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Biomedical subjects

W H Leung

Publications and source records attributed to W H Leung.

At least 19 recordsLinked to original sources
PubMed1996

Migration of the AVE Micro coronary stent.

The AVE Micro coronary stent is a balloon-expandable stent with a design that is different from the commonly used slotted tubular or coil stents. The stent delivery system is low in profile and very trackable so that it can negotiate tortuous vessels to reach distal lesions. It also can pass through proximally deployed stents easily. Its moderate radioopacity allows precise stent placement. However, as illustrated in the three case reports presented here, the stent struts did not seem to be firmly embedded into the arterial wall after initial deployment, so that stent migration occurred during subsequent passage of a balloon into the stent for poststenting high pressure balloon dilatation. This new phenomenon of stent migration has not been reported previously with other stents.

Aged↗
PubMed1995

Quantitative arteriography of apparently normal coronary segments with nearby or distant disease suggests presence of occult, nonvisualized atherosclerosis.

OBJECTIVES: The aim of this study was to evaluate, using quantitative arteriography, whether the diameter of visually normal coronary segments might be influenced by the relative proximity of visually apparent disease. BACKGROUND: Severity of coronary artery lesions is commonly referenced against a presumed normal nearby coronary segment with the presumption that visually smooth segments are relatively free of atherosclerotic disease. METHODS: Angiograms from 136 male patients with focal coronary disease were examined, and visually normal segments in the proximal portions of the major vessels were identified for measurement of mean segment diameters. Normal segments with immediately adjacent disease were compared with normal segments with distal disease in the same vessel and compared with normal segments in vessels for which the only other visible disease was in distant vessels. Angiograms with entirely normal findings from 26 age-matched men with atypical chest pain were used as controls. Segments were measured after nitroglycerin administration by means of computer-assisted quantitation. RESULTS: Mean diameters of visually normal segments with distant disease were smaller than those of control segments (p < 0.05). Normal left main and proximal left anterior descending coronary artery segments in patients with disease within the same vessel were significantly smaller than normal segments in patients with distant disease (p < 0.05). Normal segments with immediately adjacent disease had smaller mean diameters than normal segments with distal disease in the same vessel (p < 0.05). CONCLUSIONS: Visually normal coronary segments have progressively smaller lumen diameters, depending on the relative proximity of visible disease. Measurement of percent stenosis on the basis of the diameter of apparently normal adjacent reference segments can result in underestimation of coronary lesion severity.

Cardiac Catheterization↗
PubMed1994

Rate adaptive pacing in sick sinus syndrome: effects of pacing modes and intrinsic conduction on physiological responses, arrhythmias, symptomatology and quality of life.

An atrial-based pacing mode is superior to ventricular constant rate demand pacing (VVI) mode in patients with sick sinus syndrome (SSS) by providing both rate adaptation and atrioventricular (AV) synchrony. The use of a non-atrial sensor to overcome chronotropic incompetence and preserve normal intrinsic AV conduction in pacemaker therapy for SSS was investigated in 15 consecutive patients (mean age 66 +/- 2 years). All had intact AV conduction (antegrade conduction capacity > 100 beats.min-1 and an atrial paced to intrinsic R interval of < or = 220 ms). DDDR pacemakers capable of being programmed into atrial rate adaptive (AAIR), dual chamber rate adaptive (DDDR) and ventricular rate adaptive (VVIR) modes were used. Beginning with an acute study, arterial pressure was invasively assessed in each pacing mode during physiological stresses and low level exercise. In the ambulatory phase, the incidence of ventricular pacing and arrhythmias (Holter recording), diurnal blood pressure changes (ambulatory blood pressure recording), and symptom and quality of life level (questionnaires and interviews) were compared. Despite similar heart rate changes during acute physiological stresses, a higher blood pressure was recorded during AAIR or DDDR pacing compared with VVIR pacing. Systolic blood pressure over 24 h was lower in the VVIR mode (122 +/- 5 mmHg) than AAIR/DDDR pacing (129 +/- 6/128 +/- 6 mmHg, P < 0.05). VVIR pacing was associated with a higher frequency of atrial and ventricular ectopics, with two patients developing paroxysmal atrial fibrillation. Ventricular pacing was used in a higher percentage in the DDDR compared with the VVIR mode (64 +/- 11 and 39 +/- 7%, P < 0.03). VVIR pacing was associated with more palpitations, a lower level of general well being and depression. Despite the use of a sensor to overcome chronotropic incompetence, VVIR pacing is a less satisfactory pacing mode for SSS. Although AAIR/DDDR pacing may achieve similar haemodynamic and clinical status, in patients with intact AV conduction, AAIR pacing may be preferable by avoiding an abnormal ventricular activation pattern.

