Beta-adrenergic stimulation with isoproterenol enhances left ventricular diastolic performance in hypertrophic cardiomyopathy despite potentiation of myocardial ischemia. Comparison to rapid atrial pacing

Differentiating Left Atrial Pressure Responses in Paroxysmal and Persistent Atrial Fibrillation: Implications for Diagnosing Heart Failure With Preserved Ejection Fraction and Managing Atrial Fibrillation

BACKGROUND

Increased left atrial pressure (LAP) contributes to dyspnea and heart failure with preserved ejection fraction in patients with atrial fibrillation (AF). The purpose of this study was to investigate the differences in baseline LAP and LAP response to rapid pacing between paroxysmal and persistent AF.

METHODS AND RESULTS

This observational study prospectively enrolled 1369 participants who underwent AF catheter ablation, excluding those with reduced left ventricular ejection fraction. H2FPEF score was calculated by echocardiography and baseline characteristics. Patients underwent LAP measurements during AF, sinus rhythm, and heart rates of 90, 100, 110, and 120 beats per minute (bpm), induced by right atrial pacing and isoproterenol. The baseline LAP-peak in the persistent AF group consistently exceeded that in the paroxysmal AF (PAF) group across each H2FPEF score subgroup (all P<0.05). LAP-peak increased with pacing (19.5 to 22.5 mm Hg) but decreased with isoproterenol (20.4 to 18.4 mm Hg). Under pacing, patients with PAF exhibited a significantly lower LAP-peak (90 bpm) than those with persistent AF (17.7±8.2 versus 21.1±9.3 mm Hg, P<0.001). However, there was no difference in LAP-peak (120 bpm) between the 2 groups (22.1±8.1 versus 22.9±8.4 mm Hg, P=0.056) because the LAP-peak significantly increased with heart rate in the group with PAF.

CONCLUSIONS

Patients with PAF exhibited lower baseline LAP with greater increases during rapid pacing compared with individuals with persistent AF, indicating a need to revise the H2FPEF score for distinguishing PAF from persistent AF and emphasizing the importance of rate and rhythm control in PAF for symptom control.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique Identifier: NCT02138695.

Personalized accelerated physiologic pacing

Heart failure with preserved ejection fraction (HFpEF) is increasingly prevalent with a high socioeconomic burden. Pharmacological heart rate lowering was recommended to improve ventricular filling in HFpEF. This article discusses the misperceptions that have resulted in an overprescription of beta-blockers, which in all likelihood have untoward effects on patients with HFpEF, even if they have atrial fibrillation or coronary artery disease as a comorbidity. Directly contradicting the lower heart rate paradigm, faster heart rates provide haemodynamic and structural benefits, amongst which lower cardiac filling pressures and improved ventricular capacitance may be most important. Safe delivery of this therapeutic approach is feasible with atrial and ventricular conduction system pacing that aims to emulate or enhance cardiac excitation to maximize the haemodynamic benefits of accelerated pacing. This conceptual framework was first tested in the myPACE randomized controlled trial of patients with pre-existing pacemakers and preclinical or overt HFpEF. This article provides the background and path towards this treatment approach.

Towards precision medicine in heart failure

The number of therapies for heart failure (HF) with reduced ejection fraction has nearly doubled in the past decade. In addition, new therapies for HF caused by hypertrophic and infiltrative disease are emerging rapidly. Indeed, we are on the verge of a new era in HF in which insights into the biology of myocardial disease can be matched to an understanding of the genetic predisposition in an individual patient to inform precision approaches to therapy. In this Review, we summarize the biology of HF, emphasizing the causal relationships between genetic contributors and traditional structure-based remodelling outcomes, and highlight the mechanisms of action of traditional and novel therapeutics. We discuss the latest advances in our understanding of both the Mendelian genetics of cardiomyopathy and the complex genetics of the clinical syndrome presenting as HF. In the phenotypic domain, we discuss applications of machine learning for the subcategorization of HF in ways that might inform rational prescribing of medications. We aim to bridge the gap between the biology of the failing heart, its diverse clinical presentations and the range of medications that we can now use to treat it. We present a roadmap for the future of precision medicine in HF.

Inotropic and lusitropic effects of incremental doses of dobutamine in dogs with right ventricular apical pacing-induced cardiac dysfunction

This study aimed to assess the effects of incremental doses of dobutamine on diastolic function in healthy and rapid ventricular apical pacing (RVAP)-induced cardiac dysfunction anesthetized dogs. Inotropic and lusitropic effects of dobutamine (2, 4, 8, and 12 μg kg^-1  min^-1 ) were assessed through left ventricle (LV) pressure-volume relation and Doppler echocardiography in six female dogs before and after 8 weeks of RVAP. Peak rate of LV pressure fall (-dP/dt_min ) improved with doses >4 μg kg^-1  min^-1 in healthy (4,490 ± 970 vs. 3,265 ± 471 mmHg/s, p < 0.05) and >8 μg kg^-1  min^-1 in RVAP dogs (3,385 ± 1,122 vs. 1,864 ± 849 mmHg/s, p < 0.05) while the time constant of relaxation (tau) reduced with doses >4 μg kg^-1  min^-1 in both groups (healthy: 24.0 ± 3.7 vs. 28.2 ± 4.9 ms; RVAP: 32.6 ± 8.5 vs. 37.5 ± 11.4 ms, p < 0.05) comparing with baseline. Indices of relaxation (-dP/dt_min and tau) suggested preserved lusitropic response in contrast with markedly reduced indices of contractility in the RVAP group compared with healthy group at same infusion rates. Doppler echocardiography showed significant reduction of elastic recoil in failing hearts. The results of this study demonstrated maximal positive lusitropic effects of dobutamine at a dose of 8 μg kg^-1  min^-1 in ventricular pacing-induced cardiac dysfunction without further impairment of ventricular filling.

