen (Salvia miltiorrhiza) inhibits platelet activity, has antithrombin Ill-like activity, and promotes fibrinolysis. In rats fed a high-cholesterol diet, Korean ginseng (Panax ginseng) reduced serum cholesterol and triglycerides, decreased platelet adhesiveness, and decreased fatty changes to the liver. Ginseng has also been shown to reduce blood coagulation and enhance fibrinolysis.