Arrhythmogenic effect of high blood pressure: some observations on its mechanism

Left ventricular hypertrophy and sudden cardiac death

Sudden cardiac death (SCD) is among the leading causes of death worldwide, and it remains a public health problem, as it involves young subjects. Current guideline-directed risk stratification for primary prevention is largely based on left ventricular (LV) ejection fraction (LVEF), and preventive strategies such as implantation of a cardiac defibrillator (ICD) are justified only for documented low LVEF (i.e., ≤ 35%). Unfortunately, only a small percentage of primary prevention ICDs, implanted on the basis of a low LVEF, will deliver life-saving therapies on an annual basis. On the other hand, the vast majority of patients that experience SCD have LVEF > 35%, which is clamoring for better understanding of the underlying mechanisms. It is mandatory that additional variables be considered, both independently and in combination with the EF, to improve SCD risk prediction. LV hypertrophy (LVH) is a strong independent risk factor for SCD regardless of the etiology and the severity of symptoms. Concentric and eccentric LV hypertrophy, and even earlier concentric remodeling without hypertrophy, are all associated with increased risk of SCD. In this paper, we summarize the physiology and physiopathology of LVH, review the epidemiological evidence supporting the association between LVH and SCD, briefly discuss the mechanisms linking LVH with SCD, and emphasize the need to evaluate LV geometry as a potential risk stratification tool regardless of the LVEF.

Cardiac Mechano-Electric Coupling: Acute Effects of Mechanical Stimulation on Heart Rate and Rhythm

The heart is vital for biological function in almost all chordates, including humans. It beats continually throughout our life, supplying the body with oxygen and nutrients while removing waste products. If it stops, so does life. The heartbeat involves precise coordination of the activity of billions of individual cells, as well as their swift and well-coordinated adaption to changes in physiological demand. Much of the vital control of cardiac function occurs at the level of individual cardiac muscle cells, including acute beat-by-beat feedback from the local mechanical environment to electrical activity (as opposed to longer term changes in gene expression and functional or structural remodeling). This process is known as mechano-electric coupling (MEC). In the current review, we present evidence for, and implications of, MEC in health and disease in human; summarize our understanding of MEC effects gained from whole animal, organ, tissue, and cell studies; identify potential molecular mediators of MEC responses; and demonstrate the power of computational modeling in developing a more comprehensive understanding of ‟what makes the heart tick.ˮ.

Preparation and Characterization of the Sulfobutylether-β-Cyclodextrin Inclusion Complex of Amiodarone Hydrochloride with Enhanced Oral Bioavailability in Fasted State

Amiodarone hydrochloride (AMD) is used in the treatment of a wide range of cardiac tachyarrhythmias, including both ventricular fibrillation (VF) and hemodynamically unstable ventricular tachycardia (VT). The objectives of this study were to improve the solubility and bioavailability in fasted state and to reduce the food effect of AMD by producing its inclusion complex with sulfobutylether-β-cyclodextrin (SBE-β-CD). The complex was prepared through a saturated water solution combined with the freeze-drying method and then characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The solubilities of AMD and its complex were 0.35 and 68.62 mg/mL, respectively, and the value of the inclusion complex was significantly improved by 196-fold compared with the solubility of free AMD. The dissolution of the AMD-SBE-β-CD inclusion complex in four different dissolution media was larger than that of the commercial product. The cumulative dissolution was more than 85% in water, pH 4.5 NaAc-HAC buffer, and pH 1.2 HCl aqueous solution. Moreover, the pharmacokinetic study found that the C _max, AUC_(0-t), and AUC_(0-∞) of the AMI-SBE-β-CD inclusion complex had no significant difference in fasted and fed state, which indicated that the absorption of the AMI-SBE-β-CD inclusion complex in fasted state was increased and not affected by food.

Heterogeneity of ventricular repolarization in newborns with severe aortic coarctation