Differential Effects of Isoproterenol on Regional Myocardial Mechanics in Rat using 3D cine DENSE Cardiovascular Magnetic Resonance

The present study assessed the acute effects of isoproterenol on left ventricular (LV) mechanics in healthy rats with the hypothesis that ß-adrenergic stimulation influences the mechanics of different myocardial regions of the LV wall in different ways. To accomplish this, magnetic resonance images were obtained in the LV of healthy rats with or without isoproterenol infusion. The LV contours were divided into basal, mid-ventricular, and apical regions. Additionally, the mid-ventricular myocardium was divided into three transmural layers with each layer partitioned into four segments (i.e., septal, inferior, lateral, and anterior). Peak systolic strains and torsion were quantified for each region. Isoproterenol significantly increased peak systolic radial strain and circumferential-longitudinal shear strain, as well as ventricular torsion, throughout the basal, mid-ventricle, and apical regions. In the mid-ventricle, isoproterenol significantly increased peak systolic radial strain, and induced significant increases in peak systolic circumferential strain and longitudinal strain in the septum. Isoproterenol consistently increased peak systolic circumferential-longitudinal shear strain in all mid-ventricular segments. Ventricular torsion was significantly increased in nearly all segments except the inferior sub-endocardium. The effects of isoproterenol on LV systolic mechanics (i.e., 3D strains and torsion) in healthy rats depend on the region. This region-dependency is also strain component-specific. These results provide insight into the regional response of LV mechanics to ß-adrenergic stimulation in rats, and could act as a baseline for future studies on subclinical abnormalities associated with the inotropic response in heart disease.

Troponin as ischemic biomarker is related with all three echocardiographic risk factors for sudden death in hypertrophic cardiomyopathy (ESC Guidelines 2014)

BACKGROUND

Sudden cardiac death (SCD) risk stratification is the most important preventive action in patients with hypertrophic cardiomyopathy (HCM). The identification of the ischemia biomarker high sensitive troponin I (hs-TnI) role for this arrhythmic disease may provide additional information for SCD risk stratification. The aim of the study was to compare echocardiographic parameters (prognostic for risk stratification of SCD in HCM) among two subgroups of HCM patients: with elevated hs-TnI versus non-elevated hs-TnI level.

METHODS

In 51 HCM patients (mean age 39 ± 8 years, 31 males and 20 females) an echocardiographic examination, including the stimulating maneuvers to provoke maximized LVOT gradient, was performed. The hs-TnI was measured 24 h later.

RESULTS

By comparing two subgroups of patients, 26 members with hs-TnI positive versus 25 with hs-TnI negative, the study showed that the values of all three parameters were greater: provocable left ventricular outflow tract gradient (LVOTG) - 49.1 ± 45.9 vs 25.5 ± 24.8 mmHg, p = 0.019; left atrial diameter - 50.1 ± 9.6 vs 43.9 ± 9.8 mmHg, p = 0.041; maximal LV thickness - 22.1 ± 5.3 vs 19.9 ± 34 mm, p = 0.029.

CONCLUSION

The increased value of all three echocardiographic parameters used as risk factors for SCD (ESC Guidelines) is related to the elevated level of hs-TnI in HCM. Due to the high LVOTG - great hs-TnI relationship, exercise stress, both diagnostic and even rehabilitation/training, should be monitored by biomarker control.

Isoproternenol increases vascular volume expansion and urinary output after a large crystalloid bolus in healthy volunteers

BACKGROUND

The primary goal of fluid therapy is to maintain fluid homeostasis. Commonly used isotonic crystalloids are only marginally effective and contribute to fluid excess syndrome. In patients with decreased cardiovascular reserve, fluid therapy alone is not sufficient to maintain end-organ perfusion. Therefore, inotropes or vasoactive drugs are used to supplement fluid infusion. Recent animal data suggest that coinfusion of adrenergic agents modulate the distribution of fluid between the vascular and extravascular/interstitial compartments after a fluid bolus. We sought to determine if this effect would translate in humans by coadministering a β-adrenergic agonist with fluid.

METHODS

Nine healthy volunteers (aged 21-50 years) were randomly paired and received either a continuous isoproterenol infusion (ISO: 0.05 μg/kg per minute) or 0.9% saline (control [CON]) 30min prior to a 25 mL/kg 0.9% NaCl fluid bolus. Hemodynamics, ventricular volume and function, and microcirculatory determinants (capillary filtration coefficient and oncotic pressure) were measured. Vascular and extravascular volume and fluid balance were determined.

RESULTS

Compared with CON, ISO significantly increased heart rate (CON: 64.2 ± 4.1 beats/min vs. ISO: 97.4 ± 5.7 beats/min) and cardiac output (CON: 4.4 ± 0.7 L/min vs. ISO: 10.2 ± 0.9) before fluid bolus. Isoproterenol significantly increased urinary output (ISO: 10.86 ± 1.95 vs. control: 6.53 ± 1.45 mL/kg) and reduced extravascular volume (7.98 ± 2.0 vs. 14.15 ± 1.1mL/kg). Isoproterenol prevented an increase in capillary filtration coefficient (1.74 ± 0.4 vs. 3.21 ± 0.4 mL/min per mmHg · 10).

CONCLUSIONS

Isoproterenol, a nonselective β-adrenergic agonist, augments vascular volume expansion and eliminates extravascular volume via enhanced diuresis, which may in part be due to enhanced endothelial barrier function.

Case-control study of the effects of pimobendan on survival time in cats with hypertrophic cardiomyopathy and congestive heart failure

OBJECTIVE

To assess survival time and adverse events related to the administration of pimobendan to cats with congestive heart failure (CHF) secondary to hypertrophic cardiomyopathy (HCM) or hypertrophic obstructive cardiomyopathy (HOCM).

DESIGN

Retrospective case-control study.

ANIMALS

27 cats receiving treatment with pimobendan and 27 cats receiving treatment without pimobendan.

PROCEDURES

Medical records between 2003 and 2013 were reviewed. All cats with HCM or HOCM treated with a regimen that included pimobendan (case cats) were identified. Control cats (cats with CHF treated during the same period with a regimen that did not include pimobendan) were selected by matching to case cats on the basis of age, sex, body weight, type of cardiomyopathy, and manifestation of CHF. Data collected included signalment, physical examination findings, echocardiographic data, serum biochemical values, and survival time from initial diagnosis of CHF. Kaplan-Meier survival curves were constructed and compared by means of a log rank test.

RESULTS

Cats receiving pimobendan had a significant benefit in survival time. Median survival time of case cats receiving pimobendan was 626 days, whereas median survival time for control cats not receiving pimobendan was 103 days. No significant differences were detected for any other variable.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of pimobendan to traditional treatment for CHF may provide a substantial clinical benefit in survival time for HCM-affected cats with CHF and possibly HOCM-affected cats with CHF.