Aged↗
PubMed1994

Apparent extension of the atrioventricular interval due to sensor-based algorithm against supraventricular tachyarrhythmias.

Rapid ventricular tracking response to supraventricular tachyarrhythmia is one major limitation to DDD pacing. In a DDDR pacemaker, sensor-based algorithms have been used to control these arrhythmias. These include the use of an interim rate limit (conditional ventricular tracking limit) or a separate maximum tracking and sensor rate limits (discrepant upper rate). These algorithms limit inappropriate ventricular pacing rate during tracking of pathological supraventricular tachyarrhythmia and atrial flutter by Wenckebach-like prolongation of the AV interval. We observed that this may cause an unexpected extension of the AV interval in patients with high atrial rate and intact AV nodal conduction. This was due to P wave rate above the conditional ventricular tracking limit or maximum tracking limit, but AV paced interval prolongation was avoided by the occurrence of intrinsic conduction, albeit at an AV interval longer than the programmed AV interval. This might appear as failure of ventricular pacing on the ECG. This phenomenon is a modified form of "upper rate" behavior occurring in the AV interval, and should be recognized as a normal behavior rather than pacemaker malfunction.

Algorithms↗
PubMed1994

Rate adaptive cardiac pacing using right ventricular venous oxygen saturation: quantification of chronotropic behavior during daily activities and maximal exercise.

Central venous oxygen saturation (SvO2) closely reflects cardiac output and tissue oxygen consumption. In the absence of an adequate chronotropic response during exercise, SvO2 will decrease and the extent of desaturation may be used as a parameter for rate adaptive cardiac pacing. Eight patients with sinoatrial disease received a DDDR pacemaker capable of DDDR pacing by sensing either SvO2 or piezoelectric detected body movement. Both sensors were programmed to attain a rate of about 100 beats/min during walking, and with the lower and upper rates set at 50% and 90% of age predicted maximum, respectively. Chronotropic behavior of the two sensors were compared in the DDD mode with measurement of sensor responses, during everyday activities (walking, stair climbing, postural changes, and physiological stresses) and at each quartile of workload during a continuous treadmill exercise test. During walking at 2.5 mph, both sensors showed no significant difference in delay time (both react within 15 secs) or half-time (SvO2 = 36 +/- 12 sec and activity 24 +/- 3 sec; P = NS), although SvO2 driven pacing achieved 90% target rate response slower than activity sensing (124 +/- 16 sec vs 77 +/- 10 sec; P < 0.02). SvO2 pacing was associated with a more physiological rate response during walking upslope (68 +/- 12 beats/min vs 57 +/- 10 beats/min; P < 0.05), ascending stairs (59 +/- 10 beats/min vs 31 +/- 6 beats/min; P < 0.05), and standing (34 +/- 7 beats/min vs 9 +/- 2 beats/min; P < 0.05). The SvO2 sensor significantly overpaced in the first quartile of exercise (51.8 +/- 25.6% in excess of heart rate expected from workload), but the rate was within 20% of expected for the remainder of exercise. "Underpacing" was observed with the activity sensor at the higher workload. In conclusion, the SvO2 sensor demonstrated a more physiological response to activities of daily living compared with the activity sensor. Using a quantitative method, the speed of onset of rate response of the SvO2 sensor was comparable to activity sensing, and was more proportional in rate response. Significant overpacing occurs at the beginning of exercise during SvO2 driven pacing, which may be improved with the use of a curvilinear algorithm.

Adult↗
PubMed1994

Long-term stability of P wave sensing in single lead VDDR pacing: clinical versus subclinical atrial undersensing.