Sudden death is a possible occurrence for newborns younger than 1 year with severe aortic coarctation (CoA) before surgical correction. Basic research and animal experiments have shown electrophysiologic changes during mechanical ventricular pressure overload. The current study aimed to evaluate the effect of severe CoA on the heterogeneity of ventricular repolarization by examining corrected QT and JT interval dispersion (respectively, QTc-D and JTc-D) and electrocardiographic parameters of spatial heterogeneity of ventricular repolarization in newborns with no associated congenital cardiac malformations. The study enrolled 30 isolated severe CoA neonates (age, 45 ± 15 days; 17 males) with normal size and wall thickness of the left ventricle before surgical correction and 30 age- and sex-matched healthy newborns used as control subjects. Heart rate, QRS duration, maximum and minimum QT and JT intervals, and QTc-D and JTc-D measurements were performed. The healthy control group did not significantly differ from the CoA group in terms of heart rate, weight, height, and echocardiographic parameters. Compared with the healthy control group, the CoA group presented significantly increased values of QTc-D (109.7 ± 43.4 vs. 23 ± 15 ms; P = 0.03) and JTc-D (99.1 ± 43.3 vs. 65.8 ± 24.1 ms; P = 0.04). A statistically significant correlation was found between the Doppler peak pressure gradient across the coarctation site and the values of QTc-D (r = 0.48; P = 0.03) and JTc-D (r = 0.42; P = 0.04). Our study showed significantly increased QTc-D and JTc-D in isolated CoA newborns with normal left ventricular geometry.

The role of stretch-activated channels in atrial fibrillation and the impact of intracellular acidosis

The incidence of atrial fibrillation correlates with increasing atrial size. The electrical consequences of atrial stretch contribute to both the initiation and maintenance of atrial fibrillation. It is suggested that altered calcium handling and stretch-activated channel activity could explain the experimental findings of stretch-induced depolarisation, shortened refractoriness, slowed conduction and increased heterogeneity of refractoriness and conduction. Stretch-activated channel blocking agents protect against these pro-arrhythmic effects. Gadolinium, GsMTx-4 toxin and streptomycin prevent the stretch-related vulnerability to atrial fibrillation without altering the drop in refractory period associated with stretch. Changes the activity of two-pore K+ channels, which are sensitive to stretch and pH but not gadolinium, could underlie the drop in refractoriness. Intracellular acidosis induced with propionate amplified the change in refractoriness with stretch in the isolated rabbit heart model in keeping with the clinical observation of increased propensity to atrial fibrillation with acidosis. We propose that activation of non-specific cation stretch-activated channels provides the triggers for acute atrial fibrillation with high atrial pressure while activation of atrial two-pore K+ channels shortens atrial refractory period and increases heterogeneity of refractoriness, providing the substrate for atrial fibrillation to be sustained. Stretch-activated channel blockade represents an exciting target for future antiarrhythmic drugs.

Electrophysiological changes following balloon valvuloplasty and angioplasty for aortic stenosis and coartaction of aorta: clinical evidence for mechano-electrical feedback in humans

BACKGROUND

Basic research and animal experiments have shown electrophysiological changes during or after changes in mechanical loading. Electrical instability following mechanical stretch has been observed as development of after-depolarisation and dispersion of refractoriness and repolarisation. The aim of the present study was to evaluate the presence of the mechano-electrical feedback in humans, assessing the ventricular repolarisation changes following acute changes in left ventricular pressure.

MATERIAL AND METHODS

The study group comprised 30 consecutive patients (22 M and 8 F, aged 2 days-24 years) affected by severe congenital aortic stenosis and 30 patients (20 M and 10 F, aged 6 months-16 years) affected by severe coartaction of aorta. Ventricular repolarisation was evaluated before and after percutaneous balloon valvuloplasty and angioplasty in terms of absolute measures (JT, JTc, QT, QTc) and in terms of dispersion across the myocardium: QT and QTc dispersion (QTD, QTcD), JT and JTc dispersion (JTD and JTcD) and T-peak to T-end interval (Tp-Te).

RESULTS

Patients with severe aortic stenosis and patients with aortic coartaction showed a significant decrease in dispersion of ventricular repolarisation time indexes (QTD, QTcD, JTD, JTcD and Tp-Te) following valvuloplasty and angioplasty.

CONCLUSIONS

Changes in hemodynamic loading can also produce electrophysiological effects in humans. Acute reduction in left ventricular pressure overload following balloon valvuloplasty and angioplasty, decreases electrical instability, as expressed by the reduction across the myocardium of the dispersion of ventricular repolarisation.