Acute initial haemodynamic changes in a rat isoprenaline model of cardiotoxicity

The synthetic catecholamine isoprenaline (ISO) has been used as an inductor in the acute myocardial infarction model for more than a half century. Despite the fact that many articles were published on this topic, precise early haemodynamic pathology remains unknown. Acute haemodynamic changes were measured in rats; first, in preliminary experiments by the thermodilution method; and second, in main experiments continuously for 2 h using a Millar catheter. Animals received saline or ISO in the cardiotoxic dose (100 mg/kg, subcutaneously). Also, additional experiments were performed with salbutamol in order to evaluate the role of β2-receptors. ISO caused a rapid, within 1 min, approximately 40% decrease in arterial blood pressures, 30% increase in the heart rate, and 30% decrease in the stroke volume. Within the first 2 min, the changes were followed by decreases in afterload (−40%), preload (−10%), diastolic relaxation (−50%), diastolic filling (−40%), and a marked, but short-term, increase in the left ventricle contractility (+100%). Ejection fraction did not significantly change, suggesting diastolic dysfunction. Salbutamol, with the exception of diastolic pressure and afterload, did not substantially influence other parameters. In conclusion, this study demonstrated that diastolic dysfunction precedes systolic dysfunction and β2-receptor stimulation alone is not sufficient for an early induction of diastolic dysfunction.

Relation of 99mTc-sestamibi washout with myocardial properties in patients with hypertrophic cardiomyopathy

BACKGROUND

We sought to determine the relationship between (99m)Tc-sestamibi washout and myocardial properties in hypertrophic cardiomyopathy (HCM) patients.

METHODS AND RESULTS

Twenty-four HCM patients underwent biventricular cardiac catheterization, with a micromanometer-tipped catheter, both at rest and during atrial pacing, echocardiography and myocardial (99m)Tc-sestamibi scintigraphy at rest. The (99m)Tc-sestamibi washout rate (WR) was calculated using initial and delayed planar images. The HCM patients were divided into two groups as follows: Group A consisted of 13 patients showing (99m)Tc-sestamibi WR < 22.5%; group B of 11 patients showing (99m)Tc-sestamibi WR ≥ 22.5%. Significant correlations were observed between (99m)Tc-sestamibi WR and percentage changes in pressure half-time (T (1/2)), as well as those in the maximum first derivative LV pressure (LV dP/dt (max)) (r = .43, P = .033; r = -.63, P = .001). The percentage changes in LV dP/dt (max) and those in T (1/2) were significantly more reduced in group B than in group A (P < .05). The biphasic force-frequency relation was more frequently observed in group B than in group A (82% vs. 18%).

CONCLUSION

Increased (99m)Tc-sestamibi washout is associated with an impaired contractile reserve and prolonged relaxation, suggesting that myocardial (99m)Tc-sestamibi scintigraphy may be useful in noninvasively detecting the early impairment of myocardial function in HCM patients.

Pacing tachycardia exaggerates left ventricular diastolic dysfunction but not systolic function and regional asynergy or asynchrony in patients with hypertrophic cardiomyopathy

AIMS

Myocardial ischaemia and angina have been demonstrated in patients with hypertrophic cardiomyopathy (HCM). We hypothesized that left ventricular (LV) systolic or diastolic dysfunction would be provocated by pacing tachycardia in patients with HCM.

METHODS AND RESULTS

We investigated LV global and regional systolic and diastolic function in 17 patients with HCM without LV outflow obstruction and 7 normal subjects by analysing LV angiograms and simultaneously obtained high-fidelity LV pressures before and after rapid cardiac pacing (150 b.p.m.). Biplane LV silhouettes were digitized frame by frame (50 frames/s). To quantify regional dynamics, the ventricular area of the right anterior oblique projection was divided into six sections originating from the midpoint of the long axis at end-diastole. There were no significant changes in LV function after pacing in normal subjects. In HCM, the ejection fractions remained unchanged. However, LV end-diastolic pressures rose (+12 mmHg, P < 0.01), and the time constants of isovolumic pressure decay were significantly increased (T(1/2): +5.2 ms, P < 0.01; T(1/)(e): +6.8 ms, P < 0.01). The LV global diastolic pressure-volume relationships and regional diastolic pressure-area relationships of regional myocardium shifted upward (indicating decreased diastolic distensibility) in all patients. These diastolic abnormalities were not accompanied by regional asynchrony or asynergy.

CONCLUSION

Most patients with HCM have a reduced reactive capacity to chronotropic stress, which is haemodynamically characterized by evenly distributed diastolic dysfunction. In contrast with coronary artery disease, these diastolic abnormalities were not accompanied by systolic dysfunction, regional asynchrony, asynergy, or inhomogenous diastolic distensibility.

Physiological functions of the giant elastic protein titin in mammalian striated muscle

The striated muscle sarcomere contains the third filament comprising the giant elastic protein titin, in addition to thick and thin filaments. Titin is the primary source of nonactomyosin-based passive force in both skeletal and cardiac muscles, within the physiological sarcomere length range. Titin's force repositions the thick filaments in the center of the sarcomere after contraction or stretch and thus maintains sarcomere length and structural integrity. In the heart, titin determines myocardial wall stiffness, thereby regulating ventricular filling. Recent studies have revealed the mechanisms involved in the fine tuning of titin-based passive force via alternative splicing or posttranslational modification. It has also been discovered that titin performs roles that go beyond passive force generation, such as a regulation of the Frank-Starling mechanism of the heart. In this review, we discuss how titin regulates passive and active properties of striated muscle during normal muscle function and during disease.

Phosphorylation of titin modulates passive stiffness of cardiac muscle in a titin isoform-dependent manner

We investigated the effect of protein kinase A (PKA) on passive force in skinned cardiac tissues that express different isoforms of titin, i.e., stiff (N2B) and more compliant (N2BA) titins, at different levels. We used rat ventricular (RV), bovine left ventricular (BLV), and bovine left atrial (BLA) muscles (passive force: RV > BLV > BLA, with the ratio of N2B to N2BA titin, ∼90:10, ∼40:60, and ∼10:90%, respectively) and found that N2B and N2BA isoforms can both be phosphorylated by PKA. Under the relaxed condition, sarcomere length was increased and then held constant for 30 min and the peak passive force, stress-relaxation, and steady-state passive force were determined. Following PKA treatment, passive force was significantly decreased in all muscle types with the effect greatest in RV, lowest in BLA, and intermediate in BLV. Fitting the stress-relaxation data to the sum of three exponential decay functions revealed that PKA blunts the magnitude of stress-relaxation and accelerates its time constants. To investigate whether or not PKA-induced decreases in passive force result from possible alteration of titin–thin filament interaction (e.g., via troponin I phosphorylation), we conducted the same experiments using RV preparations that had been treated with gelsolin to extract thin filaments. PKA decreased passive force in gelsolin-treated RV preparations with a magnitude similar to that observed in control preparations. PKA was also found to decrease restoring force in skinned ventricular myocytes of the rat that had been shortened to below the slack length. Finally, we investigated the effect of the β-adrenergic receptor agonist isoprenaline on diastolic force in intact rat ventricular trabeculae. We found that isoprenaline phosphorylated titin and that it reduced diastolic force to a degree similar to that found in skinned RV preparations. Taken together, these results suggest that during β-adrenergic stimulation, PKA increases ventricular compliance in a titin isoform-dependent manner.