Optimal function of a single lead P wave synchronous rate adaptive ventricular pacing system (VDDR) requires reliable P wave sensing over time and during daily activities. The stability of P wave sensing and the incidence of sensitivity reprogramming in a single pass lead with a diagonally arranged bipole was assessed in 30 patients with complete atrioventricular block over a follow-up period of 12 +/- 1 months (range 6 months to 3 years). Atrial sensing was assessed during clinic visits, by physical maneuvers (postural changes, breathing, Valsalva maneuver, walking and isometric exercise), maximum treadmill exercise and Holter recordings. P wave amplitude at implantation was 1.21 +/- 0.09 (0.5-3.6) mV, and the atrial sensing threshold remained stable over the entire period of follow-up. Using an atrial sensitivity based on twice the sensing threshold at 1 month, P wave undersensing was found in 2, 4, 3, and 7 patients during clinic visit, physical maneuvers, exercise, and Holter recordings, respectively. Atrial sensitivity reprogramming was performed in three patients based on the correction of undersensing during physical maneuvers. Although eight patients had atrial undersensing on Holter recordings, the number of undersensed P waves was small (total 101 beats or 0.013% +/- 0.001% of total ventricular beats) and no patient was symptomatic. One patient had intermittent atrial undersensing at the highest sensitivity, but the VDDR mode was still functional most of the time. No patient had myopotential interference at the programmed sensitivity. One patient developed chronic atrial fibrillation and was programmed to the VVIR mode. Thus, single lead VDDR pacing is a stable pacing mode in 97% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Comparative evaluation of bipolar atrial electrogram amplitude during everyday activities: atrial active fixation versus two types of single pass VDD/R leads.

Endocardial P wave amplitude (PWA) is an important determinant of the atrial sensing capabilities of an atrial-based pacing system. Although changes in PWA during physical activities are known to occur in DDD/R pacing, there is little information on the P wave stability in single pass lead VDD/R pacemakers using floating P wave sensing. We investigated the variation of PWA during daily life activities using telemetry recorded atrial electrograms in 21 patients with DDDR pacemakers (Relay or Elite) and 29 patients with single lead VDD/R pacemakers (Unity or Thera). Physical activities resulted in marked individual variability of PWA but, as a group, there was no significant difference between PWA during sitting, standing, lying down, and coughing in both DDDR and VDD/R pacing. In the Elite II pacemaker, walking at 2 miles per hour resulted in significant reduction of PWA (11.6% compared with sitting, P < 0.05). The most consistent reduction in PWA occurred in the relaxation phase of the Valsalva maneuver (VM), with all pacemakers showing a reduction in PWA (mean reduction in PWA compared with sitting in DDDR and VDD/R were 16.6% and 12.8%, respectively). Two patients with DDDR pacemakers (Relay) and three patients with VDD/R pacemakers (1 Unity and 2 Thera) had atrial sensing failure during VM or walking. In conclusion, large variation in PWA occurs during daily life activities. The extent of variation is dependent on the patients, types of atrial lead, and the maneuvers performed. A twice sensing threshold may be insufficient to ensure adequate atrial sensing during these activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1994

Quantitative comparison of rate response and oxygen uptake kinetics between different sensor modes in multisensor rate adaptive pacing.

Although multisensor pacing may mitigate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. The cardiopulmonary performance of six patients (mean age 63.5 +/- 10 years) who had undergone the implant of combined QT and activity VVIR (Topaz) pacemakers was assessed during submaximal and maximal treadmill exercise with the rate response sensor randomly programmed to either single sensor mode, QT and activity (ACT), or dual sensor mode, with equal contribution of QT and ACT (QT = ACT). The rate of response, the proportionality, oxygen kinetics, and maximal exercise performance of the various sensor modes during exercise were measured and compared. The ACT sensor mode "overpaced" and the QT and QT = ACT sensor modes "underpaced" during the first three quartiles of exercise (P < 0.05). The ACT sensor mode also gave the fastest rate of response with the shortest delay (13 +/- 1.5 sec vs 145 +/- 58 sec and 41 +/- 17 sec, P < 0.05), time to 50% rate response (39 +/- 2.7 sec vs 275 +/- 48 sec and 203 +/- 40 sec, P < 0.05), and time to 90% of rate response (107 +/- 21 sec vs 375 +/- 34 sec and 347 +/- 34 sec, P < 0.05) and a smaller oxygen debt (0.87 +/- 0.16 L vs 1.10 +/- 0.2 L and 1.07 +/- 0.18 L, P < 0.05) compared to the QT and QT = ACT sensor modes, respectively. These differences were most significant at low exercise workloads. Thus, different sensor combinations result in different rate response profiles and oxygen delivery, especially during low level exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Coronary vasoconstriction after angioplasty of total occlusions: relation to change in coronary perfusion pressure.

