The J-Curve Between BP and CAD or Essential Hypertension
The topic of the J-curve relationship between blood pressure and coronary artery disease (CAD) has been the subject of much controversy for the past decades. An inverse relationship between diastolic pressure and adverse cardiac ischemic events (i.e., the lower the diastolic pressure the greater the risk of coronary heart disease and adverse outcomes) has been observed in numerous studies. This effect is even more pronounced in patients with underlying CAD. Indeed, a J-shaped relationship between diastolic pressure and coronary events was documented in treated patients with CAD in most large trials that scrutinized this relationship. In contrast to any other vascular bed, the coronary circulation receives its perfusion mostly during diastole; hence, an excessive decrease in diastolic pressure can significantly hamper perfusion. This adverse effect of too low a diastolic pressure on coronary heart disease leaves the practicing physician with the disturbing possibility that, in patients at risk, lowering blood pressure to levels that prevent stroke or renal disease might actually precipitate myocardial ischemia. However, these concerns should not deter physicians from pursuing a more aggressive control of hypertension, because currently blood pressure is brought to recommended target levels in only approximately one-third of patients.
The term "essential hypertension" was coined by Frank almost a century ago by stating "Because in this disease the increase in tone of the small arteries in the whole body (which leads to an increase in blood pressure) is the primary event…I will, in the following, name this disease, essential hypertension (essentielle Hypertonie)." The concept of hypertension being essential (i.e., serving to force blood through sclerotic arteries to the target organs) remained alive and well into the 1970s, and statements like "For aught we know, the hypertension might be a compensatory mechanism that should not be tampered with even were it certain that we could control it" and "May not the elevation of blood pressure be a natural response to guarantee a more normal circulation to the heart, brain and kidneys" continued to appear in published reports and spook physicians. This concept also instigated fear that, in susceptible patients, blood pressure (BP) could be lowered too much. Hence, the reluctance of many physicians to expose patients to antihypertensive therapy is not surprising, because abrupt lowering of BP in hypertensive emergencies, paradoxically, can increase target organ disease such as renal failure, encephalopathy, and coronary ischemia and even directly cause heart attacks, stroke, and death. Gradually, however, the pendulum began to swing toward the other extreme, and the dictum, "the lower the better," became the leitmotiv for most physicians treating hypertension. The large, thorough meta-analysis of Lewington et al. corroborated and amplified this concept by stating that "usual BP is strongly and directly related to vascular (and overall) mortality without any evidence of a threshold down to at least 115/75 mm Hg." Statements like these threatened to put an end to the "essentiality" of essential hypertension.
Abstract and Introduction
Abstract
The topic of the J-curve relationship between blood pressure and coronary artery disease (CAD) has been the subject of much controversy for the past decades. An inverse relationship between diastolic pressure and adverse cardiac ischemic events (i.e., the lower the diastolic pressure the greater the risk of coronary heart disease and adverse outcomes) has been observed in numerous studies. This effect is even more pronounced in patients with underlying CAD. Indeed, a J-shaped relationship between diastolic pressure and coronary events was documented in treated patients with CAD in most large trials that scrutinized this relationship. In contrast to any other vascular bed, the coronary circulation receives its perfusion mostly during diastole; hence, an excessive decrease in diastolic pressure can significantly hamper perfusion. This adverse effect of too low a diastolic pressure on coronary heart disease leaves the practicing physician with the disturbing possibility that, in patients at risk, lowering blood pressure to levels that prevent stroke or renal disease might actually precipitate myocardial ischemia. However, these concerns should not deter physicians from pursuing a more aggressive control of hypertension, because currently blood pressure is brought to recommended target levels in only approximately one-third of patients.
Introduction
The term "essential hypertension" was coined by Frank almost a century ago by stating "Because in this disease the increase in tone of the small arteries in the whole body (which leads to an increase in blood pressure) is the primary event…I will, in the following, name this disease, essential hypertension (essentielle Hypertonie)." The concept of hypertension being essential (i.e., serving to force blood through sclerotic arteries to the target organs) remained alive and well into the 1970s, and statements like "For aught we know, the hypertension might be a compensatory mechanism that should not be tampered with even were it certain that we could control it" and "May not the elevation of blood pressure be a natural response to guarantee a more normal circulation to the heart, brain and kidneys" continued to appear in published reports and spook physicians. This concept also instigated fear that, in susceptible patients, blood pressure (BP) could be lowered too much. Hence, the reluctance of many physicians to expose patients to antihypertensive therapy is not surprising, because abrupt lowering of BP in hypertensive emergencies, paradoxically, can increase target organ disease such as renal failure, encephalopathy, and coronary ischemia and even directly cause heart attacks, stroke, and death. Gradually, however, the pendulum began to swing toward the other extreme, and the dictum, "the lower the better," became the leitmotiv for most physicians treating hypertension. The large, thorough meta-analysis of Lewington et al. corroborated and amplified this concept by stating that "usual BP is strongly and directly related to vascular (and overall) mortality without any evidence of a threshold down to at least 115/75 mm Hg." Statements like these threatened to put an end to the "essentiality" of essential hypertension.