Biphasic relaxation-frequency relations in patients with effort angina pectoris: a new marker of myocardial demand ischemia

BACKGROUND

Relaxation-frequency relations (RFR) during demand ischemia have not been fully examined in patients with effort angina pectoris (AP). We sought to clarify the effects of pacing and exercise on RFR in patients with AP.

METHODS

We recorded left ventricular (LV) pressures during rapid atrial pacing and symptom-limited supine bicycle exercise. RFR were analyzed in 24 patients with AP and 10 controls.

RESULTS

LV pressure half-time (T(1/2)) in controls was gradually shortened with an increase in heart rate (HR) during pacing (-19% +/- 6% at peak HR). The changes in T(1/2) during pacing were biphasic with initial shortening (-12% +/- 5% at the critical HR) followed by prolongation (-3% +/- 7% at peak HR) in all patients with AP. The critical HR, at which T(1/2) was minimum, preceded the HR at 0.1-mV ST-segment depression, and finally chest pain occurred. The critical HR was correlated negatively with the severity of ischemia as assessed by thallium-201 scintigraphy. T(1/2) was remarkably shortened during exercise in controls (-41% +/- 10% at peak exercise). In patients with AP, 2 distinct patterns of RFR were observed during exercise. T(1/2) was shortened progressively (-37% +/- 8% at peak exercise) in 15 patients, whereas RFR remained biphasic (-21% +/- 10% at the critical HR and -11% +/- 11% at peak exercise) in the other 9 patients. Coronary angiography and exercise scintigraphy suggested more severe ischemia in patients with biphasic RFR during exercise.

CONCLUSIONS

Impaired RFR might be the most sensitive parameter of pacing-induced ischemia. The critical HR was closely related with severity of ischemia. Adverse effects of ischemia on LV relaxation may be alleviated by exercise.

Biphasic changes in left ventricular end-diastolic pressure during dynamic exercise in patients with nonobstructive hypertrophic cardiomyopathy

OBJECTIVES

The aim of this study was to clarify the serial changes in left ventricular (LV) end-diastolic pressure (LVEDP) during dynamic exercise in patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Although HCM is characterized by impaired resting LV diastolic function, serial changes in LVEDP during exercise have not been characterized.

METHODS

We simultaneously measured LV pressure and LV dimensions during symptom-limited supine bicycle exercise in 5 healthy individuals and 20 patients with HCM. Exercise thallium-201 scintigraphic studies were also performed.

RESULTS

The LVEDP (baseline: 12 +/- 5 mm Hg) progressively increased to a maximum value at peak exercise (28 +/- 8 mm Hg) in 11 patients with HCM (group I). In the remaining nine patients with HCM (group II), changes in LVEDP during exercise were biphasic, with an initial progressive increase and a subsequent gradual decline up to peak exercise (14 +/- 4 mm Hg at baseline, 27 +/- 5 mm Hg at the critical heart rate, 16 +/- 3 mm Hg at peak exercise). Exercise-induced changes in LV dimensions and LV peak systolic pressures were similar in both groups. However, the maximum first derivative of LV pressure was greater and the LV pressure half-time was shorter in group II than in group I at a similar peak exercise heart rate. The biphasic changes in LVEDP disappeared by pretreatment with propranolol. The LV hypertrophy scores were higher in group I than in group II. Exercise thallium-201 images showed more severe perfusion defects in group I than in group II patients.

CONCLUSIONS

The biphasic changes in LVEDP seen during exercise may be related to improved coronary microcirculation in response to beta-adrenergic stimulation in patients with mild to moderate HCM.

Diastolic Heart Failure

The diagnosis of diastolic heart failure (DHF) can be made when a patient has both symptoms and signs on physical exam of congestive heart failure (CHF), and normal left ventricular volume and ejection fraction. Documentation of abnormal diastolic function is confirmatory but not mandatory. Diastolic heart failure is a frequent cause of CHF (prevalence is 35% to 50%) and has a significant effect on mortality (5-year mortality rate is 25% to 35%) and morbidity (1-year readmission rate is 50%). Treatment should be targeted at symptoms, causal clinical disease, and underlying basic mechanisms. Symptom-targeted therapy: decrease pulmonary venous pressure using diuretics and long-acting nitrates, maintain atrial contraction and atrial ventricular synchrony, reduce heart rate using beta-adrenergic blockers and calcium channel blockers; increase exercise tolerance by reducing exercise- induced increases in blood pressure and heart rate using angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, and calcium channel blockers. Disease-targeted therapy: prevent or treat myocardial ischemia, prevent or regress left ventricular hypertrophy. Mechanism-targeted therapy (future directions): modify neurohumoral activation using renin, angiotensin, and aldosterone system antagonists (ACE inhibitors, angiotensin II receptor blockade, aldosterone and renin antagonist); endothelin antagonists; nitric oxide agonists; and atrial natruretic peptide agonists; alter intracellular mechanisms; alter extracellular matrix structures.