OBJECTIVES: This study evaluated the coronary vasomotor response after successful angioplasty of chronic total coronary occlusions and tested the hypothesis that the degree of distal vasoconstriction is dependent on the change in perfusion pressure. BACKGROUND: Although distal coronary vasoconstriction has been observed to occur frequently after successful percutaneous transluminal coronary angioplasty, little is known about this vasomotor response after angioplasty of chronic total occlusions. METHODS: Thirty patients with successful angioplasty of chronic total occlusions of the left coronary artery were studied. Quantitative coronary measurements were made at 0, 15 and 30 min after angioplasty and again after intracoronary nitroglycerin administration in coronary artery segments distal to the dilated lesion and in a control vessel. The change in distal perfusion pressure was defined as mean systemic arterial pressure minus residual mean trans-stenotic pressure gradient minus mean coronary wedge pressure. RESULTS: The distal segments showed greater vasoconstriction (vs. nitroglycerin) at 15 and 30 min compared with that at 0 min after angioplasty (32.3 +/- 2.2% and 35.2 +/- 2.5% vs. 12.5 +/- 1.8%, respectively, p < 0.005) and compared with control segments (32.3 +/- 2.2% vs. 12.1 +/- 2.0%, p < 0.005, and 35.2 +/- 2.5% vs. 12.5 +/- 2.0%, p < 0.005, respectively). The degree of vasoconstriction at 30 min in the distal segments was found to correlate closely with the change in distal perfusion pressure (r = 0.73, p < 0.001). CONCLUSIONS: Coronary distal vasoconstriction occurs frequently after successful angioplasty of chronic total occlusions and correlates closely with the change in coronary perfusion pressure. These findings support the hypothesis of reset epicardial coronary autoregulation in chronic hypoperfusion such that restoration of normal perfusion pressure after successful angioplasty may provoke reflex vasoconstriction.

Aged↗
PubMed1993

Beneficial effect of cholesterol-lowering therapy on coronary endothelium-dependent relaxation in hypercholesterolaemic patients.

Since hypercholesterolaemia is associated with impaired endothelium-dependent vasodilation, a study was conducted to find out whether cholesterol reduction will improve endothelial function in patients with hypercholesterolaemia and normal coronary arteries. 25 men (mean age 51 [SD 8] years) with total serum cholesterol > 6.2 mmol/L) and angiographically normal coronary arteries had their coronary vasomotor responses to intracoronary acetylcholine and nitroglycerin assessed by computer-assisted quantitative angiography at baseline and after 6 months of cholesterol-reducing diet and cholestyramine. Between baseline and follow-up mean total serum cholesterol level fell by 28.7 (SD 5.6)% (p < 0.001); mean low-density lipoprotein (LDL) cholesterol level by 35.6 (8.7)% (p < 0.001); and mean total cholesterol to high-density lipoprotein (HDL) cholesterol ratio by 29.4 (10.6)% (p < 0.001). Acetylcholine significantly reduced the mean segment diameter at baseline, by 21.7 (14.0)% (p < 0.01), but it increased the diameter at follow-up, by 6.16 (13.3)% (p < 0.01), the difference between the two occasions being significant (p < 0.001). Nitroglycerin significantly increased the mean segment diameter, both at baseline, by 18.7 (11.5)% (p < 0.01), and at follow-up, by 19.3 (12.1)% (p < 0.01), the difference between the two responses being not significant. At baseline total cholesterol and LDL cholesterol did not correlate with acetylcholine response, but they did at follow-up (total cholesterol, r = 0.67, p < 0.01; LDL cholesterol, r = 0.64, p < 0.01). Impairment of endothelium-dependent (acetylcholine-induced) dilation of the epicardial coronary arteries in hypercholesterolaemic patients with angiographically normal coronary arteries is thus reversible by reducing serum cholesterol. In addition, the degree of impairment of acetylcholine-induced vasomotor response is related to the cholesterol concentrations after therapy.