Predictors of sudden cardiac death in never previously treated patients with essential hypertension: long-term follow-up

Increased QT dispersion has been associated with ventricular arrhythmia and sudden death in a variety of cardiac disorders. Left ventricular hypertrophy (LVH) has also been associated with increased incidence of sudden cardiac death in patients with essential hypertension. Furthermore, patients with essential hypertension, particularly those with LVH, are more likely to develop ventricular arrhythmias than are the normal population. The relationship between LVH, QT dispersion, complex ventricular arrhythmia and sudden cardiac death in previously untreated patients over long-term follow-up in hypertension has not been reported before and is the purpose of this study. Fifty-nine adult subjects with essential hypertension, who had never been previously on antihypertensive treatment were followed up for a total of 119.2 +/- 26.2 months. QTc (corrected QT), blood pressure, electrocardiograms, and 24-h Holter ECG recordings were performed in all patients at the time of entry to the study. Ventricular arrhythmias were classified using a modified Lown's scoring system. During the follow-up period death occurred in 12 cases (20%) of which only six (10%) deaths were sudden. The findings of this study indicate that LVH and complex ventricular arrhythmias (Lown's score > or =3) are the only significant predictors of sudden death. Although patients who died suddenly had higher systolic and diastolic blood pressures and greater QTc dispersion compared to surviving patients, this difference was statistically not significant. Similarly, when those who died suddenly were compared to those non-cardiac deaths, LVH and complex ventricular arrhythmias were the only significant predictors of sudden death. In spite of increased QTc dispersion in hypertensive patients, this finding was not associated with increased risk of sudden death and only LVH and high grade ventricular arrhythmias identified hypertensive patients at risk of sudden cardiac death over a 10-year follow-up period.

Segmental wall motion abnormalities alter vulnerability to ventricular ectopic beats associated with acute increases in aortic pressure in patients with underlying coronary artery disease

OBJECTIVE

To evaluate whether patients with coronary artery disease are susceptible to pressure related ventricular arrhythmias, and if so to identify possible risk factors.

DESIGN

Interventional study.

METHODS

Metaraminol was given to 43 patients undergoing coronary arteriography for ischaemic heart disease to increase their aortic pressure, provided their systolic blood pressure was < 160 mm Hg and they were in sinus rhythm, without any ventricular ectopic activity (or with fewer than six ventricular ectopic beats a minute) during a five minute control period.

RESULTS

During the metaraminol infusion, systolic aortic pressure rose from 131 (15) to 199 (12) mm Hg (mean (SD)). Ventricular ectopy appeared (or ventricular ectopic beats increased by > 100%) in 13/43 patients. Ventricular ectopy was not related to age, sex, presence of hypertension, history of myocardial infarction, use of beta blockers, positive exercise test, number of vessels diseased, or heart rate change during metaraminol infusion. There was a strong relation between the appearance of ventricular arrhythmia and segmental wall motion abnormalities: 1/19 (5.3%, 95% confidence interval 0.1% to 26.0%) without abnormality; 2/12 (16.7%, 2.1% to 48.4%) with hypokinesia; and 10/12 (83.3%, 51.6% to 97.1%) with akinesia or dyskinesia, chi 2 = 22.7, p < 0.001). Ejection fraction was also a significant but not independent risk factor.

CONCLUSIONS

Patients with segmental wall motion abnormalities are predisposed to ventricular ectopic beats during an increase in systolic aortic pressure. This could be explained by associated electrophysiological inhomogeneity. The presence of mechanical inhomogeneity, as may occur in postinfarction akinesia or dyskinesia, may affect the aortic pressure above which ventricular arrhythmias appear.

Effect of preload and afterload on ventricular arrhythmogenesis

To examine whether it is an increase in preload or afterload that may cause ventricular arrhythmias, the ventricles of 13 anesthetized open-chest dogs were bandaged. Next, metaraminol, an almost pure alpha stimulator, was given, followed by removal of the bandage. The ventricles were then sucked in a plastic cup, which was finally removed. The systolic and diastolic ventricular pressures were measured, and the presence of arrhythmias (ventricular ectopic beats or ventricular tachycardia) was observed. Banding the ventricles caused a significant diminution of systolic pressure (-42 +/- 38.0 mmHg; mean +/- SD) and a rise in diastolic pressure (+3.5 +/- 3.7), starting from control values of 126 +/- 36/6.5 +/- 3.0, but no arrhythmia. Metaraminol raised both pressures (+122 +/- 58 and +9.0 +/- 10.3) and caused ventricular arrhythmias in 6 of 13 experiments. Removing the bandage further increased the systolic pressure (+45 +/- 42) and reduced the diastolic pressure (-7.2 +/- 10.3), but made the arrhythmia worse in 10 of 13 experiments. Suction reduced both pressures (-166 +/- 96 and -5.4 +/- 14) and stopped all arrhythmias. Removing the cup increased both pressures (+133 +/- 68 and +15.5 +/- 15.3, respectively) and worsened the arrhythmia in seven of eight experiments. In general, deterioration of ventricular arrhythmias was observed in 23 of 25 maneuvers with either an increase or no change in systolic pressure, but in none of the maneuvers was there a decrease (P < .0001) in systolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular dysrhythmias, left ventricular hypertrophy, and sudden death