Abnormal global left ventricular relaxation occurs early during the development of pharmacologically induced ischemia

In animal and human models, left ventricular (LV) diastolic function has been observed to be highly sensitive to myocardial ischemia. The response of LV diastolic parameters to pharmacologically induced ischemia, however, has not been characterized and might be important in the interpretation of dobutamine stress echocardiography. Eight mongrel dogs, in which were inserted a high-fidelity micromanometer LV catheter, coronary sinus sampling catheter, and ultrasonic coronary artery flow probe, underwent intravenous dobutamine infusion at escalating doses both before (control protocol) and after (ischemia protocol) creation of left anterior descending coronary artery stenosis with a hydraulic cuff occluder adjusted to maintain resting coronary artery flow but attenuate reactive hyperemia. At each dobutamine dose, epicardial short-axis 2-dimensional echocardiographic images and hemodynamic measurements were obtained. LV diastolic function was examined by calculation of peak (-)dP/dt and the time constant of isovolumic relaxation (tau). The dobutamine infusion protocol was terminated on the earliest recognition of an anterior wall motion abnormality. Peak (+)dP/dt normalized for developed isovolumetric pressure was calculated as a relatively load-independent index of global LV contractile function. Dobutamine infusion with and without ischemia resulted in comparable changes in heart rate and (+)dP/dt/IP, with no change in LV end-diastolic or -systolic pressure. The magnitude of peak (-)dP/dt increased less during the ischemia (1231 +/- 109 to 1791 +/- 200 mm Hg/sec) versus the control (1390 +/- 154 to 2432 +/- 320 mm Hg/sec) protocol (P <.05). Similarly, the observed decrease in tau was less during the ischemia (53 +/- 3 to 38 +/- 4 msec) than the control (51 +/- 5 to 23 +/- 3 msec) protocol, corresponding to a slower rate of relaxation (P <.05). In addition, the smaller decrease in tau was observed at the dobutamine dose before the dose at which an echocardiographic wall motion abnormality was first recognized. Dobutamine-induced ischemia is associated with abnormal LV diastolic function. In addition, these abnormalities seem to occur early in the development of ischemia. These observations extend to pharmacologically induced ischemia prior findings from other models of ischemia, suggesting the high sensitivity of LV diastolic function to the development of myocardial ischemia.

Beta-adrenergic stimulation enhances left ventricular diastolic performance in normal subjects

To determine the effects of beta-adrenergic stimulation on transmitral Doppler echocardiography flow characteristics of left ventricular diastolic filling, we studied 10 healthy volunteers aged 23-31 years (mean age, 26.6 years) during intravenous infusion of isoprenaline in consecutive steps of 0.1, 0.2, 0.4, 0.75, and 1.5 micrograms/min (each for 15 min). Saline control infusion was given in the same manner in a crossover and blinded protocol. Compared with the infusion of placebo, stepwise increasing doses of isoprenaline caused a dose-related increase in early and late diastolic filling velocities and velocity-time integrals, a lengthening of the acceleration time, and a shortening of the deceleration and filling time. The chosen method proved highly sensitive, as statistically significant changes were detectable at the lowest dose of 0.1 microgram/min for all variables except velocity-time integral of late filling and deceleration time (> or = 0.2 microgram/min). The effects related to dose in a log-linear fashion except for the lengthening of the acceleration time (early ceiling), the increase of peak early filling velocity (increased steepness at higher doses), and the shortening of the filling time. Inclusion of the associated increases in heart rate and systolic blood pressure and the decrease in diastolic blood pressure blunted all treatment contrasts except for the increase of peak early filling velocity. In addition, the hemodynamics with respect to heart rate and loading conditions were not altered at low dosages of drug (< 0.4 microgram/min). Effects of at least the peak early filling velocity must be interpreted as an active adrenergically mediated myocardial relaxation process. These findings have potentially important clinical implications for this noninvasive, readily available, and convenient technique in clinical pharmacology, stress testing, and possibly therapeutic interventions in diastolic dysfunction in humans.

Dobutamine stress Doppler echocardiography: reproducibility and physiologic left ventricular filling patterns

Qualitatively, dobutamine stress echocardiography has become an established procedure. Quantitative results are in great demand but this is still difficult due to limited endo- and epicardial border definition. Transmitral Doppler variables are strictly quantitative and less subjective. Furthermore, ischemic alterations precede systolic ones (ischemic cascade). There are preliminary reports of the utility of dobutamine stress Doppler echocardiography, but proof of reproducibility and left ventricular filling patterns are still lacking. Fourteen healthy volunteers (10 men, 4 women, median age 25.9 years, range 21-32 years) were investigated according to the usual dobutamine stress echocardiographic protocol (5, 10, 15, 20, 30, 40 and 40 micrograms/kg/min + 0.5 mg atropine). At each titration step a standardized transmitral PW-Doppler recording with the sample volume positioned at the opened mitral leaflet tips was analyzed three times by two independent, experienced investigators. Of the early, late, and mean velocities (VmaxE, VmaxA, Vmean), time integrals (VTI-E, VTI-A, VTI), their ratios (E/A, E/A VTI), and various time intervals (Tacc, Tdec, E- and A-duration, FillT), VmaxE (0.82 to 1.09 m/s; P < 0.0001), VTI-E (16.17 to 17.19 cm; P < 0.0001) and Vmean (0.29 to 0.82 m/s; P < 0.0001) were found to have the greatest discriminatory power, commencing already at a dose of 10-15 micrograms/kg/min dobutamine. VmaxE and VTI-E demonstrated the smallest intra- and interobserver variation without any increase in variability during incremental dose titration. Assessment of the early diastolic filling pattern by Doppler echocardiography is a valuable quantitative and reproducible adjunct to conventional dobutamine stress echocardiography. Further controlled studies in coronary artery disease patients have to confirm, whether lower dobutamine doses could be used in the test and sensitivity increased due to better data acquisition in cases of limited echogenicity, less subjectivity, and earlier onset of ischemic alterations.

Decreased inotropic but relatively preserved relaxation response to cyclic adenosine monophosphate-dependent agents in myopathic human myocardium

BACKGROUND

Increased intracellular concentrations of cyclic adenosine monophosphate (AMP) stimulate a positive inotropic and lusitropic response in healthy myocardial tissue. Heart failure results in an attenuated inotropic response to cyclic AMP-dependent agents. This study compares the inotropic versus relaxation response to cyclic AMP-dependent and cyclic AMP-independent agents in myocardium from patients with end-stage heart failure and control patients without heart failure.

METHODS AND RESULTS

Fifty-four control and 59 myopathic human ventricular trabeculae, 1 mm or less in diameter were placed in physiologic saline, 2.5 mM Ca2+, and stretched to the length at which maximal isometric force developed at 30 degrees C, 0.33 Hz. Dose-response curves plotted as percentage change from baseline versus concentration of drug were determined for acetylstrophanthidin, isoproterenol, isobutylmethylxanthine, and milrinone. Acetylstrophanthidin, a cyclic AMP-independent agent, showed similar increases in peak tension relative to baseline over the entire dose range tested for both control and myopathic heart muscle; its effect on relaxation of control and failing cardiac muscle was equivalent over the dose range tested. In contrast, the inotropic actions of the cyclic AMP-dependent agents, isoproterenol and the phosphodiesterase inhibitors, were significantly decreased in myopathic muscle compared with control muscle, but effects on relaxation in the control and myopathic groups remained relatively preserved.