Acetylcholine↗
PubMed1993

Coronary and circulatory support strategies for percutaneous transluminal coronary angioplasty in high-risk patients.

PTCA is now applied to patients with unstable acute ischemic syndromes, severe multivessel coronary artery disease, and impaired left ventricular function. To minimize the risk during angioplasty, several coronary and systemic circulation support approaches have been developed as adjuncts to high-risk angioplasty. Local coronary support techniques include the perfusion balloon catheter, the coronary stent, directional coronary atherectomy, laser balloon angioplasty, perfluorocarbon coronary perfusion, coronary sinus retroperfusion, and distal coronary hemoperfusion. Systemic circulatory support includes intraaortic balloon counterpulsation, cardiopulmonary support, the hemopump, and left heart partial bypass. These support devices, while associated with significant complications, may ultimately improve the safety of coronary angioplasty and allow its application to those who would otherwise not be candidates for revascularization.

Angioplasty, Balloon, Coronary↗
PubMed1992

A randomized double-blind crossover study comparing the efficacy and tolerability of flecainide and quinidine in the control of patients with symptomatic paroxysmal atrial fibrillation.

Patients with paroxysmal atrial fibrillation (PAF) are prone to recurrence. We compared the efficacy and tolerability of flecainide acetate in the control of PAF by means of conventional treatment with quinidine in 19 patients without structural heart disease. A randomized, placebo-controlled, crossover protocol consisting of 8 weeks of treatment with either agent was used. The recurrence of PAF was documented in a symptom diary and confirmed by event ECG recording. Complete control of symptoms was achieved in 4 of 19 and 2 of 11 of patients with flecainide and quinidine, respectively. Both agents prolonged the time to the first recurrence and significantly reduced the total duration of PAF recurrence by 40% and 47%, respectively (p less than 0.05 compared with placebo). Compared with quinidine, flecainide significantly reduced the frequency of recurrence and the rate of PAF during a recurrent episode. However, treatment with flecainide was associated with a higher incidence of symptomatic sinus pauses and visual disturbances compared with a higher incidence of gastrointestinal side effects with quinidine. During a follow-up period of 32 months, satisfactory control was achieved in 74% of patients with the use of these two antiarrhythmic agents.

Adult↗
PubMed1992

Effects of severity of the residual stenosis of the infarct-related coronary artery on left ventricular dilation and function after acute myocardial infarction.

OBJECTIVES: This study was designed to evaluate the relation between the severity of the residual stenosis of the infarct-related artery and changes in left ventricular volume and function after a first anterior myocardial infarction. BACKGROUND: Although thrombolytic therapy improves clinical outcome after acute myocardial infarction, the relations between the severity of the residual stenosis of the infarct-related artery and postinfarction left ventricular remodeling and function are unclear. METHODS: Fifty-eight patients with a first anterior myocardial infarction and significant disease only in the left anterior descending coronary artery on arteriography performed after 7 to 10 days were evaluated. All patients received thrombolytic therapy. Residual stenosis of the infarct-related artery was measured with quantitative coronary arteriography. Left ventricular volumes and ejection fraction were measured by echocardiography and radionuclide angiography, respectively, 7 to 10 days, 6 months and 1 year after infarction. End-diastolic and end-systolic left ventricular volumes were measured by two-dimensional echocardiography and normalized to body surface area. Patients were classified into three groups according to baseline residual stenosis severity: total occlusion (Group I), minimal lesion diameter less than 1.5 mm (Group II) and minimal diameter greater than or equal to 1.5 mm (Group III). RESULTS: Group I patients had significantly greater left ventricular end-diastolic and end-systolic volumes at 6 months and 1 year than did the other groups. Group II patients had greater end-diastolic and end-systolic volumes than did Group III patients at 1 year. In addition, Group I patients had a lower ejection fraction at 1 year than that of the other groups. The minimal lesion diameter was significantly correlated with percent change in end-diastolic volume at 1 year. CONCLUSIONS: The severity of the baseline residual stenosis of the infarct-related artery is an important predictor of change in left ventricular volumes in the 1st year after infarction. Total occlusion of the infarct-related artery is associated with greater left ventricular dilation and functional impairment.

Cardiac Catheterization↗
PubMed1991

Correlation of quantitative angiographic parameters with changes in left ventricular diastolic function after angioplasty of the left anterior descending coronary artery.

