"Summer Dizziness" as a Neglected Phenomenon of Antihypertensive Drug Overuse in Patients With Carotid Disease: A Hypothesis.

Abstract

Our service deals with nearly 1000 carotid endarterectomies and 200 carotid stent implantations annually. We noticed an increased incidence of cerebral ischemic symptoms in patients with carotid disease during summer. According to our database, nearly 90% of our patients with carotid disease have associated hypertension, while 70% of recently symptomatic patients were using 3 antihypertensive drugs when referred to our clinic. Sweating, dehydration, and antihypertensive drug overuse in patients with carotid disease may contribute to cerebral hypoperfusion and transient ischemic attack (TIA). Several authors reported blood pressure (BP) seasonal variations with decreased BP in summer due to heat, probable seasonal impact on the vasomotor BP mechanism, and dehydration. Rosenthal found that BP is higher in winter due to increased sympathetic tone, while lower BP in summer is the result of cutaneous vasodilatation as well as loss of water and salt from sweating. These findings suggested the need for individually tailored antihypertensive medication management. Similarly, Weiss et al reported that orthostatic BP drop was greater in the morning in summer than in winter with overall orthostatic hypotension in all patients being higher by 64% in summer than in winter. In winter, there may be a greater load of risk factors predisposing to TIA/stroke than in summer. The ‘‘summer dizziness’’ hypothesis is largely restricted to patients with carotid stenosis that affects cerebral perfusion if hypotension occurs. This may not compensate for an overall greater risk of TIA/ stroke in winter. A sudden BP drop during summer should be specially emphasized. Hypertension is involved in the pathogenesis of carotid atherosclerosis. For example, in 263 patients with hypertension, hypertension strongly influenced carotid intima–media thickness and atherosclerosis development. Nevertheless, hypotension in patients with carotid stenosis and hypertension might be associated with TIA. Transient ischemic attack is an episode of reversible focal cerebral ischemia resulting in temporary neurological deterioration that is a predictor of stroke. A probable mechanism causing a TIA in patients having hypotension with carotid stenosis is decreased cerebral blood flow, altered autoregulation, and impaired baroreceptor function. Ruff et al assessed the role of hypotension in 132 patients with diagnosed TIA. Seven patients had TIAs preceded by hypotension with an average decrease in BP during the attack of 26.4 + 5.5 mm Hg. The patients with hypotension-related TIAs had a higher incidence of hypertension (7/7 vs 14/20, P < .2) and carotid artery stenosis (4/4 vs 0/20, P < .001). Similarly, Belcaro and Marchionno reported 10 cases of hypotensive TIA in patients with hypertension and carotid stenosis. We draw attention to a potential new entity, hypotensive TIAs in patients with hypertension and carotid stenosis due to excessive use of antihypertensive drugs during summer. In patients with carotid stenosis, not yet needing intervention, the BP should be adequate to maintain cerebral perfusion. A sudden decrease in BP might result in decreased flow distal to the stenosis causing focal cerebral ischemia. In 70% of the patients referred to our clinic after TIA or stroke, BP was lower than their usual values by an average of 30 to 40 mm Hg at the time of ischemic attack according to medical records. Patients and physicians are usually driven by routine antihypertensive drug schemes regardless of time of the year. Furthermore, cardiologists focus on the BP, neurologists on rehabilitation, and vascular surgeons on revascularization. In this triangle, the hypotension concept may not be noticed. Possibly, in patients with significant carotid disease, drug dosage should be decreased during the summer to avoid cerebral ischemia and hypoperfusion that might result in TIA or stroke. Inadequate engagement and awareness of both patients and physicians might lead to adverse consequences. Frequent home BP monitoring in patients with known carotid stenosis throughout the year, and especially during summer, with antihypertensive drug dose adjustment might help prevent cerebral ischemia symptoms.