CONCLUSIONS

A relatively preserved relaxant effect is associated with the cyclic AMP-dependent agents, despite significant diminution of their inotropic effects. Thus, in advanced heart failure, patients may continue to benefit from the lusitropic effects of the cyclic AMP-dependent agents, even when the inotropic effects of these agents are severely attenuated.

Impaired response of left ventricular relaxation to exercise-induced adrenergic stimulation in patients with hypertrophic cardiomyopathy

OBJECTIVES

We investigated the effect of adrenergic stimulation on left ventricular relaxation in patients with hypertrophic cardiomyopathy.

BACKGROUND

Exercise-induced decreases in acceleration of left ventricular relaxation have been observed in patients with hypertrophic cardiomyopathy. However, data on sequential changes in left ventricular relaxation during exercise are limited.

METHODS

We measured right (fluid filled) and left (high fidelity micromanometer) ventricular pressures during moderate supine ergometer exercise and during rapid right atrial pacing in four groups of patients: 9 with severe hypertrophic cardiomyopathy, 9 with moderate hypertrophic cardiomyopathy, 10 with hypertension and moderate hypertrophy and 5 control subjects.

RESULTS

There was a curvilinear relation between the time constant of relaxation (tau) and heart rate in all groups during exercise. There was no difference in the slope of this relation between the two hypertrophic cardiomyopathy subgroups. Although the slope of this relation between tau and heart rate was steeper in the hypertensive than the moderate hypertrophic cardiomyopathy group (p < 0.001, analysis of covariance), the decrease in tau during right atrial pacing was similar in both groups. There were no significant differences in plasma levels of catecholamines at rest or at peak exercise among groups or in maximal heart rate during pacing.

CONCLUSIONS

Pacing-induced changes in tau in hypertrophic cardiomyopathy were similar to those in hypertensive hypertrophy, but remarkable decrease in exercise-induced acceleration of tau were observed only in hypertrophic cardiomyopathy. Our results may indicate a depressed left ventricular relaxation response to exercise-induced adrenergic stimulation in hypertrophic cardiomyopathy.

Effects of diltiazem on left ventricular systolic and diastolic function in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HC) is characterized by impaired diastolic function, and left ventricular (LV) outflow tract obstruction in about one-fourth of patients. Verapamil improves diastolic properties, but may have dangerous adverse effects. This study investigates the effects of diltiazem on hemodynamics and LV function in 16 patients with HC who were studied with cardiac catheterization and simultaneous radionuclide angiography. Studies were performed during atrial pacing (15 beats above spontaneous rhythm) at baseline and during intravenous diltiazem administration (0.25 mg x kg(-1) over 2 minutes, and 0.014 mg x kg(-1) x min(-1). Diltiazem induced a systemic vasodilation (cardiac index: 3.4 +/- 1.0 to 4.0 +/- 1.0 L x min(-1) x m(-2), p = 0.003; aortic systolic pressure: 116 +/- 16 to 107 +/- 19 mm Hg, p = 0.007; systemic resistance index: 676 +/- 235 to 532 +/- 193 dynes x s x cm(-5) x m(-2), p = 0.006), not associated with changes in the LV outflow tract gradient. The end-systolic pressure/volume ratio decreased (30 +/- 42 to 21 +/- 29 mm Hg x ml(-1) x m(-2); p = 0.044). Pulmonary artery wedge pressure (11 +/- 5 to 15 +/- 6 mm Hg, p = 0.006), and peak filling rate increased (4.1 +/- 1.3 to 6.0 +/- 2.4 stroke counts x s(-1), p = 0.004). The time constant of isovolumetric relaxation tau decreased (74 +/- 40 to 59 +/- 38 ms, p = 0.045). The constant of LV chamber stiffness did not change. Thus, active diastolic function is improved by the acute administration of diltiazem by both direct action and changes in hemodynamics and loading conditions. LV outflow tract gradient does not increase despite systemic vasodilation. In some patients, however, a marked increase in obstruction and a potentially harmful elevation in pulmonary artery wedge pressure do occur. Passive diastolic function is not affected.

Mechanisms, diagnosis, and treatment of diastolic heart failure

Diastolic heart failure, in the absence of LV systolic dysfunction, is a common clinical condition that can be demonstrated in as many as one third of patients with congestive heart failure. Diastolic dysfunction caused by abnormalities in LV filling can be a result of many pathologic conditions, including hypertrophy, infiltrative cardiomyopathies, or myocardial ischemia. The major physiologic determinants of LV filling can be divided into cellular mechanisms, hemodynamic characteristics, and hormonal influences. Cellular mechanisms for impaired LV inactivation are determined by the handling of calcium within the myocyte during excitation-contraction-relaxation coupling. The hemodynamic characteristics of LV diastolic filling are determined by loading conditions, the time constant of isovolumic relaxation, heart rate, ventricular nonuniformity, pericardial restraint, myocardial elasticity, chamber compliance, and coronary blood flow. The sympathetic nervous system and the renin-angiotensin system are important modulators of diastolic filling, directly or indirectly. The diagnosis of heart failure is confirmed by a combination of clinical tests including invasive and noninvasive techniques, each of which has advantages and disadvantages. Treatment of medical conditions in which diastolic heart failure is a prominent component include pharmacotherapy with calcium channel antagonists, beta-adrenergic blocking agents, diuretic agents, and angiotensin-converting-enzyme inhibitors. Certain conditions associated with diastolic filling abnormalities such as pericardial disease or severe ischemic heart disease may be best managed by surgical or percutaneous intervention. Future research will include further delineation of the cellular mechanisms of active myocardial relaxation and clinical investigation into treatment directed at improving outcome.