This study evaluates the changes in left ventricular (LV) diastolic filling after percutaneous transluminal coronary angioplasty and the relation of such changes to quantitative angiographic measurements of the severity of coronary narrowings. Pulsed Doppler echocardiographic measurements were performed in 40 patients with single left anterior descending artery narrowing before, and 10 and 30 days after angioplasty. Minimal luminal diameter and percent diameter stenosis of coronary lesions were measured by computer-assisted quantitation. The ratio of early to late diastolic flow velocities (E/A ratio), time velocity integral of early diastolic filling period (Ei) and the ratio of early and late diastolic filling periods (Ei/Ai ratio) increased gradually after angioplasty. Minimal luminal diameter correlated significantly with the percent changes in E/A ratio (r = 0.59 at 10 days, r = 0.57 at 30 days), Ei (r = 0.53 at 10 days, r = 0.55 at 30 days) and Ei/Ai ratio (r = 0.41 at 10 days, r = 0.49 at 30 days). Percent diameter stenosis showed overall weaker correlations than minimal diameter with the percent changes in E/A ratio (r = 0.39 at 10 days, r = 0.32 at 30 days) and Ei (r = 0.38 at 10 days, r = 0.31 at 30 days). Thus, LV diastolic filling improves serially after coronary angioplasty in patients with 1-vessel disease. The magnitude of improvement in diastolic filling correlates better with minimal luminal diameter than percent diameter stenosis. Therefore, minimal luminal diameter is a better predictor of changes in Doppler transmitral flow parameters after angioplasty than percent diameter stenosis.

Adult↗
PubMed1991

Coronary artery quantitation and data management system for paired cineangiograms.

A computerized system designed to optimize the quantitation of coronary vessels on 35 mm cineangiograms is described and validated. Because the system has two cine film digitizers, it processes paired coronary arteriograms for the evaluation of serial changes in coronary arteries. A database system was specifically designed for the storage of coronary artery quantitation data which resides on a file server in a local area network and may be accessed by multiple workstations. In radiographic phantom studies of nine contrast-filled lucite cylinders of known size, the overall accuracy and precision for the measured diameters were 0.069 mm and 0.066 mm respectively. Measurements of minimum diameter and percent diameter stenosis of 21 coronary lesions selected from 17 routine cineangiograms showed high degree of intraobserver and interobserver reproducibility.

Cineangiography↗
PubMed1991

Improvement of exercise capacity after nifedipine in patients with Eisenmenger syndrome complicating ventricular septal defect.

We investigated the potential benefit of a preferential pulmonary vasodilatory effect of nifedipine in 4 patients with Eisenmenger syndrome complicating ventricular septal defect. First-pass radionuclide scan was performed at rest to measure intracardiac shunting before and after nifedipine. Two hours after 20 mg sublingual nifedipine, right-to-left shunt increased from 16.3 +/- 1.4 to 20.4 +/- 1.5% (p less than 0.05), but systemic arterial oxygen saturation (SAO2) remained steady. With 4 weeks of maintenance nifedipine therapy, resting intracardiac shunting and SAO2 were unchanged from baseline. Symptom-limited cycle ergometry was performed before and after maintenance nifedipine with placebo control. Exercise duration was prolonged (8.7 +/- 0.6 vs. 6.8 +/- 0.9 min; p less than 0.02) and SAO2 at each stage of exercise was consistently increased in all patients after nifedipine. Cardiac output and the SAO2 at peak exercise were similar. Thus, chronic nifedipine therapy increases SAO2 on exercise and improves maximal exercise capacity in patients with Eisenmenger syndrome, which is not predicted by study of resting intracardiac shunting after acute therapy.

Administration, Oral↗
PubMed1991

Electromechanical concordance in alternans during sustained tachycardias.

Electrical alternans and mechanical alternans are intriguing phenomena that have been reported to occur during tachycardias. Their precise pathophysiologic mechanism and in particular their interrelation have not been well defined. This report documents an unusual electromechanical concordance in alternans during sustained supraventricular tachycardia and ventricular tachycardia in two patients, raising interesting possibilities on the underlying mechanism of the concordant phenomena. The findings highlight the principle of excitation--contraction coupling of the heart.

Adult↗