Left ventricular hypertrophy has been documented to be a powerful risk factor for sudden death, acute myocardial infarction, and other cardiovascular morbidity and mortality. The major determinant of left ventricular mass is the hemodynamic burden. However, the hypertrophic process is modified by demographic parameters (age, sex, race), nutritional parameters (salt intake, alcohol, obesity), and neuroendocrine factors (angiotensin, catecholamines, growth hormones, etc.). Ventricular ectopy and more serious arrhythmias are commonly seen in patients with left ventricular hypertrophy. Specific antihypertensive therapy will reduce left ventricular hypertrophy, although not all antihypertensive drugs are equipotent in this regard. A reduction in left ventricular hypertrophy has been shown to diminish left-ventricular-hypertrophy-associated arrhythmias. However, it remains to be shown that patients with left ventricular hypertrophy and ventricular ectopy are at a higher risk of sudden death than those without ventricular ectopy and that the reduction of left-ventricular-hypertrophy-associated ventricular ectopy indeed confers a clinical benefit that exceeds the one from the reduction in arterial pressure alone.

Effect of acute ventricular pressure changes on QRS duration

The effect of acute changes in ventricular pressure is examined on the QRS duration to clarify the mechanism of ventricular pressure-related arrhythmogenesis. Ventricular pressure was changed acutely by arterial transfusion-bleeding into an open-air ventricular pressure reservoir that was either off or on a metaraminol intravenous drip. While maintaining ventricular pressure at several levels, the QRS duration was measured at 200 mm/s paper speed. The QRS duration correlated significantly with the left ventricular pressure in all 14 dogs examined. An average change in ventricular by 100 mmHg was associated with a change of about 18% in the QRS duration. An acute ventricular pressure elevation impairs the ventricular conduction, which may contribute to ventricular pressure-related arrhythmogenicity.

Study of late potentials and ventricular arrhythmias in hypertensive patients with normal electrocardiograms

INTRODUCTION

Although an increase in the occurrence of ventricular arrhythmias has been observed in hypertensive patients, some basic questions remain unresolved regarding the prevalence and the pathophysiology of these arrhythmias. The basic aims of this study were as follows: (1) to examine the incidence and severity of ventricular arrhythmias in a substantial number of hypertensive patients without electrocardiographic indications of hypertrophy; and (2) to examine the correlation between late potentials, hypertrophy, and ventricular arrhythmias in these patients.

MATERIALS AND METHODS

We studied 78 consecutive patients (31 men, 47 women), aged 60.5 +/- 7.8 years, with a history of hypertension but a normal electrocardiogram. All patients had an echocardiographic study, 24-hour ambulatory monitoring, exercise test, and signal-averaged electrocardiogram. The latter was analyzed using a 40- to 250-Hz filter and with a noise level < or = 0.3 microV.

RESULTS

Of the 78 patients studied, 21 (26.9%) had severe ventricular arrhythmias, while 57 (73.1%) had either no ventricular ectopics or sporadic isolated ventricular extrasystoles. Left ventricular hypertrophy, defined by echocardiography, was found in 58 patients (74.3%), of which 16 (27.58%) had severe ventricular arrhythmias. Five (25%) of the 20 patients without hypertrophy also had severe ventricular arrhythmias (P = NS). Ventricular late potentials were recorded in 19 (24.5%) of the 78 patients. Of these, 11 (57.89%) had severe arrhythmias, while of the 59 patients without late potentials 10 (16.94%) had severe ventricular ectopic activity.

CONCLUSIONS

In hypertensive patients without electrocardiographic signs of hypertrophy, the higher prevalence of ventricular arrhythmias does not appear to be related to left ventricular hypertrophy but is correlated with the existence of ventricular late potentials.

Hypertension, left ventricular hypertrophy, ventricular ectopy, and sudden death

Left ventricular hypertrophy (LVH) is a common sequela of sustained arterial hypertension, although the correlation between spot blood pressure measurements and LV mass is not a close one. LVH has been shown to be a powerful blood pressure-independent risk factor for cardiovascular morbidity and mortality. LVH has been shown to trigger or to accelerate ventricular dysrhythmias, although the connection between ventricular dysrhythmias and sudden death is poorly documented. LVH can be reduced by specific antihypertensive therapy; however, not all drugs are equipotent in this regard. A reduction of LVH has been shown to be associated with a suppression of ventricular dysrythmias. Preliminary studies also indicate that the reduction of LVH may reduce its inherent excessive morbidity and mortality.