Diastolic heart function--pathophysiology, characterization, and therapeutic approaches

In recent years diastolic cardiac function has attracted increasing attention since parameters of diastolic function were found to be altered earlier or more specifically than parameters of systolic function. Diastolic cardiac function is determined by both active (muscular relaxation, redistribution of calcium, synchronization, etc.) and passive (myocardial structure, fibrosis, etc.) factors. As a consequence, a comprehensive assessment of diastolic cardiac function cannot be based on one single parameter. For a complete analysis of diastolic function it is necessary to perform invasive diagnostic procedures involving the measurement of atrial and ventricular pressures, as well as the registration of volume changes with a high time resolution. In addition, it is necessary to measure wall thickness and ventricular configuration, so that apart from filling parameters the stress-strain relationship can be obtained. Noninvasive techniques (Doppler echocardiography, radionuclear ventriculography, apexcardiography) may suggest alterations in diastolic function as well. They ought to be complemented by additional diagnostic procedures (pulmonary pressure, stress testing, etc.). Therapy must consider potentially harmful effects on diastolic function parameters, particularly if changes in myocardial oxygen consumption may result (heart rate, parietal wall stress). Calcium antagonists (verapamil, diltiazem, nifedipine), phosphodiesterase inhibitors (milrinone), beta-adrenergic agonists and antagonists with vasodilating effects (e.g., celiprolol) all have beneficial effects on diastolic myocardial function. A range of diastolic function parameters is being reviewed in the following paper. Their role in the estimation of cardiac function and their responsiveness to therapy in hypertrophy, cardiomyopathy, and coronary heart disease is being discussed.

Effects of dexmedetomidine on systemic and coronary hemodynamics in the anesthetized dog

In addition to central effects, which are the basis of their use in anesthesiology, alpha 2-adrenergic agonists have direct peripheral cardiovascular effects. Dexmedetomidine (DM) has been found to depress cardiac function in dogs, even after autonomic denervation. The present experiments evaluated the effects of DM on coronary flow, myocardial oxygen extraction, and cardiac function in intact, open chest dogs under enflurane anesthesia. Heart rate (HR), mean arterial pressure (MAP), left ventricular end-diastolic pressure (LVEDP), the first derivative of systolic left ventricular pressure (dP/dtmax), and flow in the left anterior descending coronary artery (CBF) were measured and continuously recorded. Cardiac output (CO), plasma catecholamines (CA), hemoglobin and oxygen saturation in arterial, mixed venous, and coronary sinus blood were measured at intervals. Cardiac index (CI), systemic vascular resistance index (SVRI), regional coronary vascular resistance (CVR), and oxygen concentration differences across the systemic [C(a-v)O2], and coronary [C(a-cs)O2] circulations were calculated. DM doses of 0.25, 0.5, 1.0, 2.0, and 4.0 micrograms/kg were given IV at 20-minute intervals. Measurements and samples were taken at peak drug effects and just prior to the next dose. The alpha 2-antagonist atipamezole, 0.5 mg/kg, was given after the last dose of DM. DM caused immediate dose-dependent increases in SVRI, CVR, LVEDP, C(a-v)O2, and C(a-cs)O2, and decreases in HR, and CI, with recovery between doses. DP/dtmax declined after the first two doses and stabilized thereafter, as plasma CA fell to minimal levels. Atipamezole completely reversed all changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects on left ventricular function of pindolol added to verapamil in hypertrophic cardiomyopathy

The aim of the study was to assess the effect of adding pindolol to previously used verapamil monotherapy on left ventricular (LV) systolic and diastolic function in 20 patients with hypertrophic cardiomyopathy. Patients were initially treated with verapamil in maximal well-tolerated doses for 16 +/- 14 months; pindolol, 5 mg twice daily, was added. In a Doppler echocardiographic study all patients had altered LV diastolic filling despite verapamil therapy. The control examination, which consisted of echocardiographic study and New York Heart Association functional status classification, was performed after 20 days and repeated after > or = 6 months of follow-up. Combined pindolol and verapamil therapy caused an increase in LV diastolic filling manifested by beneficial changes of transmitral flow parameters. Also, inhibition of hypercontractile LV function expressed by reduction of LV outflow tract pressure gradient and ejection fraction was observed. New York Heart Association functional class was reduced in 13 patients. The magnitude and distribution of LV myocardial hypertrophy did not change significantly. It is concluded that pindolol and verapamil combined therapy is superior to verapamil monotherapy because of improved LV diastolic function (probably due to partial agonist activity of pindolol) and reduced hypercontractile function in patients with hypertrophic cardiomyopathy.

Left ventricular flow propagation during early filling is related to wall relaxation: a color M-mode Doppler analysis

OBJECTIVES

This study was designed to evaluate the relation between the velocity of flow propagation and left ventricular relaxation by using color M-mode Doppler echocardiography to analyze flow propagation in the left ventricle.

BACKGROUND

Noninvasive attempts to identify alterations in left ventricular relaxation have been hampered because both the relaxation rate and left atrial filling pressure are the determinants of peak early velocity and filling rate.

METHODS

Color M-mode velocity data were transferred to a microcomputer and compared with conventional pulsed Doppler data to assess the ability of color M-mode echocardiography to analyze velocity field properties. The velocity of flow propagation was measured as the slope of the flow wave front during early filling in normal subjects (n = 29) and in patients with disease that alters relaxation (dilated cardiomyopathy [n = 31], ischemic cardiomyopathy [n = 8], hypertrophic cardiomyopathy [n = 5], systemic hypertension [n = 22] and aortic valve disease [n = 25]). In nine patients with end-stage dilated cardiomyopathy, echocardiographic and left heart catheterization data were obtained at baseline and during intracoronary dobutamine infusion.

RESULTS

Color M-mode and pulsed Doppler echocardiographic data were highly correlated (n = 217, r = 0.94, p less than 0.0001, velocity range 0.2 to 1.5 m/s). The velocity of flow propagation was lower in patients than in normal subjects (0.46 +/- 0.15 vs. 0.84 +/- 0.11 m/s, p less than 0.0001). The decrease was significant in all disease forms with or without left ventricular dilation. The velocity of flow propagation was related to peak early velocity in normal subjects (p less than 0.001) but not in patients. It varied inversely with the isovolumetric relaxation time constant during dobutamine infusion and the two variables were highly correlated (p less than 0.0001).

CONCLUSIONS

The velocity of flow propagation during early filling seems to be highly dependent on the left ventricular relaxation rate and could be an important tool in studying diastolic function.

Xamoterol in hypertrophic cardiomyopathy: effects on diastolic function and heart rate

The aims of this study were to determine the effects of the partial beta 1-adrenergic agonist, xamoterol, on diastolic function and ambulatory heart rate in hypertrophic cardiomyopathy. Eleven patients with non-obstructive hypertrophic cardiomyopathy were studied with cross-sectional and Doppler echocardiography and 24-h Holter monitoring before and after a single intravenous dose of xamoterol. Resting heart rate (mean +/- SD) increased from 76 +/- 16 before, to 83 +/- 15 beats/min 15 min after xamoterol, p = 0.03. In the 4-h period after xamoterol, maximum heart rate was reduced (127 +/- 21 to 112 +/- 19, p = 0.01) and minimum heart increased (60 +/- 16 to 67 +/- 17, p = 0.04) compared to the same 4-h period of the previous day. There were no significant changes in cross-sectional or Doppler echocardiographic measurements of left ventricular function following xamoterol. Xamoterol stabilises the heart rate in hypertrophic cardiomyopathy. The absence of a significant effect on Doppler measurements does not preclude a beneficial effect on diastolic function. This initial study suggests that xamoterol should be further investigated as a new medical therapy for hypertrophic cardiomyopathy.

Heart rate variations during isoproterenol infusion in congestive heart failure: relationships to cardiac mortality

A marked derangement of heart rate modulation in patients with severe cardiac heart failure (CHF) has been reported. The purpose of the study was to correlate the variations of sinus cycle length (SCL) during infusion of 4 micrograms/min of isoproterenol with the prognosis of 83 patients with CHF (mean left ventricular ejection fraction 28 +/- 9%). During a mean follow-up of 28 +/- 9 months, nine patients died from CHF (group I), nine died suddenly (group II), and 65 are alive (group III). Compared with groups II and III, a significantly weaker ejection fraction (20 +/- 8% versus 29.5 +/- 11% and 28 +/- 9%), a smaller control state SCL (571 +/- 65 versus 722 +/- 200 and 747 +/- 195), and a smaller percentage of SCL shortening during isoproterenol infusion (11.5 +/- 7% versus 36 +/- 16% and 33 +/- 13%) were noted in group I. The sensitivity and specificity of a percentage of SCL shortening during isoproterenol infusion less than or equal to 15% for predicting death from CHF were 89% and 93%, respectively. Therefore the injection of small doses of isoproterenol (4 micrograms/min) may be proposed to evaluate the prognosis of patients with CHF; a weak increase in heart rate during this infusion is a sign of bad prognosis with a high risk of cardiac death as a result of CHF.

Adrenergic hypersensitivity after beta-blocker withdrawal in hypertrophic cardiomyopathy

Withdrawal of beta-blocker therapy has been associated with the development of adrenergic hypersensitivity and adverse clinical effects in patients with coronary artery disease and hypertension. The aim of this study was to establish the occurrence and clinical significance of adrenergic hypersensitivity after abrupt withdrawal of long-term beta blockade in hypertrophic cardiomyopathy. Beta-adrenergic sensitivity was measured using the isoprenaline chronotropic dose25. Symptom assessment chronotropic dose25 calculation, bicycle exercise, echocardiography and Holter monitoring were performed while the patient received beta-blocker therapy and repeated on days 2, 4, 6, 8 (acute withdrawal period) and on day 21 after abrupt withdrawal. The study was terminated after 7 patients had been studied because all patients experienced a marked deterioration in symptoms and several clinical events had occurred. The chronotropic dose25 (mean +/- standard deviation) demonstrated beta 1-adrenergic hypersensitivity with a minimal value of 1.6 +/- 0.8 micrograms during the acute withdrawal period compared with 3.8 +/- 1.7 micrograms on day 21 (p = 0.003). Heart rates during rest and exercise showed an overshoot increase during the acute withdrawal period. The maximal 24-hour ventricular ectopic count was higher during the acute withdrawal period than during day 21 (p = 0.04). Of 3 patients with inducible outflow tract gradients, 2 developed resting gradients greater than 30 mm Hg during the acute withdrawal period. There was an increase in peak late filling velocity of mitral inflow after beta-blocker withdrawal. In conclusion, transient beta-adrenergic hypersensitivity occurs after beta-blocker withdrawal in hypertrophic cardiomyopathy and is associated with significant physiologic changes and adverse clinical consequences.

Evaluation of the calcium channel-blocking agents diltiazem and verapamil for treatment of feline hypertrophic cardiomyopathy

To determine the efficacy of and clinical response to several pharmacologic agents for treatment of idiopathic hypertrophic cardiomyopathy in cats, 17 symptomatic cats were randomized to treatment with either propranolol, diltiazem, or verapamil. Clinical, laboratory, radiographic, electrocardiographic, and echocardiographic data were obtained before treatment and after 3 and 6 months of chronic oral therapy. Too few of the cats receiving propranolol or verapamil survived long enough to obtain long-term data needed to make statistical comparisons between groups. However, all 12 cats ultimately treated with diltiazem became asymptomatic, and no adverse effects from this drug were noted in any of these cats. Treatment with diltiazem was associated with a significant reduction of pulmonary congestion assessed radiographically (P less than 0.01), and improved ventricular filling based on echocardiographic measurements of left atrial size (P less than 0.05), left ventricular internal diastolic dimension (P less than 0.05), and relaxation time index (P less than 0.001). There was also a drug-related improvement in jugular venous oxygen tension (P less than 0.001) and blood lactate concentration (P less than 0.01) suggesting improved peripheral perfusion in the cats receiving diltiazem. The results indicate that diltiazem provides an effective and apparently safe treatment for the management of feline hypertrophic cardiomyopathy.

Evidence for or against the efficacy of calcium channel blockers for management of hypertrophic cardiomyopathy in cats

The positive lusitropic and direct coronary vasodilating properties of the calcium channel blocking agents are beneficial therapeutic effects not provided by the beta-adrenergic blocking agents for the management of feline HCM. Data from cats studied at the University of Tennessee suggest that diltiazem more consistently alleviates clinical signs and more effectively prolongs survival in cats with HCM than either propranolol or verapamil. Orally administered diltiazem appears to have sustained beneficial effects on left ventricular filling and cardiac performance based on its ability to reduce resting heart rate, decrease blood lactate concentration, increase venous oxygen tension, improve echocardiographic parameters, and resolve radiographic abnormalities. Long-term diltiazem administration may also reverse myocardial hypertrophy in some patients. There appear to be few if any side effects of this drug. Diltiazem, therefore, provides a safe and effective approach for the management of feline HCM.